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## Über dieses Buch

Condition assessment and characterization of materials and structures by means of nondestructive testing (NDT) methods is a priority need around the world to meet the challenges associated with the durability, maintenance, rehabilitation, retrofitting, renewal and health monitoring of new and existing infrastructures including historic monuments. Numerous NDT methods that make use of certain components of the electromagnetic and acoustic spectrum are currently in use to this effect with various levels of success and there is an intensive worldwide research effort aimed at improving the existing methods and developing new ones. The knowledge and information compiled in this book captures the current state of the art in NDT methods and their application to civil and other engineering materials and structures. Critical reviews and advanced interdisciplinary discussions by world-renowned researchers point to the capabilities and limitations of the currently used NDT methods and shed light on current and future research directions to overcome the challenges in their development and practical use. In this respect, the contents of this book will equally benefit practicing engineers and researchers who take part in characterization, assessment and health monitoring of materials and structures.

## Inhaltsverzeichnis

### Evolution of NDT Methods for Structures and Materials: Some Successes and Failures

The development of techniques being used for the non-destructive evaluation of materials and structures is closely related to other disciplines. The examination of human beings in a non-destructive way for example was a goal of many generations of physicians leading to highly developed methods applied today in a routinely manner. Many techniques used in NDE have their equivalent in medical testing. Same is true for geophysics. The exploration for natural resources (e.g. gas, water, oil) and the desire to understand the structure and dynamics of the earth have been strong motors to develop sophisticated methods. It does not matter if one consider reflection seismic, seismology, vibration or electro-magnetic methods: all have their equivalent in the field of NDE of materials and structures. The paper will give some examples of these interconnections and successful adoptions. Since the characteristics of human beings, the earth and engineering structures are different these transitions are somehow limited what will be discussed as well.

C. U. Grosse

### Remote Detection of Debonding in FRP-strengthened Concrete Structures Using Acoustic-Laser Technique

Fiber-reinforced polymer (FRP) strengthening and retrofitting of concrete elements, such as beams, columns, slabs, and bridge decks, have become increa­singly popular. Nonetheless, rapid and reliable nondestructive testing techniques (NDT) that are capable of remotely assessing

in-situ

integrity of retrofitted systems are needed. Development of a robust NDT method that provides an accurate and remote assessment of damage and flaws underneath the FRP plates/sheets is required. In this study, a NDT based on an acoustic-laser system is proposed for remote detection of debonding in FRP-strengthened concrete structures. This technique utilizes the difference in dynamic response of the intact and the debonded regions in a FRP-strengthened concrete structure to an acoustic excitation, which is then measured using laser vibrometry. Feasibility and accuracy of the technique were investigated through a series of measurements on laboratory-sized plain, reinforced, and FRP-strengthened concrete specimens. It was shown that the difference in dynamic response could be captured by the acoustic-laser system and is in good agreement with simple calculations.

O. Büyüköztürk, R. Haupt, C. Tuakta, J. Chen

### A Quantitative Laser Ultrasound Visualization System for Investigating the Interaction of Wedge Waves with a Defect

Machine tool blades exhibit typical wedge-shaped tips where defects are very likely to exist and call for non-destructive characterization. In order to detect the defect on the wedge tip, the interaction of wedge wave with defect characteristic needs to be investigated. Antisymmetric flexural (ASF) modes are wedge waves (WW) with their particle motion antisymmetric about the mid-plane bisecting and energy tightly confined near the wedge tip. A quantitative laser ultrasound visualization (QLUV) system which employs a pulsed laser to scan over the interested area then detected with a piezoelectric transducer. With the aid of reciprocal theorem, dynamic behaviors of ASF modes encountering a defect can be reconstructed. In this research, the QLUV system is used to evaluate the characteristic of WWs and the phenomenon of defect effect including mode conversion and the scattering intensity. With the QLUVS behaviors of ASF modes interacting with a wedge-tip-crack are characterized in a quantitative way. More complex behaviors for higher-order ASF interacting with cracks are under investigation.

I. H. Liu, C. H. Yang

### NDT of Structural Timber Members by Means of 3D Ultrasonic Imaging Techniques and Modelling

The present paper describes the development and first application of ultrasonic imaging of timber (wood) by means of reconstruction calculation (3D-SAFT; Synthetic Aperture Focusing Technique). It considers the highly anisotropic ultrasonic velocity on wood. In order to validate such techniques we report on experiments carried out on test specimens made from pine and beech. Those specimens differ for the orientations of the annual rings. For the reconstruction calculation the slowness curves of the material are considered applying the elastic constants known from the literature. The anisotropic SAFT reconstruction is calculated from measured datasets and from synthetic data resulting from EFIT modelling (EFIT: Elastodynamic Finite Integration Technique).

M. Krause, P. K. Chinta, K. Mayer, U. A. Effner, S. Müller

### Enhancing the Accuracy of Off-Axis Flaw Sizing and Positioning in TOFD D-scans Using Mode-Converted Waves

Despite the recent popularity of ultrasonic time-of-flight diffraction (TOFD) as a reliable non-destructive testing technique for the inspection of weld defects in steel structures, the critical stages of data processing and interpretation are still performed manually. This depends heavily on the skill, experience, alertness and consistency of a trained operator

,

and is subject to inevitable human errors due to reduced alertness arising from operator fatigue and visual strain when processing large volumes of data. This paper presents techniques developed for enhancing the accuracy of sizing and positioning of off-axis weld flaws in TOFD D-scan data as an essential stage in a comprehensive TOFD inspection and interpretation system to aid the operator by automating some aspects of the processing and interpretation. Data manipulation and post-processing techniques have been specifically developed for the sizing of off-axis weld defects in TOFD data, significantly reducing the sizing and positioning errors. The mode-converted waves are utilised to enhance positional accuracy of flaws. The results achieved so far have been promising in terms of accuracy, consistency and reliability.

A. Al-Ataby, W. Al-Nuaimy

### Time Reverse Modeling Versus Automatic Onset Detection: A Study on the Localization of Acoustic Emissions in Reinforced Concrete

Acoustic emissions (AE) are localized using two different signal-based approaches consisting in: An iterative algorithm based on the Akaike Information Criterion (AIC) and time reverse modeling (TRM). Thereto, physical experiments (four- and three-point-bending tests) were carried out on large scale reinforced concrete (RC) slabs with the dimensions of 2620 × 800 × 200 mm. AE were recorded during the entire loading history. The AE sources were localized successfully by both methods from the AE waveforms. It is the first time that time reverse modeling was used to successfully localize AE sources in RC slabs. The results of the AIC-based and TRM localization are compared and discussed.

G. K. Kocur, E. H. Saenger, T. Vogel

### Use of Acoustic Emission Analysis to Evaluate the Self-Healing Capability of Concrete

It has been estimated that, in Europe, 50% of the annual construction budget is spent on refurbishment and remediation of the existing structures [

1

]. Therefore, self-healing of concrete structures, which are very sensitive to cracking, would be highly desirable. In this research, encapsulated healing agents were embedded in the concrete matrix in order to obtain self-healing properties. Upon crack appearance, the capsules break and the healing agent is released, resulting in crack repair. The efficiency of this crack healing technique was evaluated by using acoustic emission (AE) analysis. Breakage of the capsules was proven as events with an energy higher than the energy related to concrete cracking were noticed. Upon reloading of beams with untreated cracks, fewer emissions were detected compared to beams with healed cracks. From this study it was shown that AE is a suitable technique to evaluate self-healing of cracks in concrete.

K. Van Tittelboom, N. De Belie, F. Lehmann, C. U. Grosse

### Identification of Tendon Ducts in Prestressed Concrete Beam by SIBIE

The impact-echo method is well-known as a non-destructive testing for concrete structures. It is based on the use of low-frequency elastic waves that propagate in concrete to determine thickness or to detect internal flaws in concrete. In this method, the presence and the locations of defects in concrete are estimated from identifying peak frequencies in the frequency spectra, which are responsible for the resonance due to time-of-flight from the defects. In practical applications, however, spectra obtained include so many peak frequencies that it is fairly difficult to identify the defects correctly. In order to improve the impact-echo method, Stack Imaging of spectral amplitudes Based on Impact Echo (SIBIE) procedure is developed as an imaging technique applied to the impact-echo data, where defects in concrete are identified visually at the cross-section. In this study, the SIBIE procedure is applied to identify grouted or ungrouted post-tensioning ducts in prestressed concrete beam. It is demonstrated that the ungrouted duct can be identified with reasonable accuracy.

M. Yamada, K. Tagomori, M. Ohtsu

### Absolute Calibration of an Acoustic Emission Sensor

Calibrated sensors are essential for quantitative comparisons of acoustic emission source mechanics. We describe experimental techniques and mathematical models for implementation of an absolute sensor calibration scheme using glass capillary fracture and ball impact, two sources which can be easily implemented. Additionally, we describe the specific experimental procedures for absolute sensor calibration using the both the fracture of a glass capillary tube, and drop of a 0.4 mm ruby ball, as the calibration source. The mathematical formulation is based on a Green’s function formalism. The Glaser-type conical piezoelectric sensor, used as an example in this study, has a noise floor of approximately 1 picometer displacement when coupled to steel. The amplitude of the sensor response is flat within 3 dB from 50 kHz to 2 MHz at a level of 0 dB relative to 1 V/nm.

G. C. Mclaskey, S. D. Glaser

### NDE with Lockin-Interferometry: Principle and Applications

Speckle-interferometric imaging is a well known method where the­difference between two deformation states of an object (with and without applied load) is displayed as a fringe pattern. The standard procedure for finding hidden defects is to compare the observed fringe pattern either to the pattern that one expects or to one measured on a reference component. Observed differences are then attributed to a defect. We show how the method can be improved in terms of signal to noise ratio and resolution.

The idea is to apply the modulation principle to speckle-interferometry that makes lockin-thermography superior to conventional thermography: The inspected object is periodically illuminated to induce a thermal wave and a corresponding modulation of thermal expansion while fringe images are recorded with electronic speckle pattern interferometry (ESPI) or shearography. Then, the time-dependent content of each pixel is Fourier transformed at the excitation frequency. This way the information content is compressed into local amplitude and phase of the response at this frequency. In the phase image, defects reveal themselves as deviations from a constant background and can therefore be identified easily. The signal to noise ratio is improved by up to an order of magnitude. Depth range can be adjusted by variation of the modulation frequency. This paper shows results of model samples as well as of automotive and aerospace parts.

G. Busse, P. Menner

### Fast Defect Shape Reconstruction Based on the Travel Time in Pulse Thermography

Pulse thermography is a non-destructive testing method based on ­infrared imaging of transient thermal patterns. Heating the surface of the structure under test for a short period of time generates a non-stationary temperature distribution and thus a thermal contrast between the defect and the sound material. In modern NDT, a quantitative characterization of hidden imperfections in materials is desired. In particular, defect depth and shape are of interest. The reconstruction of the defect from thermography data is a nonlinear inverse problem, and ill-posed. We propose an algorithm for the identification of subsurface defects based on the travel time of the reflected thermal pulse. Our work extends results by Lugin and Netzelmann, taking lateral thermal flows directly into account while retrieving the defect depth. This requires significantly less computational work. Quantitative information about the defect shape and depth is obtained. Application of our method to both thermography data generated by a finite element simulation and experimental heating of PVC test specimens with different defects yields good reconstruction of the actual defects.

S. Götschel, M. Weiser, C. Maierhofer, R. Richter, M. Röllig

### The Role of Infrared Thermography in NDT

Infrared thermography (IRT) is becoming ever more popular in NonDestructive Testing (NDT) of materials and structures since it is completely noncontact and may be faster than many other techniques. In some cases, such as in the control of the envelope of a building, it is practically the unique technique, which, in one click, supplies a comprehensive image of the entire façade of the building with information about buried structures, tightness of envelope and fixtures, and presence of anomalies. The attention of this work is focused on the actual role of IRT in the NDT field. First, some basic principles of the two main techniques, which are Pulse termography (PT) and Lockin Thermography (LT) are briefly recalled and then some examples of application are presented. Such examples include laboratory tests and in situ inspections. Two types of specimens are considered: a glass fibre reinforced composite and masonry structure including different types of problems such as voids and cracks, and impact damage. Within the inspection in situ of buildings, information about the conservation state of masonry structures (overall degradation, crack network) were gained for planning of restoration.

C. Meola, G. M. Carlomagno

### Industrial Applications of Dual X-ray Energy Computed Tomography (2X-CT)

The Fraunhofer Development Center X-ray Technology (EZRT) developed an industrial dual-energy X-ray Computed Tomography (2X-CT) system in order to obtain quantitative 3-D information on the material inside arbitrary samples. The goal was to develop an easy-to-use dual-energy solution that can be handled by the average industrial CT operator without the need for a specialist. First, an introduction is given of the physical background of the method that was realized. Also, the strengths and weaknesses thereof are discussed. Next, the results of 2X-CT measurements from different fields of investigations are presented: measurements with vegetables, e.g. potatoes or bananas, quantitative assessments of bore cores in geological applications, and studies of carbon fibre reinforced plastic (CFRP). In summary, it is shown that 2X-CT can provide accurate information about the composition of a wide range of materials and objects. On the other side, there is still the need for further optimization of X-ray parameters in order to increase quantitative accuracy, and for extending the range of materials which can be assessed by industrial 2X-CT.

T. Fuchs, P. Keßling, M. Firsching, F. Nachtrab, G. Scholz

### Research on Improvement of Receiving-Detecting Circuit for Digital Radiographic Systems with Advanced Spatial Resolution

Radiographic inspection is among the most reliable methods for inspection of pipelines and metals. The worldwide trend of transition from film radiography to digital radiography requires developmentof advanceddigital radiography systems (DRS). The main task in developmentof DRS is the improvement of spatial resolution (SR). The pixel size of the X-ray film is several microns while solid-state detector pixels have dimensions of several hundred to several thousand microns. For the most common detectors of “scintillator-photodiode” (S-PD) type, it is impossible in principle to obtain the film pixel sizes. However, the detecting ability for substances that differ by their density and atomic number achieved using “scintillator-photodiode” detectors is by several orders higher. Using the known method of digital radiography with a standard experiment scheme, but with dual-energy detector arrays, this study aimed at showing that it could be possible to substantially increase the accuracy of separation of substances in the inspected object by their atomic number.The sensitivity of the method was increased by using a multi-energy approach and detectors that have substantially different sensitivity in the low- and high-energy range of the X-ray emitter spectrum. Using the developed instruments and software, dual energy CT and 3D imaging of different objects such as welding, fragment of bone and tissue, and bags containing potentially hazardous items can be performed.

V. D. Ryzhikov, O. D. Opolonin, O. K. Lysetska, S. M. Galkin, Y. F. Voronkin, V. L. Perevertaylo

### Novel Approach for Non-Destructive Evaluation of Electrochemical Potentials in Reinforced Concrete Structures

Various non-destructive diagnostic tools are available for a condition assessment of reinforced concrete structures. Potential mapping is a helpful method for locating areas with a high risk of chloride induced corrosion. The influence of the reinforcement continuity was investigated by using laboratory specimens. Furthermore the potential differences were compared between a measuring setup with a reinforcement connection and by measuring with two external electrodes. In assessing the results a novel approach was developed to locate critical areas without a reinforcement connection. The results are displayed by means of vectors similar to the needle of a compass that point to the areas of high corrosion potential, enabling an easy and non-destructive assessment.

K. Reichling, M. Raupach

### Non Destructive Monitoring of Fiber Dispersion and Flow-Induced Orientation in Self-Compacting SFRC: A Method Based on Magnetic Properties

Steel fiber reinforced concrete (SFRC) is a composite material which is becoming more and more widely employed in building construction. The mechanical behaviour of the material and the performance of structural elements may significantly depend on the fiber dispersion and orientation with respect to the stress pattern. Non-destructive monitoring of fiber dispersion related issues hence becomes of the foremost importance in order to reliably anticipate the structural performance of elements made with fiber reinforced cementitious composites, as well as for quality control during manufacturing. In this paper a new method for the detection of fiber density and orientation is presented, which is based on the employment of a probe sensitive to the magnetic properties of the steel fibers. The presence and the relative position of steel fibers modify the flux linked by the winding of the probe thus resulting in an impedance variation. The local average concentration and orientation of the fibers can be thus assessed by measuring the variation of the probe inductance. The performance of the method has been analyzed with reference to a self-consolidating high performance fiber reinforced cementitious composite slab. Besides its good sensitivity, the method is also characterized by ease of use, since it just requires to lean the probe on the surface of the specimen, without any particular care about the coupling. This guarantees a high degree of repeatability and low uncertainty in the measurements, even, e.g. on vertical elements or slabs accessible from the bottom.

L. Ferrara, M. Faifer, M. Muhaxheri, S. Toscani, R. Ottoboni

### Mobile NMR – A Powerful Tool to Measure Coating Thicknesses in Concrete Buildings

Scores of infrastructural concrete buildings possesses coating systems as protection against aggressive exposure. The functionality of these coating systems is mainly affected by the composition and thickness of there different polymeric layers. A mobile NMR sensor, the so called “NMR-MOUSE®“ (Nuclear Magnetic Resonance Mobile Universal Surface Explorer, registered trademark of RWTH Aachen University), enables for the first time ever a nondestructive determination of these controlling parameters. The current results demonstrate the capability of the NMR sensor investigating different coating systems applied on concrete. Analyzing the NMR amplitude as a function of the measuring depth, the composition of the different coating layers gets visible while an accuracy of about 5 to 20 µm can be achieved for the thickness determination. Studying the influence of steel reinforcement inside the coated concrete on the NMR signal leads to a correction of the measuring field position influenced by concrete cover, steel diameter, amount and position of steel.

J. Orlowsky

### Innovative Sensor Technologies for Nondestructive Imaging of Concrete Structures: Novel Tools Utilising Radar and Induction Technologies

Nondestructive testing methods in building construction and civil engineering are needed to avoid costly damages caused by cutting reinforcement during drilling and coring and to image structures for condition assessment and evaluation. In this paper, the technology and application of two of Hilti’s nondestructive imaging tools are presented. The handheld wall penetrating radar system is suited to locate various objects, such as rebar, tendons, conduits, pipes, cables, voids, etc. in concrete. The radar tool comprises an antenna array for quick scanning and high data quality, real-time processing and visualisation for easy interpretation and 3D data representation available at the job-site. Furthermore, reinforcement verification, measurement of concrete coverage and statistical analysis can be performed with the Hilti Ferroscan system based on electromagnetic induction.

S. Korl, C. Wuersch, J. Zanona

### Comparative Study of Nonlinear Resonance and Wave Interaction Techniques for Concrete Damage Assessment

Two nonlinear parameters extracted from different approaches have been compared on their sensitivity and reliability to detect thermal damage in concrete. One approach is based on nonlinear resonance while the other relies on wave interactions. Results show that both nonlinear parameters have a sensitivity to thermal damage of the same order of magnitude. Variations observed are much higher than in the case of linear parameters (ultrasonic pulse velocity and dynamic modulus). Coefficients of variation showed that resonance frequency technique is more reliable than wave interaction technique. However, the latter technique remains of great interest and needs further developments since it is more adapted to

in situ

measurements.

Y. Boukari, P. Rivard, D. Bulteel, G. Ballivy, N. E. Abriak

### Ultrasonic Signal Processing Based on the Combined Use of Empirical Mode Decomposition and Split Spectrum Processing Using the Prism Technique

In this work we present the application of Empirical Mode Decomposition (EMD) and Split Spectrum Processing (SSP) in non-destructive testing of materials using ultrasound. The SSP as well as the EMD technique enable to enhance target detection and the visibility of reflected echoes. The use of the EMD technique before using SSP makes the detection of any desired target-echo more flexible, when looking for a good solution to the coherent noise problem. Some types of coherent noise can be removed by frequency filtering but only provided that the amplitude spectrum of the noise does not overlap the spectrum of the desired signal. In the most practical situations, this noise may comprise refractions, multiple reflections, reflected refractions or refracted reflections, and coherent noise from grains and scatters with different sizes. The signals were obtained using a technique applied in pulse-echo mode, known as the prism technique and processed in Matlab environment. Tests carried out on trapezoidal-prism shaped specimens of mortar highlight the capability of this signal processing technique.

### Advancing the Rebound Hammer Method: A New Concrete Test Hammer

The concrete test hammer patented by Proceq’s Ernst O. Schmidt at the beginning of the 1950’s is without a doubt the most widely used NDT instrument worldwide for rapid assessment of the condition of a concrete structure. Despite this fact, the validity of the method remains a hotly debated topic amongst experts in the NDT field. This is largely due to two factors; (a) since the original Proceq patent expired, there has been a proliferation of imitations with widely varying quality. Some are good, others are poor and the unreliability of the poor quality instruments has damaged the method in general; (b) the validity of the method in its primary use, i.e. for uniformity testing, is undisputed; however, incorrect use of the hammer for estimating compressive strength, (i.e. blind reliance on the manufacturer’s conversion curves) is a major cause for concern amongst NDT experts. Furthermore, since its introduction, not much has been done to improve the test method itself. This paper describes how recent advances in rebound hammer technology together with extensive research into the various factors that influence the results can improve the rebound hammer method, providing users with more reliable results and reducing doubts concerning the viability of the method.

D. Corbett

### Phenomena Investigation of Guided Waves Propagation in a Multiple-Wire Cable with Gradually Increasing Cut Depths

In this study, the propagation phenomena of guided waves in a multiple-wire Aluminium Conductor Steel Reinforced (ACSR) cable with artificial cuts were investigated. A two piezoelectric transducers system, in a pitch and catch configuration, together with the wavelet transform, was employed for analyzing guided wave propagation. An ACSR cable, 0.9m in length and total diameter of 22.1mm, made of 7 steel wires and 26 aluminium wires was employed. Artificial damage was made at 0.45m from the emitter transducer; cut depth in the cable was gradually increased from 1mm to 9mm. The transducers were attached to the ends of the ACSR cable using a liquid coupling medium. A function generator was used to drive the transmitter transducer with five cycles of 500 kHz sinusoidal waves. The received guided wave signals were amplified and acquired by a digital oscilloscope that sent the data to the computer for further analysis. From this, the following conclusions were obtained: a) the modes identified using time- frequency analysis before and after the cut were

L

(0,1) and

F

(1,1) for steel and aluminium, respectively; b) the amplitude of the received

L

(0,1) signals increased with the increase of the cut depth, depicting an exponential behaviour, conversely the

F

(1,1) modes decreased, suggesting a mode conversion from

F

(1,1) to

L

(0,1) modes due to loosed friction contact among individual wires.

R. Mijarez, A. Baltazar

### Use of Acoustic Emission Method for Detection of Two-Phase Flow in Service Open Type Water Pipeline

Damage evaluation of a pipeline system is normally used by non-destructive testing method (i. e. elastic wave method). For effective maintenance and management of pipeline system, it is necessary to evaluate not only the degree of damage but also the water-flow conditions (i.e. gas-liquid flow). In this study, acoustic emission (AE) method was applied to be detecting a gas-liquid flow in service open type water pipeline system. Two experiments were conducted: laboratory model tests and in service open type pipeline monitoring. The results show that a gas-liquid flow conditions could be quantitatively evaluated by using AE para­meters, such as AE generation behavior, average frequency and AE energy. Thus, AE monitoring is effective for qualifying the water flow conditions in an open type pipeline system.

T. Suzuki, T. Naka, M. Ohtsu

### Acoustic Emission Diagnostics of Roller Bearings Damage

This paper shows potential applications of the AE method for identification of damage at early stages in rolling bearings. The experimental part is concerned with the results of AE application during durability testing of axial and radial bearings. The recent group of experiments was carried out on durability test stations for radial bearings. Sensing of AE signal on these devices was complicated by the position of the tested bearing inside the station, making it to place the AE sensors in its direct vicinity. As a solution, waveguides were used, with one end touching the outer ring of the bearing and the other end connected to the sensor. Other sensors were placed on the surface of the testing station. Despite these complications with AE signal sensing, an optimal setting was found for the measuring chain resulting in collection of high-quality data from damaged radial bearings. Examples of basic AE signal records from rolling bearing and potentials of the new generation AE analysers are mentioned. These devices allow for continuous AE signal sensing. The results prove the AE technique enables reliable determination of running-in period, stabilised run and the prediction of the stage where surface damage forms. It is shown that the AE method can be used to predict bearing defects or can be used to complement traditional vibration bearing monitoring.

P. Mazal, F. Hort, F. Vlasic

### Wireless Sensors for Measuring Wind-Borne Pressures During Hurricanes

A third generation of wireless sensors was developed to study wind-borne pressure variations in low-rise buildings during hurricanes. The system has the capability of measuring pressure and temperature along a roof, collecting data and sending it to a server to process and publish on the web in near real-time. Also wind speed and direction are measured by the system with the use of an anemometer. Sensors are placed inside individual custom-made plastic weatherproof cases. Small size of all components allows an aerodynamic shape, reducing the shape effect of the sensor on the flow. Low power consumption combined with Li-Ion batteries provide several days of continuous data collection. The platform created allows using almost any type of sensor via a planned expansion port. The paper presents some preliminary results.

J.-Paul Pinelli, C. Subramanian, I. Kostanic, G. Lapilli, J. Chandiramani

### Overview of Fiber Optic Sensors for NDT Applications

Optical fiber sensors have seen an increased acceptance as well as a widespread use for structural sensing and monitoring in civil engineering, aerospace, marine, oil & gas, composites and smart structure applications. Optical fiber sensor operation and instrumentation have become well understood and developed. Fiber sensors are attractive sensing devices for non-destructive testing (NDT) applications given their small size, lightweight and dielectric glass construction that renders them immune to electrical noise and EM interference—unlike most conventional electronic sensing systems. To date, fiber sensors have been embedded inside composite materials to determine curing, internal stresses and deformations as well as to detect the onset of cracks and damage. Surface mounted devices allow for the on-line monitoring in real time of deformations and strains in a variety of test specimens. Furthermore, some specific fiber sensor types allow for multi-point sensing at different locations using a single fiber, or even continuous, distributed sensing of temperature and strain based on Raman and Brillouin scattering systems. This paper reviews the operating principles, sensor types, benefits and applications of optical fiber sensors for non-destructive testing of materials and structures in different fields such as composites, aerospace, civil engineering, oil & gas and others.

A. Méndez, A. Csipkes

### Evaluation of Concrete Properties by Combining NDT Methods

The combination of NDT methods is currently considered as one of the more relevant way to improve the quality of the diagnosis of concrete structures. Indeed, many research actions involve the use of several families of NDT methods (ultrasonic, electromagnetic…) for the imaging of structures (voids detection, tendons and reinforcement localisation). Previous studies have shown that this approach is particularly suitable for assessing concrete properties, because concrete is a complex material in which the properties are interacting. For instance mecha­nical properties depend on moisture which also affects the NDT measurements. On one hand, moisture can be considered as a bias factor which affects the measurement but on the other hand, moisture has also to be considered as a durability indicator, as in such conditions the penetration of aggressive agents and the development of internal reactions is favoured. The combination of NDT methods, some being mainly sensitive to mechanical properties and others being more affected by moisture could be really relevant. Another approach concerns the assessment of chloride content which is also significantly affected by moisture. This paper will describe how the role of NDT methods regarding some concrete properties can be quantified. A specific procedure is also proposed to assess the complementarity of different NDT methods regarding the evaluation of two conjugated properties.

J. P. Balayssac, S. Laurens, D. Breysse, V. Garnier

### Thermography and Ultrasound for Characterizing Subsurface Defects in Concrete

A combination of non destructive testing (NDT) techniques is applied for subsurface damage inspection. Thermography and ultrasound are used complimentarily to detect and characterize near surface cracking. In this paper, specimens with subsurface cracks, are scanned by an infrared camera in order to indicate the position of the cracked area. For cases of small and thin cracks the cooling off curves over a specified time span are examined in order to identify the damage areas more reliably. At the specific position indicated by thermography, ultrasonic sensors are placed in order to make a more detailed assessment for the depth of the crack. Although there is no visual sign of damage, ultrasonic waves are influenced in terms of velocity and attenuation.

E. Z. Kordatos, D. V. Soulioti, M. Strantza, T. E. Matikas, D. G. Aggelis

### Determination of the Frequency Dependent Dynamic Modulus for Asphalt Concrete Beams Using Resonant Acoustic Spectroscopy

The objective of this paper is to study the application of resonant acoustic spectroscopy (RAS) to beam shaped asphalt concrete samples. Natural modes of vibration are generated by a small load impulse at different temperatures and an accelerometer measures the resulting acceleration through the specimen. By using the Fast Fourier Transform the obtained information is transformed to frequency domain from which the solid’s damped natural frequencies can be determined. For each frequency and temperature the corresponding complex modulus is calculated using the approach of RAS. Results of the dynamic modulus from RAS are presented and compared with results of the dynamic modulus calculated according to ASTM E 1876-99 [1]. By using ASTM E 1876-99 only the fundamental frequency of each type of vibrational mode can be used. However, using RAS several resonance frequencies from the same temperature can be used in the evaluation. This opens the possibility of determining the high frequency (or the low temperature) part of the dynamic modulus mastercurve directly from RAS.

A. Gudmarsson, N. Ryden, B. Birgisson

### Assessment of Fire Damaged Concrete via the Hammer-Drill Pulse Transmission Technique

The point-by-point measurement of the resistance to hammer-drilling is a viable way to scan the steep gradients of residual mechanical properties exhibited by fire damaged concrete members. Despite the interesting pros of this technique (rapidity and immediate availability of the results), previous studies pointed out its insensitivity to low levels of damage and the significant variation that can be attributed to the coarse aggregate. In order to overcome these limitations, a renewed version has been developed, based on the continuous monitoring of two further phenomena during the drilling operation. The first observation is through acquisition of the compressive pulses generated by the hammering mechanism of the drill, which propagate along the bit shank and are partly reflected in the form of tensile stress waves. The amplitude of the reflected waves provides some meaningful information on the local acoustic impedance of the drilled material. The second observation involves measurement of the time of flight of the pulses propagating from the tip of the drill-bit to a fixed ultrasonic receiver on the surface of the member. This translates into an acoustic scan of the concrete volume enabled by the drilling process. Besides the technical challenges associated with the monitoring of these two phenomena, the paper discusses their sensitivity to fire damage and the ability to detect steep gradients in the residual material properties.

R. Felicetti

### Assessment of the Residual Strength of Fire-Damaged Steel-Rebars

Concrete structures are known to exhibit a good behaviour in fire, thanks to the low thermal diffusivity of the material, which provides an effective protection to steel reinforcement. Moreover, a significant strength recovery occurs when the bars cool down to room temperature, though this markedly depends on their metallurgical properties. Since the surviving structure is still required to bear the noticeably-higher loads assigned by the ultimate limit state, the post-fire strength of the reinforcement has to be carefully weighed up. To this purpose, two different Non-Destructive Techniques are investigated in this study. The first one is the Dynamic Hardness Test (also known as Leeb Test), which is quite sensitive to steel decay. The test can be performed onsite by means of a small specifically-designed device, provided that the surface of the bar has been smoothed prior to testing. The second technique is based on the continuous monitoring of the drilling resistance via a special setup, which allows to measure the thrust to be exerted on the bit in order to keep a constant feed rate. This latter method requires no sample preparation, but the correlation with steel decay is rather uncertain, due to the conflicting effects of the decreasing yield strength and the increasing hardening and strain capacity of fire damaged steel. The pros and cons of these two methods are discussed in the paper, in view of their practical implementation for assessing the post-fire safety of actual structures.

R. Felicetti, P. G. Gambarova

### Damage Assessment by Ultrasonic Images in Concrete Subjected to Freeze-Thaw Cycles

This paper reports on damage evaluation of concrete subjected to freeze-thaw cycles using ultrasonic images. The use of automated ultrasonic inspection systems supplies velocity and attenuation maps, providing the spatial variations in velocity and attenuation in concrete specimens with high resolution. Assessment of damage in concrete specimens is conducted defining several parameters extracted from the ultrasonic images obtained before and after the freeze-thaw cycles. These parameters are related to surface scaling and internal cracking. Experimental trials were carried out using different concrete specimens with and without air-entraining agents. Comparisons between the parameters obtained from the ultrasonic images and the failure criterion defined by the standard ASTM C666/C666M-03 are performed. As a result, this work shows the feasibility of using ultrasonic images as an effective tool for evaluating freeze-thaw damage in concrete.

M. Molero, G. Al-Assadi, S. Aparicio, M. J. Casati, M. G. Hernández

### Evaluation of Temperature Influence on Ultrasound Velocity in Concrete by Coda Wave Interferometry

Ultrasonic methods are valuable tools for the assessment of concrete quality and for imaging inclusions in concrete. In such applications, accurate and reliable determination of ultrasonic wave velocities as affected by various experimental and environmental factors is essential. In this research Coda Wave interferometry (CWI) was used to determine the influence of temperature (20 to 50° C) on ultrasonic wave velocity in concrete samples. A resolution of better than 10

-2

% was achieved in the measurement of relative velocity changes. In addition the influence of sensor (transmitter and receiver) positioning errors on the results of the interferometric algorithm was evaluated. The presented results can be used to correct and refine data from monitoring systems, which may enable improved quality assessment and imaging by use of CWI.

C. Wunderlich, E. Niederleithinger

### Monitoring the Stress Level of Concrete Structures with CODA Wave Interferometry: Experimental Illustration of an Investigated Zone

The use of Coda Wave Interferometry (CWI) to Non Destructively assess concrete structures is an emerging topic. CWI has recently been proposed to determine the stress level of in situ pre-stressed concrete structure as well as to monitor damage of concrete material. The idea is using ultrasonic waves with a wavelength similar to the aggregate size to be in the diffusive regime, and so to probe very small changes of the material. The velocity change is of the order of 0.1% for classical concrete under a 10MPa strain which can be measured with CWI. This velocity variation can be linked to the stress level modification by Murnaghan’s theory. While CODA theory and experiments are emerging in the civil engineering NDT laboratory, it becomes relevant in parallel to know what is actually the investigated zone for,

in fine

, relating the velocity changes to a given distribution of stress or damage as a function of depth in

in situ

condition. In this paper we show an experiment that illustrates the existence of an investigated zone in a concrete beam of 0.8 m x 0.2 m x 0.1 m.

Y. Zhang, O. Abraham, A. Le Duff, B. Lascoup, V. Tournat, E. Larose, T. Planes, R. El Guerjouma, O. Durand

### Non-Destructive Measurement of Steel Fiber Dosage and Orientation in Concrete

Steel fiber reinforced concrete is nowadays frequently used in civil ­engineering and in the building industry. Apart from the general state of the concrete, the dosage and the distribution of the steel fibers are of prime importance for the quality of the structure. The current standard methods to determine the fiber dosage and the fiber orientation are complicated, time-consuming and expensive. In order to determine the steel fiber dosage in drilling cores, the samples have to be destroyed. A better non-destructive and competitive method is high in demand to supervise the steel fiber dosage not only during the production of new structures and buildings but also to examine drilling core samples from damaged structures.

H-Joachim Wichmann, H. Budelmann, A. Holst

### Application of an Electromagnetic Method for Evaluation of Chlorine Distribution in Concrete

Presence of chloride ions in cover concrete leads to an enhanced ­deterioration of reinforced concrete structures. Prediction of the resultant damage in early stages of development is not possible, unless the distributions of chloride ions across the concrete section are known. This paper presents an on-going study of evaluating such distribution by a non-destructive method using electromagnetic wave. The technology is introduced in a separate paper in the symposium, shows in laboratory experiments its applicability to structures whose concrete properties are known. The ability to estimating the said distribution in cross section in existing concrete structure has been investigated in field tests and the method to be equally usable has been found by modifications of the method based on actual concrete properties in question. Once established, the method will ­provide a valuable means of readily collecting, not a limited and point-based data from cores, but information of area-wide chlorine ions non-destructively. This should, in turn, allow the owner of the concrete structure to identify chlorine deterioration at an early stage and to formulate effective strategies against the resultant damage.

J. Nojima, M. Arai, T. Mizobuchi

### A Study on the Variability of Electrical Resistivity of Concrete

The article presents results stemming from two French collaborative research projects (SENSO and APPLET). Electrical resistivity measurements are studied either as a tool of control of on-site structure, or as an indicator of durability. The results concern the evaluation of resistivity measurements variability at various scales. They enable to make the part between the real material information and spurious variations of various origins. We distinguish the repeatability, the reproducibility, the local variations, then, the variations on one batch, between batches and between concretes. The results show that the measurement technique is adapted to needs, and that the various variabilities remain smaller than the variations of properties looked for.

J-F. Lataste, D. Breysse

### Factors Affecting the Electrical Resistivity of Concrete

Field experience indicates that the traditional design methods are not effective for obtaining durable structures and performance-based methods are attaining more interest. For the production of new concrete structures in severe environments, requirements to chloride diffusivity are increasingly being used as a performance-based specification for concrete durability. As a basis for the concrete quality control during concrete construction, however, the testing of chloride diffusivity is both time-consuming and elaborate. Therefore, the relationship between chloride diffusivity and electrical resistivity should first be established. Then the chloride diffusivity can indirectly be controlled by routine-based measurements of the electrical resistivity during concrete construction. Electrical resistivity is a non-destructive testing method, which allows rapid inspection of concrete structures. Several factors affect such measurements. To provide more information about some of those factors that may affect the results and establish some simple procedures for a routine-based quality control of the electrical resistivity during concrete construction, an experimental program was carried out. The test program included different environmental conditions such as temperature and humidity as well as different concrete mixtures and factors such as binder type, and aggregate content were investigated.

O. Sengul

### A Study of the Parameters that Affect the Measurements of Superficial Electrical Resistivity of Concrete

The electrical resistivity of concrete is an important property in the ­reinforcement corrosion kinetics, since this property and the oxygen access govern the process. Measurement of the electrical resistivity of concrete performed on the concrete surface using Wenner method (called the “superficial electrical resistivity of concrete” in Brazil) is nondestructive and can be rapidly performed in laboratory or in situ. However, this technique is not standardized in Brazil for concrete yet. There is a need to adapt test techniques and evaluation criteria established and used in other countries, with proper justification. Thus, this paper aims at quantifying and discussing some parameters that influence the measurements of superficial electrical resistivity as a contribution to the adoption of a test procedure in Brazil. Investigatins included the influence of the steel bar presence and the proximity to the edges of the concrete elements on measurements, as well as the evolution of the electrical resistivity with increasing hydration. Preliminary results show that it is necessary a minimum distance of 4 cm from the steel bar to avoid the interference of the reinforcement on the measurements; measurements made near the edges can provide more than 80% higher resistivity values; and that the electrical resistivity can increase more than 100% in 6 months due to the cement hydration process.

J. W. Lencioni, M. G. de Lima

### Non-Stationary Identification of Thermal Characteristics of Building Materials

The pore space of building materials can act as an accumulation space, as well as a free space for liquid or gas flows. Such changes in material structure force substantial modification of its effective thermal conductivity and heat capacity. The traditional methods of stationary analysis for the thermal conductivity and calorimetric measurements for the heat capacity are often inaccurate or quite not applicable to a lot of materials of practical importance. The paper demonstrates the original non-expensive non-stationary measurement device for thermal characteristics of building materials, open to a reliable uncertainty analysis of all measurements. Its very simple structure, inspired by the “hot-wire” method, controlling the heat flux generated into a layered structure, is compensated by the non-trivial computational approach, based on the semi-analytical solution of initial and boundary value problems for corresponding differential equations of heat transfer. The numerical discretization uses the Hermite finite-element interpolation technique for the temperature field and its gradient in the Euclidean space and the Crank-Nicholson scheme in time. The required material characteristics are obtained as outputs from the least squares optimization, supported by certain iterative algorithm of the Newton type.

J. Vala, S. Šťastník

### Quantitative Evaluation of Thermal Diffusivity and Thickness of Mortar Cover Using Induction Thermography

This paper presents an inverse method used to determine the thermal ­diffusivity and the cover thickness of a reinforced beam. The steel reinforcement bar was heated with an induction heating device and surface temperatures were recorded with an infrared camera. Then, a numerical modelling was developed in order to simulate the surface temperature. An alternate difference implicit algorithm was used to solve the thermal transfer equation. The method was implemented in an inverse problem that leads to the identification of the thermal diffusivity and the cover thickness. A study of the sensitivity functions revealed that both parameters can be simultaneously estimated during the heating phase. The computational results are in good agreement with reference values.

T. Du, F. Brachelet, D. Defer, E. Antczak

### Three NDT Methods for the Assessment of the Concrete Permeability as a Measure of Durability

This contribution deals with the extensive measurements of the air permeability using TPT (Torrent Permeability Tester), of the water permeability by GWT (German Water Tester) and ISAT (Initial Surface Absorption Test) methods. The measurements were complemented with the determination of compressive strength. By the combination of these methods and their evaluations, it is possible to obtain the data enabling an assessment of the concrete cover quality from the viewpoint of durability on the high level of relevance.

### Use of Dynamic Modulus of Elasticity to Assess the Durability of Self Consolidating Concrete

This paper presents the effect of freezing-thawing on self consolidating concrete (SCC) that contains different percentages of fly ash (FA) and air entraining agents (AEA). The effect of freezing-thawing on concrete is assessed on the basis of the change in the dynamic modulus of elasticity. The dynamic modulus of elasticity is determined from both ultrasonic pulse velocity and resonant frequency tests. An in-house resonant frequency test apparatus was developed using an accelerometer and a data acquisition system. During the development of the test apparatus, structural eigenvalue analysis was also utilized to understand if the correct modal frequency of cylindrical test specimens is detected or not. The dynamic modulus of elasticity is then used to compute the durability factor of SCC specimens that are subjected to freezing-thawing cycles. The relationship between durability factor – FA – AEA content was evaluated, and the highest degree of reduction in durability factor was observed at mixes including maximum FA content, and no AEA and maximum AEA content. Furthermore, when FA was used in the range of certain limits, it was observed that SCC specimens were resistant to freezing-­thawing cycles.

N. G. Özerkan, İ. Ö. Yaman

### Effect of Concrete Mixtures on Estimation of Porosity by Ultrasonic Velocity

The most used measurement is undoubtedly the measurement of porosity accessible to water. The relationship between concrete mixtures, porosity and ultrasonic velocity of concrete samples measured by ultrasonic NDT is investigated. This experimental study is interested in the relations between the ultrasonic velocity measured by transducers of 49.5mm [1,98in.] diameter and with 54 kHz frequency. Concrete specimens (160 mm [6,3in.] diameter and 320 mm [12,6in.] height) are fabricated with concrete of seven different mixtures (various W/C and G/S ratios), which gave porosities varying between 7% and 16%. Ultrasonic velocities in concrete were measured in longitudinal direction. Finally the results showed the influence of ratio W/C, where the porosity of the concretes of a ratio W/C ≥ 0,5 have correctly estimated by ultrasonic velocity. The integration of the concretes of a lower ratio, in this relation, caused a great dispersion. Porosity estimation of concretes with a ratio W/C lower than 0,5 became specific to each ratio.

A. Benouis, A. Grini

### Nondestructive Assessment of Alkali-Silica Reaction in Concrete: A Review

This paper presents state-of-the-art information on the theory and application of nondestructive testing (NDT) techniques used for assessing alkali-silica reaction (ASR) in concrete. The focus is on the application of both linear and nonlinear acoustics (LA and NLA) for detecting ASR. Previous studies have shown that LA methods are less sensitive to early detection of damage in concrete and reliable interpretation of their results depends on the initial condition of the concrete. In contrast, NLA are more sensitive to early cracking and may distinguish ASR from other types of damage. The fundamental concepts of LA and NLA and their application to concrete for detecting ASR are presented with a critical review of their capabilities and limitations.

### Homogeneity Detection of Fibre-Concrete Structures Using Radiographic Technique

Fibre-concrete structures have many advantages compared to standard reinforced concrete, for example, higher strength and higher tensile strength of fibre-concrete. However, fibres are often incorrectly distributed in structure during their manufacture. Wires are often clustered, which reduces the overall homogeneity as well as the quality of fibre-concrete structures. The aim of the research team of the workers from three technical universities in the Czech Republic was to develop an objective method of control that would allow establishing the homogeneity of wire distribution in finished fibre-concrete structures.

L. Hobst, O. Anton, J. Vodicka, J. Scucka

### Use of Acoustic Emission Data Clustering to Identify Damage Mode in Concrete Structures

Acoustic Emission (AE) technique gained increasing interest in the last two decades as monitoring methodology and as assessment tool for safety and reliability evaluation of reinforced concrete structures, historical and masonry buildings. However a widely accepted analytical instrument for AE data handling and interpretation is still missing. Cluster and discriminant analysis have been recently applied to classify AE patterns and to identify damage modes. Aim of this paper was to develop a cluster analysis procedure devoted to identify cracking mechanisms in concrete structures. Unsupervised methods, k-means as well as Principal Component Analysis and Self Organizing Map, have been used as analytical instruments. A procedure aimed to remove environmental AE noise has been also proposed.

L. Calabrese, G. Campanella, E. Proverbio

### NDT of LWC with Expanded Clay

(lwc

) is increasingly used in construction, namely

lwc

with aggregates of expanded clay type called Liapor. It is often necessary to perform tests for the characteristics of cast-in-place concrete during building construction as well as after the construction. One of the ways to control the quality of LWC in a structure is using non-destructive testing (NDT) methods. For compressive strength, there are reflective rebound methods and ultrasonic pulse method (UPM) which may also be used for determination of dynamic modulus of elasticity. This paper presents the results of NDT of LWC with expanded clay using above the mentioned methods and as well as the associated calibration relations. A comparison of conversion coefficients obtained from modulus of elasticity tests on normal-weight concrete (NWC) and LWC is also provided. The developed calibration relations resulted in a high degree of correlation between the NDT results and the results of compression tests on concrete specimens.

J. Brozovsky, D. Benes, J. Zach

### Evaluation of Rebound Hammer Test as a Combined Procedure Used with Drill Core Testing for Evaluation of Existing Structures

Rebound hammer is a non-destructive test method often used to assess the surface hardness of engineering materials. The method is used as a part of the procedure applied to evaluate existing structures. The concrete core tests are usually combined with rebound hammer tests to decrease costs and damage to the structure. Various studies attempted to establish a reliable relationship between the concrete strength and the rebound coefficient. Proposed formulas and correlation coefficients stayed reliable for narrow limits on factors like concrete age, composition, moisture content, etc. Despite the high uncertainty of the raw data the methodology remains in use. This paper presents the evaluation of rebound hammer and drill core test data from 256 different buildings in Antalya, Turkey. With uncontrolled parameters like environmental factors, age, compressive strength of concrete, the rebound hammer test results showed very little correlation with concrete core test results even for the statistically large data set.

S. Yeşilmen

### An Experimental Study on the Evaluation of Concrete Test Results

The compressive strength test applied to standard samples is one of the most important tests indicating the quality of concrete in structures. The results of the standard tests are compared with the values used in design calculations to check for specification compliance and quality assurance. Although the standard tests are well accepted by the construction industry, they may not represent the in-situ strength of concrete due to the differences between the degree of compaction and curing conditions of concrete and those of standard samples. The quality of concrete can be assessed by means of minor-destructive methods. Pull-out test is an example of minor-destructive tests. The test causes only minimal destruction to the structure and the hole is repaired easily after testing. In the present study, the results from pull-out tests, and maturity method were extensively analysed for the assessment of concrete strength.

O. Arioz, K. Kilinc, M. Tuncan, K. Ramyar, A. Tuncan

### Detection of Incipient Decay of Wood with Non- and Minor-Destructive Testing Methods

For inspections of timber structures it is important to find defects, damages and material heterogeneities in the interior of wooden construction components. Undetected decay (especially interior rot) can result in a sudden failure of the construction. In the usual structural safety analysis of timber structures, damages and their extent are estimated by visual inspection of drilling cores and by the determination of the drilling resistance. Both reveal information only about this single point of measurement. Often repeated sampling (numerous drilling cores) becomes necessary, which still may be insufficient to assess larger buildings. The destruction from drilling cores must be considered, it´s not suitable for statically highly stressed parts (which should all be covered). In heritage-protected buildings, drilling cores and the drilling resistance method are rather limited. With the visual inspection of the drilling cores without further magnifying devices, decay can only be detected in the advanced stage. Incipient fungal attack, which already has a significant influence on the elasto-mechanical properties, can´t be detected. The drilling resistance method and drilling cores are compared with the ultrasonic echo technique with regard to their suitability for structural health monitoring of timber constructions. The low reliability of assessing the drilling cores by visual inspection for incipient fungal attack shall be improved by further non-destructive tests of the drilling cores. The applications of non- and minor-destructive test methods are considered, particularly their use in cultural timber structures.

K. Frühwald, A. Hasenstab, K. Osterloh

### Coupling AE Monitoring with Discrete Element Fracture Models

The monitoring and analysis of acoustic emissions related to fracture can be a trade-off between the simplistic yet practical empirical relationships and the more tedious yet fundamental relationships. In an intermediate area between these extremes, we are using acoustic emissions to monitor progressive fracture energy of small specimens of clear-grained wood. The wood specimens were modeled using a statistically variable lattice to represent material heterogeneity and disorder. The central hypothesis of the work is that a microfracture event captured by AE should correspond to the fracture of lattice elements in the simulation. Furthermore, the energy of the AE event should correspond to the local fracture energy released in the lattice simulation. By coupling lattice simulations with laboratory tests, we were able to establish a ratio between the cumulative fracture energy released in the simulation with the relative energy monitored by the AE system up to peak load. The magnitude of this ratio varies with failure mode, but in all cases, the shape of the cumulative AE energy captured mirrors the shape of the cumulative lattice fracture energy released. The results allow us to better match lattice element properties with the physical microstructure that the lattice elements are meant to represent.

E. N. Nagy, W. G. Davids, E. N. Landis

### Use of High Resolution Digital Images and NDT Imaging Techniques for Characterization of Timber Elements

In this paper the combined use of high resolution images of wood texture and non destructive imaging of internal defects of wood is proposed for the characterization of structural timber on site. Experimental results are presented, based on the integrated use of digital photogrammetry, ultrasonic tomography and image analysis techniques. The implemented methodology aims at investigating the exploitation of some digital imaging techniques as complementary tools to be used during visual inspection.

M. Riggio, F. Prandi, R. De Amicis, M. Piazza

### Relative Effects of Porosity and Grain Size on Ultrasonic Wave Propagation in Marbles

Grain size determinations by various ultrasonic techniques have been considered by several researches. Among the known methods, the ultrasonic seems to stand out because the method could be used to determine many properties of the materials. In this paper, we investigated that relative effect of porosity, mean grain size on ultrasonic velocity in marbles. We have represented ultrasonic velocity–porosity and porosity-grain size master graph. Using this graph, we have compared mean grain size of marble samples by optic microscope images. The experimental data are compared with the velocity versus porosity curves calculated according to ultrasonic methods. We see that ultrasonic velocity and porosity has showed a linear relation with the mean grain size of samples.

V. Özkan, İ. H. Sarpün, S. Tuncel

### Defect Detection in Porcelain Tiles Using Ultrasound

The main point of this work is the optimization of ultrasonic methods for the non-destructive testing of sintered porcelain tiles containing defects. Zirconia and steel balls of different diameter and rubber with different thicknesses were imbedded in porcelain tile granules before pressing. After being sintered at 1473 K, the tiles were inspected using ultrasound. This method may allow defect detection using an A-scan. It can be observed that the amplitude of the back wall echo for a defective part is smaller than for a part without defects. Depending of the size, shape and position of the defect, a defect peak can be observed. An immersion pulse-echo C-scan was used to differentiate defects. The shape and place of the defects can be defined.

E. Eren, S. Kurama

### Characterization of Synthetic Emeralds Based on the Morphology of their Inclusions

The aim of the presented work was the characterization of synthetically manufactured emeralds by means of X-ray micro computed tomography (CT). As the result of the CT measurements, a three-dimensional volume representation of the gemstones became available. Three synthetic emeralds were measured containing different kinds of inclusions. For data evaluation, an image processing chain was designed, which is adapted to the particular requirements of emerald analysis. An essential aspect was the extraction of inclusions and inhomogeneities from the reconstructed volumetric data and their characterization regarding morphology. Furthermore, results of microscopic investigation of the samples have been compared to results of CT measurements demonstrating the suitability of CT for finding inclusions in emeralds.

A. Mueller, U. Hassler, J. Zaeh

### Can Proteoglycan Change in Articular Cartilage be Detected by Ultrasound Evaluation?

This paper assesses the capacity of high-frequency ultrasonic waves for detecting changes in the proteoglycan (PG) content of articular cartilage. 26 cartilage-on-bone samples were exposed to ultrasonic waves via an ultrasound transducer at a frequency of 20

MHz

. Histology and

ImageJ

processing were conducted to determine the PG content of the specimen. The ratios of the reflected signals from both the surface and the osteochondral junction (OCJ) were determined from the experimental data. The initial results show an inconsistency in the capacity of ultrasound to distinguish samples with severe proteoglycan loss (i.e. >90% PG loss) from the normal intact sample. This lack of clear distinction was also demonstrated for samples with less than 60% depletion, while there is a clear differentiation between the normal intact sample and those with 55-70% PG loss.

I. Afara, S. Wallace, S. Singh, A. Oloyede

### Near Infrared for Non-Destructive Testing of Articular Cartilage

The concept of non-destructive testing (NDT) of materials and ­structures is of immense importance in engineering and medicine. Several NDT methods including electromagnetic (EM)-based e.g. X-ray and Infrared; ­ultrasound; and S-waves have been proposed for medical applications. This paper evaluates the viability of near infrared (NIR) spectroscopy, an EM method for rapid non-destructive evaluation of articular cartilage. Specifically, we tested the hypothesis that there is a correlation between the NIR spectrum and the physical and mechanical characteristics of articular cartilage such as thickness, stress and stiffness. Intact, visually normal cartilage-on-bone plugs from 2-3yr old bovine patellae were exposed to NIR light from a diffuse reflectance ­fibre-optic probe and tested mechanically to obtain their thickness, stress, and stiffness. Multivariate statistical analysis-based predictive models relating ­articular cartilage NIR spectra to these characterising parameters were ­developed. Our results show that there is a varying degree of correlation between the ­different parameters and the NIR spectra of the samples with R

2

varying between 65 and 93%. We therefore conclude that NIR can be used to determine, nondestructively, the physical and functional characteristics of articular cartilage.

I. Afara, T. Sahama, A. Oloyede

### Characterization of Fresh and Early Age Concrete Using NDT

The paper reviews a few methods which are suitable for the continuous measurement of the stiffening and hardening behavior of mortar and concrete. These are the dielectric method, the nuclear magnetic resonance method, the ultrasonic methods as wave-reflection method and wave-transmission method. The first two methods detect mainly the distribution of water in the sample as function of hardening time, while the other two methods rely on the development of the mechanical properties. The measurement principles are discussed and testing devices are described.

H. W. Reinhardt

### Factors Affecting the Monitoring of the Early Setting of Concrete by Ultrasonic P-Waves

Ultrasonic P-wave measurements are widely used to monitor concrete setting. Although the largest wave velocity increase occurs during setting, the earliest increase is rather caused by other factors. Air bubble migration, internal settling, formation of ettringite and early C-S-H, workability loss and thixotropy might affect the velocity change in time. Tests on mortar in which cement was replaced by bentonite, confirmed the possible influence of thixotropy on the measurements. The effect of air bubble migration, internal settling and workability loss was proven to be restricted by testing a mixture in which the cement was replaced by inert material. In a cement mixture, the precipitation of hydration products might however accelerate settling and workability loss. During cement hydration simulations, the change in porosity due to the formation of early C-S-H and ettringite was considered for the calculation of the elastic properties of the granular framework. Nevertheless, the calculated velocity hardly increased before percolation and thus could not confirm that the first velocity increase is attributed to formation of early hydration products. Thus, apart from thixotropy, none of the other factors could unarguably be indicated as the cause of early velocity increase.

N. Robeyst, C. U. Grosse, N. De Belie

### Automated Shear-Wave Techniques to Investigate the Setting and Hardening of Concrete in Through-Transmission

Ultrasonic methods have been developed in the past few decades to study the properties of cement based materials in fresh and hardened state. However, most of the methods consider only a certain type of ultrasonic waves. To derive elastic parameters of fresh concrete like the Poisson’s ratio and elastic modules it is required to measure shear waves as well as compression waves. It is relatively much more difficult to establish a setup to transmit and record shear waves in a way that the onset of these slower waves can be detected sufficiently clear to calculate the shear velocity with the required accuracy. In this paper, an experimental setup for testing concrete with different ultrasonic waves is presented and methods for automated onset determination of p- and s-waves are described.

M. Krüger, C. U. Grosse, F. Lehmann

### Effects of Experimental Parameters in Monitoring the Hydration of Cement Mortars by Ultrasonic Testing

In ultrasonic pulse velocity testing, frequency and the travel path length are important parameters that determine the attenuation rate and the influence of near-field effect. Higher frequencies and longer distances result in higher attenuation. On the other hand, smaller path lengths are not desirable due to near-field effect. This study investigated the effect of transducer frequency and the length of path used to determine ultrasonic wave velocity in monitoring the hydration process of fresh cement mortars. For this purpose, an experimental set-up was prepared to observe the ultrasonic pulse velocity (UPV) development in cement mortars during the first 24 hours after mixing. Mortar mixtures with a water/cement ratio of 0.5 were tested for 15, 10 and 5 cm travel path lengths at 54, 82 and 150 kHz frequencies. UPV curves were obtained in each test and some characteristic points on the curves were determined. The results showed that choosing the appropriate frequency and travel path distance is important in monitoring the UPV development in fresh cementitious materials.

Ö. Kasap Keskin, İ. O. Yaman, M. Tokyay

### Ultrasonic Monitoring of Capillary Porosity Evolution and Strength Gain in Hydrating Cement Pastes

An ultrasonic test procedure for determining the capillary porosity in hydrating cement paste is presented. The response of hydrating cement paste through setting is monitored using horizontally polarized shear waves (SH). Changes in the ultrasonic signal through setting are related with changes in the porosity and stiffness of an equivalent water-filled poroelastic material, which provides identical acoustic impedance. The porosity obtained from the ultrasonic measurements, is identical to capillary porosity obtained from the conventional themo-gravimetric analysis. A unique relationship between capillary porosity and compressive strength is established for hydrating cement pastes.

K. V. L. Subramaniam

### Elasticity Modulus Monitoring Through an Ambient Vibration Response Method – Application to Cement Based Pastes

The E-modulus of cement-based materials is a property that experiences a high rate of change at early ages, and its continuous monitoring since casting is fundamental to identify the phase transition from fluid to solid. This paper presents a study with a recently developed non-destructive method for continuous monitoring the E-modulus of cement-based materials since casting. Based on the evaluation of the first resonant frequency of a composite cantilever containing the material under testing, it is possible to detect the E-modulus growth, and also to identify the changes on its evolution due to modifications on the mix composition. Twenty one compositions are tested, encompassing cementitious pastes with five types of cement and five w/c ratios, as well as three different contents of limestone filler, fly ash, silica fume and metakaolin.

L. Maia, M. Azenha, R. Faria, J. Figueiras

### Characterization of Fresh Mortar with Chemical Admixtures Based on Stress Wave Dispersion

The performance of any concrete structure strongly depends on the quality of the fresh material used. This quality should be evaluated at an age as early as possible, even before concrete is placed in the forms. In the present paper fresh cementitious material is examined by means of ultrasonic through-transmission measurements. The frequency is varied in order to apply different wavelengths, the propagation of which is influenced in a different way by the constituent materials, e.g. air bubbles and sand grains. The wave velocity vs. frequency curves obtained for different mixes show that the existence of sand plays an important role due to interaction with different wave lengths. The effect of chemical admixtures is also examined through the release of air bubbles and the change in viscosity they impose. The possibility to characterize the effectiveness of chemical admixtures by a single measurement of dispersion is discussed.

D. G. Aggelis, D. Grammenou

### Analysis of Thermal Properties of Cement Paste During Setting and Hardening

An experimental investigation is made in order to study changes of thermal properties of hardening cement paste. Using a hot disc principle for determination of thermal properties, specific heat capacity, effusivity and thermal conductivity are analyzed during first 4 days of hydration. Specific heat capacity value changed only slightly during hydration. Thermal conductivity decreased with the progress of hydration 20% compared to initial value. Hydration process was monitored using ultrasonic pulse velocity (UPV) test. A discussion of results is made taking into account porous nature of cement paste and transformation of liquid and hardened phases i.e. water and clinker minerals, into hardened structure.The motivation for conducted research is improvement of numerical models for calculating temperature changes in mass concrete structures using hydration dependant thermal properties. Also, another field of application could be the quality control of cement based materials.

D. Mikulić, B. Milovanović, I. Gabrijel

### Application of Ultrasonic Method for Determining Set Times of VMA Modified Cementitious Composites

Viscosity modifying agent (VMA) is added to mortar to increase water retention so that more rendering plaster and tile can be installed. But, VMA would increase viscosity of pore solution to slow down water movement, and thus a dry shell may form due to evaporation. Consequently, Vicat needle test seems improper to determine set times of VMA modified mortars. The ultrasonic pulse velocities (UPV) of early-age VMA modified paste (VMA paste) are ­compared with Vicat test results in this paper. UPV were found to be clearly depicting the dosage effect of VMA on cement retardation, whilst Vicat test could not. Without adding VMA, initial set of Vicat test was found to be near the timing of UPV at 1420 m/s and final set was found no clear relationship with UPV values. However, with the addition of VMA, more investigations by UPV are needed before new criteria on determining both initial and final set times can be proposed.

S. -T. Lin, R. Huang

### The Use of Wireless Sensor Networks to Monitor the Setting and Hardening Processes of Self-Compacting Concrete

Traditionally, the study of cementitious materials has been performed using wired sensor technologies. Because these technologies are expensive and difficult to install, the use of wireless sensor networks has gained increasing importance. In this paper, the study of setting and hardening processes for two different types of self-compacting concrete (SCC) using a wireless monitoring system is reported. The monitoring system used to perform such study consists of a wireless sensor network using Cricket motes. These motes were purchased from Crossbow Technologies. For our research, the most important capability of Cricket motes is that they host a transmitter/receiver in the ultrasonic wavelength region. For monitoring the setting and hardening processes, the velocity of the ultrasonic pulse traveling across the material was measured, along with the humidity and temperature values both inside and outside the concrete sample. Multi-hop data transmission techniques were considered to monitor the velocity data.

Several experiments were performed at the laboratory. A set of samples were manufactured with two types of SCC, in one type some portland cement was replaced by limestone filler. These specimens were exposed to different curing conditions. Although it was found that the ultrasonic acquisition was not very robust, the wireless sensor networks are an efficient technology for monitoring the early stages of self-compacting concrete.

S. Aparicio, J. V. Fuente, J. Ranz, J. Aliques, M. A. G. Izquierdo, R. Fernández

### Early-Age Ultrasonic Testing of Concrete and Shotcrete using Embedded Sensors

This paper presents the results of preliminary laboratory testing of early-age concrete properties using disposable, embedded ultrasonic sensors. These tests were carried out during the development of a field system for monitoring the early-age physical properties in concrete and shotcrete. The design is particularly suitable for applications in Fibre Reinforced Shotcrete (FRS), commonly used for ground support in underground mine tunnels in Australia, where the determination of early-age properties is critical for establishing safe re-entry times. The embedded system used in these experiments comprises a pair of piezoelectric transducers mounted to an open frame, which is designed to hold them within the concrete at a fixed offset separation. The probe is implanted at the time of placement, and connected via wire leads to an external control system. The implanted transducers are configured to excite longitudinal (P) waves, at a nominal resonance frequency of 40 kHz, and P-wave transmission is detectable soon after the initial set time. The data presented herein includes evolution of early-age P-wave velocity. This data is compared to conventional unconfined compressive strength (UCS) and dynamic (low strain) elastic modulus, as specified in ASTM C215, for equivalent batches and curing conditions. The embedded P-wave measurement is functionally equivalent to the conventional dynamic modulus testing procedure, and these results may be further used to infer UCS during the early stages of hydration. The ability to perform in-situ, real time, nondestructive testing offers significant advantages to the safe and efficient use of FRS in underground mining applications.

A. Gibson, D. Ciancio

### Continuous Monitoring of Setting and Hardening of Epoxy Resin

A problem in the manufacturing of composite materials is the monitoring of the curing process in order to distinguish the different stages of the structural formation and to provide adequate conditions for proper epoxy impregnation. The method used to monitor the setting and hardening of epoxy in this study is based on ultrasonic propagation. A wave generator was connected to a sensitive broadband acoustic emission transducer in order to transmit elastic waves through the thickness of setting and hardening epoxy. The acquisition was conducted by another sensor of the same type acting as receiver. Different parameters like the wave velocity and attenuation are monitored in order to examine the rate of hardening. The changes in viscosity and elastic modulus with time can be monitored by the changes in the wave parameters. The effect of temperature is also discussed.

S. Grammatikos, D. G. Aggelis, A. S. Paipetis

### Characterization of Steel Microstructures by Magnetic Barkhausen Noise Technique

Optimization and control of the microstructure is vital for improving performance and service life of the steel components. Development of non-destructive techniques for microstructure characterization has been a challenging task for many years. Magnetic Barkhausen Noise method is a non-destructive evaluation technique with high potential for characterization of steels. This paper summarizes the related studies performed at METU.

C. H. GüR

### Magnetic NDE with Magnetic Yoke-Probe for Degradation and Mechanical Properties of Steel

Magnetic NDE techniques for an estimation of distribution of degradation in tensile-tested structural steel and for an evaluation of mechanical parameter alike hardness in low carbon steel have been developed. In order to scan magnetic properties of steel promptly, a magnetic yoke-probe having primary and secondary coils wounded around the yoke was adopted. To simplify the detection procedure, the same principle as a transformer and the impedance measurement using the secondary coil were employed. The voltage induced at and the impedance of the secondary coil decrease with the increase of applied tensile stress. As for the spatial distribution of the measured parameters, the induced voltage and the impedance at the center part of specimen which was subjected to a large stress decrease, and the area where the induced voltage and the impedance decrease becomes wider with increasing applied tensile stress. The induced voltage and the impedance decrease with increasing hardness in low carbon steel.

H. Kikuchi, Y. Kamada, S. Kobayashi, K. Ara

### Magnetic Inspection of Low-Carbon Steels Subjected to Plastic Deformations up to Failure

The possibility of magnetic inspection of plastic deformations preceding the failure of strained steel constructions was studied by locally magnetizing them with an attachable U- shaped electromagnet. Field dependences of the differential magnetic permeability of a plate made of low-carbon steel (0.09% C, 1.4-1.8% Mn) on the applied and residual stresses were determined. Critical fields of 90 and 180 degrees domain-wall motion at different deformations were calculated using a model taking into account the contribution of these domain walls to magnetization reversal processes.

A. N. Stashkov, A. P. Nichipuruk, V. N. Kostin, M. K. Korkh, S. A. Murikov

### Thermography and Acoustic Emission for Monitoring the Fracture of Aluminium Plates

Acoustic Emission (AE) supplies information on the fracturing behavior of different materials. In this study, AE activity was recorded during fatigue experiments in metal coupons with a V-shape notch which were loaded in fatigue until final failure. AE parameters exhibit a sharp increase approximately 1000 cycles before than final failure. Therefore, the use of acoustic emission parameters is discussed both in terms of characterization of the damage mechanisms, as well as a tool for the prediction of ultimate life of the material under fatigue. Additionally, an innovative nondestructive methodology based on lock-in thermography is developed to determine the crack growth rate using thermographic mapping of the material undergoing fatigue. The thermographic results on the crack growth rate of aluminium alloys were then correlated with measurements obtained by the conventional compliance method, and found to be in agreement.

E. Z. Kordatos, D. G. Aggelis, T. E. Matikas

### Nonlinear Acoustic Effect due to Evolution of a Crack and Detection of Micro-Scale Cracks in a Fatigue Process

Nonlinear acoustic effect is sensitive to a micro-scale crack or pre-cracking stage of the fatigue process. A resonant ultrasound spectroscopy technique was used for a diagnosis of micro-scale crack in a compact tension (CT) specimen. Information on the normalized amplitude and resonance frequency was analyzed to quantify the degree of nonlinearity and diagnose the micro-cracks. The damage produces a nonlinear stress-strain relationship and the nonlinearity can be measured by increasing excitation amplitudes. The more damage, the larger is the level of a nonlinearity, and it can be used for diagnosis of micro-cracks. The amount of nonlinearity is highly correlated to the damaged state of the material. A shift of resonance frequency as a function of driving voltage or strain is chosen as a nonlinear parameter to correlate the micro-cracks or damage. In addition amplitude of a normalized resonance pattern also reflects the nonlinearity. The normalized pattern of an intact CT specimen and cracked CT specimen were compared.

Y-M. Cheong

### New Ultrasonic Methodology for Determining Temperature Gradient and Its Application to Heated Materials Monitoring

In various fields of science and engineering, temperature measurement has become one of the most fundamental and important issues. For example, in industrial materials processing, it is required to measure the temperature gradient and its transient variation in the material being processed at high temperatures because the temperature state during processing crucially influences the quality of final products. Such temperature measurements are also required for making structural health monitoring at high temperature environments. In this work, a new ultrasonic method for monitoring temperature gradient of a material being heated or cooled is presented. The principle of the method is based on the temperature dependence of the velocity of ultrasonic wave propagating through a material. An effective analysis method coupled with a finite difference calculation is developed to determine one-dimensional temperature distributions in a heated material. To verify the practical feasibility of the method, some experiments have been made. A single side of a steel plate of 30 mm thickness is heated by contacting with a heater and subsequently cooled down by water. Ultrasonic pulse-echo measurements are performed during heating and cooling, and the measured transit time of ultrasound across the steel is used for the analysis to determine the temperature gradient in the steel. Furthermore, rapid heating by contacting with molten aluminium at 700 degree C and rapid cooling by contacting with an ice are evaluated and the transient variations of the temperature gradient in the steel have successfully been monitored.

I. Ihara, M. Takahashi, H. Yamada

### Inverse Problem for Material Analysis by Ultrasound

Internal defects detection by ultrasound non destructive testing is widely used in industry. Ultrasonic time signal data are difficult to interpret since they require continuous signal analysis for each point of the piece. Inverse problem in materials analysis puts some challenges because the composition variables are both discrete and continuous and because the engineering properties are highly nonlinear functions.

In this paper we address the non linear features of back scatted ultrasonic waves from steel plate, for understanding its micro structural behaviour. The experiments show a challenging interface between material properties, calculations and ultrasonic wave propagation modelling.

F. Bettayeb, M. Hakem

### Use of Acoustic Emission Signal and X-ray Diffraction Analysis for Detection of Microstructural Changes in Cyclically Loaded AlMg Alloys

This paper summarizes basic experimental results of microstructural changes during high cycle fatigue loading of AlMg alloys (EN AW-6082 and EN AW-2017). These changes are detected by using of acoustic emission (AE) method. The authors targeted the main attention on more exact identification of causes of changes of AE signal activity in the stage of fatigue damage cumulation. The method of X-ray diffraction analysis of the structure is used for explanation of this phenomenon. The results of presented experimental works indicate the connections between changes of acoustic emission signal and cyclical changes of so called “mosaic blocks” of the crystal structure identified by means of X-rays diffraction during fatigue loading of material.

P. Mazal, P. Liskutin, F. Vlasic, F. Hort, J. Fiala

### Investigating Eddy Current Response to Microstructural Changes to Determine Case Depth of Induction Hardened Parts

The ability to characterize hardness profile in induction hardened steel part is important from quality inspection point of view. Traditional destructive methods such as plotting hardness profile are generally time-consuming. Besides, the tests can not provide 100% quality control in a mass production line. Eddy current response of steel is sensitive to changes in microstructure of the material under investigation. So, the non-destructive method can be used in determining the depth of the hardened layer in steel parts due to the change in the microstructure from the surface to the core of the hardened part. In the present study, induction hardening technique was used to produce different case hardened depths in identical rods of CK45 carbon steel. Plotting hardness profile, effective and total case depths were determined. In order to investigate the applicability of the eddy current technique, relation between effective and total case depth and eddy current outputs (such as primary and secondary voltages and normalized impedance) were studied. High correlation coefficients of these relations indicate an acceptable level of accuracy in comparison with destructive method.

S. Kahrobaee, M. Kashefi Torbati

### Surface Characterization of Carburized Steel by Eddy Current

In the carburizing process, it is necessary to control the surface carbon content in order to obtain desirable materials properties. Although quantometry is the most common method for determination of surface carbon content, being destructive, costly and time consuming are some disadvantages of this method. Eddy current testing has long been used as a technique for investigation of defects. However, determination of surface carbon content in carburized steels is a new application for this method which has been studied in this research. Sixteen AISI 4118 steel samples have been carburized in an enriched carbon gas carburizing furnace. Carbon potentials in the furnace were different for each sample; therefore, samples with various surface carbon contents were produced. Subsequently, the carbon content of all samples was measured using quantometry. Finally, determining the optimal frequency, eddy current testing was applied for all samples and the relationship between surface carbon content and various parameters such as norma­lized impedance and phase angle has been established. The study shows a good relationship between the carbon percent and phase angle can be established (R

2

=0.91) using phase angle. Besides, the effect of temperature on the relationship was also investigated using three levels in 0, 30 and 80 °C. The formulas presented, shows improvement in corresponding corrections in experimental data.

S. Kahrobaee, M. Kashefi Torbati, M. Sheikh Amiri

### Guided Waves for Nondestructive Testing – Experiment and Analysis

Use of ultrasonic waves is continuously increasing for nondestructive evaluation (NDE) and structural health monitoring (SHM) in civil, aerospace, electrical, mechanical and bioengineering applications. Between bulk waves and guided waves, the latter is becoming more popular for NDE/SHM applications because the guided waves can propagate long distances and reach difficult to access regions. Recent advances in the research related to nondestructive testing (NDT) of composites and metals are discussed in this paper. To analyze the experimental results one often needs to understand the mechanics of wave propagation in various structures. Unfortunately, only for simple structures, such as homogeneous and layered half-spaces, plates, rods and pipes, the analytical solutions are available. Complex structural geometries with internal defects are difficult to solve analytically or numerically by the popular finite element method because at high frequencies the size of the finite elements becomes prohibitively small. An alternative mesh-free technique called the distributed point source method (DPSM) is being developed for solving such problems and is discussed here in addition to the experimental results.

T. Kundu

### Ultrasonic Guided Waves for Hidden Damage Detection in Composite Structures: Theory and Experiments

In this paper the theoretical knowledge base required for the ­development of a reliable structural health monitoring system based on ultrasonic guided waves is considered. An exact theory is used for relatively rapid calculation of the PZT driven surface motion in a plate recorded in an ultrasonic experiment. The theoretical results are compared with those obtained from an explicit finite element code for their mutual verification, showing excellent agreement. To determine the location and the severity of a damage with a minimal operator intervention, the ultrasonic wave propagation data are analyzed using a damage index approach carefully designed to overcome the complexity and variability of the signals in the presence of damage as well as the geometric complexity of the structure.

F. Ricci, E. Monaco, S. Tancredi, L. Lecce, S. Banerjee, A. K. Mal

### Nonlinear Ultrasound: A Novel Approach to Flaw Detection and Imaging

Conventional ultrasonic NDT equipment is normally a mono-frequency instrument which makes use of the amplitude and phase variations of the input signal due to its scattering by defects. The nonlinear approach to ultrasonic NDT (NNDT) is concerned with the nonlinear response of defects, which is related to extreme frequency changes of the original input signal. These spectral changes are caused by a high nonlinearity of micro- and macro-scale defects. In the paper, basic mechanisms responsible for frequency conversion by nonlinear defects are discussed and major features of the nonlinear spectra derived. Experimental methodologies of nonlinear scanning laser vibrometry (NSLV) and nonlinear air-coupled emission (NACE) are used to study nonlinear elastic wave-defect interactions. Applications for defect-selective imaging and NNDT are demonstrated for a series of hi-tech materials and industrial components.

I. Solodov, N. Krohn, G. Busse

### Evaluation of Material Degradation of Composite Laminates Using Nonlinear Lamb Wave

This study introduces a new approach to evaluate material degradation caused by thermal fatigue in composite laminates by using nonlinear Lamb waves. The correlation between normalized nonlinear parameters and degradation states is studied. S1 Lamb mode which has phase and group matching features is chosen for the practical generation of nonlinear Lamb wave. The measured acoustics normalized nonlinearity is directly related to material degradation. It could be concluded that it is possible to use nonlinear Lamb waves to evaluate composite laminates degradation.

W. Li, Y. Cho, T. Ju, H. S. Choi, N. Kim, I. Park

### New Opportunities in Ultrasonic Characterization of Stiffness Anisotropy in Composite Materials

Two new ultrasonic approaches to NDT of in-plane stiffness anisotropy have been developed and applied to various composite materials. The first approach is based on polarization measurements of ultrasonic shear waves which manifest birefringence due to asymmetry of in-plane stiffness. Birefringence is applied for monitoring of fibre orientation and evaluation of in-plane stiffness anisotropy in various composites and multi-ply composite laminates. The other approach uses mode conversion of air-coupled ultrasound to zero-order plate waves for remote NDT of the in-plane stiffness anisotropy. A non-contact ultrasonic evaluation of the in-plane anisotropy of Young`s modulus is based on air-coupled measurements of the

$${a}_{0}$$

-wave dispersion extrapolated to a “static” case. Depth-resolved measurements of stiffness anisotropy are demonstrated in multiple composite laminates. The methods and instrumentation developed are capable of detecting improper ply positions and orientation in composite laminates in production phase, variation in stiffness anisotropy due to material aging or damage progression in operation.

I. Solodov, D. Döring, M. Rheinfurth, G. Busse

### Plate Wave Propagation as Damage Indicator in FRP Composites Under Fatigue Loading

Dispersive behavior of plate waves in composite [±45]

S

Gl/Ep specimens is studied through acousto-ultrasonic measurements. Aiming to associate material damage, in this case being matrix cracking, with the propagating wave mode characteristics, acousto-ultrasonic, AU, tests are conducted in the as-received state and repeated after imposing tensile constant-amplitude cyclic loading, interrupted well before failure. Propagating plate waves are captured at several distances from the source and then processed, using two spectral techniques, in order to reconstruct segments of the dispersion curves of the orthotropic medium. Although experimental dispersion curves are in good agreement with theoretical predictions, quantitative damage assessment cannot be achieved. Limitations of the experimental procedure, as well as of the respective data processing, are commented upon. Additional tests, conducted on an isotropic aluminum specimen, are presented to enhance understanding of the complicated phenomenon.

T. T. Assimakopoulou, T. P. Philippidis

### Monitoring of Failure of Composite Laminates using Acoustic Emission

Acoustic emission (AE) is suitable for monitoring the evolution of degradation in structural components as well as for localizing damage. In the present study acoustic emission is employed for the location and identification of the service induced damage in cross ply laminates. The sequence of the different failure mechanisms, i.e. transverse matrix cracking and the subsequent delamination propagation at the 0°/90° interface is followed closely by advanced indices which quantify the attributes of the received AE waveforms. The AE activity can be successfully correlated to the damage accumulation of the cross ply laminates, while specific acoustic emission indices proved sensitive to the various modes that evolve during loading.

A. S. Paipetis, N. M. Barkoula, M. Xyrafa, T. E. Matikas, D. G. Aggelis

### Acoustic Emission of Failure in Fiber-Metal Laminates

This paper studies the failure modes of Glare grades under tensile loading by means of Acoustic Emission (AE). AE transients produced by various types of microdamage, such as yielding, matrix crack initiation, matrix-fiber debonding, matrix cracking and fiber fracture, were recorded as functions of strain for various Glares and fiber orientations. Experiments showed that different microdamage mechanisms produced characteristically different AE signals which can be classified into categories based on peak amplitude and total counts parameter ranges. Moreover, it was observed that AE percent count rate is a function of the normalized strain and metal volume fraction (MVF) in similar Glare lay-ups. In addition, AE profiles were found to exhibit exponential growth behavior in the initial region of the profile and a power growth behavior after the knee point.

R. Kuznetsova, H. Ergun, B. Liaw

### NDE Using Lockin-Thermography: Principle and Recent Developments

Conventional thermography provides colourful images of surface ­temperature fields. If the temperature on a solid surface is periodically modulated, the temperature field propagates into the inspected object as a “thermal wave”. Internal reflections at thermal boundaries are superposed to the original thermal wave. They affect the signal and thereby provide information on thermal features hidden underneath the surface. This information is derived from a stack of thermographic images that are recorded when the sample is periodically excited: Along each pixel of the stack a Fourier transformation is performed of the time dependent signal at the modulation frequency. This way the information content is finally compressed into just two images one of which is the local phase shift between excitation and local thermal modulated response.

The information of such images depends both on the kind of excitation and on modulation frequency: With remote optical excitation, such images display thermal features in a depth that depends on modulation frequency. With excitation by ultrasound, the heating mechanism is local conversion of elastic energy into heat by mechanical losses, e.g. by the relative motion of boundaries in a crack. This way a crack is turned into a thermal wave transmitter. As intact material and boundaries are largely suppressed in such an image, it displays selectively defects. Data fusion of images taken at different frequencies or with different kinds of excitation allows for feature extraction and for additional information on the kind of the defects.

The techniques and their applications will be illustrated by examples that were obtained on various industry-relevant components.

G. Busse, A. Gleiter, C. Spiessberger

### Detection of Very Thin Defects in Multi-Layer Composites Made of Carbon Fibre with IR Thermography Methods

The paper presents issues related to detection of very thin defects in multi-layer composite materials based on carbon fibres. Defects that may occur in this type of multi-layer composite materials include delaminations and incomplete bonding of composite layers. Thermal non-destructive tests (NDT) have been recognised as an effective method of defect detection in multi-layer materials.

W. Swiderski

### A Comparison Between Optimized Active Thermography and Digital Shearography for Detection of Damage in Aerospace Composite Structures

The main goal of this research is to compare capabilities of two different Non-Destructive Testing (NDT) methods, thermosonics and digital shearography (DISH), to recognize and image back drilled hole defects. Thermosonics was optimized by varying magnitude of the heat flux, the excitation frequency, the number of excitation cycles, acquisition time, frame rate etc. DISH was optimized by investigating the test objects by dynamic loading approach in order to identify per each defect the (0 1) mode shape and the corresponding resonance frequency. In this way, whilst thermosonics provided the initial infrared imaging of the panel for a pass/fail test, DISH has been performed to provide the delamination quantitative assessment.

G. De Angelis, M. Meo, D. P. Almond, S. G. Pickering, S. L. Angioni

### Analysis of Laminar Fiber Composites with Computed Tomography Using Shape-Fitted Layers

Fiber composites often consist of several layers with different fiber orientations and are formed in a three-dimensional shape. For non-destructive testing of these components industrial computed tomography (CT) can be used to analyze the internal structures and to detect inhomogeneities or defects. A set of several hundred X-ray projection images is acquired from which the local attenuation coefficients of the components are reconstructed to a three-dimensional volume. Difficulties arise when the three-dimensional volume representation of a laminar component is visualized. Often these components are curved and thus it is difficult to analyze the individual layers of the laminate by scrolling through the slices of the Cartesian volume.

This presentation describes a method for the extraction of laminate layers from CT data and their subsequent evaluation. The surface of the component is described by Bézier-patches. Shifting and sampling of this surface description allows the calculation of a virtually “planar” volume. The laminate layers are aligned in parallel planes in the resulting volume and can be analyzed and visualized layer by layer. With the help of subsequent image analysis applied to each layer irregularities in the fiber layout like undulations or defects like pores and voids can be detected. The application of this method is demonstrated on a typical example.

S. Mohr, U. Hassler

### Magnetic NDE Using a Double Rectangular Coil and a Hall Effect Sensor: A Simple Analysis

In this paper a simple analysis and measurement device in eddy current NDE are presented. A Hall probe is associated to a double rectangular Printed Circuit Board PCB. The configurations examined involve the double coil in air and above aluminum plates, either with or without cracks of various depths. The agreement between experimental and theoretical results is very good, showing that our model accurately describes the electromagnetic fields.

L. Bettaieb, H. Kokabi, M. Poloujadoff

### A Study of Microcracks and Delaminations in Composite Laminates

With the rapid increase of composite usage on aircraft primary structures, the damage of composite laminate and its nondestructive testing are of high interest to the aerospace industry. Composite laminates, typically without reinforcement in the out-of-plane direction, are prone to impact damage. While the characteristics and the NDT of impact-induced delaminations are well known, the precursor to failure has not attracted equal attention. In this paper, we report an investigation of microcracks and delaminations in carbon composite and glass composite laminates fabricated from unidirectional and woven prepregs. Microcracks were induced by low energy impact and by thermal cycling to cryogenic temperature. The density, distribution and orientation of the microcracks caused by impact were mapped out in detail by photomicrographs. Specimens containing microcracks were then fatigued to observe the initiation and development of delaminations. With before-and-after micrographs, the changes of individual microcracks were followed and documented. The delaminations grown from microcracks in a woven glass laminate during fatigue were found to be localized, short, and tight. These “micro-delaminations” are characteristically different from the “macro-delaminations” caused by impact energy above the delamination threshold. Unlike macro-delaminations, the ultrasonic detection of micro-delamination zone has proven more challenging.

D. K. Hsu, V. Dayal, M. Gerken, A. Subramanian, K-H. Im, D. J. Barnard

### Robotic High-Speed 3D Scanner Automatically Scans Spacecraft Heat Shields

A novel robotic high-speed 3D scanner has been developed to demonstrate the capability of rapidly inspecting the surface of the entire Crew Exploration Vehicle (CEV) heat shield (5 meters in diameter), and its individual components. The scanner is used to measure defects (cracks, holes) in the heat shield and to see if the shield was constructed within acceptable geometrical tolerances from the design. A patented NASA 3D laser sensor is mounted onto a six-axis robot arm. The sensor uses the principle of laser triangulation and projects a laser line onto the target surface while the robot arm moves the sensor over the surface. Because of the sensor’s very high 3D point generation capability and the robot arm’s precise position control, scanning the entire heat shield at high-resolution takes about one hour rather than the many hours or days required by existing 3D scanning technologies.

J. P. Lavelle, J. W. Steele

### Inspection of Underwater Metallic Plates by means of Laser Ultrasound

Guided Ultrasonic Waves (GUWs) are increasingly considered in the nondestructive testing of engineering systems. This paper shows a non-contact laser/immersion transducer system for the detection of damage in submerged structures. A pulsed laser was used to generate stress waves in an aluminium plate immersed in water; a pair of immersion transducers was used to detect the signals. The waveforms were processed using wavelets to extract information about the attenuation of the propagating modes. Damage was simulated by devising a notch and a circle on the face of the plate exposed to the probing system.

P. Rizzo, E. Pistone, P. Werntges, J. Han, X. Ni

### Influence of Water Flow through Pipe Networks for Damage Detection using Guided Waves

Researchers have been trying to develop techniques for early forecasting of the degradation process in pipe networks. Different Non Destructive Testing Techniques are used for detecting damages in a variety of materials and structures. Guided wave technique is a suitable non-destructive technique which can be used for pipe inspection by generating cylindrical guided waves. In this research, steel pipes are inspected using cylindrical guided waves. The purpose of this paper is to investigate the influence of flowing water through the pipe on the guided wave propagation in the pipe wall. Investigations are also carried out when the pipes are in open air which gives the traction-free boundary condition. It is also investigated whether the direction of the flow influences the propagation of the guided waves. Experimental V(f) curves are extracted from the received signals for defect free and defective pipe specimens and compared to study the effect of water flow on the strength and other characteristics of various guided wave modes.

### Monitoring Hydrogen Release from 4140 Steel Using the LCR Ultrasonic Technique

Hydrogen build-up and release in steel microstructure is of considerable interest in studying the mechanical performance of the material. L

CR

ultrasonic waves are a potential research tool that will enable the nondestructive evaluation of this reversible hydrogen buildup since their speed is affected by stress and their travel path is through affected layer just below the surface. The present study used three blocks of 4140 steel cut from a longer sample. Frequency spectrum data also were collected. The assumed model was of hydrogen occupying the vacancies in the steel block during the high temperature high-pressure period in the autoclave, and then being purged upon removal as the block contracted, creating a residual tensile stress in the surface area of the block. As the hydrogen is purged, the tensile stress should decrease. The L

CR

results confirmed this trend, although it was more strongly seen for the 11.7 MPa (1691 psia) block. Photomicrographs confirmed no cracks in the surfaces, although there was considerable decarburization. Frequency analysis showed that the decarburization did affect the frequency spectrum but did not affect the L

CR

wave speed.

D. E. Bray, R. B. Griffin

### Theoretical Modeling and Simulation Studies as a basis for NDT

Computer modelling of non-destructive testing methods has come a long way from the beginnings in the mid 90s to today. Radiographic modelling for components with higher wall thicknesses, as they are typical for nuclear applications, must include precise predictions of scattered radiation and its impact in terms of contrast reduction. Dedicated or general purpose Monte Carlo methods with the ability to calculate higher order scattering events are the state of the art for these applications. Aerospace applications, on the other hand, have stronger requirements on the modelling code’s capabilities to import complex CAD geometries, and can benefit from faster analytical scatter models, limited to first or second order scattering events. Similar distinctions can be made for the various approaches proposed to accurately model geometrical and film unsharpness, film granularity, film responses, film/foil cartridges and photon noise. This article presents a state-of-the-art review of radiographic modelling from the perspective of two important application domains with very different requirements, nuclear and aerospace.

A. Schumm, P. Duvauchelle, V. Kaftandjian, R. Jaenisch, C. Bellon, J. Tabary, F. Mathy, S. Legoupil

### Microwave Imaging of Plain and Reinforced Concrete for NDT Using Backpropagation Algorithm

The focus of this paper is implementation of backpropagation algorithm as a solution for the inverse source problem for microwave imaging of plain and reinforced concrete targets for nondestructive evaluation (NDE). The data used in imaging was obtained from numerical simulation of microwave scattering by concrete targets using a finite difference-time domain (FD-TD) technique. Electromagnetic (EM) properties of concrete were obtained from previous experimental research. Simulations were performed using a Gaussian pulse wave excitation for dry concrete cylinders with and without a rebar at the center. Images reconstructed using the backpropagation algorithm showed the potential of the method for concrete NDE while drawing attention to its limitations mainly due to the linearizing assumptions in the algorithm’s formulation.

O. Güneş, O. Büyüköztürk

### Accuracy of Potential Mapping Assessed Through Numerical Models

Potential mapping is a widely used inspection method for detection of ongoing corrosion in reinforced concrete structures. Usually based on the results from potential mappings, further inspection strategies and repair actions are scheduled. Unfortunately the probability of detection (PoD) of the method is an unknown factor. To obtain values for the PoD of potential mapping, it is necessary to compare potential measurements of reinforced structures with their true corrosion condition state. The true corrosion condition state is only identifiable by replacement of concrete cover. In general, owners will not agree to open a whole structure for evaluating the accuracy of an inspection method. Therefore, in this research, an approach based on numerical models with known condition state is pursued.

S. Kessler, C. Gehlen

### Model-Assisted Non-destructive Monitoring of Reinforcement Corrosion in Concrete Structures

Half-cell potential mapping is a non-destructive technique that helps ­predict the probability of steel corrosion in concrete. A major shortfall of this technique is that it does not give insight into the rate and the nature of corrosion. In the case of localized corrosion, the predictions of half-cell measurements can even lead to wrong interpretations of the severity of corrosion. This paper presents an inverse numerical tool that can be used to better interpret the results of half-cell potential measurements. This tool quantitatively relates the potential readings on the surface of the concrete to the rate of probable localized reinforcement corrosion, allowing engineers to gain supplementary information from half-cell tests. Numerical experiments demonstrate the potential benefits of the proposed approach when typical half-cell measurements may not be able to predict the localized corrosion mechanism.

P. Marinier, O. B. Isgor

### Estimation of Pre-stress in Tendons Using Elastic Wave Propagation in the Anchor Head

Application of pre-stress on a structure is a way to reinforce materials with low tensile strength like concrete and soil against tensile overload. After years in service, the strands may lose the pre-stress due to corrosion or other reasons endangering the whole structure. Since the strands inside the structure are not easily accessible, any inspection should be conducted on the anchor head. In this study, elastic waves are numerically applied on the anchor head. Parameters like the wave amplitude, propagation time, frequency content and others are influenced by the stress of the strand wires which affects the contact between the steel strand, and the surrounding bolt of the anchor head influencing the acoustic impedance mis-match on the interfaces. The change of contact pressure between the strands and anchor head is simulated by modifying the rigidity of a model interphase material. Therefore, an easy and fast procedure for non destructive inspection of the pre-stress load on the strands is discussed.

D. G. Aggelis, D. Kleitsa, K. Kawai, T. Shiotani

### Modeling of Ultrasonic Signals Received by a Focused Circular Transducer from a Side-Drilled Hole

This paper presents a model that allows us to predict the ultrasonic signal received by a focused circular transducer from a side-drilled hole (SDH). In order to develop a model for the entire ultrasonic testing system, we first need to develop models for the following three parts of the problem: 1) the ultrasonic beam field, 2) the system function, and 3) the scattered waves from the SDH. To calculate the beam field, we use the multi-Gaussian beam modeling. To model the system function, the front surface reflection signal is used as a reference reflector, and to get the scattered field, both Kirchhoff approximation and the separation of variables (SOV) method are used. By combining these three subsidiary models, we obtain a complete model for the entire ultrasonic measurement system. Experimental results are used to verify the accuracy of the developed model.

F. Honarvar, M. D. Khameneh, A. Yaghootian, M. Zeighami

### A Theoretical Study on Scattering of Surface Waves by a Cavity Using the Reciprocity Theorem

Scattering of surface waves by a two-dimensional cavity, which is on the free surface of an elastic half-space, is theoretically investigated in the current paper. It is shown that the expressions for the scattered field displacements are derived in an elegant approach by using the reciprocity theorem and the decomposition technique that decomposes the total field into incident and scattered fields. The displacements of the scattered field then can be analytically obtained by the reciprocity theorem. The achieved solutions are verified by the Boundary Element Method (BEM) modeling of two-dimensional wave propagation in elastic half-spaces that applies a truncation of the infinite boundary to account for the contribution of the omitted part. The comparisons of displacements are graphically displayed and show the agreements between analytical and numerical results.

H. Phan, Y. Cho, J. D. Achenbach

### Half-Space Dynamic Stiffness Models Compatible with the Thin Layer Formulation for Use in Response Analysis of Soil Profiles

This work presents two new wave propagation models for the half-space compatible with the thin layer formulation (TLF). The TLF is based on a polynomial expansion in the wave number

κ

of the exact matrix of the dynamic stiffness of a layer. The advantage of the TLF with respect to the exact model is that it allows transforming the soil profile response between wave number and spatial domains in analytical form through the decomposition of response in wave propagation modes. The expansion in

κ

applied to the exact matrix of the half-space does not produce a satisfactory approximation for moderate or large values of

κ

. Therefore, the TLF in its original form only reproduces with good accuracy the response of soil profiles composed by an assembly of layers over an infinitely stiff half-space. The proposed models eliminate such shortcomings and adequately represent the half-space stiffness in the wave number domain. The techniques used for adjustment of mechanical soil profiles generally represent the half-space through an assembly of strata with increasing thickness in depth. Such approach produces acceptable accuracy in the wave propagation velocity of the fundamental mode for normally dispersive profiles (with increasing stiffness in depth), although it generates spurious modes not related with higher propagation modes. The adjustment of mechanical parameters of inversely dispersive profiles requires an adequate approximation of the half-space dynamic behavior given the significant contribution of the higher propagation modes to the response. The proposed models are suitable for the adjustment of soil profiles with an arbitrary distribution of stiffness in depth and for evaluating the dynamic stiffness of foundations.

M. A. Ceballos, C. A. Prato

### Automated NDE of Structures with Combined Methods

Non-Destructive Evaluation (NDE) of structures is complex due to the uniqueness of almost all structures and their sizes. A single NDT method typically is not sufficient to meet the testing requirements, which cover different areas, such as material and structural properties. Measuring geometrical properties require other test methods than e.g. the detection of corrosion. Automation has proven to be necessary for aquiring large amounts a of high quality data in a short time. Examples of succesful method combinations from different areas of non-destructive testing in civil engineering are briefly described and their application is shown. Some of the examples also include automated inspection.

H. Wiggenhauser

### State of Art Image-Based Inspection Methods Used on Japanese Expressways

The tunnel and bridge assets on the Japanese expressways constitute a very large sum of investment. These tunnes and bridges deteriorate quickly due to various factors such as aging,environmental exposure, and mechanical effects. The cracking of pavements constitutes serious maintenance item. Proper inspection and investigation are essential to evaluate the condition of structures and efficient non-destructive test methods are important for improved asset management. This paper presents a pavement crack investigation technology adopted automatic image processing, a damage evaluation technology for steel bridge paint which adopted analysis of digitized photos, and a crack investigation technology on tunnel concrete lining adopted laser measurement equipment which is mounted on high speed vehicles.

S. Shimeno, T. Saeki, T. Kazato, T. Sakuraba

### Use of NDT in Condition Assessment of RC Buildings

Condition assessment and serviceability of existing reinforced concrete (RC) buildings becomes a major issue especially when substandard material and workmanship quality are used. Low quality construction materials and methods accelerate especially the corrosion of the steel reinforcement and decrease the service life of RC structures, which should maintain a service life of at least 50 years according to the EN standards. Several 40-year-old RC buildings were investigated and their serviceability condition was determined based on non-destructive testing in conjunction with semi-destructive in-situ tests. Cores were taken from the structures to determine the mechanical strength and unit weight of in-situ concrete. Microstructural studies were performed on the thin sections and plane sections to evaluate the quality of materials and methods used in the construction. Non-destructive tests such as; Schmidt hammer, impact-echo and magnetic signals were used to determine the surface hardness of concrete members, cracks and voids within the concrete, location and size of steel reinforcement throughout the structure. Extensive carbonation and high level of chlorides were measured from the cores taken. Impact-echo measurements indicated high level of deterioration of concrete and damage. It has been shown that impact-echo method could provide valuable information for the in-situ condition assessment of structures coupled with other experimental laboratory techniques.

A. A. Ozbora, N. U. Basar, Y. Akkaya, M. A. Tasdemir

### NDT Methods for the Assessment of Concrete Structures After Fire Exposure

This paper studies the application of the Schmidt Rebound Hammer and colorimetry as tool to assess the fire damage of concrete structures. Firstly, experimental data is acquired under laboratory conditions on small specimens. Secondly, this information is used to evaluate the damage of a case study consisting of a girder exposed to a real fire. Both techniques show to be very useful in evaluating the fire damage and can provide the necessary information for a calculation of the residual load bearing capacity.

E. Annerel, L. Taerwe

### Damage and Defect Detection Through Infrared Thermography of Fiber Composites Applications for Strengthening of Structural Elements

Fiber Reinforced Polymer (FRP) composites are today widely used for the strengthening and seismic retrofitting of structures. The efficiency of this technology is strongly dependent on the correct positioning and bonding of the fibers on the surface of the structure to be reinforced. The connection between the surface of the substrate (concrete, masonry or steel) and the fibers is assured by the adhesives. The control of the application may be performed with different Non Destructive Evaluation (NDE) techniques but presently there are no standard procedures to assess the quality of the applications in civil engineering structures. Infrared thermography represents a valid tool for the detection and measurement of bonding defects or damage in the composite strips and can be used even for the definition of possible damage progression. The paper presents a series of results obtained using infrared thermography on masonry walls and concrete beams.

L. Cantini, M. Cucchi, G. Fava, C. Poggi

### Thermographic Investigation of Delaminated Plaster on Concrete

Active thermography is sensitive to inhomogeneities at and below the surface of objects investigated. Thus, it should be useful for detecting plaster delaminations on concrete. In this paper, the results of field and laboratory investigations into plaster-covered concrete were compared. For evaluating the bonding state of the plaster it is not sufficient to study only the thermal contrasts at the surface of the investigated objects. The experimental results suggest that the overall thermal behaviour has to be considered.

R. Krankenhagen, C. Maierhofer, M. Röllig

### Multi Layer Microwave Moisture Scans at Large Areas in Civil Engineering

A new mobile microwave scanner was developed for moisture mapping on large areas with high lateral resolution, working like a multidimensional microwave camera. The readings are taken position dependent in one track for three depth layers. The scan image can already be visualized with the scanner, making possible detection of moisture, water paths or similar water inclusions right at the place of measurement. Large area buildings like basement garages, indoor pools or flat roofs can be investigated quickly, simply and most of all complete.

A. Göller

### Holographic Subsurface Radar as a Device for NDT of Construction Materials and Structures

A relatively rare type of subsurface radar – holographic radar – is described in this paper as a tool for non-destructive testing (NDT) of construction materials and structures. Its principle of operation, advantages and disadvantages are considered. Holographic subsurface radar, operating several discrete frequencies, is used to illuminate a sufficiently extensive area of a surface of opaque dialectical medium to be inspected to register interference between reflected from objects and reference waves. In a lossy media with low level of microwaves attenuation, reconstruction algorithms could be applied for obtaining the subsurface image in such a manner as in optical holography. An attempt is made to highlight significant application areas and problem cases where this type of radar could potentially be applied as a device for NDT of construction materials and structures. The paper describes results of different building surveying including objects of historical heritage. Space shuttle thermal protection system tiles were investigated in some other experiments. Each application area is illustrated by relevant data acquired in laboratory experiments or field tests.

S. I. Ivashov, V. V. Razevig, I. A. Vasiliev, A. V. Zhuravlev, T. Bechtel, L. Capineri, P. Falorni, T. Lu

### Infrared Imaging of Roof Systems for Moisture Detection

The cost of constructing roofing systems is high as they must be designed with water-proofing capability and must form thermal barriers for ­buildings. The traditional and inverted roof systems are typically used in Kuwait. Occasionally, due to faulty practices, incorrect materials and/or improper design, roofs fail to be watertight and let moisture penetrated into the roofing layers causing water leakage, degradation of the roofing materials and other damages. Moisture problems in roof systems require quick action and maintenance. It is prevalent to rip off the roofing layers to detect the location and extent of damage that has been caused by moisture penetration. This method could be very costly and impractical. This paper looks into the use of Infrared Thermography as a non-destructive technique for determining water leakage in roofing systems. An experimental building unit (EBU) was constructed with six different models of roof sections on the top. For each roof section, controlled injection of moisture was performed at certain points between the roof layers to simulate the leakage process. Infrared imaging studies have shown that the technique is reasonably successful in detecting roof moisture although further evaluation and improvement of the technique was deemed necessary due to the heavy roof construction types and weather conditions in Kuwait.

J. S. Al-Qazweeni, H. A. Kamal

### Practical Applications of Ultrasonic-Echo and Impulse Radar

Determining the condition of an existing structure is a common task for engineering firms concerned with planning and consulting. In the case that reinforced concrete structures need to be repaired, the actual state must first be determined according “Instandsetzungsrichtlinie DAfStb Rili-SIB 2001”. In the course of renovations and conversions, the condition of the structure must be known, which is often not the case due to a lack of planning documents. Also in many cases doubts exist as to whether the work contracted was actually carried out in full. In all of these cases one should aim to perform the tests as accurately as possible, but with minimum effort and the least possible damage to the building and inconvenience to its users. Through the development of ultrasonic echo and impulse radar methods, numerous inspection tasks have become possible, which were previously only achievable with a much larger effort and through destructive testing methods. In the following article, examples of structural investigations that were carried out using the ultrasonic echo method, the impulse radar method, or a combination of both methods, are presented and explained.

Ch. Sodeikat

### Non-Destructive Testing of Bosphorus Bridges

The two suspension bridges over the Bosphorus Strait, namely Bosphorus Bridge and Fatih Sultan Mehmet (FSM) Bridge form a vitally important link for the economy of Istanbul, Turkey and the Eastern European region. On the Bosphorus Bridge, the majority of its traffic is light vehicles and over 100.000 vehicles pass a day in each direction; heavy goods vehicles were wisely banned in the 1990s following the opening of the Fatih Sultan Mehmet Bridge. This restriction on Bosphorus Bridge is intended to be maintained in future. This situation strengthens the importance of Fatih Sultan Mehmet Bridge for Turkish economy until the third bridge is constructed. The indispensable roles of these bridges necessitate safe operation throughout their lifetimes. To investigate the needs for safeguarding these long form the behaviour analysis along with general and local surveys of these structures. In the content of the studies, a variety of NDT tests were targeted at different parts of the bridge elements, and have been conducted as part of a major investigation into the bridges. The NDT tests performed included; Magnetic Flux Leakage Tests and Radiographic Tests at hanger sockets and Dye Penetrant Testing / Magnetic Particle Testing of the welding, non destructive testing on the concrete parts in anchorage rooms comprised of Schmidt Hammer Tests and Carbonation Depth Tests of ­concrete. The findings of these NDT tests have been also evaluated to be used in determination of remaining life of the structures together with other studies performed.

Y. Dost, N. Apaydın, E. Dedeoğlu, D. K. MacKenzie, O. Z. Akkol

### Non-Destructive Evaluation for Horizontal Cracks in RC Slabs of Highway Bridges Based on Analysis-Aided Impact Elastic-Wave Methods

In this study, impact elastic-wave method was performed at the bottom surface of RC slab cut from an existing highway bridges to survey horizontal cracks. Before measurements by impact elastic-wave method, impact response analysis was applied to determine elastic wave input method, elastic wave detection method and frequency analysis method. Efficiency of analysis-aided impact elastic-wave method was confirmed by drilling and observing the interior of the RC slab by a rod-shaped scanner. Evaluation results by this method are similar to those of visual inspection. Thus, the feasibility of analysis-aided impact elastic-wave method on detection of horizontal cracks in RC slabs of highway bridges was demonstrated.

S. Uchida, T. Kamada, T. Iwasaki, H. Tsunoda

### Non-Destructive Testing of FRP-Structural Systems Applied to Concrete Bridges

With the increasing application of fiber-reinforced polymer (FRP) ­structural systems to repair and strengthen concrete structures - in particular reinforced-concrete (RC) bridges - owners are faced with the issue of how to evaluate and predict the long-term performance of FRP systems applied to RC bridges. Methods to measure over time the performance of FRP-strengthened bridges are not fully developed. For a number of concrete bridges in the Republic of Macedonia strengthened with carbon FRP (CFRP) structural systems there is a need, ten years after application, to test and evaluate the performance of the CFRP-strengthened bridges by evaluating the tri-layer CFRP-epoxy-concrete bond. The bonding structure defines bridge load performance. For 19 bridges this involves testing the bond for over 14,000 linear meters of CFRP plates. While a number of non-destructive testing (NDT) methods to measure CFRP-concrete bond performance are used in the laboratory, an effective NDT method to evaluate in the field the bond condition of large quantities CFRP material applied to RC bridges is currently not available. This paper presents an NDT method using a mobile impact-echo device configured to generate an acoustic signal that identifies areas of CFRP material de-bonding from concrete bridge members. The NDT device is designed to test efficiently large areas of bonded CFRP plates. Identification of de-bonded areas of the CFRP-concrete bridge members will provide bonding structure data necessary to support the owner’s CFRP-bridge maintenance program.

K. C. Crawford

### Inspection of Timber Bridges with Ultrasonic Echo Technique

In timber engineering, damages, defects and inhomogenities inside wooden construction components (e. g. interior rot, knots) or at inaccessible surfaces present an important problem as they can cause sudden failure of the component or structure. For a reliable structural safety analysis using non-destructive test methods, information on the wood specie(s), wood degradation and conservation as well as the inspection of different timber grading criteria (e. g. knots, cracks, …) and their influence on the mechanical properties of in-situ, “old” timber members is essential. This paper presents an ultrasonic echo technique that makes use of transverse waves for the inspection of wooden constructions. The method was used in the inspection of numerous timber bridges. In case of missing back wall echoes during ultrasonic echo measurements, the results were complemented by the drilling resistance method. Combined use of these two methods enable evaluation of the internal structure and prediction of the remaining load bearing capacity of cross-sections. The potentials and limitations of ultrasonic methods related to the evaluation of timber structures were taken into account in the evaluations. The typical damages and their potential causes were shown for various timber bridge types. By the use of the developed method, several timber bridges were prevented from demolition.

A. Hasenstab, K. Frühwald

### Acoustic Emission Monitoring of Conventionally Reinforced Concrete Highway Bridges Under Service Conditions

Acoustic Emission (AE) monitoring offers the unique possibility to monitor structural bridge components in real-time and detect sudden changes in the integrity of the monitored element. AE are stress waves initiated by sudden strain releases from within a solid such as crack formation and propagation, material crushing, or bond fracture of two materials in a composite due to over-loading. The present study focuses on methods for in-service monitoring of conventionally reinforced concrete (RC) bridges. Extensive laboratory experiments on two full-scale reinforced concrete bridge girders were carried out to study existing evaluation methods and to identify potential applications that will also work for in-service bridges. A novel evaluation approach based on the well-known

b

-value analysis that worked particularly well was developed and is proposed. It was found that this new method can help estimate operating load conditions and detect overloading of existing bridges. Additionally, an in-service highway bridge was monitored during structural load testing and while experiencing ambient traffic to collect real service-level AE data for comparison. Preliminary data from both the laboratory experiment as well as the in-service test are presented and compared.

T. Schumacher, C. Higgins, S. C. Lovejoy

### Review of NDT Assessment of Road Pavements Using GPR

The pavement structural condition is one of the main factors to be taken into account for pavement maintenance planning. Therefore, more efficient methods for pavement monitoring and structural evaluation are required in order to ensure a good serviceability and to provide adequate maintenance solutions for the pavements. Non destructive testing (NDT) provides ideal means to test pavement structure in rapid and convenient manner, without traffic disruption and without causing any damages to the existing pavement structure. On this basis, over the past few years, Ground Penetrating Radar (GPR) technology has led to a powerful NDT technique that features several major advantages. GPR has been used successfully in a variety of pavements application such as determining layer thickness, detecting subsurface distresses, estimating moisture content, detecting voids and others. In GPR process an important parameter is the dielectric properties of road materials. This paper investigates the feasibility of GPR use in pavement assessment taking into account the sensitivity of the related results due to the variability of the materials dielectric properties.

C. Plati, K. Georgouli, A. Loizos

### Condition Assessment of Mixed Paved Roads by GPR and CCR: Material Properties

Severe climatic conditions and poor methodology of maintenance and rehabilitation in Quebec make assessment survey of pavement a necessary however difficult task. In order to support prior results obtained with numerical modeling and to address optimal design of equipments, we determined physical properties of concrete, asphalt and foundation soil. These materials have been sampled from a street in the city of Montreal for which pavement had to undergo complete rehabilitation. The last complete rehabilitation of this street was done more than 30 years ago and material properties and composition were largely unknown. Before removal of pavement, we carried out a GPR survey with two distinct pairs of antennae (450MHz and 900MHz). Laboratory tests on concrete and asphalt were conducted on wet and dried samples, trying to reproduce the variability of physical properties due to changes in climatic conditions for a whole year. We measured complex dielectric constants in the range 50MHz-900MHz with a recently developed dielectric probe, and electrical resistivity using a simple laboratory system. Results show low variability of properties of asphalt depending of the saturation compared to larger variability in concrete. Finally all collected data are used as input to numerical modeling, and results compared with the survey data.

C. Kaouane, M. Chouteau

### Portable Wireless High Power Air-coupled GPR System for Highway Inspection

A FCC compliant 1GHz portable wireless high power air-coupled ground penetrating radar (GPR) system has been successfully designed and implemented with the sponsorship of Texas Department of Transportation, United State. The differential transmitting pulses have 1ns pulse width and ±30V amplitude. The GPR receiver uses differential sequential sampling architecture and has 60dB dynamic range. With its high transmitting power and low-noise system design, the detecting depth of this air-coupled GPR can reach 2 meters in asphalt. The GPR data acquisition and processing software is developed. Lab tests and pavement tests were made to verify the performance. A high way survey was executed on HW69 at in Paris District northeast of Dallas, TX. The first layer dielectric constant and thickness, and other layer feature were measured. Accuracy of the GPR measurement is within -3% to +4%, comparing with the sample cores measurement.

W. Ren, H. Wang, C. Liu

### Feasibility of Detecting Debonding of Hot Mix Asphalt Layer with Nondestructive Testing

Sufficient bonding between the hot mix asphalt (HMA) layers is essential to ensure the desired structural capacity of a pavement. Undetected delamination can ultimately result in the peeling of thin overlays of asphalt concrete from the surface of the roadway. Further progression of delamination may result in stripping of the lower layers due to the intrusion of moisture. Rapid nondestructive test (NDT) methods determine the existence and extent of delamination or stripping within the asphalt pavements. In this paper, several NDT procedures and/or equipment that have the potential to address the problem were identified, and their effectiveness and potential for success were evaluated. The identified NDT methods, which included the Ground Penetrating Radar, Thermography, sonic/seismic and impulse response, were evaluated on a controlled pavement section that was specifically constructed with various levels of debonding at different depths and with different asphalt mixes. Strengths and limitations of different methods are discussed in this paper.

M. Celaya, F. S. Ertem, S. Nazarian, M. Saltan

### Estimation of Chloride Content in Cover Concrete of Coastal Structures Using Electromagnetic Wave

Reinforcement corrosion caused by the presence of chloride ions in the neighborhood of the re-bars has been identified as one of the major causes of deterioration of concrete structures. The chlorides could find their way to concrete either as part of constituent materials when sea sand is used, or, by gradual permeation and diffusion as in the case of marine structures, etc. Thus, determination of chloride content in a concrete structure is an important part of periodic nondestructive testing carried out for structures identified to be vulnerable to chloride induced reinforcement corrosion. In this report, the applicable method which is possible to estimate the distribution of chloride content included in cover concrete in the existing structures using electromagnetic wave method which is non-destructive testing is reported.

T. Mizobuchi, K. Yokozeki, R. Ashizawa

### In-Service Inspection and Structural Integrity Assessment of Atmospheric Storage Tanks

This paper presents a series of advanced inspection techniques for assessing the structural integrity of atmospheric storage tanks, in a global (floor, annular ring, shell & roof) and integrated fashion while the tank is in-service. The methods presented with sample results and advantages include floor condition assessment using Acoustic Emission, on-line tank floor annular ring corrosion evaluation using long range automated Ultrasonics and on-line tank shell or roof corrosion mapping using automated Ultrasonics C-Scan. The paper discusses means of management of the data acquired from all above techniques, according to codes and state-of-the-art risk-based inspection (RBI) programs. This is done using a combination of structural drawing software, specially designed for the needs of incorporating on stream inspection results and plant condition monitoring software.

A. A. Anastasopoulos, S. E. Kattis, D. A. Kourousis

### Application of Acoustic Emission to High-Voltage Electric Power Equipment Diagnostics

Acoustic emission has been applied in identifying evolving failures of electrical, mechanical or thermal nature in power transformers and reactors. Different kinds of failures can be identified by the characteristics of the signals received and also give the location of the source of the signals. Also, operating sequence and contact timing of on-load tap changers can be evaluated with the aid of acoustic emission.

The technique has the advantage of being utilized with in-service, energized equipments, avoiding downtime to perform tests. Case studies of acoustic emission tests performed to condition monitoring of several high-voltage power transformers and reactors, rated 230 and 500 kV are presented. Results have demonstrated the effectiveness of the acoustic emission technique as a tool for the condition diagnostic of electric power equipments.

O. G. Santos Filho, F. S. Brasil, F. F. Silva Neto, R. C. Leite, S. L. Zaghetto

### A De-Noising Algorithm for EMAT on Wheels

Presently electro-magnetic acoustic technology (EMAT) has been widely adopted by the China Railway High-speed (CRH). In this paper, the principle of wheels tread detection by using EMAT is introduced. To solve the noise problem existing in the detecting procedure, an integrated algorithm combining the wavelet algorithm and the phase difference algorithm is presented. Under the premise of saving the necessary signal wave, the Fast Fourier Transform based on the Blackman window is adopted to calculate the signal phase, and then the integrated algorithm is chosen to process the signals. Compared with the wavelet algorithm or the phase difference algorithm, the rate of the noised data after being processed by the integrated one is reduced by more than 45%. This algorithm will improve the waveform quality and has an enlightening function to raise the detection accuracy in the EMAT system.

K. Yang, C. Peng, Y. Zhang, J. Peng, X. Gao

### Impact Echo Q-Factor Measurements Towards Non-Destructive Quality Control of the Backfill in Segmental Lined Tunnels

A non-destructive method for quality control of the backfill material in segmental lined tunnels is presented in this study. The proposed method is based on the Impact Echo (IE) amplification factor (

Q

-factor). Initial results indicate that the measured IE

Q

-factor can be directly related to the quality of the backfill material. This opens up the possibility for more efficient future quality control of the backfill in segmental lined tunnels.

N. Ryden, O. Aurell, P. Nilsson, J. Hartlén

### Monitoring DC Stray Current Corrosion at Sheet Pile Structures

Steel is discarded by railway owners as a material for underground structures near railway lines, due to uncertainty over increased corrosion by DC stray currents stemming from the traction power system. This paper presents a large scale field test in which stray currents interference of a sheet pile wall was monitored in realistic conditions. The field test was representative for a sheet pile wall of 220 m length and 10 m depth. Also an anchor was incorporated. A specially designed coupon sensor was used. Measured stray current interference was very low, maximum values were found for the anchor. A conservative interpretation of the measured results showed that additional corrosion due to stray currents was smaller than 10 % of the expected natural corrosion, based on the applicable standards.

W. H. A. Peelen, E. A. C. Neeft, G. Leegwater, W. van Kanten-Roos, W. M. G. Courage

### Inspection of Deteriorated Coastal Embankments Using Radar, Thermography, and Impact-Echo

Erosion and cavitation are threatening the structural integrity of the concrete embankment along the coast line of Taiwan. Task force is formed to investigate the embankment deterioration. Images of subsurface anomaly have been obtained based on the data coming from different techniques. The techniques applied include ground penetration radar, infrared thermography, and impact-echo method. The results are in good agreement among cross-sectional radar images, thermal images, and normalized impact-echo spectrum measurements.

C.-H. Chiang, C.-C. Cheng, K.-T. Hsu

### Laboratory Characterization of Mining Cemented Rockfill by NDT Methods: Experimental Set-up and Testing

Many types of backfill are used as supporting technique in underground mines to optimize ground control stability and to minimize environmental problem at the surface. In theory cemented rockfill can yield optimum strength resistance, yet it is the least implemented in practice due to difficulties related to laboratory analysis of coarse particles in the material. This paper focuses on finding an appropriate protocol to use nondestructive testing techniques to characterize a cement-based material and to study the evolution of the properties during a curing period of 120 days. The testing techniques are the electrical resistivity and sonic methods. The resistivity technique highlights the changes in resistivity caused by hydration processes and the bond developing between the backfill constituents. The sonic technique measures the P and S waves. Knowing the velocity of the waves, changes of the geotechnical properties can be evaluated using known relationships between velocities and mechanical properties. Overall the mechanical strength can be indirectly monitored by these two techniques. Both techniques are complementary to one another and their joint application should improve the interpretation of strength. A concrete sample was made to test these two techniques on a slightly heterogeneous material. The experiment shows that the techniques are sensitive to the physical property changes and they enable monitoring of hardening and strength development. The far-reaching outcome of this research could help assess the properties of different compositions of mining rockfills in the laboratory before using them in mines. Alternatively, these techniques may be used on other cement-based material with coarser particles.

C. L. Chou, M. Chouteau, M. Benzaazoua

### A Case Study of the Self-Potential Method to Characterize Seepage and Earth Dam Materials

This paper presents a case study of the self-potential (S.P.) method applied at the junction of two embankment dams to characterize seepage. Sensitivity of the S.P. method to water runoff can be used to delineate the preferential flow paths. However S.P. can be caused by other sources, therefore only anomalies caused by water flow, described by the electrokinetic (EK) mechanism, are the targets of our study. We take advantage of the controlled progressive emptying and impounding of the upstream reservoir to monitor changes of S.P. due to changes of water flow and the displacement of materials. Also, time-lapse electrical resistivity tomography is used to control the variation of electrical conductivity of the dam material together with changes in water level. It allows for a better discrimination and interpretation of the various self-potential sources. The effective EK coupling coefficient of the dam materials was computed from the variation of potential with water level and flow rate. The S.P. monitoring allowed displaying a positive anomalous zone associated with the reservoir water level changes. It can be related to visible seepage. It is difficult to make a quantitative interpretation of the S.P. data collected at different periods of time using coupled modeling because of the poor knowledge of the hydraulic and physical properties of dam materials.

L. A. Nzumotcha Tchoumkam, M. Chouteau, B. Giroux, P. Rivard, K. Saleh, A. Côté

### Microgravity Application for Detection of Underground Cavities in a Desert Karst Terrain

A number of sinkholes were detected in a residential area located close to the northeast coastal side of the Arabian Peninsula. The sinkholes occurred suddenly with different sizes and a maximum depth of 31 m. Comprehensive investigation studies were conducted for understanding the causes of the sinkhole occurrence and to recommend remedial measures. Microgravity survey method was used for geophysical investigation of the area to detect subsurface cavities. The validity of the microgravity survey was confirmed after applying a drilling program. After 15 years, another microgravity survey was conducted in selected locations of the same residential area for the purpose of verifying the current underground status and assessing its development. In this paper, the nature of the desert Karst terrain under study is described. The results of the two microgravity surveys are presented. The results confirmed the capability of the microgravity method to detect density anomalies and ground disturbances. The maps showed evolution of the anomalies in some locations within the studied area.

H. A. Kamal, M. F. Taha, S. A. Al-Sanad

### 20 Years of Experience with Structural Health Monitoring of Objects with CFRP Components

The application of carbon fiber reinforced polymers (CFRP) in bridge construction was before 1991 unknown. Therefore the bridge owners did not want to rely only on the laboratory experiments made in the 1980ties. They asked for structural health monitoring. This was also in the interest of the involved R&D community. The used devices range from “old fashioned” demec gauges for off-line measurements to classical foil resistance strain gauges, self-sensing systems for unidirectional CFRP wires, and also sophisticated integrated fiber optical sensors with Bragg gratings. In the most important applications different independent systems were used in parallel. Twenty years are for devices which are exposed to outdoor weathering a fairly demanding time span. Therefore the surprisingly high reliability of most of these systems is a largely appreciated result. Applications on post-tensioned reinforced concrete bridges, stay cables, and pretensioned powerline pylons will be discussed.

U. Meier, R. Brönnimann, P. Anderegg, G. P. Terrasi

### Review of a Null Space Strategy for Damage Localization

The damage localization strategy reviewed here rests on the fact that stress fields that can be computed from the kernel of changes in transfer matrices are identically zero over the subset of the domain where damage (reductions in stiffness) have taken place. Damage can be located, therefore, by extracting these loads and inspecting the associated stress fields. In structures identified from output signals it is not possible to compute changes in transfer matrices but the methodology can be used by replacing the transfer matrix change with a surrogate that shares the same null space. The paper reviews the essential theory and discusses the issues that arise when the strategy is applied in practice.

D. Bernal

### Embedded NDT with Piezoelectric Wafer Active Sensors

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive enablers for a large class of embedded NDT applications such as structural health monitoring (SHM). After a brief review of PWAS physical principles and basic modeling, the paper considers several ultrasonics SHM methods such as: (a) embedded guided-wave ultrasonics, i.e., pitch-catch, pulse-echo, phased arrays; (b) high-frequency modal sensing, i.e., the electro-mechanical (E/M) impedance method; (c) passive detection, i.e., acoustic emission and impact detection. Recent developments in PWAS phased arrays are presented and discussed. The paper ends with conclusions and suggestions for further work to achieve the full potential of this promissing new technology.

V. Giurgiutiu

### Rapid Identification of Critical Structural Components to Inspect or Monitor After an Extreme Event

Nondestructive evaluation techniques can be used for condition ­assessment of structures after an extreme event such as earthquake or blast in order to obtain information about the overall integrity of the structure. The aim of this study is to present an approach for rapid identification of the critical components to inspect or monitor after an extreme event. The methodology is based on reliability importance of components within a system. The importance ranking of components is different under various loading conditions. The methodology is illustrated by using a truss bridge under blast. The critical components for ­condition assessment are identified.

D. Saydam, D. M. Frangopol

### A Fast Automated Impact Hammer Test Method for Modal Parameter Extraction: Implementation on a Composite Bridge Beam

The experimental modal properties of subs-structures of larger civil ­engineering structures are rarely measured on-site. In fact, usually, their dynamic characteristics are only evaluated numerically. There are a number of reasons for the lack of experimental verifications, but most probably these are due to the time and cost required to obtain the experimental modal parameters accurately within the context of challenging environmental on-site conditions. For smaller civil engineering structures, experimental dynamic testing significantly increases the overheads of the overall cost of the construction. This paper presents a dynamic identification method based only on experimental and statistical procedures, which highlights and solves some of the practical aspects of experimental identification, allowing extraction of the main modal properties speedily with a reduced cost of human resources and instrumentation. The methodology is described using as an example a composite bridge-beam, made of concrete and fibre-reinforced composite material, which constitutes the first composite bridge applied on a motorway in Europe. The use of the reciprocity of the transfer functions combined with some self-checks of the measurements is shown to be an efficient way to speed up the signal processing, without reducing the accuracy of the results. The Impact Hammer test method described here, uses a list of functions developed as a MATLAB toolbox, and is part of the SERIES project.

### Case Studies of Structural Health Monitoring of Bridges

Structural Health Monitoring of a number of bridges in Kentucky has proven to be an economical and effective method for extending the life of bridges and for providing the tools for immediate response and decision making. Three bridges are highlighted in this paper. The first bridge is on I-65 in Louisville where instrumentation that continuously monitors the bridge, permitted the design of an economical retrofit. The second bridge is on I-64 over US 60 where instrumentation continuously monitors the bridge for possible impact on the girders resulting from over the height limit trucks. The third bridge is on US 41 North over the Ohio River where instrumentation has been placed on the bridge piers to monitor for barge impact. For the I-64 and US 41 bridges, and in the case of an incident, selected personnel are notified via text messages on their cell phones along with e-mail messages. The messages identify the type of incident and its severity, and list the web site where the incident can be viewed along with data from the instrumentation on the bridge. Decisions can be made in minutes in regard to the course of action.

I. Harik, A. Peiris

### Long-term Data Intensive Wireless Structural Monitoring: Three Years of Experiences on the Stork Bridge

In the last decade, wireless sensor networks have become an intensively investigated tool for monitoring applications. Many field experiments with short-term deployments demonstrated their advantages. Very little, however, is known about the performance of wireless sensor network in mid- and long-term deployments. This paper reports about the experiences in developing, deploying and maintaining a wireless monitoring system on a cable stay bridge.

G. Feltrin, O. Saukh, R. Bischoff, J. Meyer

### Identification of Structural Changes on a Movable Bridge

Movable bridges are unique structures in terms of their design, operation and maintenance. Florida has the highest number of bascule type movable bridges in the United States. According to Florida Department of Transportation (FDOT) engineers, movable bridges maintenance cost is considerably higher than that of a fixed bridge because of the problems encountered due to their proximity to waterways and special operational demands. Therefore, Structural Health Monitoring (SHM) can be used to track and evaluate incidents, anomalies, damage and deterioration in movable bridges. In this study, two most critical structural problems of a pilot movable bridge are monitored and evaluated by using a correlation based data analysis method. It is shown that the proposed methodology can be used to monitor the structural condition of the movable bridges effectively using traffic induced strain data.

F. N. Catbas, M. Gul, H. B. Gokce

### Experiences with Real-Life Fiber Optic Bridge Monitoring Installations

We present a brief overview of real-life bridge structural health monitoring (SHM) installations using fiber Bragg grating sensing technology. We review and describe the associated successes, challenges and lessons learned for SHM projects. In general, project successes are coupled to improved sensing tools: better sensor packages, simpler and less expensive instrumentation, improved installation techniques, and more efficient data analysis tools. Some shortcomings are the direct result or poor project planning and communications. Particular attention is given to the benefits and economics of instrumenting civil structures – when and how it pays.

T. Graver, A. Mendez, K. Chandler

### Wireless Long-Term Monitoring of Asphalt Layer on a Motorway Bridge and Comparative Testing of Displacement

Monitoring of civil structures is a growing application in nondestructive testing. Wireless systems supersede wired systems mainly by being easily deployable under various local structural conditions. The vast majority of today’s existing structures are not equipped with monitoring systems by design. Wireless systems can still be installed as a retrofit. In the demonstration project described here, a 1350 m long motorway bridge over the Neckar River near Heilbronn, Baden-Württemberg, Germany was equipped with ambient and material temperature sensors as well as humidity sensors. The test setup is described in detail and interpretation of the data from initial measurements is provided. Furthermore, an assessment of the wireless monitoring system is presented, giving information about the packet drop rate, radio frequency calculations and wide-area network connectivity.

S. A. Bachmaier, A. Gordt, S. Jungmann, M. Krüger

### Eigenvector Normalization from Mass Perturbations: A Review

Stochastic identification results are not sufficient to determine input-­output relations because one constant for each identified mode is missing. Since the product of a mode and its constant is unique the constant can be absorbed into the modal scaling and it is in this context that the term eigenvector normalization is used in this paper. The seminal contribution in the normalization of operational modes is from Parloo et. al., whom, in a paper in 2002, noted that the required scaling can be computed from the derivative of the eigenvalues to known perturbations. This paper contains a review of the theoretical work that has been carried out on the perturbation strategy in the near decade that has elapsed since its introduction.

D. Bernal

### Health Monitoring of a Benchmark Structure Using Vibration Data

Aging and deterioration of existing structures and the need for rapid assessment and evaluation of these structures for hazard mitigation has significantly expanded the research efforts in the field of structural health monitoring (SHM). SHM involves monitoring of a structure using periodically sampled measurements, extraction of damage sensitive features from these measurements, and assessment of the current health state/integrity of the system. The approach known as the Damage Locating Vector (DLV) technique is an SHM tool that interrogates changes in the flexibilities synthesized at sensor locations using the vibration data with respect to the location of damage. This paper presents the damage identification results of the Phase II Experimental Benchmark Structure of the IASC-ASCE Task Group on Structural Health Monitoring.

B. Gunes

### Applying Alternative Identification Methods in Eccentric Mass Shaker Experiments

When eccentric mass shakers are used for forced vibration testing of actual structures, the Peak Picking Method is generally used for identifying modal parameters. Here we investigate the applicability of two time domain methods, namely the Eigensystem Realization Algorithm applied with Auto Regressive Exogeneous Models and the Covariance Driven Stochastic Subspace Method, and one frequency domain method, namely the Frequency Domain Decomposition Method, as alternatives to Peak Picking. To this end, a finite element model of a 3-storey building is prepared and forced vibration tests are simulated on this model based on the properties of the eccentric mass shaker present at the Boğaziçi University Structures Laboratory. Biases in modal parameter estimates are analyzed via Monte Carlo simulations and it is observed that identified mode frequencies and damping ratios fall within

$$\pm 3\%$$

of the actual values, and that the identified mode vectors have MAC numbers higher than 0.95.

### Cost-Effective Dynamic Structural Health Monitoring with a Compact and Autonomous Wireless Sensor System

Dynamic Structural Health Monitoring (D-SHM) in an attractive holistic approach to Non-Destructive Testing (NdT), based on the premise that damage influences the dynamic behaviour of a structure by altering its stiffness, mass or energy dissipation properties.

At present, the fact that the dynamic behaviour of a structure is severely affected by a variety of additional boundary and environmental conditions confines D-SHM to industrial applications where repeatability or environmental conditioning reduce the complexity of the problem, or where the technical and economical implications of costly and time-consuming test campaigns are not an issue.

In this work, the “Smartbrick” platform - an autonomous battery-operated wireless device purpose-built for environmental and structural monitoring - has been equipped with a vibration sensor that captures detailed acceleration data in response to natural occurrences such as small seismic or human-induced events. This enhancement makes the SmartBrick a D-SHM-ready platform with multi-year battery life, which allows a dramatic reduction in both equipment and installation costs, thus potentially expanding the practice of D-SHM to a considerably larger number of existing and new structures.

F. Bastianini, S. Sedigh, G. Pascale, G. Perri

### Preliminary Identification of Dynamic Characteristics of a Unique Building in Chile Following 27 February 2010 (Mw=8.8) Earthquake

Following the 27 February 2010 (M

w

= 8.8) Offshore Maule, Chile earthquake, a temporary, real-time data streaming array comprising 16 channels of accelerometers was deployed throughout a recently constructed 16 story tall building with three additional basement stories in Vina del Mar, Chile. This building was not damaged during the mainshock; however, it is similar in design to many other buildings with multiple shear walls that were damaged but did not collapse in Vina del Mar and other parts of Chile. The temporary array recorded low-amplitude response of the building from aftershocks. The recordings provided dynamic response characteristics of the cast-in-place reinforced concrete building. Available dynamic characteristics from mathematical modal analyses are compared to the observed responses. Distinct “major-axes” translational and torsional fundamental frequencies as well as frequencies of secondary modes are identified. Response data from each earthquake provide evidence of beating.

M. Çelebi, M. Sereci, R. Boroschek, R. Carreño, P. Bonelli

### Behaviour of Corrosion Damaged Reinforced Concrete Beams Strengthened Using CFRP Laminates

This paper presents experimental results on the behaviour of corrosion damaged reinforced concrete beams repaired using a cementitious patch repair material and strengthened using carbon fibre reinforce polymer (CFRP) plates. Four RC beams (154 mm × 254 mm × 5000 mm long) were used. Three of the beams were subjected to different levels of accelerated corrosion (using an impressed anodic current and 5% NaCl solution) under sustained service loads while one beam acted as a control. The service load was estimated as 80% of cracking moment. The three corrosion-damaged beams were using a repair mortar; further, two of the patch-repaired beams were strengthened with carbon fibre reinforced polymer (CFRP) laminates. The effect of damage on the stiffness of the beams was inferred from natural frequencies, strain measurements and deflection measurements. The effect of patch repair and strengthening on corrosion damaged beams was deduced from the changes in their ultimate capacities. The results reveal that the stiffness and the ultimate capacity are improved by about 25% and 50% respectively when both patch repair and CFRP are applied on a damaged beam. Patch repair only, improved the stiffness by approximately 5% but did not improve the ultimate capacity.

M. Tigeli, P. Moyo, H. Beushausen

### Diagnosis of Historic Masonry Structures Using Non-Destructive Techniques

An accurate diagnosis of the state of conservation of historic structures is based on an extensive experimental investigation and on an appropriate structural analysis. A methodology of investigation to be applied to Cultural Heritage (C.H.) buildings is presented by the authors, based on a long experience in the field. The investigation steps are described, from the collection of historical documents and the visual inspection to: the geometrical and crack pattern survey, the detailed masonry section and quality description through on site mechanical and physical tests and use of Non Destructive (ND) techniques to the material characterisation and the structural monitoring.

L. Binda, L. Cantini, C. Tedeschi

### Monitoring of Salt Content in Mineral Materials Using Wireless Sensor Networks

The recrystallization of salts due to changes in moisture content is one of the major damage mechanisms in historic materials like natural stones, bricks, plasters, and mortars. This paper presents a new development in the field of wireless monitoring the salt content in historic mineral materials. In this investigation ion selective potential sensors (electrodes) are used for monitoring salt displacement in time, influenced by changes in moisture content. Different kind of electrodes and electrode couplings are tested in laboratory, and in field measurements. For measuring the potential, low power data acquisition hardware was developed that is optimized for using it in wireless sensor networks. Data acquisition uses a competitive wireless sensor network system that is further developed in the SMooHS-Project (Smart Monitoring of Historic Structures, Collaborative Project in the 7

th

Framework Programme of the EU) to operate under harsh environments. First results of the laboratory and field test are presented, showing that long-term monitoring of salt content is feasible.

J. Frick, F. Lehmann, K. Menzel, H. Pakdel, M. Krüger

### Development and Application of Active Thermography for Monitoring of Deterioration Processes of Historic Structures

As shown recently, the quantification of damage in historic masonry structures is possible by using active thermography. In this paper, a case study is presented concerning systematic studies of the determination of damage size and prognosis of damage increase inside a sandstone column by using different approaches of active thermography. Various heating sources as well as impulse and periodic heating have been compared. Reproducible investigations in regular time intervals for structural monitoring are possible.

C. Maierhofer, R. Krankenhagen, M. Röllig, U. Kalisch, J. Meinhardt

### GPR Spectral Decomposition to Monitor Cracks in a Historic Building

The paper deals with the ability of high-frequency multi-component GPR data to detect and monitor evolution of cracks over time. For this purpose, multi-component GPR data and advanced processing, based on spectral decomposition of GPR signal, are used. The study takes into account theoretical forward models and actual data acquired on the floor of an ancient building where cracks, with displacements from about 0.001 to 0.02 m and evolving during the time, are present. In-line and cross-line electric field components with x- and y-directed antennas were acquired. The 2x2 data matrix was collected along ten transects over five years. Time lapse analysis of spectral decomposition allows to overcome environmental influence on the data (as the coupling of the antenna-structure depending on the season in which the measurements were collected) and to discover and locate the zones affected by displacement variations which are not detectable by time slices.

L. Orlando

### Using an Ultrasonic Echo Technique to Inspect the Structure of a Pumice Brick Vault in a Church

Currently, the assessment of ultrasonic methods on pumice bricks is not a state-of-the-art technology. The vault of a neo-Gothic church made of pumice brick showed large cracks resulting from World War II and the structure of other areas was damaged. Normally, tasks like these are solved by visual inspection combined with drilling cores at a few measuring points. By this means, only the surface and just a few areas of the structure can be inspected. With ultrasonic echo it is possible to study the internal structure of the vault laminar. The investigations are non-destructive and have no effect on the monument.

The entire vault of the nave and aisles was examined, using the ultrasonic echo technique. The structural constitution differs even in one nave. The results show the need for quality control of the various restoration measures (some of which are only “cosmetic”) by means of the ultrasonic echo technique. With the results, a detailed restoration concept and a priority list were developed in which the areas that need chemical strengthening (e. g. with silicic acid esters) are defined. By metering the application of the chemical strengthening agent to improve the structure, significant savings in material costs are possible.

In addition, the wooden roof structure was examined visually, tapped with a hammer, examined by an ultrasonic echo and drilling resistance technique and core samples taken. Areas with strong degradation caused by brown rot as well as other areas with active insect infestation were identified.

A. Hasenstab, G. Hilbert, K. Frühwald

### Acoustic Emission as a Non-Destructive Method for Tracing Damage: From Laboratory Testing to Monitoring Historic Structures

Acoustic emission (AE) technique has recently become an important non-destructive tool to gain insight into the evolution of damage in materials. It is widely used as a laboratory method in material science and civil engineering. However, it has not been applied sufficiently in the field of cultural heritage, mainly due to the great variety of historic materials and limited knowledge about their physical properties. In comparison with other non-destructive techniques AE possesses some very important advantages – it is simple in application and does not require any external stimulation of the object.

In this paper a comparison of AE signals measured for different materials (stone samples, timber joist specimens) and different destructive and non-destructive processes, including mechanical tests, is presented. The proper evaluation of the results obtained in the laboratory can help to distinguish between AE signals related to material damaging and non-damaging processes. The presented work demonstrates the potential of AE as a practical tool to assess the risk of mechanical damage to historic building materials also at different moisture contents or in varying state of decay.

M. Strojecki, M. Łukomski, C. Colla, E. Gabrielli

### Thermographic Investigation of “leccese” Stone Masonry Structures

InfraRed Thermography (IRT) is a wireless, contactless and smart technique potentially suitable for the qualitative and/or quantitative buildings long-term monitoring. However, the monitoring of a particular object/defect in a masonry structure can succeed only if the thermographic survey is performed with a suitable experimental setup, defined after a specific laboratory calibration, leading to the proper definition of the operational parameters (active/passive approach, distances, time-windows, etc.). The aim of this document is to describe the advanced testing of “

leccese

” stone masonry samples, in order to evaluate the effectiveness of IR thermography to qualitatively detect defects and inhomogeneities (voids, irregular mortar joints, wooden and metallic inclusions) inside masonry textures or behind plaster layers, as well as evaluating the capacity of IR thermography to detect the beginning of material deterioration and its long term evolution. At the end of the experimental work the calibration of an infrared technique to be used for the NDT of historic structures was defined, by identifying the best set of operative parameters.

A. Largo, R. Angiuli

### Non Invasive Measurements of Moisture in Full-Scale Stone and Brick Masonry Models After Simulated Flooding: Effectiveness of GPR

Within the framework of a European Commission project entitled Cultural HEritage against Flood (CHEF), a research was carried out in Milan on full-scale stone and brick masonry models by means of a simulated flood to investigate the effects of floods on historic and masonry buildings. The objective was to evaluate the post-flood moisture content and the drying process through non-destructive or minor-destructive techniques. Several non-destructive testing (NDT) were applied (thermography, sonic tests, radar) and were compared with the powder drilling test. Thermography and radar tests were the most useful; the attention is here more concentrated on radar tests which revealed interesting results. A high frequency GPR system was used to perform measurements on selected points of the models at selected intervals during the drying period. Radar velocity, radar amplitude in transmission and in reflection mode, radar waveform distortion and spectra were analyzed as a function of time after flooding and were compared to moisture content assessed by the powder drilling method. Measurements of radar velocity and radar waveform distortion were found meaningful and in agreement with the expected drying process.

G. Cardani, L. Cantini, S. Munda, L. Zanzi, L. Binda

### Damp and Salt Rising in Damaged Masonry Structures: Numerical Modelling and NDT Monitoring

Existing research on structural deterioration of historic structures generally concentrated on direct mechanical causes of deterioration rather than on physical-chemical effects of aggressive agents on the mechanical parameters of masonry and their interaction. The research presented herein studies deterioration of masonry in a unified environmental framework which accounts for both the mechanical and the physical-chemical effects and their coupling. Numerical models and experiments have considered various cases including mechanically damaged and undamaged masonry walls with moisture capillary rise from foundations, with and without salt inclusions at different concentrations. Examples from on-going work are shown.

C. Colla, L. Molari, E. Gabrielli, S. de Miranda

### Simulation and Test Procedures to correlate Structural Damage with Moisture and Salts Migration in Masonry

In historic masonry structures – focus of the 7FP European project SMOOHS – the monitoring and effects of environmental agents in walls and of structural problems is being investigated in a joint perspective. Numerical simulations and experimental work aim to correlate the decay effects of moisture and salt transport in masonry, with structural damage. To better address the problem, a cross-feeding collaboration is set up between numerical and experimental studies. Initial experimental data obtained in the lab on masonry materials become the main input data for hygro-thermal simulations of behaviour of masonry specimens in aggressive environment, that is solutions of sodium sulphate (Na

2

SO

4

). Simulation output helps to improve the experimental accelerated ageing procedures. Later, the salt damage process development in these specimens and their reduced structural capacity will be mechanically evaluated. A function relating these parameters will couple hygrothermal and structural simulations to predict a structural damage index for historical buildings.

C. Colla, P. Baldracchi, A. Troi, F. Ubertini, R. Carli

### Wireless Monitoring of Moisture Content in Mineral Materials by Electrical Impedance Measurements

Changes in the moisture content and the resulting recrystallisation of the entrained salts is one of the major damage causes in historic materials like natural stones, tiles, plasters and mortars. This paper presents a new development in wireless monitoring of the moisture content in historic mineral materials. In this ongoing research, electrical impedance measurements are carried out to monitor the changes in the measured electrical conductivity of materials, as affected by both the total moisture content and the salt concentration. A measurement system consisting of a pair of electrodes, a sensor board and a low power data acquisition hardware was developed which was optimised for use in wireless sensor networks. Initial results of the laboratory validation tests are presented in the paper.

F. Lehmann, J. Frick, M. Krüger, K. Menzel

### Determination of Mechanical Properties of Natural Stone and Brick Elements in Masonry Heritage Buildings

The paper presents the results of investigation and documentary research conducted by the authors upon the constituent material of stone and brick masonry structures located in Dobrudja county. It’s important to mention that in Dobrudja are encountered a great number of heritage buildings belonging to 18

th

– 19

th

century that have a stone and brick masonry structure resistance. For these reasons the main objective of the study is to determine the mechanical properties of materials which structure is made of. In order to achieve this objective the authors have determined the mechanical characteristics of brick and stone elements in masonry with nondestructive methods for various heritage buildings in Dobrudja area. To verify and validate the results obtained by nondestructive methods, those results were compared with the ones obtained by applying destructive methods in the laboratory of the Faculty of Civil Engineering, “Ovidius” University of Constanta. The results have been summarized and constitute the beginning of a database of mechanical characteristics. The obtained results offer a valuable amount of information in establishing measures for interventions in restoration.

A. M. Grămescu, S. Gelmambet, M. Drăgoi, B. D. Pericleanu

### Mobile UV-VIS Absorption Spectrometry Investigations in the “Alexander-Sarcophagus” in Istanbul

For several years, UV-VIS-spectrometry has been employed to identify colorants used in the polychromy of diverse art objects such as paintings, textiles and ancient sculptures. UV-VIS-spectrometry is a non-destructive method used to identify colorants (pigments and dyestuffs). The surface to be examined is briefly illuminated by white light. Part of the white light is absorbed and part is reflected. The reflected light is detected and split by a spectrometer. Achromatic materials can also be identified if the spectral range is adjusted to the visible light in the near UV and the near infrared region. The spectra can be compared with those in specially created data libraries. The combination of high efficient optical equipment such as light source, fibre optics and diode-array detector together with the mathematical preparation of the spectra enables us to identify successfully nearly 90% of the colorants without taking samples. The various technical options for this analytical method and the results obtained by examining the Alexander-sarcophagus owned by the Archaeological Museum of Istanbul will be illustrated. It was possible to identify more than 24 colorants.

H. Piening

### Structural Monitoring and Investigation Campaign in the Church of St. Giuseppe dei Minimi in L’Aquila, After the 6th of April 2009 Earthquake

The oratory of St. Giuseppe dei Minimi in L’Aquila, Italy, sustained ­serious damage after the seismic events of April 2009. The earthquake caused out-of-plane overturning of the façade, with wide cracks on both lateral walls. Such rotation caused the “sinking” in the crack of one of the pillars of the belfry, which did not collapse, but remained in a very dangerous situation.

After the initial stabilisation measures, carried out during the months following the seismic event, field investigations were carried out by the authors in spring-summer 2010, to guide the final strengthening intervention, supervised by the Italian Ministry of Culture.

The investigation campaign involved intensive use of non and minor destructive techniques, such as thermography, radar, sonic tests, core sampling, single and double flat jack tests and chemical analysis on sampled materials. Moreover, the overall dynamic characteristics of the church were extracted from vibrations measured in the upper areas of the building, using output only techniques.

Finally, a structural monitoring system was installed in the church (involving also the adjacent St. Biagio church), to monitor the damage progression and to evaluate the effectiveness of strengthening applications.

F. Casarin, M. Dalla Benetta, C. Modena, F. da Porto, M. R. Valluzzi, L. Cantini, C. Tedeschi, P. Condoleo

### Investigation Methodology Applied to the Structure of the Church of St. Biagio in L’Aquila

After the earthquake that stroke the city of L’Aquila during the night of April 6

th

2009, many historical buildings at the city centre were severly damaged. Nevertheless many others survived the seismic event with only local damages, showing a good mechanical behaviour against vertical and horizontal actions. In order to continue preserving these buildings, a careful investigation is necessary before applying any repair technique, new or traditional to understand the past design practices for building durable and safe structures. In order to understand the structural behaviour of the church of St. Biagio in L’aquila, an extensive diagnostic investigation based on non-destructive and minor destructive techniques was carried out by the authors. The paper describes mainly the applied methodology which can produce some guidelines to be followed in the future study of other Cultural Heritage (C. H.) buildings hit by the earthquake.

L. Cantini, P. Condoleo, S. Munda, C. Tedeschi, C. Tiraboschi, F. Casarin, E. Simonato, L. Binda

### Use of Thermovision for the Survey of a Timber Vault in Torino

In order to study the building technology of an old 19

th

century timber vault in the Palace of the Academy of Sciences in Torino, authors performed several diagnostic tests to detect the construction technique and the damages to this structure. The vault has the peculiarity of being a timber structure, made with a specific technology that is not easily visible from intrados and extrados. For this reason the interpretation of its mechanical behaviour must be based on the knowledge of its construction technology. The non destructive technique that provided the most interesting information was IR thermography. This technique provided valuable data about the timbering used to build the shell of the vault and enabled correct execution of other minor destructive tests, such as light sampling and stratigraphic investigation on the painted plaster.

L. Cantini, C. Tedeschi, C. Tiraboschi, L. Binda

### Wireless Monitoring of Heritage Structures –Selected Case Studies

Monitoring of cultural heritage structures is an application area for Wireless Sensor Networks (WSNs) which is implemented in the project “Smart Monitoring of Historic Structures (SMooHS)”, funded by the European Commission within the 7th Framework Programme. The project aims at the development of a WSN system especially designed for use on real structures to enable smart interpretation of acquired data and comparison of results with those obtained from established laboratory tests in an effort to evaluate the usefulness of the WSN system. While the development of the WSN system is still ongoing by the partners, many sensor types are already supported. This paper presents WSN implementations on the Holy Cross Minster in Schwäbisch Gmünd, Germany, Schönbrunn Castle Chapel in Vienna, Austria, archaic houses in Hebron, Palestine, and Bode Museum in Berlin, Germany. The system design, including hardware and software, sensor types and their characteristics, and their adaptation to the system is described. System setup is described for each case study and results of initial measurements are shown, including smart automatic interpretation mechanisms. An assessment of the wireless monitoring system concludes the paper, stating research needs and future work.

S. A. Bachmaier, M. Krüger

### Differences in International Strategy for the NDT of Concrete

Clients worldwide face increasing pressure to obtain best value for money from NDT surveys. Yet this gives rise to the dilemma of whether a high quality survey and analysis is being undertaken. ACI 228 Committee provides documentation on the available NDT test methods, but stops short of giving advice on the interpretation of data. RILEM TC Committee on the NDT of Concrete does give advice – but the Committee has a fixed term of operation.

This paper discusses progress towards international standards of NDT of concrete and makes specific comments on differences in international practice. Finally, examples of best international practice in NDT will be highlighted. The American Concrete Institute (ACI) is identified as a leader in translation from research to practice.

M. C. Forde

### NDT Planning for Fatigue Sensitive Structures Under Uncertainty

Timely maintenance actions on deteriorating structures depend on the quality of the non-destructive testing (NDT) method. Damage detection with less delay can lead to less maintenance delay. The efforts to detect existing fatigue cracks and predict fatigue crack propagation reliably will contribute to reduce the damage detection delay, and furthermore to establish optimum maintenance and management strategies of fatigue sensitive structures. In this paper, a probabilistic approach for optimum NDT planning for deteriorating structures subjected to fatigue is presented. The optimum NDT plan is obtained by minimizing the expected damage detection delay. Uncertainties associated with fatigue damage occurrence / propagation and quality of the NDT are considered to formulate the damage detection delay. Effects of number and/or quality of the NDT on optimum planning are studied. The approach presented is illustrated using a realistic example of a fatigue sensitive structure.

D. M. Frangopol, S. Kim

### A Proposal for Reliability Improvement of Non-Destructive Evaluation Technology for Concrete

The subcommittee of the JSCE (Japan Society of Civil Engineers) ­concrete committee for the improvement of the reliability of non-destructive evaluation technology for concrete chaired by Professor Toshiro Kamada of Osaka University (Committee 339 below) has discussed measures for the improvement of the reliability of non-destructive evaluation technology from two perspectives: education, and standards and specifications. This paper describes the roles that standards and specifications play in terms of improving the reliability of these technologies. Moreover, a pattern of reliability based on the client-engineer correlation is identified. As a result, it was found that the reliability of non-destructive evaluation can be enhanced to some extent by identifying the scope of application and standardizing the method of non-destructive testing. For ultimate improvement of reliability, the pattern of reliability itself should be changed through technical innovation for non-destructive testing or the enlightenment of the client.

T. Kamada, M. Iwanami, T. Shiotani, Y. Oshima, S. Uchida

### Data Fusion to Improve the Concrete Diagnosis

Numerous non-destructive testing (NDT) methods are used for concrete structures to obtain relevant data about material properties and damage states for reliable condition assessment. Whether the objective is to determine physical properties such as the porosity and the water saturation rate, or mechanical properties such as the elastic modulus or the compressive strength, sensitivity of NDT techniques to many characteristics of the material and its environment is a commonly encountered problem. Thus, accurate and reliable information is often difficult to extract due to the high level of uncertainty involved. Complementary use of different NDT methods for coherent combination of information obtained from each method is a sensible strategy to improve evaluation. The data fusion methodology presented in this paper makes use of the complementary data obtained from different non-destructive or destructive techniques to improve diagnosis reliability. In the case of imprecise and uncertain data, an assessment can still be made with a quantitative measure of the uncertainty involved. The methodology is based on the possibility theory and allows the selection of the best combination of data and techniques to evaluate the material. Applications of the methodology are presented and the results are discussed. Results show good agreement between estimations by data fusion and measured values. Also shown by the results is that the selection of complementary techniques is essential for a better estimation of indicators and improved diagnosis.

V. Garnier, M. A. Ploix, D. Breysse

### Approach for the Life-Cycle Management of Structures Including Durability Analysis, SHM and Maintenance Planning

A tailor-made model was developed, which utilizes state-of-the-art ­information from literature as well as VCE’s experience gained in the course of performing bridge monitoring and bridge inspection worldwide. Probabilistic methods are used for the service life calculations of the whole structure as well as for individual structural members. The reason is to cover occurring uncertainties which have to be also implemented into the established maintenance plan in terms of lower & upper bounds of life expectancy. The starting point of the bridge’s service life – in terms of the safety level – is according to the initial over design and depends on the applied design code and certain safety considerations in the course of the static calculations. This paper presents a custom model developed for service life prediction of bridge structures based on the state-of-the-art information from the literature and VCE’s worldwide experience in bridge monitoring and inspection. The developed model was implemented in an urban highway extension project with more than 100 existing and new bridges.

P. Furtner, R. Veit-Egerer

### A New Crane System for Remote Inspection and NDT

For non-destructive investigation of structures and materials, a crane ­system was developed to enable easy access and implementation of different non-destructive methods, such as high-resolution photography and detailed 3D scanning of surfaces. The crane was specifically designed for remote inspection and documentation of cultural assets. It was constructed from the world’s smallest crane base that allows access through standard doorways. The crane is self-propelled by a non-abrasive caterpillar drive and has a small turning circle. The hydraulic outriggers ensure a level and secure ground base. A newly constructed telescopic mast mounted on the crane’s original arm enables compactness in retracted state and the ability to reach an extension length of up to 22 meters. With the help of an extra mast, which is driven by an electric motor, the mast can be extended and retract by remote control. A high-resolution camera with a flash unit can be installed on the 3D head placed at the front of the crane. The head is controlled from the ground and can be placed in a variety of positions. The camera is operated remotely and features a live-image view on the ground based computer that allows easy positioning in front of the object. Examples from initial applications are provided in the paper.

R. Drewello, N. Wetter, B. Beckett, N. Beckett

### Integration of NDT in Rapid Screening of Concrete Structures

Ageing of infrastructures is a major concern for the civil engineering community world over. Buildings, bridges, and every other structure are expected to serve for the designed life provided periodic inspection and proper maintenance is done. However maintenance is a word seldom associated with civil infrastructure. Non Destructive Testing (NDT) has gained relevance in this context as more and more infrastructure are getting aged and replacement of a existing ­structure with a new one is not feasible every time and within a short span of time. Testing, evaluation of the existing condition and retrofitting of the structures will extend the service life and hence give the authorities time to think about future course of action. This paper intends to provide a scheme to evaluate the existing condition of any concrete structure and suggests ‘points’ based evaluation. The scheme consists of standard NDT techniques both field and laboratory tests that are generally employed individually and their results analyzed separately. The formulated scheme has been employed on two existing buildings and its applicability demonstrated.

S. Sundar Kumar, B. H. Bharatkumar, G. Ramesh, T. S. Krishnamoorthy

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