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2022 | Book

Proceedings of the 3rd RILEM Spring Convention and Conference (RSCC 2020)

Volume 3: Service Life Extension of Existing Structures

Editors: Dr. José Sena-Cruz, Dr. Luis Correia, Prof. Miguel Azenha

Publisher: Springer International Publishing

Book Series : RILEM Bookseries


About this book

This book gathers peer-reviewed contributions presented at the 3rd RILEM Spring Convention and Conference, held at Guimarães and hosted by the University of Minho, Portugal, on March 9-14, 2020. The theme of the Conference was “Ambitioning a Sustainable Future for Built Environment: comprehensive strategies for unprecedented challenges”, which was aimed at discussing current challenges and impacts of the built environment on sustainability. The present volume is dedicated to the topic “Service life extension of existing structures”, which covers the most recent scientific and technological developments in the understanding of the evolution and degradation of construction materials and structural systems. Analytical and numerical, as well as experimental approaches, aimed at characterizing, modelling and predicting the evolution of the physical, chemical and mechanical properties of construction materials and structural systems are regarded. Multiphysics models are also considered, as well as other strategies that contribute for an accurate characterization and prediction the service life and the evolution of existing and novel construction materials under normal or extreme environmental exposure or loading conditions. New strategies to promote the smart repairing or the recovery of material properties, as well as the service life extension, are also considered. The following subtopics are included: service life models and multiphysics approaches; smart structures, innovative monitoring and intervention strategies; management and optimized maintenance strategies; integrated rehabilitation and strengthening approaches.

Table of Contents

Experimental Analysis of the Bending Behavior of Structural Metal Joints Based on the Use of Girder Clamps to Service Life Extension of Existing Structures

The objective of this work is mainly focused on the structures that support the facilities and machinery present in industrial plants. Service life extension of existing structures is one of the current objectives of the industry. The lay-out of the production has to constantly adapt to changes in production, variations in demand and new products. These changes of model or demand, usually imply important changes in the facilities and machinery and therefore in the structures that support them. Currently, these support structures are destroyed at each lay-out change, mainly because an easy reconfiguration of the support structures is not possible. To achieve service life extension of existing structures it is necessary to use easily reconfigurable, reusable and removable structures. Currently there are already solutions of structures that are removable and reconfigurable but mainly in aluminum beams. Nowadays, there are no definitive solutions for steel structures manufactured with standard shapes (standard steel beams). The use of clamp joints for steel profiles would be a very interesting solution and would allow the manufacture of completely removable and reconfigurable structures. This paper proposes and uses a methodology for the experimental analysis of the bending behavior of this type of joints depending on the length of the profile flange.

Manuel Cabaleiro, Cristina González-Gaya, Fernando Gonzalez
Corrosion of Carbonated Structures. Real Cases of Structures in Spain

One of the main causes of deterioration of structures is the corrosion of the reinforcement, and within this one possible source of deterioration is the carbonation of the concrete cover. There are numerous studies about carbonation of concrete but the great majority have been carried out with samples taken in the laboratory and their behaviour in real structures is not known. This work presents the evaluation of three types of structures during several months in which the conditions to which the structure is exposed and the corrosion speed have been measured by means of in-situ measurements.

Nuria Rebolledo, Julio E. Torres, Javier Sánchez
Bond Behaviour of NSM FRP Strengthening Systems on Concrete Elements Under Sustained Load

During the last decades, Near Surface Mounted (NSM) Fibre Reinforced Polymer (FRP) strengthening system has been widely accepted as an efficient methodology in structural rehabilitation. The bond behaviour of the FRP-concrete joint has resulted to be governing the overall performance of the strengthening system. Moreover, due to the susceptibility of the materials used in the NSM strengthening system in front of high temperatures and sustained loads, their performance under service conditions can be affected. Although the short-term bond behaviour has been largely studied in the literature, there is still a lack of experimental data to better understanding the long-term performance. The paper aims to experimentally study the evolution of bond damage of the concrete-FRP bonded joint of an NSM FRP strengthened concrete element, and how it affects to the slip between the strengthening system and the concrete For this purpose, a total of eight NSM pull-out specimens with two different bonded lengths (150 and 225 mm) and two different groove thicknesses (7.5 and 10 mm) have been loaded with two different levels of sustained load (15 and 30% of the ultimate load) at room conditions up to 40 days. Specimens were previously characterized under a short-term test. Slip at the loaded end was measured to capture the evolution of slip during time. Results showed that the slip caused by creep increased with the sustained load level, whilst it decreased with the bonded length.

J. Gómez, C. Barris, M. Baena, R. Perera
Assessment of Different Coastal Defence Structures to Promote Wave Energy Dissipation and Sediments Retention

Coastal areas are an apprized environment by society that will continue to expand rapidly. Traditional coastal protection structures are commonly deployed to protect coastal areas endangered by natural extreme weather events. However, due to their limited efficiency and very high costs, more efficient and sustainable strategies to deal with coastal erosion are imperative. This research work focuses on the assessment of engineering solutions to mitigate and delay coastal erosion. Three different structure geometries (triangular prism shape, single detached breakwater and group of two detached breakwaters) are analysed on a realistic bathymetry, using a combination of numerical models (SWAN and XBeach) to study the influence of those structures on the coastal hydro- and morphodynamics. SWAN was used for hydrodynamics and XBeach for hydrodynamics and morphodynamics assessments. In addition, a comparison between SWAN and XBeach hydrodynamics results was also performed. Structures considered in this study have regular shaped geometries, and are characterized in terms of their efficiency regarding wave height and wave energy dissipation considering different wave regimes and performance in terms of long-term beach morphodynamic impact (sediments accumulation and erosion). The analysis is concentrated in two scenarios, one for low and the other for highly energetic hydrodynamics (the most challenging to coastal zones defence). The obtained results allowed classifying their performance in terms of the impact on wave energy and wave height dissipation, and sediment erosion/deposition patterns.

B. F. V. Vieira, J. L. S. Pinho, J. A. O. Barros
Concrete Drying Modelling in a Variable Temperature Environment

EDF studies the behavior of double walls Concrete Containment Buildings (CCB) in nuclear power plant, for which the inner wall is prestressed and has no metallic liner. The inner wall of CCB is subjected to delayed strains of concrete (which are highly related to concrete drying) causing prestress loss and increased leakage with time. Moreover, the permeability of concrete itself is vastly dependent on its water saturation ratio. For these reasons, a good prediction of strains and leak-tightness of CCB must start with a good estimate of the moisture profile on concrete. On the EDF Lab Les Renardières site in France, the VERCORS mock-up, a 1/3 scale CCB without a liner, has been built to improve the understanding and the modelling capabilities of ageing and leakage of double walls CCB. The inner wall of the VERCORS mock-up is subjected to a variable temperature drying environment, both in space and in time. In this work, a simplified drying model which take into account effects of temperature on concrete desorption isotherm and drying kinetics is proposed. In order to define a strategy for fitting model parameters, a sensitivity analysis based on Sobol’ indices is performed. Next, the model is calibrated against independent sets of experimental data available on VERCORS concrete specimens up to temperatures of 70 $$^\circ $$ ∘ C. The calibrated model is validated by predicting the mass loss kinetics of several specimens which experience variable temperature drying conditions. Then, the fitted model is compared to direct RH profiles measurements of 40 cm thick blocks installed at different locations in the VERCORS mock-up. Finally, the prediction of the calibrated model is compared to the saturation profile of VERCORS mock-up measured by Time Domain Reflectometry (TDR) method.

Jean-Luc D. Adia, Herman Koala, Justin Kinda, Julien Sanahuja, Laurent Charpin
Hydric Characterisation at Different Temperature of Nuclear Waste Package’s Concrete

In the frame of its electro-nuclear activity, EDF has to deal with nuclear wastes. Containment of waste packages must be demonstrated. The latter is strongly influenced by the delayed strains of cement materials that can lead to cracking. Moreover, the permeability of concrete itself is vastly dependent on its saturation degree. For these reasons, a good prediction of strains and leak-tightness of concrete containment must start with a good estimate of the moisture profile on concrete. In this framework a large panel of experiments and studies are performed in order to demonstrate the package containment. The temperature experienced by waste packages is closed to 50 $${}^{\circ }\text {C}$$ ∘ C in the concrete shell and 60 $${}^{\circ }\text {C}$$ ∘ C in the filling slurry. Moreover, traditionally, the identification of the parameters of concrete drying constitutive laws is based on mass measurement of samples exposed to a constant humidity and temperature. However, it has been observed for different drying laws that this methods leads to a multiplicity of solutions, potentially corresponding to different moisture profiles and also to different extrapolations of the mass-loss beyond the end-time of the experiment used for the identification [1]. As an attempt to calibrate drying model, this study is interested in both obtaining drying experimental data in temperature and also original experimental data set that can discriminate between numerical parameter sets. Thus, data regarding relative mass variation, desorption isotherm at various temperature and relative humidity are carried out. Finally an easy way of achieving cup test is presented in order to assess water vapor permeability for different RH levels.

François Soleilhet, Patrick Sémété, Laurent Charpin, Ginger El Tabbal
Modelling the Three-Stage of Creep

Over the last years, several studies have addressed the time-dependent mechanical behaviour of polymeric composites. When subjected to a constant stress, viscoelastic materials experience a time-dependent increase in strain. This phenomenon is known as viscoelastic creep and manifests as a tendency of a solid material to deform permanently under the influence of constant stress: tensile, compressive, shear or flexural. When applied to polymers, creep is the result of the inherent viscoelastic nature that causes time dependency of behavior. As well known, the initial strain in a material is roughly predicted by its stress-strain modulus. Then, the material will continue to deform slowly with time indefinitely or until rupture or yielding causes failure. A typical creep curve reveals a three-stage behavior, (1) the transient stage, where the deformation rate decreases with time, (2) the steady-state, characterized by a “relatively” uniform rate gradient and (3) the accelerated phase, where the strain rate increases until rupture. In polymers at low strains (nearly to 1%), creep is essentially recoverable after unloading. However, in certain cases, creep failure is the most important degradation mode of a structure (turbine blades, aircraft parts). Furthermore, in civil engineering works, this kind of deformations may be substantial throughout the required service life. The investigation of the creep response of selected engineering materials should integrate the design of structures subjected to mechanical loads over a long time of operation (self-weight, static loads). The aim of “creep modeling for structural analysis” is the development of methods to simulate and analyze the time-dependent changes of stress and strain states in engineering structures up to the critical stage of creep rupture, passing through service state. In particular, the key in identifying these three stages above described lies in the location of the transition points between stages. This work presents a study conducted to estimate the 4 instants of time of the creep curve: (1) the first transition point, that is the transition point between transient and steady creep; (2) the secondary point, that is the inflexion point of the creep curve where the strain rate reaches its minimum; (3) the second transition point, that is the transition point between steady and accelerated creep; and (4) the instability point. This research follows the work publish by Crevecoeur [3] and is based on a combination of an exponential and a power law approach to the creep test data of HDPE pipe sample.

Vitor Dacol, Elsa Caetano
Effects of the Thermal Conditioning on the Mechanical Properties of an FRCM (Fiber Reinforced Cementitious Matrix) Strengthening System

Fiber reinforced composite materials are starting to have very widespread use for rehabilitation and strengthening of existing concrete structures. As demonstrated by several experimental results, the use of composites made with fibers and inorganic matrix (such as cement based or lime based matrix) is very useful from a mechanical point of view. The performances of existing reinforced concrete structures strengthened in bending and shear with FRCM systems evidenced a significant improvement both in strength and ductility. The durability of FRCM strengthening systems are not adequately analysed; due to a limited number of experimental studies and research carried out. Moreover, the effects on the environmental conditions on the mechanical properties of strengthening systems are not well investigated. In this paper, the effects of the thermal conditioning on the mechanical properties of the FRCM system was experimentally investigated. The examined strengthening system consists of PBO (short of Polyparaphenylenebenzobisthiazole) fabric meshes embedded into a cement-based matrix. The system was exposed to thermal cycles at different temperature values (100 and 200 °C) and, then, tested to evaluate its mechanical properties (ultimate strength, ultimate strain and elastic modulus). Five thermal cycles were developed by daily exposure of PBO fabric mesh, matrix and PBO-FRCM specimens at constant temperature value, over six hours and subsequently cooling down freely to ambient temperature (20 °C). After the thermal treatment, specimens were tested until failure, at room temperature. Results of tests analysed in terms of stress–strain relationships allowed influence evaluation of the thermal treatment on the structural response of PBO fibers, matrix and PBO-FRCM specimens.

L. Ombres, P. Mazzuca, S. Verre
Durability Under Thermal Actions of Concrete Elements Confined with an Inorganic Matrix Fiber-Reinforced Composites

Fiber reinforced composite materials are starting to have very widespread use for rehabilitation and strengthening of existing concrete structures. As demonstrated by several experimental results, the use of composites made with fibers and inorganic matrix (such as cement based or lime based matrix) is very effective from a mechanical point of view. Nevertheless, there are legitimate concerns with the durability aspects of strengthened elements, which have hindered the widespread use of these composite materials in structural applications. The exposure of confined concrete elements to environmental actions could reduce the beneficial effects of the strengthening. For a better understanding of this aspect, through an experimental campaign, the paper aims to investigate the effects of thermal actions on the structural response of concrete elements confined with an inorganic matrix fiber-reinforced composite system, consisting of high strength fibers in the form of fabric embedded into a cement-based matrix. Cylindrical concrete specimens confined with one-layer of PBO (Polyparaphenylenebenzobisthiazole)-FRCM (Fiber Reinforced Cementitious Matrix) system were exposed to several (five) thermal cycles at different temperatures (100 and 200 °C) and, then tested under compression loads at ambient temperature (20 °C). When the desired temperature was reached, it was kept constant for 6 h and subsequently, the concrete specimens were cooled down freely to ambient temperature. The obtained results in terms of failure modes, peak strength, axial and radial strains were analysed, in order to evidence the effects of the thermal actions on the mechanical properties of confined concrete elements.

L. Ombres, P. Mazzuca, S. Verre
Accelerating the Hardening of Lime Mortar on Addition of Organics for Repair in Heritage Structures

Repair and restoration of heritage structures have become important as they are the evidence of cultural and historical significance. Strength and durability of lime mortar makes it a good repair material for achieving movement with the old mortar and therefore compatible. Hardening of lime mortar may take centuries to complete and therefore accelerating the hardening process helps in achieving the desired strength earlier. This work aims at studying the impact of organic addition on the physical, mechanical, chemical and durability properties of hydraulic lime mortar to accelerate the hardening. A comparative study of lime mortars with addition of three different organics namely Vitis vinifera (Raisins), Vita vinifera (Zante currant) and Phoenix dactylifera (Dates) were performed. The lime mortar was prepared with binder to aggregate ratio of 1:3, water to binder ratio of 0.75 and with addition of organics in various concentrations (0, 2, 4 and 6%). Bulk density, porosity and water absorption were the physical properties analyzed. The compressive strength was determined for the specimens. The rate of carbonation was determined through the phenolphthalein test. The mineralogical composition of the mortar was identified by using analytical techniques like XRD and FTIR. Capillary rise test was conducted to study the durability of the lime mortar. It was observed that organic addition to lime mortar has enhanced its properties along with an increase in the rate of carbonation and thereby accelerating the hardening. The carbohydrate rich organic additives increased the CO2 content throughout the mortar. Hence increased the strength and durability of lime mortars used in the repair of heritage structures.

Celesta Issac, Simon Jayasingh
Effect of Relative Humidity on Cement Paste: Experimental Assessment and Numerical Modelling

In this study, the objective was to verify whether or not the classical Richard-Fick model was able to take into account the size effect on drying. First, mass loss experiments are made on ordinary cement paste cylinders of 3.6 × 18 cm geometry that enable us to calibrate the model parameters. Second, the quality of identification and drying model was checked by predicting mass loss evolution of small prism of 1 × 5 × 10 mm size dried at different steps of relative humidity. The results demonstrate that the present drying model is able to predict the drying of specimen for different sizes and levels of humidity at ambient temperature. And finally, drying shrinkage experiments for different rates of drying are performed on cement paste cylinders of 3.6 × 18 cm; then, the prediction of drying shrinkage evolution was made using a simple model where the drying shrinkage is supposed to be linear with respect to the relative humidity. The result appears to be satisfactory. Since the spatio-temporal evolution of water content is needed as input to shrinkage prediction, the latter result confirms that the identification of drying model parameters is trustworthy.

J. Kinda, L. Charpin, R. Thion, J.-L. Adia, A. Bourdot, S. Michel-Ponnelle, F. Benboudjema
Self-healing Capacities of Mortars with Crystalline Admixtures

The aim of this research study consists of determining the self-healing capacities of cement-based materials incorporating Crystalline Admixtures (CA) such as permeability and shrinkage reducers. Mortars with three different types of CA were studied. At 28 days old, specimens were cracked by means of a three-point bending test to obtain a single crack characterized by a width varying from between 120 and 200 $$\upmu $$ μ m. Thereafter, the specimens were kept under water and the self-healing process was monitored by means of the crack width and area measurements at 35 and 120 days after cracking. From these first experimental results, it appears that specimens without CA and with calcium sulphate are characterized by a higher healing rate. This difference of behavior between the mortar mixtures is probably related to their microstructure. To confirm this hypothesis, their hydration products and their porosity were characterized at 28 days.

Lina Ammar, Kinda Hannawi, Aveline Darquennes
In-Plane Behavior of Clay Brick Masonry Wallets Strengthened by TRM System

Due to the poor shear capacity of unreinforced masonry (URM) walls, it is necessary to strength these elements in the masonry structures. Textile-reinforced mortar (TRM) composites have received extensive attention as a sustainable solution for seismic strengthening of masonry and historical structures. This new system is composed of textile fibers embedded in an inorganic matrix such as lime-based mortar and is applied on the masonry substrate surface as an externally bonded reinforcement (EBR) system. Lime-based mortars are preferred for application to masonry and historical structures due to compatibility, sustainability issues, breathability and capability of accommodating structural movements.Owing to the novelty of these materials in application to masonry structures, several aspects related to their performance with URM wallets ‏are still not clear. To that end, a new study has been lunched that looks at the effect of textile-reinforced mortar system ‏on the improvement the shear capacity of clay brick wallets. For this purpose, hydraulic lime-based mortar and the glass fiber are used, as TRM system. The results show TRM composite increases the ultimate load of strengthened wallet, in comparison to the URM wallet. Another key point to remember is that TRM system causes the failure mode of wallet to change and improve its performance under diagonal compression test.

Ali Dalalbashi, Bahman Ghiassi, Daniel V. Oliveira
Meso-Scale Study of Plain Concrete Beam Under Both Ambient and High Temperature

In this study, concrete is modelled at meso-level (10–4 −10 cm), where concrete is assumed either to be a two-phase or a three-phase composite. First the aggregates are placed in the structural domain randomly following a uniform distribution with the specific size and shape in order to capture actual aggregate gradation and placement process. The remaining space in the domain of concrete structure is then filled with the cement mortar in case of a two-phase assumption. However, in three phase modelling, part of the mortar of finite thickness surrounding the aggregates is assumed as ITZ which happens to be the weakest zone in the concrete structures. In this study, beam specimen in two dimensions (2D) has been considered and its behaviour under 4-point bending before and after it is subjected to a heating–cooling cycle is simulated. A finite element method (FEM) based approach is adopted here for the simulated study. A convergence study has been performed at ambient condition for different number of simulate beam specimens. The simulated load–deflection responses of the beam specimen subjected to different temperatures are then validated with the corresponding available experimental data.

Biswajit Pal, Ananth Ramaswamy
Electrochemical Realkalisation of Carbonated “Dalle de Verre” Windows

Concrete-glass windows or commonly referred to as “Dalle de Verre” windows are prevalent in historical monuments across Europe. “Dalle de Verre” windows were made by placing cut stained glasses, of various shapes and sizes, into a steel reinforced concrete frame. In addition to the steel reinforcement, a few steel wires run across the concrete elements to hold the glass windows into place. Much of these structures have been damaged due to carbonation of the thin concrete covers and consequent corrosion of the steel reinforcement; and exhibit several cracks due to the expansive nature of corrosion products formed at the steel–concrete interface. This study focussed on understanding the efficacy of electrochemical realkalisation in reinstating the passive state of the steel reinforcement embedded in such concrete-glass windows. Simulant “Dalle de Verre” windows (representative of windows at Kaiser-Wilhelm Gedächtniskirche) were produced using different cements with a water/cement ratio of 0.6 and carbonated under accelerated conditions. Post carbonation, the concrete glass windows were electrochemically realkalised using a sacrificial anode. The influence of highly alkaline conditions due to electrochemical realkalisation on the glass-concrete interface has also been investigated. This study shows that the passive state of the steel reinforcement in “Dalle de Verre” windows, particularly at the Kaiser-Wilhelm Gedächtniskirche (memorial church) in Berlin, can be reinstated using the electrochemical realkalisation method.

Shishir Mundra, Götz Hüsken, Hans-Carsten Kühne
Micro-To-Meso Scale Mechanisms for Modelling the Fatigue Response of Cohesive Frictional Materials

This work deals with a research study on the fatigue behavior of cohesive frictional materials like concrete or mortars. A two-scale approach will be proposed for analyzing concrete specimens subjected to either low- or high-cycle fatigue actions. The multiscale technique is based on a combination of a micro-scale procedure, to describe the microstructural defects affecting the cyclic response, which is subsequently homogenized to the upper meso- and macroscopic failure. More specifically, projected microscopic representative volume elements, equipped with a fracture-based model and combined with a continuous inelastic constitutive law that accumulates damages induced by cycle behaviors, represents the lower scale. A plastic-damage based model, for concrete subjected to cyclic loading, is developed combining the concept of fracture-energy theories (within the family of fictitious crack approaches) with stiffness degradation, the latter representing the key phenomenon occurring in concrete under cyclic responses. The work will numerically explore the potential of the various techniques for assessing the fatigue formation and growth of (micro-, meso- and macro-) cracks, and their influence on the macroscale behavior.

Antonio Caggiano, Diego Said Schicchi, Swati Maitra, Sha Yang, Eddie A. B. Koenders
Deployment of a High Sensor-Count SHM of a Prestressed Concrete Bridge Using Fibre Optic Sensors

To deploy an accurate safety-relevant structural health monitoring, one must assure the utmost care and in-depth knowledge of the monitored structure, which may present challenges such as the reliability to detect unexpected anomalies due to the failure of a component, the correct setting of thresholds and triggers to discern changes due to environmental conditions from critical events, and the high expense in terms of hardware and personnel availability. The fibre optic (FO) technology can provide integrated sensing along with extensive measurements lengths with high sensitivity, durability, and stability, which makes them ideal for SHM of concrete structures. Therefore, an SHM system using quasi-distributed FO FBG sensors is proposed to continuously monitor the strain changes of a 57 m long prestressed concrete bridge due to traffic loads and environmental changes. A total of 89 long-gauge strain sensors were installed to monitor the strain distribution in two lines along the complete length and five arrays in the shear direction. Additionally, 2 FO acceleration sensors and 94 FO FBG temperature sensors were installed for correct and precise temperature compensation of the strain sensors and to correctly detect the strain changes due to temperature variation on the bridge. In this work, the installation processes of the FO sensors and the operational hardware is shown. Furthermore, initial measurement values are presented to demonstrate the potential of FO to provide a reliable SHM system to monitor large concrete structures.

F. I. H. Sakiyama, F. Lehmann, H. Garrecht
Enhanced Fatigue Life of Old Metallic Bridges—Application of Preloaded Injection Bolts

There is a significant number of old metallic bridges with high levels of structural degradation due to their long service period. Fatigue problems are especially important in these structures since the majority of them were not designed taking into account this phenomenon. Several investigations showed that riveted joints are critical details since several fatigue cracks were found in these joints. In this sense, strengthening methodologies need to be studied. The strategy that has been considered a good solution is the implementation of injection bolts to replace faulty rivets. The structural performance of injection bolts has been demonstrated essentially under quasi-static conditions presenting good results. This paper intends to contribute to the scientific knowledge regarding the fatigue behavior of connections with preloaded injection bolts in the context of a bridge strengthening scenario. An experimental investigation was conducted to compare the fatigue performance of connections with preloaded injection bolts and preloaded standard bolts. Single and double shear connections were tested. New S–N design curves were proposed based on a statistical analysis of the results and compared with the S–N curves proposed in EC3-1–9. The obtained results showed that the use of injection bolts lead to lower scatter and improvement of fatigue life. It was verified that the Eurocode 3 is not able to represent the fatigue strength of connections whose performance is influenced by old metallic materials. Additionally, the fatigue behavior of these connections was assessed by numerical analysis. The relevance of the fatigue crack initiation was evident.

Bruno A. S. Pedrosa, Carlos A. S. Rebelo, José A. F. O. Correia, Milan Veljkovic, Luís A. P. S. Silva
Efficient Labelling of Air Voids in Hardened Concrete for Neural Network Applications Using Fused Image Data

Every concrete structure incorporates a system of air pores of different sizes which is characterized by design parameters according to the respective building codes. The system’s characteristics affect properties of the material, specifically the durability of concrete exposed to freeze-thaw action. Testing techniques like the traverse line method, the point count method or the enhanced contrast method have been established and standardized to determine the relevant parameters according to construction material standards in order to empower the future life cycle analysis of the structure. These procedures are typically governed by a major effort in terms of specimen preparation and microscopic examination. We present an approach for a time-efficient procedure to analyze the air void system in optical microscopic images of hardened concrete by means of a neural network that is reliable and highly reproducible at the same time. Height-based segmentation of images using confocal laser scanning microscopy data allowed the composition of an image dataset with automatically labelled air voids. The set consists of 32,750 images of air voids with diameters between 25 µm and $$1.1\,\times \,10 ^3$$ 1.1 × 10 3 µm. By translating the gained information about the size and the location of air voids via a binary mask, we created a corresponding dataset generated by means of an optical microscope. The dense one-stage object detector RetinaNet with a Resnet backbone, fed with the optical microscopic image dataset, demonstrates the effectiveness of the method referring to localization and characterization of air voids in images of hardened concrete. The presented approach supports the successive characterization of the standardized parameters of the air void system and advances the modelling and prediction of structural durability with regard to freeze-thaw resistance.

Fabian Diewald, Nicolai Klein, Maximilian Hechtl, Thomas Kraenkel, Christoph Gehlen
Evaluation of Electromigration Desalination of Granite Contaminated with Salts–A Contribution to the Conservation of Architectural Surfaces

Different cleaning technologies have been available for cleaning monumental façades, of stone or mortar. This is not only necessary for aesthetic reasons, but for the removal of salts that promotes conservation, as surface erosion may affect the long term preservation of buildings. The main advantage of eletromigration treatment is its efficacy in the salts removal or reduction in very porous materials, without damaging the original material. Many monuments of North of Portugal have granitic masonry and stonework structures that, sometime, as a result of continuous exposure to the rainwater infiltrations, or in the case of buildings near maritime cost, due to the marine-aerosols influence, salt efflorescence and disaggregation occurs. Hence, it is important to proceed in removal of chloride salts from the contaminated granite walls. This research work deals with electromigration desalination of contaminated “Mondim Yellow Granite” samples, presenting the physical properties, mineral composition, porosity and internal structure. This type of granite was selected because is frequently used in traditional buildings and monuments of the North of Portugal. The aim of the research was to evaluate the desalination effectiveness of electromigration. By its application chloride salts were completely removed and sulfate ions reduction was significant. Differences in effectiveness of the desalination were analyzed and are attributed to the shape of granite specimens. Results obtained demonstrate the viability of application of this electro kinetic procedure for removal of chloride and sulfate ions of granite ashlars of the monuments.

José N. Marinho, Eunice Salavessa, Said Jalali, Luís Sousa, Carlos Serôdio, Maria J. P. Carvalho
Pathological Manifestations of Neoprene Support Devices in Infrastructure

The so-called works of special arts are constructions of high complexities that allow the advancement of widening gaps and overcoming obstacles previously unthinkable. With the increase in the magnitude of these structures, in addition to greater investments, the maintenance of these structures becomes an increasingly important factor for engineering. Among the elements of bridge structures, the support devices are components with important structural functions, being essential for their proper functioning and especially the durability of the entire structure. The culture of inspection and maintenance of road bridges, railroads, and viaducts in Brazil is recent. Only in 2016 was approved a specific standard for the inspection work on bridges, viaducts and concrete walkways, ABNT NBR 9452. This paper aims to evaluate the pathological manifestations in neoprene support devices so, according to inspections performed and the diagnosis of causes, define their best practices and treatments for the maintenance and mitigation of the pathologies found. In the practical study, the following steps were performed: survey and selection of the structures currently under maintenance of MetrôRio; selection of criteria for the evaluation of pathologies; carrying out inspections; comparative analysis between the viaducts to determine the priority order for negotiations; and definition of conduct. The results obtained were the result of the evaluation of the field analysis, diagnosis, and comparison with tests performed in support devices. Having as input the tests in the support devices, the best treatments and suggestions to avoid new pathologies were proposed. With the definition of the pillars that concentrated the largest number of critical devices, aiming at better use of the operation, the decision was made to replace 12 units, from the perspective of urgent replacement. The novelty of this work was the development of better informed and more systematic approaches to condition assessment, deterioration forecasting, and maintenance decision making over the life-cycle of the built asset.

Fernando R. Gonçalves, Mohammad K. Najjar, Ahmed W. A. Hammad, Assed N. Haddad, Elaine G. Vazquez
Experimental Investigation on Organic Water Slaked Lime Mortar

Lime has been used as the most sustainable binder for the conservation and restoration of heritage buildings. The repair properties of lime based mortars are found superior to other mortars due to the compatibility issues of other mortars with ancient heritage structures. To increase the compatibility, the fresh lime mortar needs to be hardened by carbonation which is a slow process. Various researches showed that admixtures added advantage to lime mortar by increasing carbonation rate which increases the mechanical strength, weather and water resistance of the lime mortar. In India, plants, fruits and some part of vegetables were used as organic admixtures that increased the carbonation rate thereby promoting sustainable and eco-friendly repair mortar. This paper deals with how the slaking of lime putty with organic additives affect the carbonation and other properties of the repair mortar. To enhance the carbonation rate, organic was mixed with water and this organic water was added for slaking the lime putty. Raisins were added as the organic additive at an amount of 0, 2, 4 and 6 percentages. The process was monitored for a month and cubes were casted. Compressive strength test was performed to measure the mechanical resistance property of lime mortar. Analytical tests such as XRD analysis and FT-IR were performed to determine the chemical compatibility after curing it for 90 days. It was seen that the carbonation rate and the mechanical strength of lime was greatly influenced by the organic water slaked lime mortar.

Riya Susan George, Simon Jayasingh
Effect of HPFRCC on Cyclic Behavior of Diagonally Reinforced Coupling Beams

Coupled shear wall system have been widely used in building construction due to their effectiveness in resisting lateral loads. In this system, individual shear walls are connected by concrete diagonally reinforced coupling beams (DRCBs), by which the coupled shear walls act as a single unit. However, difficulties are often arisen when placing reinforcement in DRCBs at construction sites because of congestion and interference of diagonal, transverse, and longitudinal reinforcement. To alleviate such difficulties, high performance fiber-reinforced cementitious composite (HPFRCC) can be used to construct DRCBs instead of concrete. In this study, two concrete and four HPFRCC DRCBs were made and tested under cyclic loads. Test variables were the amount of diagonal and transverse reinforcement as well as the application of HPFRCC. Test results showed that the HPFRCC DRCB specimen exhibited superior cyclic behaviour to the code-compliant standard concrete DRCB specimen, although HPFRCC specimens had only 50% of the transverse reinforcement placed in the standard specimen. However, the application of HPFRCC alone was not effective to reduce diagonal reinforcement.

Sang Whan Han, Jongseok Jang, Taeo Kim
Production of Recycled Aggregate Concrete Using Construction and Demolition Waste

The objective of this research was to evaluate the performance of concrete containing recycled aggregates of different sizes and replacement percentages. Mixtures were prepared using a combination of natural and recycled aggregates. The recycled aggregates were treated in a concrete mixer truck to partially remove the adhered cement paste in order to compare their performance in concrete as opposed to natural aggregates and non-treated recycled aggregates. One high-strength concrete series of mixtures was prepared to employ the concept of internal curing. The mixtures were tested for their mechanical properties and durability. The results showed that the addition of recycled aggregates in concrete up to a specific replacement percentage did not adversely affect the concrete properties. The specific research suggests that recycled aggregates can be a very good alternative source to reduce natural aggregates consumption and utilize waste material.

K. Oikonomopoulou, P. Savva, S. Ioannou, D. Nicolaides, M. F. Petrou
Contribution of Thermodynamic Modeling to the Understanding of Interactions Between Hydrated Cement Pastes and Organic Acids

In numerous contexts, concrete can be exposed to chemically aggressive conditions that can damage their microstructure and reduce their lifespan. The concrete facilities from the agricultural and agro-food industries dedicated to the storage or the treatment of effluents are more particularly exposed to organic acids coming from the microbial activity naturally occurring in such media. This biodeterioration leads mainly to mineralogical transformations, such as hydrated and anhydrous phase dissolution, and to ion exchanges between acidic effluents and cement-based materials. The poorly crystalline mineralogy of hydrated cement pastes and their reactivity makes the geochemical behavior of such materials difficult to investigate and thus to predict over large periods of time and wide variety of chemical conditions. The degradation of cementitious materials in these aggressive conditions mainly leads to the leaching of calcium and the precipitation of amorphous secondary phases. The purpose of this work is (i) to assess the stability of the cement phases involved in such chemical conditions as well as to identify the alterations products, and (ii) to understand the evolution of concentration and the behavior of elements in solution such as aluminum or silicon. A thermodynamic model of cement pastes subjected to acid attacks has been developed, in order to reproduce, experimental data also presented here. Our model reproduces a major part of the behaviors shown by the experiments, i.e. a progressive decalcification of solid matrix (successive dissolution of portlandite, aluminates hydrates and C-S-H) during acid degradation and the identification of alteration zones in agreement with the experimental observations.

Cédric Roosz, Marie Giroudon, Laurie Lacarrière, Matthieu Peyre-Lavigne, Alexandra Bertron
An Analytical Approach for Pull-Out Behavior of TRM-Strengthened Rammed Earth Elements

Rammed earth constructions, beyond being largely spread in the built heritage, are known for their high seismic vulnerability, which results from high self-weight, lack of box behavior and low mechanical properties of the material. Hence, to mitigate this seismic vulnerability, a compatible textile reinforced mortar (TRM) is here proposed as a strengthening solution, because of its reduced mass and high ductility. The few research about the structural behavior of TRM-strengthened rammed earth elements addresses the global behavior, overlooking the local behavior of the system. An analytical approach to infer the bond stress-slip relationship following the direct boundary problem is proposed. Based on a previous series of pull-out tests, an adhesion-friction constitutive law is portrayed considering also a damage model that considers the degradation of the reinforcing fibers due to friction.

A. Romanazzi, D. V. Oliveira, R. A. Silva
Self-Healing Concrete Research in the European Projects SARCOS and SMARTINCS

Self-healing concrete and preventive repair of structures will slow down the development of cracks and/or arrest the ingress of aggressive agents. When the cracks are closed or a decrease in crack width is achieved, this will be associated with improved durability of the structure. This paper describes the literature review and inter-laboratory comparison carried out within the COST Action CA15202 (SARCOS), as well as the research planned within the recently started International Training Network SMARTINCS.

Nele De Belie, Kim Van Tittelboom, Mercedes Sánchez Moreno, Liberato Ferrara, Elke Gruyaert
Strengthening of Hollow Core Slabs to Reduce Excessive Vibrations: A Case Study

The LB Building 6 is the main logistic building of the Total Agility Logistic Co. Ltd located in Bang Phi district, Samut-Prakan province, Thailand. The building consists of a 2 storey steel structure having steel beams with a typical span of 6.0 m supported by reinforced columns. After a few months of service, cracking and spalls was found on the concrete overlay on the 2nd floor. Preliminary investigations were first performed by the building engineer and it was reported that deflections occurred at the 1-ton forklift moving path zone. Therefore, the capacity of structural elements in the building had to be re-assessed and field measurements of vibration levels were also taken during the peak operation period. To reduce the vibration level as well as deformation of the floor under normal operation, a structural strengthening intervention was made by adding additional steel beams under the hollow core slab as a span shortening technique. Field measurements have shown that the vibrations of the strengthened concrete slab reduced by up to 35% compared to the pre-strengthening measurements, thus confirming the effectiveness of the strengthening intervention. The work reported in this paper also sets the scene for identifying the major decisions for a design engineer starting from on-site inspection to the post-construction supervision.

Thanongsak Imjai, Surin Suthiprabha, Fabio P. Figueiredo, Reyes Garcia
3D Thermo-Hygro-Mechanical Simulation of a RC Slab Under Restrained Shrinkage and Applied Loads: Influence of the Reinforcement Ratio on Service Life Behaviour

The structural design of reinforced concrete (RC) structures requires the use of adequate methodologies for control of crack widths, in order to ensure proper service life behavior. When RC elements are subjected to the combined effect of restrained deformations and external loads, which is a relatively common situation in civil engineering structures, current design codes and recommendations generally fail to provide specific/clear instructions for measures to be taken for reinforcement design in view of crack width control. This paper intends to show the influence of different approaches for quantification of the necessary reinforcement on the service life behavior of these structures, through conduction of a parametric study. Such study is performed in order to understand how the variation of the longitudinal reinforcement affects the structural behavior of a solid one-way RC slab subjected to restrained shrinkage and external applied vertical loads (in quasi-permanent load combination). The structural behavior of the slab is simulated for 5 distinct quantities of longitudinal reinforcement, with a 3D thermo-higro-mechanical model, where the non-uniform distribution of stresses due to heat of hydration and drying shrinkage are considered. The attained results allowed conclusions to be withdrawn in regard to the expected behavior when reinforcement is underdesigned (by neglecting restraint) or overdesigned (by considering the cracking force of concrete when evaluating axial restraint). Intermediate solutions, matching some simplified approaches in the literature where found to be the most reasonable.

José Gomes, Rui Carvalho, Carlos Sousa, José Granja, Rui Faria, Dirk Schlicke, Miguel Azenha
Morphological and Chemical Characterization of Self-Healing Products in MgO Concrete

This work presents the results of the measurements carried out by the Laboratory of Archaeological and Building Materials of NCSR “Demokritos” in the framework of the Interlaboratory Test (ILT) organized by SARCOS COST action CA15202. The overall aim of ILT was to assess the self-healing properties of concrete with the addition of a self-healing agent. Following the ILT tentative methodology, the concrete samples were initially subjected to controlled cracking after curing for 30 days. Their sealing efficiency−as part of the self-healing process−were assessed by water permeability tests carried out in disk specimens cured for 1, 3 and 6 months under water, as a healing regime. At the same time, crack width of all samples was measured each time, by examination at the stereomicroscope. Besides the measurements regarding the sealing efficiency, Scanning Electron Microscopy (SEM) was also performed, in order to understand the contribution of the healing agent on the sealing mechanism. In this context, samples were collected from the crack face and the secondary healing products inside the cracks were studied by SEM combined with X-ray spectroscopy (EDS) in samples with and without the healing agent. The interpretation of the results suggests that the main methodological parameter affecting the sealing efficiency is the initial crack width. This indicates that during the quantitative evaluation of the sealing results, the initial level of damage attributed to the specimens should always be considered. In addition, SEM examination revealed the composition and the morphology of the healing products that were identified in the fractured surfaces and thus, the relative contribution of both healing agent and cement hydration.

Maria Amenta, Stamatoula Papaioannou, Vassilis Kilikoglou, Ioannis Karatasios
Activated CFRP NSMR Ductile Strengthening System

This paper presents some of the initial results from an ongoing research project which concerns a new NSMR strengthening method, expected to provide high ductility and strengthening effect as well as increased response consistency. A prestress of 1100 MPa activation was applied to the ductile NSMR system and compared to a reference beam. Ductility in this system is provided by a response controlling anchorage system, which interacts with the adhesively bonded NSMR. The proposed adhesive has a low E-modulus which is expected to reduce stress concentration issues of adhesively bonded joints when compared to stiffer epoxy adhesives are used, where IC-debonding seems to be the dominating failure mode. A beam deflection increase of approximately 105% has been observed when using the low E-modulus adhesive compared to the the epoxy adhesive. Change in the failure modes were furthermore observed, where the brittle de-bonding failure modes were mitigated thus extending the yielding regime with approximately 150%.

Jacob Wittrup Schmidt, Christian Overgaard Christensen, Per Goltermann, José Sena-Cruz
Proceedings of the 3rd RILEM Spring Convention and Conference (RSCC 2020)
Dr. José Sena-Cruz
Dr. Luis Correia
Prof. Miguel Azenha
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