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About this book

This compendium gathers the latest advances in the area of Accelerated Pavement Testing (APT), a means of testing full-scale pavement construction in an accelerated manner for structural deterioration in a very short term. Compiling novel research results presented at the 5th International Conference on Accelerated Pavement Testing, San Jose, Costa Rica, the volume serves as a timely and highly relevant resource for materials scientists and engineers interested in determining the performance of a pavement structure during its service life (10+ years) in a few weeks or months.

Table of Contents


Overview of Accelerated Pavement Testing


A Brief History of Full-Scale Accelerated Pavement Testing Facilities to 1962

Full-scale accelerated pavement testing (APT) facilities developed throughout the world since the AASHO Road Test 1958–62 were described by Metcalf (Application of full-scale accelerated pavement testing. National Academy Press, Washington, 1996). The purpose of this paper is to document facilities in operation before the 1960’s. Some facilities were identified where details are very limited.

John B. Metcalf

Four Decades of the Circular Test Track at the Institute of Engineering UNAM Contributing to Pavement Research in Mexico

The circular test track at the Institute of Engineering UNAM was built four decades ago, between 1970 and 1971. Since its construction, this device has been very valuable for the development, research, and validation of flexible pavement design in Mexico. To date, 40 studies have been conducted on the circular track. It is common for each experiment to build three different sections of pavement to maximize the number of variables to be analyzed. With the information obtained from the experimental sections under service, data on the behavior of sections in different locations throughout Mexico, and experimental results from the circular track, a method for the structural design of flexible pavements was developed. This research program was carried out by the Institute of Engineering, UNAM. The latest version of the pavement design method was published in 2014, called the Structural Design of Flexible Pavements (DISPAV-5 3.0), and is currently the most used method in Mexico for the design of such structures. This resource has a mechanistic-empirical background and includes models to predict asphalt fatigue and permanent deformation damage. However, the models are over 15 years old and are unable to incorporate current characteristics of materials and traffic conditions. This paper describes the role and significance of the circular test track in the development of flexible pavement design in Mexico, the characteristics of the variables that influence pavement behavior and future directions proposed to develop a method of pavement design that considers current needs.

Noé Hernández, Alexandra Ossa, Francisco A. Rangel

Establishment of New Accelerated Pavement Testing Facilities


Design and Engineering Challenges in the Development of the FAA’s Full Scale Accelerated Pavement Test Facility NAPMRC

Accelerated Pavement Test Facilities are not a common type of facility for Architecture and Engineering (A/E) firms to have experience with. The Federal Aviation Administration (FAA) commissioned the design of their APT Facility, the National Airport Pavement and Materials Research Center (NAPMRC) in 2012. Personnel from the FAA’s National Airport Pavement Test Facility near Atlantic City, NJ USA worked with an A/E firm to develop a facility to utilize the FAA’s Heavy Vehicle Simulator for Airfields (HVS-A). The HVS-A commissioned by the FAA and built by Dynatest Corporation is the largest HVS ever constructed by Dynatest. Challenges were encountered in working with designers to build pavements “designed to fail” and to gather information from those pavements as they fail. This included educating the designers to the build, test, fail and repeat concept of accelerated pavement testing. The NAPMRC encompasses both indoor and outdoor test pavements. Electric power required to run the HVS-A needed to be provided throughout the facility to make full use of the six lanes of test pavement being constructed. Data collection and communications networks that could deliver pavement sensor information were designed with flexibility to handle a variety of sensor for the original and future test pavement builds.

Murphy Flynn, Navneet Garg, Wilfredo Villafane, David Traverzo

Heavy Vehicle Simulator and Accelerated Pavement Testing Facility at Rowan University

The use of full-scale accelerated pavement testing is gaining more prominence in recent years due to (1) the several advantages such tests offer and (2) the development of portable and non-portable accelerated pavement testing equipment that facilitate conducting these tests. For instance, conducting accelerated pavement testing offers the advantage to simulate long-term traffic conditions in a short period of time that ranges between three to six months. It can also help in better simulating field conditions simply because full-scale sections are constructed using paving equipment and procedures utilized by contractors in the field. Therefore, it can be argued that full-scale accelerated pavement testing can provide results that are more representatives of field conditions that does laboratory testing. To keep up with current transportation and pavement research trends, Rowan University is currently in the process of constructing an accelerated pavement testing facility. In fact, the mission of the Civil and Environmental Engineering Department at Rowan University is to grow the program to become one of the nationally recognized research programs in the areas of transportation and pavement engineering. To accomplish this mission, the department along with the College of Engineering at Rowan University, the State of New Jersey (NJ), and the United State Department of Defense (USDoD) have established a state-of-the-art transportation research center known as the Center for Research and Education in Advanced Transportation Engineering System (CREATEs). CREATEs houses an AMRL (AASHTO Materials Reference Laboratory) certified Rowan University Construction Materials Laboratory (RUCOM) and the Rowan University Accelerated Pavement Testing Facility (RUAPTF). Therefore, CREATES is envisioned to provide states and local agencies as well as the pavement industry in the northeastern region of the United States (US) with both laboratory and full scale accelerated pavement testing capabilities. This paper documents the design and construction processes currently being implemented for building RUAPTF.

Ayman W. Ali, Yusuf Mehta

General Accelerated Pavement Testing


A Link of Full-Scale Accelerated Pavement Testing to Long-Term Pavement Performance Study in the Western Cape Province of South Africa

The development of a new mechanistic-empirical pavement design method by the South African National Roads Agency Ltd (SANRAL) is at its finalization stage. The new design method, referred to as the South African pavement design method (SAPDM) will heavily rely on Long-Term Pavement Performance (LTPP) and Accelerated Pavement Testing (APT) data to calibrate performance models for cracking and rutting. This paper discusses more than 10 years APT and LTPP data established from LTPP sections in the Western Cape province of South Africa. In addition, the paper presents updated field results of an expanded LTPP program that links both field and laboratory data to pavement performance. In comparison, the rut data from the LTPP section are similar to or higher than the HVS rut data depending on the type of pavement (i.e. surfacing material, layer materials, layer thickness and so forth). Similarly, deflection data could be similar or varied for different pavement types. Based on the conclusions from this paper, it is envisaged that the LTPP and APT data will provide the basis for the calibration of cracking and rutting models for the SAPDM. This would require in some cases, an introduction of shift factors to adjust APT data to LTPP (real life) data.

J. K. Anochie-Boateng, W. JvdM Steyn, C. Fisher, L. Truter

Accelerated Pavement Testing in Slovakia: APT Tester 105-03-01

This article presents the APT facility constructed and operated by University of Zilina. The machine is called APT tester 105-03-01. The article describes its technical properties, operational capabilities, sensory equipment embedded in the pavement and data gathering procedures. The device has several unique design solutions that make it stand out from similar facilities in the world: (1) The principle of fixed linear APT facility which loading unit is not positioned in a fixed frame, but instead moves itself held only by a guiding rail to better simulate traffic loading. (2) Loading unit consists of fixed and movable frame held by support connected by joints, better simulating suspension like those found on truck axles. (3) The construction of the electric motor, gear box and frequency inverter and its mounting system on the loading unit. Frequency converter controlled acceleration and deceleration ramps and speed during movement. (4) Hydraulic stabilization system stabilizing the movable frame, since the load tends to tip the loading unit in the acceleration and deceleration stage. (5) Autonomous hydraulic system placed on the outer frame able to lift the loading unit and allows for free manipulation without burdening the pavement.

Lubos Remek, Jan Mikolaj, Matej Kyselica, Milan Škarupa

APT with the Mobile Load Simulator MLS10 Towards Non-destructive Pavement Structural Analysis

In 2014 a research program has been started about non-destructive test methods to evaluate the structure of pavements. This task has been given to two research groups—first research group is led by RWTH Aachen University (Rheinisch-Westfälische Technische Hochschule) and the second by University of Siegen. This paper focuses on the initial findings of the running research program. The assessment of the existing infrastructure and its condition will be one of the main tasks during the next years in order to use the available budget for maintenance accurately and efficiently. Therefore, it is necessary to identify possible damages and examine their effects on the road construction. BASt (Federal Highway Research Institute) is using the Mobile Load Simulator MLS10 for accelerated pavement testing (APT) on different types of pavements. In addition to non-destructive test methods, sensors are applied to measure structural impacts. The overall objective of this research program is to develop a non-destructive test method that allows the calculation of the remaining life time and load cycles of pavements. To simulate realistic wheel loads in a short period of time the MLS10 on German full scale standard pavement constructions has been used. The first pavement test section was loaded with 3 × 106 50 kN wheel loads while the second, thinner pavement test section was loaded with 3 × 105 50 kN wheel loads. Both loads are equivalent to the pavement design load. Three different strategies have been used to analyze and monitor structural changes. The innovative measurements have been realized by the two research groups to collect data for their models. The RWTH Aachen collected data with twelve geophones aligned in a row parallel to the wheel path. The geophones measure the entire vertical deflection basin of the pavement surface that exists due to the passing real truck wheels. These measurements were done for different truck speeds and at different transverse distances to the wheel path. The University of Siegen collected data by using acceleration sensors on the surface of the road construction. After recording the data they were integrated into displacement signals and evaluated. Additionally to those measurements BASt used conventional equipment to monitor the pavement structure and surface characteristics. The measurements and evaluation tools used for the innovation program have a high potential to validate APT programs in the future. Based on this research it is possible to start further research activities to push the non-destructive evaluation of pavements structures—not only in APT—into an improved direction.

Bastian Wacker, Frédéric Otto, Pengfei Liu, Dawei Wang, Markus Oeser, Micha Buch, Ulf Zander

Evaluating Nonlinearity on Granular Materials and Soils Through the Use of Deflection Techniques

The nonlinear behavior of soils and granular materials is widely known. Its proper evaluation is essential for the accurate determination of the stiffness of pavement layers and their structural evaluation. If this phenomenon is not considered appropriately, it can lead to significant errors in estimating the pavement responses. As part of the investigation of accelerated tests on full-scale pavements by the National Laboratory of Materials and Structural Models of the University of Costa Rica, four instrumented pavement sections were built and evaluated using a Heavy Vehicle Simulator. The wheel load was used at an average speed of 10 km/h, with various loading levels, at an average temperature of 23 °C and with a lateral wandering of 10 cm. The deflection profile of each pavement was studied by means of Multi-Depth Deflectometer sensors (MDDs), the Road Surface Deflectometer (RSD), and; the Falling Weight Deflectometer (FWD). This paper summarizes a comparison among the differences in the deflection basin measurements, and the related estimated moduli. Additionally, the pavement response modeling was performed by means of Multi-layer Elastic (MLE), Finite Element (FE) and Linear Visco-Elastic (LVE) methods. The objective of this study was to compare the results of different deflection measuring methods and their correspondent backcalculated moduli. The analysis showed similar results in the deflection curves and hence, back-calculated moduli obtained by the MDDs and the RSD. Both devices captured, as expected, nonlinear behavior of the granular materials as well as the subgrade. The FWD was not able to report such behavior.

Fabricio Leiva-Villacorta, Luis Loría-Salazar, Edgar Camacho-Garita

Full Scale Accelerated Pavement Tests to Evaluate the Performance of Permeable and Skeletal Soil Block Pavement Systems

The increasing proportion of paved surface due to urbanization means that the conditions for urban trees and vegetation to survive have deteriorated. Factors such as air pollution, poor drainage, and the lack of usable soil for root growth contribute to the short life expectancy of urban trees. To meet this challenge, several permeable and “structural” or “skeletal soils” have been developed as alternatives to the typical compacted soil required to bear the weight of vehicular traffic in urban areas. The main objective of this study is to evaluate the resistance to permanent deformation of permeable and skeletal soil pavement structures based on full scale accelerated pavement tests (APT) using a heavy vehicle simulator (HVS). Interlocking paving stones of various types were used as permeable surface layer for the test structures. The results demonstrated that the permeable test structures exhibited higher permanent deformation than the corresponding impervious structures. The skeletal soil with bituminous base layer, however, produced performance comparable to the impervious reference test structures.

Abubeker Ahmed, Fredrik Hellman, Sigurdur Erlingsson

In-Situ Validation of Three-Dimensional Pavement Finite Element Models

Mechanistic-based pavement design guides gained popularity in the last decade. Accurate computation of stress, strain, and the deformation field within pavement, which are used in pavement design guides, is important to realistically predict pavement performance over the design life. The layered elastic theory and finite element method (FEM) are commonly used to compute the critical responses of pavement structure. Although the layered elastic theory analysis is relatively faster and easier to implement, it hinders real loading and pavement material characterization. Therefore, FEM has become more attractive to pavement researchers for investigating pavement behavior under tire loading since the last two decades. Although several studies have been conducted for developing FE model for pavement, limited work has been done to validate the finite element (FE) models using in-situ pavement responses. This study presents an advanced three-dimensional (3-D) pavement FE model validated using four pavement sections. Good agreement was noted between the FE analysis results and pavement field instrument responses to loading, especially for vertical pressures and horizontal tensile strains in the transverse direction. When using proper material characterization parameters and accurate tire loading, the FE model is capable of realistically simulating tire-pavement interaction in the field.

Osman Erman Gungor, Imad L. Al-Qadi, Angeli Gamez, Jaime A. Hernandez

Investigation of 3D-Move Responses Under Traffic Speed Deflection Devices (TSDDs)

Traffic Speed Deflectometer (TSD) and Rolling Wheel Deflectometer (RWD) that measure surface deflections at posted traffic speeds (up to 80–96 kph) are being used in several countries to evaluate structural condition at network level. Incorporating these devices to Pavement Management System (PMS) application requires an analysis methodology for enabling the use of device measurements. 3D-Move Analysis evaluates pavement response using a continuum-based finite-layer approach. Since 3D-Move has the capability of modeling moving load and the resulting dynamic pavement responses, it is ideally-suited to simulate pavement responses generated by these devices that move at high-speeds. A recently completed FHWA study conducted field trials that used TSDDs where in situ pavement response measurements at the MnROAD test site were made and calibration of the 3D-Move model for application with TSDD loading was carried out. Many calibration runs were performed and 3D-Move model provided a good match with a variety of independent pavement responses that included surface deflection bowls (measured using embedded geophone sensors) as well as horizontal strains at the bottom of the Asphalt Concrete (AC) layers (measured using embedded sensors). Using the calibrated 3D-Move software, an analytical investigation was then undertaken to explore relationships between load-induced pavement structural-related responses and the corresponding surface deflection basin related indices from TSDDs.

Mahdi Nasimifar, Raj S. Siddharthan, Elie Y. Hajj, Ramin Motamed

Long-Term Pavement Performance Monitoring and the Revision of Performance Criteria for High Modulus Asphalt in South Africa

Enrobé à Module Élevé (EME) technology, a High Modulus Asphalt (HiMA), was originally developed in France. The technology is primarily suitable for construction of heavily trafficked routes, airports and container terminals. The key performance characteristics of EME are high stiffness, high resistance to permanent deformation and fatigue cracking. EME is also designed to offer good moisture resistance and good workability. The EME technology has been successfully introduced to South Africa. The development of EME design guidelines in South Africa started in 2006. A major outcome was the publication of Sabita Manual 33: “Interim design procedure for high modulus asphalt in South Africa.” The performance criteria/specifications stipulated in Manual 33 were based on limited data. Based on further work against French mix design and analysis of data collected in South Africa, a revised fatigue and stiffness specifications were adopted in July 2015. Implementation of EME technology in South Africa started in 2011, when a trial section consisting of an EME base layer was constructed on the heavily trafficked South Coast Road in Durban. The section is a major entry route for heavy vehicles travelling to the Durban harbour. Several attempts to rehabilitate the section using conventional asphalt mixes had failed as a result of premature rutting due to the heavy traffic volumes entering the Durban harbour. The heavy traffic volumes at the section offered an ideal setting for an experiment in Accelerated Pavement Testing (APT) without the use of a Heavy Vehicle Simulator (HVS), which enabled the accelerated validation of the South African EME design procedure. The objective of this paper is to present the outcomes of the Long-Term Pavement Performance (LTPP) monitoring programme that was undertaken to assess the field performance of EME, and discuss the development of the newly adopted South African EME performance specifications.

Julius Komba, Joseph Anochie-Boateng, Johan O’Connell, Benoit Verhaeghe

Optimum Properties of Geocell Reinforcement for Sustainable Low-Volume Paved Roads

Geocells are three-dimensional honeycomb-like geosynthetic structures filled with available geomaterials that vastly improve shear strength of those materials. Geocells provide a possible viable solution for thinly paved roads that use marginal infill geomaterials. The objective of this study was to find an optimum geocell design that utilizes various infill materials and a thin hot-mix asphalt (HMA) overlay. To achieve this study objective, four pavement test sections were constructed at the accelerated pavement testing (APT) facility of the Civil Infrastructure System Laboratory at Kansas State University. Three out of the four lanes contained geocell-reinforced bases with three individual infill geomaterials: crushed limestone, quarry by-products, and recycled asphalt pavement. The fourth test lane, the control section, consisted of a crushed stone base. All sections were heavily instrumented. Repeated loads (80 kN, single axle) were applied using an APT load assembly. Sections with an HMA layer of 50 mm reached the failure criteria of a 12.5 mm rut depth after 10,000 passes due to excessive stress in the subgrade. Redesigned sections with HMA overlay of 100 mm carried more than 1,000,000 passes. Numerical simulation of the APT tests was done using the finite element model. The optimum infill geomaterial property, geocell height, and overlay thickness were obtained from this simulation.

B. Bortz, M. Hossain

Perspectives on Trends in International APT Research

The National Academies sponsored a series of three APT Syntheses since 1996. The last synthesis was conducted in 2011. This was followed by the fourth, most recent international APT conference that was held in Davis, California in 2012. It is thus now an opportune time to look back at the information identified in these syntheses, the trends predicted and the actual development since 2011. The paper starts with a brief evaluation of the trends identified in the 2011 synthesis, identifying those that were deemed to be new and receiving attention in the immediate future. This is compared to the APT work published in the last 5 years to compare the generation of new knowledge in the area of APT, and a discussion and analysis of the trends. At the same time, the synthesis of 2004 is scrutinized to capture aspects that may still have been left without being addressed. Finally, an opportunity is provided for updating the database of international APT facilities with respect to the new international APT programs that were initiated since the 2011 synthesis.

W. JvdM Steyn, F. Hugo

Potential Benefits of APTF for Evaluation of Flexible Pavement for Its Permanent Deformation Behaviour

More than 95 % of road network in India is made up of flexible pavement, especially due to the relative lesser initial cost, ease of construction and maintenance. The design of flexible pavement in India is done with criteria of load associated fatigue cracking and permanent deformation (rutting). While design methods try to consider these failure modes, more rational inputs based on intrinsic evaluations are required for better and improved designs. The Accelerated Pavement Testing Facility (APTF) is regarded as a versatile tool all over the world in pavement evaluation and performance monitoring due to its advance evaluation capabilities within a short time. This paper presents the rutting performance characteristics of a typical flexible pavement built as per Indian design practice, evaluated using APTF. APTF is capable of evaluation with regard to total structural ability of a pavement based on number of standard axle load passes which represents time period and load sustainability of a pavement with respect to defined failure criteria. The pavement was instrumented with interfacial response monitoring, wherein deflections were effectively measured using state of art instrumentation technique. The study result and possible rutting mechanism under the operational capabilities of APTF and test condition have been discussed in the paper.

M. N. Nagabhushana, Shahbaz Khan, Abhishek Mittal, Devesh Tiwari

Study of the Bearing Capacity of Swiss Standard Pavements Under MLS10 Loading

Accelerated Pavement Testing (APT) is an efficient testing procedure to evaluate the performance of different pavement concepts. With APT, it is possible to determine and measure the structural response and pavement performance under a controlled, accelerated accumulation of load damage that simulate the long-term in-service condition, but in a compressed period of time. The repeatability of the loads applied permits making accurate predictions about the bearing capacity and lifespan of the pavement under study. It also allows making comparative assessments of potential long term performance of any type of pavements. This paper summarizes the results of a series of initial tests carried out on pavements with similar structure but different stiffnesses designed following Swiss standards. Each pavement was loaded with the Mobile Load Simulator MLS10 until reaching its bearing capacity limit. The aim of these tests was to use the results as a benchmark to compare it to other non-standard structures with similar stiffness in terms of dimensioning and/or materials. It was found that the pavements’ life-spans were basically longer to the ones anticipated by the standards. This difference was larger for the pavements with lower stiffness. Further, as expected, the distress mechanisms were similar for all the pavements considered.

Martin Arraigada, Andreas Treuholz, Manfred N. Partl

The Development of APT Methodology in the Application and Derivation of Geosynthetic Benefits in Roadway Design

Geosynthetic materials are used in roadway pavement construction to improve performance. In order to quantify performance it is necessary to carry out trafficking trials, the results of which may be used empirically to establish or modify pavement design methods. Several such trials have been carried out over the last 30 years, in various configurations. Eight trials carried out by TRL over the period 2000–2013 are described in detail, providing information on both the pavement construction and the performance testing. These trials were all carried out in a consistent manner on a single layer of sub-base quality material over a clay subgrade, with relatively small test areas constructed indoors in a pit, and then trafficked with an automated wheel load. Important trends and findings from examining the results of all 93 test panels are summarised in order to establish whether the geosynthetic improves pavement performance by confinement or by tensioned membrane. Of these two mechanisms only confinement is relevant to permanent pavements, and performance limits are established which should be achieved for confinement to be the dominating mechanism.

Jonathan Cook, Michael Dobie, David Blackman

Tire Type Effect on Pavement Responses; Accelerated Pavement Testing Results

The proposed paper summarizes the accelerated pavement testing database obtained from various locations, including a database of recent studies. Test sections built as part of a study investigating the effect of new generation wide-base tire (NG-WBT 445/50R22.5) and dual-tire assembly (DTA 275/80R22.5) on flexible pavement response were used. These test sections were established at three different test locations throughout the U.S.—Florida, Davis-California, and Ohio State. Various instrumentations were installed at several locations within the pavement system to capture the most critical pavement responses. Instrumentations installed include strain gauges, pressure cells, thermocouples, multi-depth defloctometers, surface strain gauges, and strain gauge rosettes. Critical pavement responses, including strain at bottom of AC and stress on top of subgrade, were analyzed. Moreover, the effect of temperature, differential tire pressure, and near surface responses were investigated for NG-WBT versus DTA.

Mojtaba Ziyadi, Imad L. Al-Qadi

Accelerated Pavement Testing Focused on Mechanistic—Empirical Pavement Design Procedures and Models


Analysis of Dynamic Response of Asphalt Pavement in Heavy Vehicle Simulator Tests

In order to analyze the dynamic response of asphalt pavement, heavy vehicle simulator (HVS) was used to test with variables of axle load, speed, and temperature on five full-scale test sections with different structures. Pre-embedded strain sensors and pressure cells were used to measure the strain response at the bottom of the surface layer and the vertical stress at the top of the subgrade under wheel load. The results of tests show that the tensile strain at the bottom of surface layer of semi-rigid base asphalt pavement and rigid base asphalt pavement is small. The vertical stress at the top of the subgrade has a good positive exponential relationship with axle load. The maximum tensile strain at the bottom of surface layer gradually decreases with speed and increases with temperature. The tensile strain at the bottom of surface layer of flexible base asphalt pavement is affected by the speed most significantly. The increase rate of strain increases with temperature, which demonstrates the temperature has significant effects on the mechanical properties of the asphalt pavement. Based on the results of HVS tests, a prediction model of tensile strain at the bottom of the surface layer was established. Therefore, this paper could contribute to deepening the understanding of the dynamic response characteristics of asphalt pavement and improving the design of pavement structure.

Aimin Sha, Jie Wang, Liqun Hu, Xiaolong Zou

Automating Mechanistic-Empirical Pavement Design Calibration Studies

Accelerated pavement testing (APT) applies intensive traffic loading for the purpose of observing long-term performance of pavements in a short time. The testing is beneficial for researchers as a timely and valuable data resource. As Mechanistic-Empirical (M-E) pavement design approaches emerge as a favorable alternative to traditional empirical approaches, there is a need for conducting calibration of the performance models in the M-E design framework. Data from APT testing may be considered advantageous for calibration due to research-grade accuracy conducted over shorter time intervals, but even so, M-E calibration is still time-consuming because many combinations of the respective calibration coefficients need to be evaluated against observed performance from pavement sections. The current version of the AASHTOWare™ Pavement ME Design software, though serving as a powerful pavement design and analysis tool, is not necessarily conducive to calibration studies as many interactions are needed by the user to populate the software with trial calibration coefficients and extract performance predictions after simulations have been completed. This study proposes using automation to facilitate calibration studies whereby the repetitive manual operations required by the software are recorded and built into a macro that greatly reduces the required human interactions. The software automation is demonstrated through a calibration study conducted at the National Center for Asphalt Technology (NCAT) Test Track that examined fatigue cracking calibration. The efficiency of the automated approach is compared against conducting calibration requiring human interaction with the software.

Xiaolong Guo, David H. Timm

Calibration of ME Design Using a Combination of APT and PMS Data

The ultimate goal of ME design, and much of the pavement engineering behind it, such as APT, is to provide true estimates of how pavements will perform in the field. In the past, most design methods have been calibrated with APT data, and there has been some difficultly in calibrating to field data, including LTPP data. While this is partly due to a lack of understanding of the performance of pavements, much of the difficultly seems to arise because there is a disconnect between how performance is explained in design methods and how it is measured in the field. This paper details a framework for understanding APT data and PMS data, and for jointly modelling both sets while calibrating an ME design method.

Jeremy D. Lea, Rongzong Wu, John T. Harvey

Key Concepts in Dynamic Signal Processing from Instrumented Pavement Sections

Accelerated pavement test facilities have often featured dynamic pavement response instrumentation, such as strain gauges, pressure plates and multi-depth deflectometers since the 1960s. While the instrumentation and data acquisition systems have rapidly evolved since then, researchers still face the fundamental problem of converting raw dynamic signals gathered at high sampling rates into meaningful information. These signals are inevitably infused with electronic noise that complicates extraction of useful information. Furthermore, the resources to collect and store raw data often far outpaces the capabilities to process and analyze the signals efficiently. The National Center for Asphalt Technology (NCAT) Pavement Test Track has utilized dynamic strain gauges and earth pressure cells since 2003 within structural pavement research studies and NCAT has also been involved in live-traffic instrumented test sites in China, Oklahoma and New Mexico. Each test site experienced the problems described above and also faced unique challenges related to site-specific conditions. This paper provides lessons-learned from the past 14 years of dynamic signal processing at each of these test sites. A common set of practices is described and applied to two of the sites that demonstrates the effectiveness and efficiency of the developed processing schemes. Emphasis is placed on speed of data processing and visual inspection for quality control.

David H. Timm

Protocols for Accelerated Pavement Testing of Fully Permeable Pavements

Fully permeable pavements are used as an alternative means of managing stormwater on roads, parking lots, and other paved areas. In the past, they have primarily been used only in areas with very light traffic, and designs have been empirical. With road agencies coming under increasingly stricter stormwater management requirements, there is growing interest in using these types of pavements under heavier traffic loads. A study was therefore initiated by the Interlocking Concrete Pavement Institute (ICPI) and the UCPRC to better understand the behavior of fully permeable pavements and to formalize the design process using a more mechanistic type approach. The study was undertaken in phases and included laboratory testing, modeling, accelerated load testing, development of design procedures, life-cycle cost assessment, and environmental life cycle assessment. Most fully permeable pavements include a subbase/reservoir layer of large (75 mm) railway ballast aggregate, to support the load under wet conditions, and a base of smaller (25 mm) open graded aggregate as an intermediate layer between the large subbase aggregate and the surfacing. The use of this large open-graded aggregate limit the use of the testing protocols, instrumentation (e.g., multi-depth deflectometers), and data analysis procedures traditionally used in accelerated loading tests. Alternative testing protocols ad analysis procedures were therefore developed for the UCPRC study. This paper summarizes the design procedures and protocols developed for accelerated pavement testing of fully permeable pavements and discusses how the results were used to develop a mechanistic empirical design procedure to optimize layer thicknesses.

D. Jones, R. Wu, H. Li

Accelerated Pavement Testing on Asphalt Concrete Pavements


Behavior Evolution on Performance of UV-Irradiation Aged Asphalt Mixtures Under Reduced-Scale Accelerated Trafficking

In order to investigate the actual behavior evolution of asphalt pavement after the Ultra Violet irradiation (UV-irradiation) aging, reduced-scale accelerated pavement tests were conducted on two separate asphalt mixtures with a stone matrix asphalt (SMA-13) structure, respectively, crumb-rubber modified asphalt mixture and its matrix asphalt mixture, at ambient air temperature. In each group, UV-irradiation aged asphalt mixture after ultraviolet irradiation of 300 h and its corresponding non-aged asphalt mixture were trafficked at the same time by the 1/3 model mobile load simulator (MMLS3) till the cumulative loading applications up to 500,000. The test results show that the performance attenuation degree of the crumb-rubber modified asphalt mixture was lower than that of the matrix asphalt mixture, so the rubber additive helps to reduce the effect of the UV-irradiation aging. Rutting deformation, three-dimensional dynamic strain and seismic modulus were measured during the accelerated loading test. The rutting results (including the rutting depth, rutting area and its development rates), the surface dynamic strains, and the decay rate of the seismic modulus from the UV-irradiation aged asphalt mixture were greater than those of non-aged sample, and the difference narrowed after the cumulative loading applications reached more than 100,000. In addition the analysis of the modification rutting factor from the dynamic shear rheometer (DSR) test, the UV-irradiation aging weakened the high temperature stability and mechanical strength. Therefore, the UV-irradiation aging aggregated the performance decay of asphalt mixture and will inevitably shorten its service life.

Jinting Wu, Fen Ye, Frederick Hugo, Yinting Wu, Feng Wang, Xinhui Ding

Effects of Binder and Mix Properties on the Mechanistic Responses of Fatigue Cracking APT Sections

One of the major benefits of Accelerated Pavement Testing (APT) as a research tool is that the performance of pavement materials and structures can be evaluated at a reduced cost and in a short period of time. The Civil Infrastructure Systems Laboratory (CISL) for APT at Kansas State University was established in 1997. Six fatigue pavement sections that had 100 mm thick hot mix asphalt layer were constructed for APT in CISL. The sections had the same base and subgrade materials. The sections were instrumented using strain gauges and pressure cells to measure pavement responses under APT loading. They were loaded with a 100 kN single axle load at 20 °C. The main objective of this paper is to investigate the effects of binder content, binder grade, and mixture nominal maximum aggregate size (NMAS) on the mechanistic responses from the experimental sections. Stress, strains, deflections, and profile data were collected periodically. Normalized falling weight deflectometer (FWD) deflection data were used to back-calculate moduli using the EVERCALC software. Measured pavement temperatures were used to adjust back-calculated moduli to a temperature of 20 °C. The stiffer the binder, the lower the longitudinal strain, permanent deformation, and roughness, but the higher the transverse strain, stress on the top of subgrade in general, and back-calculated moduli. Higher binder content results in a higher longitudinal strain, transverse strain, stress on top of subgrade, permanent deformation, rut depth, and roughness. The larger the NMAS, the higher the transverse strain, back-calculated moduli, permanent deformation, and roughness, but the lower the longitudinal strain, stress on the top of subgrade, and rut depth.

Daba S. Gedafa, Mustaque Hossain, Stefan A. Romanoschi, Mbakisya A. Onyango

Evaluating Resistance of Hot Mix Asphalt Overlays to Reflective Cracking Using Geocomposites and Accelerated Loading

Placing a structural asphalt overlay atop existing pavements is one of the conventional methods used in pavement rehabilitation. However, reflective cracking in the new overlay continues to be a challenge associated with pavement rehabilitation. Traffic loading and environmental effects are the primary external causes of reflective cracking. A properly designed geocomposite or geogrid may help delay or reduce reflective cracking by providing reinforcement and strain relief. This study was conducted to evaluate the effectiveness of using such a geocomposite interlayer to improve pavement performance, specifically in terms of resistance to reflective cracking. Asphalt concrete was placed on the top of concrete slabs. The underlying concrete slab was placed in two different thicknesses, with a space between slabs to simulate the joint. The thinner slab was placed on a rubber mat to deliver uniform thickness and flat surface for placement of asphalt. Two slabs were made, one as the control system without a geocomposite interlayer, and the other as the experimental system with a geocomposite interlayer. Accelerated loading of the asphalt overlay was conducted using a 3rd Scale Model Mobile Load Simulator (MMLS3) system. The bottom-up reflective cracking could not be developed during this test in neither the control nor the experimental slabs. However, it was clearly observed that, the geocomposite significantly improved the top-down cracking resistance of the asphalt overlay.

Mansour Solaimanian, Ghassan Chehab, Marcelo Medeiros

Optimum Tack Rate for Hot-Mix Asphalt Bonding

Construction of hot-mix asphalt (HMA) pavement involves spraying tack coat on an existing surface in order to promote an acceptable interlayer bond and to ensure that multiple pavement layers behave monolithically. Insufficient tack coat application has been linked to premature cracking failure, a major factor in reduced HMA overlay life in Kansas. The Kansas Department of Transportation (KDOT) currently specifies that a slow-setting polymer-modified emulsion (SS-1hP) tack coat be applied at a rate of 0.23 L/m2 (0.05 gal/yd2) for overlays. This study utilized accelerated pavement testing (APT) to determine the optimum rate of SS-1hP tack material. At the APT facility at Kansas State University, an existing pavement pit (20 ft long × 14 ft wide) was milled and cleaned with a broom and compressed air. The pit was then divided into four test sections with varying rates of SS-1hP (50, 100, 160, and 240 % of 0.05 gal/yd2). Inlay paving was done with a 12.5 mm (0.5 in.) Nominal Maximum Aggregate Size Superpave mixture. An 89 kN (20 kip) single-axle load was bi-directionally applied over a 6.1 m (20 ft) long lane at approximately 11.3 km/h (7 mph). Rut depth and strain measurements at the overlay interface were done at periodic intervals during application of 550,000 load repetitions. Results showed that the section with 50 % (of 0.05 gal/yd2) SS-1hP tack coat had higher rutting when compared to other sections.

A. Sufian, M. Hossain, G. Schieber

Rutting Resistance of Asphalt Mixes Containing Highly Modified Asphalt (HiMA) Binders at the Accelerated Pavement Load Facility in Ohio

Highly modified asphalt (HiMA) mixes have been proposed as a stronger alternative to standard asphalt concrete mixes that will enable thinner perpetual pavements in Ohio. HiMA uses a polymer-enhanced binder has a higher unit cost, but has the potential to reduce the thickness of perpetual pavements, resulting in savings compared to conventional HMA perpetual pavement projects. Test sections containing HiMA in the surface, intermediate, and base layers were constructed with total thicknesses of 20, 23, and 25 cm, created by varying the depth of the AC treated base, in the Accelerated Pavement Load Facility (APLF) at Ohio University in Lancaster, Ohio. An additional 28 cm section was installed as a control with a non-HiMA base layer and HiMA surface and intermediate layers to compare with the experimental sections. Each pavement was subjected to 10,000 passes with a single axle load of 40 kN while the pavement was held at each of two pavement temperatures of 21.1 and 37.8 °C. Rutting on the surface of the pavement was measured using a rolling wheel profilometer after 100, 300, 1000, 3000, and 10,000 wheel passes at each temperature. The four sections showed no significant rutting damage after being subjected to a total of over 20,000 passes, and remained well below ODOT’s “low rutting” threshold of 3.2 mm. Extrapolating the rutting data indicated the worst-performing section would reach the low rutting threshold after more than a million passes of the load. The rutting data were compared to those obtained in a previous perpetual pavement study in the APLF that had surface courses including Aspha-min warm mix asphalt and a conventional hot mix asphalt, which crossed the low rutting threshold well before 10,000 passes at the high temperature.

Issam Khoury, Shad Sargand, Roger Green, Benjamin Jordan, Paul Cichocki

Structural Study of Perpetual Pavement Performance in Ohio

Three perpetual pavement test sections were constructed on U.S. Route 23 in Delaware, Ohio (DEL-23) with AC thicknesses 28, 33, 38 cm and instrumented to detect strains in Fatigue Resistant Layer (FRL) and base layers. The 28 and 33 cm sections were constructed on lime stabilized subgrade, while the 38 cm section was constructed on compacted subgrade. Four additional test pavements were built in the Accelerated Pavement Load Facility (APLF) and instrumented similarly to DEL-23. The sections were thinner, but included Highly Modified Asphalt (HiMA) with Kraton polymer binder in sections of depth 20, 23, and 25 cm. An 28 cm section used conventional asphalt in the base as a control with HiMA in surface and intermediate layers. There was no FRL. All sections were placed on 46 cm of cement stabilized subgrade. Strains at bottom of FRL during Controlled Vehicle Load (CVL) testing on DEL-23 in summer indicated the 33 cm section on stabilized subgrade and 38 cm section on compacted subgrade met the perpetual pavement criteria of NCHRP Project 9-44A, while 28 cm section on stabilized subgrade did not. Testing at the APLF included thoroughly heating the pavement to 37.8 °C and subjecting each section to 10,000 passes of a 40 kN wheel load. Pavement strains at the bottom of the base and intermediate layers in the longitudinal and transverse directions were measured after 1000, 3000, and 10,000 wheel passes using test loads of 27, 40, and 53 kN. The serviceability of the pavements was determined by comparing the longitudinal strains within the base layer of each pavement to fatigue endurance limits (FEL) calculated by using flexural stiffness standards from NCHRP 9-44A and a method recommended by Kansas researchers. At the APLF, the thinnest section produced maximum average strains higher than the calculated FEL at 37.8 °C using the NCHRP 9-44A equation, while the 25 and 28 cm sections met the perpetual pavement criteria. Using the Kansas researchers approach, all four test sections were found to have lower longitudinal strains than the calculated FEL.

Issam Khoury, Shad Sargand, Benjamin Jordan, Paul Cichocki, Matthew Sheer

Study of In-Service Asphalt Pavement High-Temperature Deformation Based on Accelerated Pavement Test

This paper explores high temperature deformation regularity of asphalt pavement/asphalt mixture test specimen under different conditions: in-service asphalt pavement, 10 cm milled and overlaid asphalt course with and without vibration rolling, normal overlaid asphalt pavement section, based on full-scale accelerated pavement testing equipment MLS66 and lab repeat wheel rolling test. The research findings reveal that asphalt pavements under different conditions show similar high temperature deformation regularity apparently in three-stage deformation. The degree of compaction and the age have significant impact on high temperature deformation performance of asphalt pavement. Based on the number of accumulation loading applied to the pavement and rutting depth, preliminary conversion relationship between accelerated loading actions and actual standard loading actions is drawn from the perspective of resistance to deformation. The concept of deformation stability is introduced to indicate the high-temperature deformation resistance of asphalt pavement and the high-temperature APT deformation stability results could be converted to the lab test deformation stability results with a conversion coefficient of 1.2–2.8.

Liping Liu, Yu Yuan, Lijun Sun

Thickness and Binder Type Evaluation of a 4.75-mm Asphalt Mixture Using Accelerated Pavement Testing

An increasing number of transportation agencies are investing in thin overlays consisting of small aggregate size asphalt mixtures to address routine maintenance needs and pavement preservation initiatives. Reported benefits of thin overlays include a smooth riding surface, reduced tire-pavement noise, and the ability to more easily maintain and control grade and cross-slope. The smallest aggregate size mixture the Florida Department of Transportation (FDOT) currently specifies is a 9.5-mm nominal maximum aggregate size (NMAS) mixture. When used as a dense graded friction course, the 9.5-mm NMAS mixture is placed in 1.0 in. lifts, which allows more flexibility and better optimization of milling depths, as well as structural or overbuild lift thickness to achieve a structurally appropriate and economical pavement. However, the ability to place an even thinner asphalt layer may potentially provide designers with more cost-effective alternatives. FDOT recently investigated the layer thickness of a 4.75-mm NMAS mixture using accelerated pavement testing (APT). During the APT study, overlay thicknesses of 0.5, 0.75, and 1.0 in. were placed with PG 67-22 (unmodified) and PG 76-22 (polymer modified) asphalt binders. Pavement instrumentation, laboratory data, and results from a field test section were also considered. This report documents the findings of the APT study and provides recommendations for the use and appropriate thickness of a 4.75-mm NMAS overlay.

James Howard Greene, Bouzid Choubane

Towards Understanding Tyre-Pavement Contact in APT Research on Flexible Pavements

An important element of Accelerated Pavement Testing (APT) is the selection of appropriate test tyre(s) to be used for APT testing. By far the majority of full scale (or scaled) APT devices uses pneumatic rubber tyres. Tyres differ not only in size, but also in composition stiffness, tyre tread patters, etc. Together with selected tyre loading scenarios, tyre inflation pressure plays a very important role and which is often neglected during planning the APT research. The thinner the flexible surfacing layers or the higher the pavement temperature within the asphalt surfacing and base layers, the more important the tyre-pavement interaction becomes. This is so because of the magnitude and non-uniformity of the tyre-pavement contact within the tyre contact patch, amongst others. The general (traditional) assumption is that the tyre-pavement contact is uniformly distributed within the tyre contact patch. A multitude of studies indicated that it is not only the tyre tread pattern and surface friction that influences these tyre contact stress patterns, but mainly the tyre loading/inflation pressure combination. In order to address these issues, the concept of “tyre fingerprinting” is proposed for APT users. Each tyre load/inflation pressure combination produces a different contact pattern inside the contact patch. For example, tyre loadings combined with high inflation pressure results in peak stresses (higher than inflation pressure) to develop in the centre portion of the contact patch, where relatively low inflation pressures combined with relatively high tyre loadings as often used to accelerate testing during APT research, may result in tyre edge loading/stresses, also much higher than the tyre inflation pressures. The aim of this paper is to address and clarify above with respect to selecting the appropriate tyre loading/inflation pressure levels for flexible pavement research using APT devices.

Morris De Beer, Colin Fisher

Use of APT for Validating the Efficiency of Reinforcement Grids in Asphalt Pavements

Reinforcement of flexible asphalt pavements with interlayer systems containing grids is increasingly used to extend service life of roads. Typically, reinforcements are placed between layers. They can be utilized to prevent the propagation of reflective cracking, prolonging the service life of asphalt pavements. Many research and practical experiences have shown the advantages of using reinforcements to increase the life-span of a pavement. However, only few tests were done using Accelerated Paving Testing (APT), where the application of loads is carried out with controlled passing of truck tires. Further, there is still insufficient research carried out to predict the actual effect on the extension of the pavement’s life-span. This information is critical for pavement design purposes and to improve the design standards. This research focuses on the effect of different reinforcement systems on the life-span extension of two-layered slabs and an asphalt pavement, using scaled and full scale APT with the Model Mobile Load Simulator MMLS3 and the Mobile Load Simulator MLS10 respectively. Laboratory and full-scale results with MMLS3 and MLS10 show that the different grids used in the test will extend the life-span of the tested pavements up to two times. The full-scale tests show, that the effect of the construction of a reinforcement system combining a grid with a stress absorbing membrane (SAMI) with the grid, increases the rutting of the pavement.

Martin Arraigada, Federico Perrotta, Christiane Raab, Gabriele Tebaldi, Manfred N. Partl

Accelerated Pavement Testing on Airports


Estimation of In-Situ Shear Strength Parameters for Subgrade Layer Using Non-destructive Testing

The Falling Weight Deflectometer (FWD) test has been widely used for evaluating the structural condition and load-carrying capacity of asphalt pavement systems as a non-destructive testing device. Conventionally, the in situ stiffness properties of the various pavement layers are estimated from the analysis of the surface deflection measurements using a backcalculation procedure. In this pilot study, an innovative and novel approach was investigated for estimating the shear strength parameters (C and ϕ) of the subgrade layer by means of FWD testing. Such parameters become important and necessary when assessing the risk of instantaneous shear failure in asphalt pavement layers under non-standard heavy vehicles. In order to assess the applicability of proposed approach, numerically simulated FWD test as well as measured FWD field data conducted on the APT asphalt pavement sections at the National Airport Pavement Test Facility (NAPTF) were analyzed. The surface deflection measurements from the FWD testing at multiple load levels were used in conjunction with backcalculation process to capture the stress dependent behavior of unbound layers and subsequently used to determine the shear strength parameters of the subgrade layer. It was found that the proposed approach was capable of estimating the in situ shear strength parameters of the subgrade material and the results were consistent with those obtained from conventional laboratory testing. Based on the findings from this study, work is currently undergoing to extend and validate the proposed approach for different type of asphalt pavement structures and subgrade properties.

Hadi Nabizadeh, Elie Y. Hajj, Raj V. Siddharthan, Sherif Elfass, Peter E. Sebaaly

Understanding Airfield Pavement Responses Under High Tire Pressure: Full-Scale Testing and Numerical Modeling

This paper aims to investigate airfield flexible pavement responses under heavy aircraft loading with high tire pressure through an integration of full-scale testing and numerical modeling. The new generations of aircraft, such as Boeing 787 and Airbus 350/380, have tire pressure close to or exceeding 232 psi. Limited information is available on the effect of high tire pressure on HMA pavement responses. A new series of high tire pressure tests were conducted at the Federal Aviation Administration’s (FAA) heavy vehicle simulator-airport version (HVS-A) Test Strips. An advanced three-dimensional (3-D) finite element (FE) model was developed that characterized the hot-mix asphalt (HMA) layer as a viscoelastic material to predict time- and temperature-dependent pavement responses under various loading conditions. The accelerated pavement testing results indicate that there is an insignificant effect of tire pressure on pavement rutting. The effect of tire pressure was more significant beyond failure (1 in. surface rut). This is consistent with the previous findings from high tire pressure tests. The numerical modeling results show that as the critical pavement responses in the asphalt layer increased slightly as tire pressure increased from 210 to 254 psi. The cross-anisotropic non-linear behavior of granular base affects the tensile strains at the bottom of asphalt layer significantly. The comparison between predicted and measured strains emphasizes the importance of considering the realistic tire-pavement interaction and the appropriate constitutive model for each pavement layer. The numerical modeling can support and supplement the full-scale testing results and provide valuable suggestions for mechanistic-based airfield pavement design under heavy aircrafts with high tire pressure.

Hao Wang, Navneet Garg, Maoyun Li

Use of Ground Penetrating Radar at the FAA’s National Airport Pavement Test Facility (NAPTF)

The Federal Aviation Administration (FAA) in the United States has used a ground-coupled Ground Penetrating Radar (GPR) at the National Airport Pavement Test Facility (NAPTF) since 2005. One of the primary objectives of the Accelerated Pavement Testing (APT) at the facility is to provide full-scale pavement response and failure information for use in airplane landing gear design and configuration studies. During the traffic testing at the facility, a GSSI GPR system was used to develop new procedures for monitoring Hot Mix Asphalt (HMA) pavement density changes that is directly related to pavement failure. A new methodology showing HMA density changes in terms of dielectric constant variations, called dielectric sweep test, was developed and applied in full-scale pavement test. The dielectric constant changes were successfully monitored with increasing airplane traffic numbers. The changes were compared to pavement performance data (permanent deformation). The measured dielectric constants based on the known HMA thicknesses were compared with computed dielectric constants using an equation from ASTM D4748-98 Standard Test Method for Determining the Thickness of Bound Pavement Layers Using Short-Pulse Radar. Six inches diameter cylindrical cores were taken after construction and traffic testing for the HMA layer bulk specific gravity. The measured bulk specific gravity was also compared to monitor HMA density changes caused by aircraft traffic conditions.

Injun Song, Albert Larkin

Relating Laboratory Tests to Performance Using Accelerated Pavement Testing


Development and Calibration of Permanent Deformation Models

As part of the first accelerated pavement tests completed in Costa Rica, laboratory permanent deformation tests were performed on asphalt mixture, granular base and soil samples from the test sections. The objective of this study was to calibrate prediction models using measured rutting data collected from instrumented flexible pavements. For the asphalt concrete the laboratory test was performed using unconfined cyclic loading at three different temperatures. Permanent deformation was found to be a function of the resilient strain, temperature and number of loading cycles. For the granular base and soil samples, the test was performed under repeated axial cyclic stress at different magnitudes and different confining stresses. Permanent deformation was found to be a function of the confining stress, deviator stress, moisture content, and number of loading cycles. Four instrumented flexible pavements were subjected to heavy vehicle simulator testing. Backcalculated moduli from multi depth deflectometers were introduced into an elastic multilayer system to obtain pavement responses. The number of equivalent standard axle load repetitions, the effective asphalt concrete mean temperature, and the in-place moisture content along with computed responses were used to calculate permanent deformation for the different layers. By comparing the measured rut depths with the predicted values from laboratory based models, the optimum combination of field calibration factors was determined so that the coefficient of variation was minimal by means of ordinary least squares.

Fabricio Leiva-Villacorta, Adriana Vargas-Nordcbeck, José Pablo Aguiar-Moya, Luis Loría-Salazar

Laboratory Tack Coat Investigation of Factors Contributing to Debonding Observed at the NCAT Test Track

Asphalt pavement structural integrity relies heavily on proper bonding at lift interfaces. While it is intuitive that interface debonding leads to pavement failure, the factors contributing to debonding in the field are not well understood. The objective of this research was to further investigate layer interface debonding that occurred in the 2012 research cycle at the NCAT Test Track, where debonding was observed in several sections with relatively large amounts of recycled materials. Pavement construction and the tack coat application were closely monitored and are not believed to have contributed to the debonding. Since debonding did not occur immediately, it was suspected that environmental aging, moisture damage, recycled binder content, and mixing temperatures may have been contributing factors. This study investigated these factors by comparing the interface bond strengths—measured with a shear collar in a Marshall stability tester, of plant-mixed materials that were laboratory compacted—to field performance of the full scale sections. The same non-tracking tack type and rate used in construction was applied in the laboratory to fabricate specimens matching the field sections. To investigate time and environmental effects, a set of specimens was subjected to laboratory long term conditioning (AASHTO R30) and a set was subjected to 35 day aging. Specimens were then subjected to accelerated moisture damage (ASTM D7870). Statistical analyses of the results from the sections allowed for identification of debonding causal factors.

Michael C. Vrtis, David H. Timm

Research Partnership Between the National Center for Asphalt Technology (NCAT) and the Minnesota Department of Transportation MnROAD Facility for a Nationwide Pavement Performance Experiment

Full-scale accelerated pavement testing (APT) has been conducted at the National Center for Asphalt Technology (NCAT) Pavement Test Track since 2000. Practical research in surface mix performance, structural pavement design, and pavement preservation has been cooperatively funded in 3-year research cycles by state departments of transportation (DOTs) located primarily in the southeastern United States (US). The Minnesota DOT’s Road Research Facility (MnROAD) has been conducting research in these same focus areas for northern states since 1994. Although the two programs have collaborated informally for many years, no formal experiments have been executed that simultaneously address the needs of both northern and southern states. The 6th research cycle at the NCAT Pavement Test Track and the 3rd phase of MnROAD research are for the first time officially connected in a nationwide study through two group experiments that are cooperatively funded by numerous state DOTs from all over the country. The objective of the preservation group (PG15) experiment is to quantify the benefit of pavement preservation on both low volume and high volume roadways. The objective of the cracking group (CG15) experiment is to identify laboratory tests that accurately predict both top-down and thermal cracking in mixes produced with diverse materials and a broad range of expected cracking susceptibilities. Construction of experimental pavements and surface treatments for these two experiments are planned for 2015 and 2016. An overview of the experiment design, constituent materials, mix designs, construction quality, baseline pavement condition measurements, and analysis methodologies are summarized in this document.

R. Buzz Powell, Ben Worel

Instrumentation for Accelerated Pavement Testing


Development and Validation of a Nondestructive Methodology to Measure Subgrade Moisture Contents at the NCAT Pavement Test Track

The Pavement Test Track is a full-scale, accelerated performance test (APT) facility for flexible pavements managed by the National Center for Asphalt Technology (NCAT) at Auburn University. Forty-six unique 200-foot test sections are installed around a 1.7-mile oval and subjected to accelerated damage via a fleet of tractors pulling heavy triple trailers in order to compress 10 million equivalent single axle loadings (ESALs) of pavement damage into 2 years of fleet operations. Methods and materials that produce better performance for research sponsors are identified so that future pavements can be constructed based on objective life cycle comparisons. Test sections are built on the NCAT Pavement Test Track with a focus on surface mixes, structural pavement design, or pavement preservation. Off-Track test sections with a focus on pavement preservation were built in the summer of 2012 on a nearby low volume roadway where electronic instrumentation was impractical; however, changing subgrade moisture content was needed in both treated and untreated test sections in order to fully document the benefit of pavement preservation. A nondestructive methodology was developed in order to quantify changing subgrade moisture content without using imbedded sensors. An overview of the measurement methodology and observed relationships between cracking and subgrade moisture content measurements are summarized in this document.

R. Buzz Powell

Development of a New Pavement Strain Coil Measuring System at CAPTIF

The Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF) has been measuring plastic and elastic strain in unbound pavements for more than 40 years. The systems used for this type of measurement are based around inductive coil sensors. CAPTIF’s current system relies on commercially produced electronic circuit boards for LVDT instrumentation. These boards are being phased out by the manufacturer. This has necessitated a need to develop a replacement system. This paper documents the development of new instrumentation that will replace CAPTIF’s current system. The criteria for the new system was to be equivalent or better than CAPTIF’s current system providing stability for measuring plastic strains over long periods and high resolution when measuring elastic strains from dynamic loading events. The new instrumentation is based around a special purpose integrated circuit for LVDT signal conditioning, the Analog Devices AD698. By developing this instrumentation ‘in house’, CAPTIF has been able to meet the criteria with a significantly lower cost system than in the past. In addition, the new instrumentation is more adaptable to taking portable field measurements because of its simpler setup and programming requirements.

F. R. Greenslade

Effects of Surface Condition on Non-uniform Contact Stresses of APT Tests

Traditionally, uniform circular contact stresses were assumed between tires and the pavement surfacing in pavement analysis. In recent years, the measurement of static tire-road surfacing contact stresses on a rigid support with a uniform texture led to an improved understanding of these interactions, as well as improved analysis of the data. Furthermore, the measurement of tire surfacing contact stresses on surfaces with a range of textures has led to an improved understanding of the effects of surface textures on contact stresses and subsequently pavement response. In this paper the effect of such a range of surface textures on scaled APT tire-surfacing contact stresses is evaluated and the potential consequences discussed.

W. JvdM Steyn, J. Maina

Electronic Upgrade of a Standard Benkelman Beam to Enable Capture of Full Bowl Deflections

The New Zealand Transport Agency (NZTA) decided it should revisit the design of electronic instrumentation that could be attached to standard Benkelman Beams to measure surface deflection. This has been attempted several times in the past but resulting devices were often complex and expensive. A low cost solution would encourage uptake by pavement construction companies that have easy access to the Benkelman Beam apparatus. Information gathered from the Benkelman Beam has been restricted to a few data points that must be read by an operator from a dial gauge and recorded manually. This requires some degree of skill and is prone to subjectivity. By upgrading existing Benkelman Beams with electronic measurement sensors and data recording equipment then full deflection bowl data could be acquired with improved reliability when compared to manual methods of recording. The Benkelman Beam test requires two measurements to be taken, pavement deflection and distance from the loading vehicle. A suitable deflection sensor was chosen. The criteria for choosing a distance sensor was that there would be no mechanical connection to the loading vehicle. A laser sensor was found with a suitable range and resolution. A low cost data acquisition module with software was successfully developed. The completed kit can be built for under $2000USD in parts. This is a fraction of the cost of purpose built electronic beams. The whole test can be completed by one operator.

F. R. Greenslade

Evaluation of Weight in Motion Sensors on the IFSTTAR Accelerated Testing Facility

This paper presents an experiment, performed on the IFSTTAR circular accelerated testing facility, to evaluate the performance of different weight in motion (WIM) sensors. This project, carried out with the French ministry of transport, aims at improving the performance of these WIM sensors, to allow automated overload control. Four different types of sensors were evaluated in the project: piezo-quartz sensors (2 types), piezo-ceramic sensors and piezo-polymer sensors. The full scale experiment was performed on a thick bituminous pavement. A total of 10 WIM sensors were installed, as well as other sensors (temperature probes, vertical displacement transducers, geophones). Accelerometers were also used to monitor dynamic load variations. The response of the sensors was evaluated under a wide variety of loading conditions (different loading speeds, temperatures and lateral positions of the wheels). In the first phase of the experiment, the 4 arms of the carrousel were all equipped with single wheels (with wheel loads of 45 or 55 kN). In a second phase, different wheel configurations were tested, on each arm of the testing facility (single wheel, dual wheels, tandem, tridem). A large database, of about 30000 WIM signals, was collected. The full scale tests have allowed to evaluate the repeatability of the different types of sensors, and the influence of different loading conditions (temperature, load type, loading speed..). The results indicate that the sensitivity of the different types of transducers to loading conditions is very different. Recommendations for correcting and improving WIM sensor response have been made.

Pierre Hornych, Jean-Michel Simonin, Jean-Michel Piau, Louis-Marie Cottineau, Ivan Gueguen, B. Jacob

Influence of Tire Footprint Area and Pressure Distribution on Pavement Responses

For most pavement analyses, it is assumed that the tire load is uniformly applied over a circular area. Also, it is generally assumed that tire inflation and contact pressures are uniform throughout the contact area. Several studies on this topic have shown different non-uniform pressure patterns. Therefore, a full understanding of the interaction between tires and pavement is necessary to obtain more accurate pavement responses. The objective of this study was to evaluate the effects of truck tire contact pressure on pavement responses at different loading conditions. A tire footprint system was used to capture contact pressure patterns statically and dynamically (low speed) at three inflation pressures and three wheel loads. All testing conditions were performed using a Heavy Vehicle Simulator HVS Mark VI with a five-rib tire type 11R22-5. A flexible pavement section instrumented with asphalt strain gauges, pressure cells and multi depth deflectometers was used to measure pavement responses. Measured tire-pavement contact stress data were input into a finite element analysis program to compute pavement responses and compare them to the measured responses. The contact pressure patterns obtained for the five-rib tire indicated that higher pressures were obtained for the inner ribs based on the controlled variables. In general, the results indicated that the contact area decreased for a given load as the inflation pressure was increased. Statistical analysis confirmed that pavement responses were significantly related to tire pressure distribution.

Fabricio Leiva-Villacorta, Adriana Vargas-Nordcbeck, José P. Aguiar-Moya, Luis Loría-Salazar

Instrumentation of an Innovative Pavement Section on Motorway A10

Recently, the French motorway company Cofiroute has decided to reconstruct the slow lane of a section of the motorway A10, located west of Paris. This section supports a very heavy traffic, of about 4000 trucks/day (corresponding to 4800 french standard equivalent 130 kN axle loads). The solution adopted for the reconstruction consists in retreating in situ, with a hydraulic binder, the existing bituminous subbase, and adding new base and surface layers, incorporating 30 % of recycled materials from the old pavement. To validate this novel solution, and in particular the in situ retreatment, Cofiroute asked IFSTTAR (the French Institute of Science and Technology for Transport, Development and Networks) to instrument this pavement structure. Four sections were instrumented with classical strain gage sensors, placed at different levels in the pavement (subgrade, treated subbase, bituminous base), and temperature sensors. On a fifth section, a more innovative instrumentation, including geophones, crack opening sensors, and temperature sensors was installed, associated with a remote data acquisition system. The instrumentation was installed during construction, in November 2011, and most transducers are still functioning. The paper presents the monitoring of these experimental sections. The strain gage measurements were used to fit a mechanical model of the pavement structure, and to evaluate the modulus of the different pavement layers, and their evolution with time. The results confirmed the good performance of the in situ retreated subbase, and validated the technical choice of the road owner. The geophones are very sensitive sensors, which measure vertical displacement velocity. Different methods of treatment of the geophone measurements were proposed, to monitor pavement deflections, and also to identify and classify truck silhouettes, and estimate truck loads.

Ngoc Son Duong, Juliette Blanc, Pierre Hornych

Accelerated Pavement Testing on Portland Cement Concrete Pavements


Design, Instrumentation and Construction of Bonded Concrete Overlays for Accelerated Pavement Testing

Bonded Concrete Overlay of Asphalt (BCOA) are being investigated for rehabilitation of asphalt pavements in California’s dry climate as part of a cooperative project led by the University of California Pavement Research Center for California Department of Transportation. Heavy Vehicle Simulator (HVS) is going to be used to evaluate future performance and develop a design and construction guide for Caltrans. This paper consists in a design of an Accelerated Pavement Testing (APT) test track for analyzing the performance of the BCOA structures under the use of a HVS. Besides it summarizes the findings from previous BCOA experiences, the results from the concrete mix designs and initial modeling. Second, a detailed design, construction and instrumentation plan is presented for the 15 sections that have been built in the test track. Construction of the test track already occurred, therefore a brief summary of important facts and initial responses of the instrumented sections are shown at the end.

Julio Paniagua, Fabian Paniagua, Angel Mateos, John Harvey, Rongzong Wu

Performance of Thin RCC Pavements Under Accelerated Loading

Thin Roller Compacted Concrete (RCC) surfaced pavement has a potential to be used as a cost-effective design alternative for a low-volume road where heavy truck trafficking is often encountered, such as oil and gas exploration, logging and agricultural activities. In this study three full-scale RCC pavement test sections, each having a structure of 4-, 6-, or 8-in. RCC surface over an 8.5-in. soil cement base, were tested at the Louisiana accelerated loading facility. The objective was to evaluate the structural performance and load carrying capacity of thin RCC pavements under accelerated pavement testing. A sequence loading of using dual-tire loads of 9-, 16-, 20-, 22-, and 25-kip was applied on each RCC section till pavement failure of fatigue cracking. The cracking performance of tested RCC sections was analyzed. Based on the measured surface cracking and the comparison results between measured and predicted load-induced pavement responses, a RCC fatigue model for thin RCC pavements was developed, which can be used to predict pavement fatigue life under different heavy loads for the thickness design of thin RCC pavements.

Zhong Wu, Moinul Mahdi, Tyson Rupnow

The Design, Construction and First-Phase Heavy Vehicle Simulator Testing Results on Full Scale Ultra-Thin Reinforced Concrete Test Sections at Rayton, South Africa

Ultra-Thin Reinforced Concrete Pavements (UTRCP) are successfully being used in residential streets and low-volume road applications in South Africa. Due to its popularity in this domain the Gauteng Provincial Department of Roads and Transport (GPDRT), in conjunction with CSIR Built Environment, started a research project to determine whether this type of technology can be used in higher-order roads such as collector roads (bus routes) or secondary and tertiary provincial roads where the traffic loading is significantly higher than what is found on residential streets. The research project consists of the testing of full-scale test sections with the Heavy Vehicle Simulator just outside Rayton in the Gauteng Province. The bulk of this paper deals with the structural design and construction of the various test sections. Four sections were constructed using different types of substructure support and different configurations of steel reinforcement. The paper also includes a summary of the results of the first HVS test conducted at the Rayton testing site.

L. du Plessis, G. J. Jordaan, P. J. Strauss, A. Kilian

The Design, Construction and Heavy Vehicle Simulator Testing Results on Roller Compacted Concrete Test Sections at the CSIR Innovation Site and on a Full-Scale Test Road at Rayton

Although the use of Roller Compacted Concrete (RCC) is not new in South Africa, the use of it to construct roads is not that well known or studied. The Gauteng Provincial Department of Roads and Transport (GPDRT) in conjunction with CSIR Built Environment in South Africa and Cosal Consultants CC started a research program on the use of RCC technology for roads. Whereas RCC is normally constructed with a relatively low labor component using heavy mechanical equipment, one of the aims of this investigation was to evaluate the structural performance of RCC constructed with a relatively high labor component using hand-operated equipment. The evaluation was done using the Heavy Vehicle Simulator (HVS) of the GPDRT. This paper briefly details two investigations. One HVS RCC test was conducted at the CSIR innovation site and the other on a full-scale test road at Rayton, Gauteng. Through HVS testing it has been shown that this type of pavement performed well in the dry state, even when constructed on a substandard support system. Test results indicate that this type of pavement exceeded its predicted performance. The use of hand-labor for layer compaction is discouraged as this can lead to layer densities lower than acceptable standards, which result in poor performance. The importance of proper RCC mix design to mitigate the negative effects of shrinking and crack forming is highlighted in this study.

L. du Plessis, G. Rugodho, W. Govu, K. Mngaza, S. Musundi

Accelerated Pavement Testing to Evaluate Functional Performance


Assessment of Flexible Pavement Response During Freezing and Thawing from Indoor Heavy Vehicle Simulator Testing

During the spring thaw period, pavements experience a significant decrease of their bearing capacity, which leads to increased deterioration during that season. The Ministry of Transportation of Quebec enforces load restrictions during the thawing and the recovery of the pavement structures to ensure they are protected from excessive thaw associated damages. The main objective of this paper is to present the results of an investigation of the structural behaviour of pavement structures during freezing and thawing under laboratory controlled conditions using the Laval University Heavy Vehicle Simulator (HVS). The results of the study will be used to develop criteria to assist the authority in the decision making process for the implementation and the removal of load restrictions. A typical four-layer flexible pavement structure was built inside an indoor concrete test pit at Laval University. The pavement section was instrumented to monitor horizontal strains in the asphalt concrete layer as well as vertical stress, vertical strain, and water content in each unbound layer and in the subgrade soil. Temperature was also monitored in all layers. The new HVS was used to impose 5000 kg (normal conditions), 5500 kg (winter premiums) and 4000 kg (spring load restrictions) loads on a standard dual-tire assembly. The load simulator was also used to induce freezing up to a depth of 1.5 m in the pavement structure and to induce thawing. The results obtained showed that during the thawing, the maximum strains occurred when the thaw front reached a depth of 0.9 m. Finally, it was found that the spring load reduction policies used in Quebec Province reduce the weighted annual damage by approximately 13 % during thawing, the strains and stresses decreased rapidly when the frost front reached subbase. Pavement damage caused by the standard load in these conditions can be considered negligible.

Ahmed El-youssoufy, Guy Dore, Jean-Pascal Bilodeau, Fritz Prophète

Development of IRI Models Based on APT Data

As with most pavement deterioration models, pavement monitoring is required during long time in order to properly capture deterioration trends. In this sense, roughness modeling, whether based on subjective parameters such as serviceability or indicators such as the International Roughness Index (IRI), requires significant amounts of data on structural pavement distresses such as rutting, patching, and cracking. Consequently, the initial roughness after construction, the evolution of roughness and surface deterioration in time have to be properly documented. Accelerated pavement tests permit an enhanced roughness data generation process. Furthermore, one of the most important factors in determining the future roughness is roughness after construction that can be carefully monitored and measured. Consequently, an IRI model has been developed based on results obtained at the PaveLab facility containing an HVS equipped with dual profile lasers for monitoring roughness along each test section. The model is based on four experimental sections, each of which has been divided into several tracks to make use of the collected data. The model was defined as a function of loss of support, as measured by means of layer moduli, surface rutting, initial IRI and number of load repetitions. Model estimation was based on a random effects model to account for unobserved heterogeneity and using the aforementioned parameters to reduce instrumental variable bias which can occur when using transfer function estimates as proxy for fundamental material properties in the model estimation process. The estimated parameters showed an increase in efficiency, as compared to Ordinary Least Squares estimated parameters.

José P. Aguiar-Moya, Pablo A. Torres-Linares, Edgar Camacho-Garita, Fabricio Leiva-Villacorta, Luis G. Loría-Salazar

Permanent Deformation of an Unbound Granular Pavement Subjected to Accelerated Multiple-Axle Group Loads

Road network owners are being faced with the need to make predictions of the long-term effect of heavy vehicle loading changes on their networks. Exploration of future mass-distance and incremental pricing for heavy vehicles requires an understanding of the effects of different axle group loads and types on pavement performance. The current Australian approach to assess the relative damaging effects of different axle groups on road pavements is by comparison of the peak static pavement deflection response under the axle groups. This ignores the contribution to pavement damage made by the axles in the group which do not correspond with the peak response. The assumption that the deflection response is the most appropriate indicator of pavement damage is also open to question and is not consistent with the current mechanistic design procedures, in which strains rather than deflections are used to calculate the performance of pavement materials. As part of a larger research exercise, the Accelerated Loading Facility was used to apply single, tandem and triaxle (tridem) axle group loads to a typical Australian, full scale, unbound granular pavement and subgrade. Analysis of permanent deformation data was hampered by significant moisture change during the testing period. However it was possible to demonstrate that the current standard load value used for triaxle groups is appropriate. This standard load value assumes that the interaction between axles of a multiple-axle group do not affect the relative permanent deformation damage caused by the same number of ungrouped axles.

Michael A. Moffatt

Three Years’ Monitoring of IRRF Instrumented Test Road

The IRRF’s test road, nearly 500 m in length, is unique to Western Canada. Situated in Edmonton’s east end, the road consists of two test sections and a control section designed to investigate the use of Tire Derived Aggregate as embankment material and the performance of bottom ash and polystyrene board as insulation layers in cold climate conditions. During construction, the road was instrumented with more than 250 pavement and geotechnical sensors. The installed geotechnical instrumentation monitors compression behaviour, internal temperature, and drainage characteristics of the test sections, while the pavement instrumentation monitors the mechanistic responses of the pavement to traffic and environmental conditions. Data collected from these sensors is relayed in 15-s intervals to the IRRF’s laboratory facilities, where it is used to study pavement performance. Various activities are scheduled to study how seasonal changes affect the pavement. Falling weight deflectometer tests are conducted monthly on the test road to monitor seasonal changes in the pavement layers’ moduli, while the effects of temperature, moisture variations, and traffic loads on the different pavement layers are also evaluated. This paper summarizes the effect of seasonal variation on pavement responses as a result of 3 years’ monitoring of the control section, tire embankment and insulated sections of the IRRF instrumented test road. By analyzing several Falling weight deflectometer testing results and temperature data collected from different instrumented sections during the time of monitoring, this paper investigates the impact of freeze and thaw on subgrade soil resilient modulus and the benefits of using insulation layers to protect the subgrade soil.

Leila Hashemian, Alireza Bayat

Accelerated Pavement Testing to Evaluate Sustainable Materials


Comparative Evaluation of Performance of Warm Mix RAP Asphalt Under Accelerated Unidirectional Wheelload Trafficking

The paper focuses on testing comparative evaluation of fatigue performance of composite asphalt pavement layers constructed at the Turner-Fairbank Highway Research Center (T-F) under full-scale trafficking with the ALF and the one third scaled MMLS3 (also known as MLS 11, since January 2015) of Virginia Tech in Blacksburg. The goal was to enhance economics of APT testing. Virgin 100 mm asphalt slabs of the composite 50 mm dual layers were extracted from the in situ un-trafficked sections of the test lanes after unidirectional testing with the ALF using a formalized process. The process was developed to overcome constraints due to traffic and temperature control as well as minimizing logistics during field testing. After extraction, the slabs were transported by vehicle to Blacksburg, VA where the MMLS3 testing procedure was formalized by means of a proof test on the lower 50 mm of a slab from Lane 9. For this, a 25 mm neoprene slab was used as interlayer between the asphalt and the underlying in situ concrete floor. After successful completion of the proof test, four further tests were completed. Two were done on the extractions from Lane 9B and 9A, and the other two were done on the extraction from Lane 5. The latter three tests all had two 25 mm neoprene interlayers. Aspects that were considered in the comparative evaluations were rutting, strain response, seismic stiffness using the Portable Seismic Pavement Analyzer (PSPA), cracking and contact stress under the MMLS tire. The effects of the respective material characteristics were also discussed. From the findings it was concluded that the monitored parameters found from the scaled tests were comparable to the related full-scale ALF test results in terms of intrinsic material characteristics and pavement performance. This is similar to earlier reported comparative studies. The authors consider this finding to be an economic benefit that should be utilized in pavement engineering studies.

Yucheng Huang, Fred Hugo, W. JvdM Steyn, Haocheng Xiong, Linbing Wang

Evaluation of the Optimum Percentage of RAP and RAS in Asphalt Mixes in Texas Using Accelerate Pavement Testing

The first APT project at the University of Texas at Arlington took place between May 2012 and August 2015. The project, funded by the Texas Department of Transportation (TxDOT), aimed to validate the maximum allowable percentage of Recycled Asphalt Pavement (RAP) and Recycled Asphalt Shingles (RAS) allowed by TXDOT Specifications. To accomplish the validation, twelve pavement structures were built and subjected to APT loading. The experiment was a factorial combination of four asphalt surface mixes with different percentages of RAP and RAS tested for their resistance to rutting, fatigue cracking and reflection cracking. The project also aimed to validate that poor results on lab prepared asphalt mixes containing RAP and RAS translates to poor field performance under full-scale axle loads and to verify overlay design tools recently developed by Texas A&M Transportation Institute (TTI) to predict mix cracking and rutting of new asphalt overlays. The paper presents the development of the APT experiment, briefly discusses the recorded performance of the studied mixes and provides a summary of the results obtained in this experiment.

Stefan A. Romanoschi, Tom Scullion, Fujie Zhou, Reza Saeedzadeh

Field Performance Evaluations of Large Sized Unconventional and Recycled Aggregates for Subgrade Improvement

Illinois Department of Transportation has recently introduced new gradation bands to accommodate large sized unconventional and recycled materials in subgrade remedial applications. Existing standardized test protocols cannot characterize these materials properly. To this end, an accelerated pavement testing study was undertaken to evaluate rutting performance trends of pavements constructed with such aggregate materials. An advanced field image segmentation technique was implemented for the in situ characterization of aggregate size and morphological properties, i.e. shape, texture and angularity, texture. Four pavement working platform test sections were constructed with railway ballast or riprap sized virgin aggregates as well as large-sized concrete demolition waste capped with densely graded dolomite and reclaimed asphalt pavement (RAP) materials. Construction quality control was achieved through nuclear gauge density checks and modulus measurements, the latter utilizing lightweight deflectometer and soil stiffness gauge. Next, the full scale test sections constructed over weak engineered subgrades were tested with unidirectional wheel loading in accelerated pavement testing. Periodic rut measurements were taken to quantify the rutting progression. Contributions of the subsurface layers to surface rut accumulation were assessed by the use of the following field equipment: variable energy lightweight penetrometer, ground penetrating radar (GPR), and geo-endoscopic probe for visualization of layer compositions and interfaces. Despite higher modulus properties obtained, RAP capped sections typically accumulated higher permanent deformation. Geo-endoscopic imaging revealed that presence of shallow water table led to early failure in one of the test sections. According to the study results, current Illinois subgrade stability design framework was found to be adequate for utilizing large sized unconventional and recycled materials in subgrade remedial applications.

Hasan Kazmee, Erol Tutumluer, Debakanta Mishra

Structural Assessment of the Effect of a Cement-Stabilized Base Combined with a Cold Central-Plant Recycled Layer at the NCAT Test Track

Two full-scale pavement sections built in 2012 at the National Center for Asphalt Technology (NCAT) Test Track were used to assess the effectiveness of combining a cement-stabilized base and a cold central plant recycled (CCPR) layer, from the perspective of the structural performance under accelerated traffic loading. The two sections had similar asphalt concrete (AC) layers over CCPR while one was built over an aggregate base and the other was built over a cement-stabilized base resulting from a full-depth reclamation (FDR) process. The two test sections performed adequately, presenting no evidence of pavement damage during a two-year period (10 million ESALs) of accelerated traffic loading. Furthermore, ride quality was not significantly affected with the application of traffic. Frequent deflection testing over the duration of the study revealed that the section over the cement-stabilized base exhibited much less temperature sensitivity and higher moduli when compared to the section over the aggregate base. Similarly, based on stress and strain measurements performed over the duration of the experiment, it was inferred that the cement-stabilized base layer appears to cure over time, limiting the strain levels and improving the structure over time.

M. A. Díaz-Sánchez, D. H. Timm, B. K. Diefenderfer
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