Amirhossein Norouzi

Mechanistic evaluation of fatigue cracking in asphalt pavements

Abstract Over the last several decades, significant research has been conducted to predict the fatigue cracking performance of asphalt pavements. Recently, the simplified viscoelastic continuum damage (S-VECD) model was developed as an efficient method of characterising the fatigue performance of asphalt mixtures under a wide range of loading conditions. Two important material properties that can be determined from the S-VECD model are the damage characteristic curve that defines how damage evolves in a specimen and the energy-based failure criterion that defines when the specimen fails. These two material functions are unique for a given mixture regardless of temperature, mode of loading, stress/strain amplitude and loading history. This study presents the application of the Layered Viscoelastic Crirtical Distresses (LVECD) programme to predict the fatigue performance of 18 pavement sections from different locations in the United States and Canada. The capability of the LVECD programme to capture crack initiation, crack propagation and damage in the pavement sections is investigated by comparing the simulation results with field observations. This study found reasonable agreement in trends between the damage growth throughout the pavement cross sections as predicted by the LVECD programme and the surface crack growth as evidenced by field observations.

Determining Specimen Geometry of Cylindrical Specimens for Direct Tension Fatigue Testing of Asphalt Concrete

This paper presented a specimen geometry study of cylindrical specimens used in the direct tension cyclic (DTC) fatigue testing of asphalt concrete using an asphalt mixture performance tester. The current specimen geometry for DTC fatigue testing is 100 mm in diameter and 150 mm in height with a linear variable differential transducer (LVDT) gauge length of 70 mm in the middle of the specimen. In order to use the displacement data for mechanistic fatigue performance modeling, specimen failure must occur within the length of the LVDT gauge. However, recent experiments using stiff mixtures have shown that failure often occurs outside the LVDT gauge length. This specimen geometry study was conducted to determine the specimen geometry that enhances the propensity of the failure inside the gauge length without sacrificing the advantage of the DTC testing that provides uniform stresses and strains in the middle of the specimen. Laboratory experiments were performed on cylindrical specimens of different geometries (i.e., different diameters and lengths). Test specimen diameters of 75 mm and 100 mm and specimen heights of 130 mm and 150 mm were used in this study. The specimen geometry effects on damage characteristic curves and failure criteria were identified through ANOVA tests and layered viscoelastic pavement analysis for critical distresses (LVECD) program. Based on analysis results and experimental verification tests, the specimen geometry recommended for the DTC testing is 100 mm in diameter and 130 mm in height with a 70-mm gauge length. The recommended specimen geometry is applicable when the gyratory-compacted specimen geometry is 150 mm in diameter and more than 178 mm in height.

Fatigue life and endurance limit prediction of asphalt mixtures using energy-based failure criterion

Abstract Fatigue cracking is one of the major types of distress in asphalt mixtures and is caused by the accumulation of damage in pavement sections under repeated load applications. The fatigue endurance limit (EL) concept assumes a specific strain level, below which the damage in hot mix asphalt (HMA) is not cumulative. In other words, if the asphalt layer depth is controlled in a way that keeps the critical HMA flexural strain level below the EL, the fatigue life of the mixture can be extended significantly. This paper uses two common failure criteria, the traditional beam fatigue criterion and the simplified viscoelastic continuum damage model energy-based failure criterion (the so-called GR method), to evaluate the effect of different parameters, such as reclaimed asphalt pavement (RAP) content, binder content, binder modification and warm mix asphalt (WMA) additives, on the EL value. In addition, both failure criteria are employed to investigate the impacts of these parameters in terms of the fatigue life of the study mixtures. According to the findings, unlike an increase in RAP content, which has a negative effect on the mixtures’ fatigue resistance, a higher binder content and/or binder modification can significantly increase the EL value and extend the fatigue life as was proved before by other researchers, whereas WMA additives do not significantly affect the mixtures’ fatigue behaviour. A comparison of the model simulation results with the field observations indicates that the GR method predicts the field performance more accurately than the traditional method.

Comparison of Fatigue Cracking Performance of Asphalt Pavements Predicted by Pavement ME and LVECD Programs

Mechanistic–empirical pavement design has received significant attention from the pavement community as the method for designing asphalt pavements in the future. Currently available software for mechanistic–empirical pavement design includes the AASHTOWare Pavement ME Design (Pavement ME) program. The Pavement ME program allows users to predict pavement distresses by applying layered elastic theory for the mechanical responses and using empirical models for the distress predictions. The layered viscoelastic pavement design for critical distresses (LVECD) program, which employs three-dimensional viscoelastic finite element analysis with moving loads, can also be used to predict the fatigue and rutting performance of pavements. The LVECD program employs the simplified viscoelastic continuum damage (S-VECD) model as the material model for the fatigue performance predictions of asphalt mixtures under complex loading and environmental conditions. This paper examines and compares the performance of 33 pavement sections from five research projects located in the United States, Canada, and South Korea by using both the Pavement ME and LVECD computer programs. To verify the results obtained from these two programs, the simulations were compared with the field performance data. In terms of ranking, the LVECD simulations provided better agreement with the field performance data than did the Pavement ME simulations. One of the main reasons for the better predictions obtained by the LVECD program is that its fatigue performance predictions depend on the mixture properties of all the layers, whereas the Pavement ME program considers the fatigue properties of only the bottom layer mixture.

Effect of Silo Storage Time on the Characteristics of Virgin and Reclaimed Asphalt Pavement Mixtures

Many hot-mix asphalt plants store material in heated silos before it is ready to be transported to construction sites. The time that material is stored in the silo is not controlled and varies widely, depending on several factors. As the material is exposed to elevated temperatures, short-term aging of the binder may occur. Another important consideration is the interaction between reclaimed asphalt pavement (RAP) and virgin binders, as blending or diffusion could occur between the binders. In this study, a virgin and 25% RAP mixture were sampled at incremental silo storage times up to 10 h. Characterization testing included performance grading, rheological indexes, Glover–Rowe parameter evaluation, rolling thin film oven aging on the binders, complex modulus, a simplified viscoelastic continuum damage model (S-VECD) for fatigue, and thermal stress restrained specimen testing of the mixtures. Simulations that used layered viscoelastic critical distresses pavement analysis to predict fatigue behavior from the S-VECD model were used to show the potential effects of silo storage time on pavement life. Results from all tests indicated that mixtures aged with an increase in silo storage time. RAP materials experienced a greater effect; this effect may be a function of the air void content or indication of blending–diffusion in the silo. Rolling thin film oven aging showed that current laboratory conditioning methods do not necessarily simulate asphalt plant production. Production parameters, such as silo storage time, have a significant impact on mixture performance.

Ruggedness Study of Dynamic Modulus Testing of Asphalt Concrete in Indirect Tension Mode

The modulus is one of the primary asphalt mixture properties used for the mechanistic performance prediction of asphalt pavements. Dynamic modulus testing is a common method of measuring mixture modulus as a function of loading frequencies and temperatures. This paper presented the results of a ruggedness study of dynamic modulus testing in indirect tension mode to evaluate the factors that were most likely to affect the final results. Specimen thickness, air void content, gauge length, test temperature, and horizontal strain level, which are the critical factors that affect the dynamic modulus of asphalt concrete, were selected for the ruggedness analysis. Two different asphalt mixtures with the participation of two laboratories were used in the study. Based on the selected values for the different variables, air void content was found to be the significant factor that affected dynamic modulus testing and dynamic modulus values. The other factors did not appear to have a major impact on the test results; however, reasonable tolerances were obtained for the other parameters investigated in this paper.

Effect of Reclaimed Asphalt Pavement Content and Binder Grade on Fatigue-Resisting Performance of Asphalt Mixtures in Georgia

AbstractThis paper examines the effects of reclaimed asphalt pavement (RAP) content and binder grade on the fatigue resistance of Georgia asphalt concrete mixtures. The asphalt concrete mixtures we...