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This thesis presents results from an experimental study on the dynamic modulus testing of hot mix asphalts (HMAs) commonly used in North Carolina in uniaxial compression mode. Forty two mixtures with varying aggregate sources, aggregate gradations, asphalt sources, asphalt grades, and asphalt contents are included in this study. With the dynamic modulus database developed, several issues are investigated in this research. Effects of confining pressure on the dynamic modulus are evaluated by comparing results from uniaxial and triaxial compression tests. A modified dynamic modulus test protocol is developed by reducing the required testing time using more frequencies and fewer temperatures based on the time-temperature superposition principle. Hirsch and Witczak predictive models are evaluated. During this analysis a case study was conducted to determine how much pavement performance changes due to the predictive errors. Finally, effects of different mixture variables on dynamic modulus of asphalt concrete are evaluated.
Advances in Materials and Pavement Performance Prediction contains the papers presented at the International Conference on Advances in Materials and Pavement Performance Prediction (AM3P, Doha, Qatar, 16- 18 April 2018). There has been an increasing emphasis internationally in the design and construction of sustainable pavement systems. Advances in Materials and Pavement Prediction reflects this development highlighting various approaches to predict pavement performance. The contributions discuss links and interactions between material characterization methods, empirical predictions, mechanistic modeling, and statistically-sound calibration and validation methods. There is also emphasis on comparisons between modeling results and observed performance. The topics of the book include (but are not limited to): • Experimental laboratory material characterization • Field measurements and in situ material characterization • Constitutive modeling and simulation • Innovative pavement materials and interface systems • Non-destructive measurement techniques • Surface characterization, tire-surface interaction, pavement noise • Pavement rehabilitation • Case studies Advances in Materials and Pavement Performance Prediction will be of interest to academics and engineers involved in pavement engineering.
The purpose of this research is to present the results from an analytical/experimental study on the dynamic modulus testing of hot mix asphalt (HMA) using the indirect tension (IDT) mode. The analytical solution for dynamic modulus determination in IDT was developed by Kim (14) using the theory of linear viscoelasticity. To verify the analytical solution, temperature and frequency sweep tests were conducted on 24 asphalt mixtures commonly used in North Carolina, using both axial compression and IDT test methods. In doing so, a modified dynamic modulus test protocol is introduced that reduces the required testing time by using more frequencies and fewer temperatures based on the time-temperature superposition principle. A comparison of results from the axial compression and IDT test methods shows that the dynamic modulus mastercurves and shift factors derived from the two methods are in good agreement. It was also found that Poisson's ratio is a weak function of the loading frequency; its effect on the phase angle mastercurve is discussed. After verification of the analytical solution, another study was conducted to evaluate the effect of aggregate size on the variability of test results, where the coefficient of variation (CV) was computed for each aggregate size and the results were compared. It was found that mixes with a larger nominal maximum size of aggregate (NMSA) had a greater CV than those with a smaller NMSA. Digital image Correlation was used to further support the findings and reveal physical explanations for the results obtained from this statistical analysis.
Keywords: Dynamic Modulus, IDT, Phase Angle, Viscoelasticity.
This project evaluated the procedures proposed by the Mechanistic-Empirical Pavement Design Guide (MEPDG) to characterize existing hot-mix asphalt (HMA) layers for rehabilitation purposes. Thirty-three cores were extracted from nine sites in Virginia to measure their dynamic moduli in the lab. Falling-weight deflectometer (FWD) testing was performed at the sites because the backcalculated moduli are needed for the Level 1 procedure. The resilient modulus was also measured in the lab because it is needed for the Level 2 procedure. A visual pavement rating was performed based on pavement condition because it is needed for the Level 3 procedure. The selected cores were tested for their bulk densities (Gmb) using the AASHTO T166 procedure and then for their dynamic modulus in accordance with the AASHTO TP62-03 standard test method. Then the cores were broken down and tested for their maximum theoretical specific gravity (Gmm) using the AASHTO T-209 procedure. Finally an ignition test was performed to find the percentage of binder and to reclaim the aggregate for gradation analysis. Volumetric properties were then calculated and used as input for the Witczak dynamic modulus prediction equations to find what the MEPDG calls the undamaged master curve of the HMA layer. The FWD data, resilient modulus data, and pavement rating were used to find the damaged master curve of the HMA layer as suggested for input Levels 1, 2, and 3, respectively. It was found that the resilient modulus data needed for a Level 2 type of analysis do not represent the entire HMA layer thickness, and therefore it was recommended that this analysis should not be performed by VDOT when implementing the design guide. The use of Level 1 data is recommended because FWD testing appears to be the only procedure investigated that can measure the overall condition of the entire HMA layer.
The MEPDG (ARA, Inc., "NCHRP 1-37A Final Report: Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures," NCHRP Program 1-37A Project, National Research Council, Washington, D.C., 2004) introduces the dynamic modulus as the material property to characterize asphalt concrete. One of the challenges of acquiring the dynamic modulus from existing pavements is the standard dimensions of the test specimen. The specimen size specified in AASHTO TP62-07 (2007, "Standard Method of Test for Determining Dynamic Modulus of Hot-Mix Asphalt Concrete Mixtures," AASHTO, Washington, D.C.) cannot be obtained from many pavement layers. This study evaluates two other geometries, indirect tension specimens and prismatic specimens, to determine whether the measured dynamic modulus is the same as the modulus obtained from TP62 protocol. This study provides a comparison of the effects of a non-uniform state of stress and anisotropy. These effects are isolated by comparing specimens prepared by Superpave gyratory compaction and vibratory steel-wheel compaction. The comparisons are verified using four 12.5-mm surface course mixtures with different aggregate shapes and binder types, and one 25.0-mm base mixture. The results show that the difference between the dynamic modulus values obtained from different geometries is statistically insignificant. The results provide justification for using alternative methods for acquiring the dynamic modulus experimentally?specifically, for previously constructed pavements.