Fujie Zhou

Case Study: Evaluation of Laboratory Test Methods to Characterize Permanent Deformation Properties of Asphalt Mixes

Extensive laboratory tests were conducted and the results were compared to the known field performance results of Specific Pavement Studies-1 (SPS-1) sections on US281. The objective was to establish which of the available laboratory test procedures could match the observed field performance. The laboratory tests included the diametral resilient modulus, Asphalt Pavement Analyzer (APA), Hamburg Wheel Tracking Test (HWTT), Repeated Simple Shear Test at Constant Height (RSST-CH), dynamic modulus test, and repeated load permanent deformation test. It was found that both RSST-CH and repeated load permanent deformation test could differentiate the performance of different sections, and the results matched closely with the field performance. The total permanent strain was also found to be a reasonable indicator of field rutting performance. For the wheel tracking tests, the APA performed better than HWTT, but both failed to differentiate some mixes. The moduli at high temperature, including dynamic modulus, axial resilient modulus, shear resilient modulus, and E*/sin δ could screen out the bad mixes. However, those moduli (except for shear resilient modulus) failed to further differentiate the performance of mixes once they were grouped as generally “good” or “bad”.

Analysis of Rutting Performance Impacting Factors in HMA Overlay Mixture Design

It is reasonable to assume that hot-mix asphalt (HMA) overlay rutting occurs only in HMA overlay(s) because of rutting from the existing pavement, if any, most of which had already occurred before the HMA overlay(s) was placed. So, this paper focuses only on the HMA overlay itself. Many factors—such as the asphalt binder grade, the aggregate gradation, the types of aggregates, the volumetric parameters of the mixtures, etc.—potentially influence the HMA rutting performance when designing an HMA overlay mix. In this paper, a Hamburg Wheel Tracking Test (HWTT) device is employed in order to evaluate the rutting performance of HMA overlay mixes in terms of the rut depth at specified wheel passes. An experimental design is developed to cover the different combinations of aggregates, gradations, and asphalt binder types. Through extensive laboratory tests and statistical analyses, the most significant impacting factors were identified. The corresponding HWTT rut depth prediction models were developed with high R2 values (>0.80). With these models and established rut depth criteria, the maximum allowable asphalt content that can be used without causing rutting problems was estimated for different overlay mixes. Furthermore, the models and estimated maximum allowable asphalt content were preliminarily verified by performance data of the National Center for Asphalt Technology test track sections and WesTrack test sections.

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.