The introduction of modified asphalt binders provided transportation agencies an effective tool to design balanced mixtures that can resist conflicting distresses while maintaining good long-term durability. While conventional polymer modified asphalt mixtures have shown improved long-term performance, it is also believed that asphalt mixtures with high polymer (HP) content may offer additional advantages in flexible pavements subjected to heavy and/or slow moving traffic loads. While no unique and detailed handy guide that discusses the HP modification of binders and mixtures exists at this time, and while asphalt industry is moving towards the use of much more durable materials for a better long-term performance of newly constructed roads, this manuscript summarizes the findings from the literature review on the performance of HP asphalt binders and mixtures. The reviewed laboratory studies indicated that the increase in polymer content continues to improve the performance properties of binders and mixtures. The reviewed field projects showed encouraging early field performance without exhibiting any construction related issues. In addition, this article presents attempts that were explored to estimate a structural coefficient of HP mixes based on the available information from literature. This analysis led to the conclusion that the designed HP mixtures may lead up to 40% reduction in the asphalt layer thickness resulting in considerable upfront cost-savings.

In recent years, two types of test methods have emerged to evaluate the susceptibility of asphalt mixtures to cracking at intermediate temperatures as part of performance-related mix design specifications: the indirect tensile (IDT) test and the semi-circular bending (SCB) test. In parallel, several associated analysis approaches have been utilised to evaluate cracking characteristics of these mixtures. The objective of this paper was to evaluate various cracking indices obtained from IDT and SCB tests in terms of their ability to provide a low-variability and high-discrimination response. In addition, the ranking potential of the considered indices in terms of cracking performance of asphalt mixtures was evaluated and inter-correlated. The cracking indices were able to capture the asphalt mixture performance with the fracture strain tolerance (FST) index and cracking resistance index (CRI) showing better performance when compared to other cracking indices. Generally, the IDT test results better distinguished the cracking performance of asphalt mixtures when compared to the SCB test results. The Ideal-CT index (CT_index) from the IDT test and the flexibility index (FI) from the SCB test demonstrated a fair correlation. Overall, the results demonstrated the suitability of both tests for predicting the cracking performance of asphalt mixtures at intermediate temperatures.

The Virginia Department of Transportation (VDOT), like many owner agencies, is interested in ways to facilitate the increased durability of asphalt mixes in an effort to make its roadway network more sustainable, longer lasting, and more economical. The balanced mix design (BMD) method proposes to address this through the incorporation of performance criteria into mix design and acceptance. VDOT has committed to the implementation of the BMD method in an effort to improve asphalt mix performance. The purpose of this study was to continue advancing efforts toward implementation of BMD through the evaluation of 13 asphalt mixes using performance-indicating laboratory tests, validation of the initial performance tests selected for BMD use, and validation of the initial test threshold criteria. Based on the results, the asphalt pavement analyzer (APA) rut test, indirect tensile cracking test (IDT-CT), and Cantabro test were found suitable for continued use in BMD. The current threshold criteria for all three tests were found reasonable based on additional mix testing. The study recommends that APA rut test and IDT-CT results should be compared and correlated to fundamental rutting and cracking tests, respectively, as well as to performance predictions obtained from mechanistic-empirical pavement design simulations, and to field performance for full assurance that test threshold values are appropriate. It was further recommended to evaluate the Cantabro, IDT-CT, and APA rut tests to determine acceptable variability and establish precision statements.

The objective of this study was to assess the impact of aging on high polymer (HP)-modified asphalt binders when compared with conventional polymer-modified asphalt (PMA) binders on the basis of rheology- and chemistry-based parameters. An extended asphalt binder aging experiment that considered multiple combinations of PMA and HP binders from different sources was conducted. Long-term oven-aged asphalt binders at multiple temperatures and durations and asphalt binders aged in a pressure aging vessel (PAV) for multiple durations were tested using the dynamic shear rheometer. Several parameters were determined including low shear viscosity and Glover-Rowe parameters at various temperatures. The PAV-aged asphalt binders were further evaluated in terms of critical low temperature difference using the bending beam rheometer. All PMA and HP combinations were evaluated using Fourier transform infrared spectroscopy for characterization of chemical composition and assessment of polymer degradation. Overall, the measures indicated reduced susceptibility to aging of HP binders when compared with PMA binders, shown by a flatter slope with respect to oxidation with the low shear viscosity measures and Glover-Rowe parameters. In addition, the potential of polymer degradation for HP binders when compared with PMA binders was minimal with aging, thus indicating an increased longevity from a chemical-characteristic standpoint.