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.

Chip seal treatments are used by many state departments of transportation and counties to cover minor fatigue and low-temperature cracks, retard raveling by reducing the moisture infiltration, and improve friction. Long-term performance of a chip seal treatment is affected by several factors including the type and morphology of the aggregates, emulsion/binder type, and most importantly, the microstructural characteristics such as the percent embedment of aggregates. This paper documents the efforts towards establishing performance-based threshold values of the percent embedment to minimize the common chip seal distresses (i.e. aggregate loss and bleeding). The laboratory performance tests were performed to evaluate aggregate loss and bleeding using a retrofitted Hamburg wheel tracking device. Two emulsion types (CRS-2M and CSEA) and two aggregate sources (slag and natural aggregates) were included in the testing program. Digital image analysis techniques were utilized to quantify and analyze the laboratory test results with respect to the percent embedment as well as chip seal macrotexture. Based on the test results, the minimum and maximum percent embedment thresholds for chip seals are established as 58% and 70%, respectively.

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.

The Virginia Department of Transportation (DOT) has taken initiatives to implement the Balanced Mix Design (BMD) method to assure the long-term service life of its pavement network from a mixture quality standpoint. As part of this initiative, the cracking tolerance (CT) index obtained from the indirect tensile (IDT) test at intermediate temperature in accordance with ASTM D8225-19 was selected for evaluating the cracking potential of dense-graded surface asphalt mixtures. This prompted the need to generate the precision estimates (repeatability and reproducibility) for the test method for proper implementation during quality measurement practices. Thus, this interlaboratory study was undertaken to determine the precision estimates of the CT index calculated from the IDT test and to develop the associated precision statements. In addition, fracture strain tolerance (FST) and indirect tensile strength were included. Two asphalt mixes with significantly different CT index values were designed for the evaluation. Forty-six pairs of five replicate sets of compacted specimens (one set for each mix) were sent to 41 participating laboratories to be tested at 25°C. The test results were checked for data quality. The effects of loading rate and manufacturers on the indices were also evaluated. The test results indicated that one third of the sets were not tested in full accordance with the ASTM standard, indicating a need for training. The results also indicated that the specified loading rate of 50 ± 2 mm/min in ASTM D8225-19 for the IDT test may need revision. Finally, the precision estimates and associated statements for the three indices were presented.