Comparing Different HWTT Analysis Methods for Asphalt Mixes Containing RAP and Correlating with MIST-TSR

The use of recycled asphalt pavement (RAP) is associated with economic and environmental benefits. There is a general consensus that RAP leads to an improvement in the rutting and moisture damage resistivity of asphalt mixes. The Hamburg wheel tracking test (HWTT) is adopted to ascertain these distresses and is gaining popularity in the asphalt community. However, there is no step-by-step procedure to analyze the results of HWTT in AASHTO T324, Standard Method of Test for Hamburg Wheel-Track Testing of Compacted Asphalt Mixtures. Hence, there has been a rapid increase in number of analysis methods. A comparative study of these analysis methods is needed. At the same time, the moisture-induced stress tester (MIST) has been recently developed to quickly simulate stripping due to repeated pore pressure generation. A correlation between tensile strength ratio after MIST conditioning (M-TSR) and HWTT is warranted. In this study, asphalt concrete grade 1 mix containing 0, 10, 20, 30, and 40 % RAP by weight was designed and subjected to HWTT, MIST conditioning (varying stress cycles of 0, 1,000, 2,000, 3,500, 5,000, and 10,000), and indirect tensile (IDT) strength test. HWTT results were analyzed using eight different analysis methods viz. Iowa Department of Transportation (DOT), Oklahoma DOT, Texas DOT, third order (cubic) model and curvature, Francken model, rutting index and area, three-stage deformation model, and three-stage Weibull method. Based on results, this study recommends the Texas DOT and rutting index and area method for analyzing HWTT results. M-TSR was found to have a good correlation with HWTT moisture damage parameters except the moisture damage parameter from rutting index and area method and three-stage deformation model method.