ABSTRACT
Top-Down Cracking (TDC) is a primary distress in asphalt pavements leading many researchers to pursue a test that accurately predicts its occurrence. This pursuit has proven especially challenging because TDC is not fully understood, although most literature suggests that TDC occurs as a combination of high tensile stresses and age-hardened asphalt binder at the surface of asphalt pavements. Furthermore, very little is understood about the effects of adding sustainable materials to a mixture that may alter TDC susceptibility. This paper presents a TDC study conducted at the National Center for Asphalt Technology (NCAT) Pavement Test Track analyzing the effects of innovative and sustainable construction materials including Reclaimed Asphalt Pavement (RAP), Reclaimed Asphalt Shingles (RAS), Ground Tire Rubber (GTR), and Highly Modified Polymer Asphalt (HiMA) on top-down cracking potential. The methodology focused on using the Energy Ratio (ER) approach to estimate cracking resistance and the test results were compared against actual field performance of full-scale test sections. The mixtures were tested in a laboratory and the ER results were used to rank the test sections according to predicted performance. The test section with the 5% RAS in the surface mix resulted in the highest ER value while the GTR mixture had the lowest ER. These results were somewhat contradictory to the expectation of higher cracking potential in the stiff RAS-modified asphalt. Continued monitoring of the full-scale sections will serve to validate or refute these results and provide guidance regarding ER usage to predict top-down cracking.
