Forensic Evaluation of a Dry-Process Rubber-Modified Asphalt Pavement

Abstract

Atypical horizontal cracking and shear distress, paired with extensive bottom-up fatigue cracking, were identified in a dry-process rubber-modified flexible pavement section belonging to the Additive Group experiment at the National Center for Asphalt Technology Test Track. Exposed to the same accelerated trafficking level, the wet-process styrene butadiene styrene- modified control section displayed no such distress. An initial forensic evaluation characterized the distress and proposed mechanism(s) for distress initiation/propagation using analyses of the asphalt mixtures, backcalculated layer moduli, measured pavement responses, structural response simulation via Waterways Experiment Station Layered Elastic Analysis (WESLEA) for Windows 3.0 (WFW), and fatigue cracking damage evolution simulation via FlexPAVE 1.1 (FP). The objective of this paper was to provide support for the theories established in the previous investigation (on the mechanisms responsible for distress). Therefore, shear strength testing of the mixtures was performed, where a significant reduction in shear stress resistance was observed for the rubber-modified material versus the control material. Structural response simulation via FP confirmed the presence of significant internal horizontal shear stress development with the asphalt concrete (AC) layer under dual-tire loadings similar to the conditions found at the Test Track. Therefore, this could have led to the initiation and propagation of horizontal cracking and shear distress, given the rubber-modified mixture’s reduced capacity for shear resistance. The horizontal cracking condition in the rubber-modified section was modeled via WFW. The resulting tensile strain responses showed the best agreement with the field-measured quantities, indicating that horizontal cracking in the rubber-modified AC layer magnified the measured tensile strain responses.