An alternative of crack length extension in R-curve analysis of asphalt concrete

Abstract

This study applies the Digital Image Correlation (DIC) technique to capture the displacement field on the specimen surface in the SC(B) fracture test of asphalt concrete for the construction of R-curves. Previous research, utilizing a displacement method, did not capture the micro-cracking that occurs during the formation of the cohesive zone in a fracture specimen. A Crack Opening Displacement Matrix (CODM) is defined based on the DIC displacement field. Five CODMs are used as alternatives of crack length extension to construct the displacement-based R-curve for asphalt concrete. The cohesive energies and energy rates are determined by those displacement-based R-curves. The influences of test temperature, loading rate, aggregate size, and polymer modification on cohesive energies and energy rates are then investigated. The following lists the major findings of the this study: (1) The cohesive energies determined by displacement-based R-curve are generally lower in value compare to the cohesive energy determined by crack-extension-based R-curve, which indicates the displacement-based R-curve and its cohesive energy may separate crack initiation and propagation by invisible micro crack; whereas the crack- extension-based R-curve separate the crack initiation and propagation by visible crack; (2) The test temperature is statistically significantly impacting on cohesive energies; loading rate is significantly impacting on cohesive energy determined by the R-curve using the CODM that is distant from the crack tip; (3) Higher loading rate, lower test temperature and larger aggregate size may lead to higher energy rate; but these trends are not statistically proved in this study. In all, the crack length and CODMs quantify the crack extension in different ways (length growing and wideness opening). Thus, by complementing the existing displacement-based R-curve, the R-curve system of both CMOD and CODM has the potential to fully characterize the fracture behaviour of asphalt concrete.