Fracture properties of asphalt concrete under various displacement conditions and temperatures

Abstract

Fracture mechanics has been widely applied to asphalt concrete (AC) materials to evaluate the cracking potential of AC pavements under traffic and thermal loadings. While AC materials behave as quasi-brittle at low temperature and high loading rate, its behavior becomes more viscous as temperature increases and/or loading rate decreases. Considerable fracture tests have been developed to capture the fracture properties of AC materials; however, fracture properties may be misinterpreted when using various fracture tests, especially in bending-mode. This would result in an erroneous characterization of AC cracking potential, which leads to a misestimate of pavement service life. The objective of this study is to investigate common fracture test methods for the AC materials, compare the fracture energies from various displacement measurements to capture true fracture property, and examine the effect of temperature on fracture energy and Flexibility Index (FI). Fracture energy from the semi-circular bending (SCB) geometry was compared to that from the disk-shaped compact tension (DCT) test. The effect of misinterpretation of test results on fracture energies was investigated. This study also suggests a proper method to capture fracture properties from the SCB test using the basic understanding of work and energy concepts in physics. The effects of test temperature on (1) fracture energy values, (2) FI, and (3) the overall ability to discriminate the cracking potential of AC mixtures are presented. Results show that while the crack characteristics can be captured more reasonably with a Load-Crack Mouth Opening Displacement (CMOD) curve, the fracture energy is better obtained using load-Load Line Displacement (LLD) curve. Moreover, performing fracture tests at a relatively higher temperature increases the ability to distinguish between various AC mixtures’ cracking potential.