Low-temperature fracture behavior of asphalt concrete in semi-circular bend test.

Abstract

Asphalt concrete mixtures behave as quasi-brittle materials at temperatures close to the glass transition of the component asphalt binder. A salient feature of structures that consists of quasi-brittle materials is that there exists an intricate size effect on the structural strength. The existence of such size effect is mainly attributed to the presence and the stable growth of a relatively large fracture process zone (FPZ) that develops ahead of the crack tip prior to failure (maximum load) of the structure. This inelastic region is characterized by non-linear material deformation and fracture energy dissipation that ultimately generate stress redistribution and govern the strain-softening of the material. Understanding this size effect is crucial for two purposes: a) extrapolation of small-scale laboratory testing results to full-scale design, and b) identification of material fracture properties. In this research work, laboratory experiments and numerical simulations were conducted to investigate the size effect of asphalt concrete tested in semi-circular bend (SCB) test at low temperature. Geometrically similar specimens of different sizes and with different notch lengths were tested. The experimental results were analyzed with the energetic-size effect theory, and were used to develop type I and II strength scaling laws, respectively, for the notchless and deep notched specimens. The validity of the scaling laws at large sizes was evaluated through finite element simulations of mode I crack growth in the SCB test. A cohesive zone model (CZM) was successfully calibrated by experimental data, and implemented to predict the nominal strength in large SCB specimens. The strengths predicted from the numerical models were in good agreement with the scaling laws' strength prediction. Based on the analyses of the strength scaling laws derived, important conclusions on the fracture behavior of asphalt concrete at low temperature, as well as size of FPZ were drawn.