The fracture process zone in asphalt mixture at low temperature

The fracture process zone (FPZ) is a key factor to mechanistically characterize material fracture. This study investigates the FPZ of asphalt mixture at low temperature. The fracture process under a semi-circular bend (SCB) test of seven asphalt mixtures that represent a combination of different factors was monitored using an acoustic (AE) system with eight piezoelectric sensors. The size of FPZ was estimated by locating micro-cracks that correspond to 95% AE energy before peak load in the vicinity of the initial crack tip. The experimental data illustrates the significant influence of test temperature on the behavior of the asphalt mixture. Comparison results showed that the size of the FPZ significantly depends on air voids and aggregate type, but is less depend on the asphalt content. It was found that at a very low temperature, different loading rates produced very close FPZ, both for the width and length. No obvious difference was observed on the width of the FPZ for the three different initial notch lengths, whereas the length of the FPZ was found significantly increases with the decrease of the notch length. The size of FPZ was also numerically estimated for one case with the cohesive zone model (CZM) calibrated by experimental data from the same SCB test. The FPZ size obtained with both methods agrees reasonably with each other.