Fracture resistance study for hot mix asphalt mixture under out of plane sliding mode

Abstract

Cracked pavements can be subjected to out-of-plane sliding or mode III deformation due to movement of vehicles. In order to design suitable asphalt mixture for manufacturing high resistance pavements against mode III failure, it is necessary to determine a characteristic parameter called mode III fracture toughness (KIIIc) for these materials. In this research a comprehensive experimental study is performed to obtain the value of (KIIIc) for hot mix asphalt (HMA) mixtures under different geometrical and testing conditions. An edge notch disc bend specimen was utilized for conducting the mode III fracture toughness experiments on HMA mixture at low temperature conditions. Several discs with three thicknesses were cut from HMA mixtures made by gyratory compactor machine and with different air voids. The experiments showed that by increasing the size of test specimen, mode III fracture toughness can increase significantly. Furthermore, KIIIc value is increased by decreasing the test temperature from 0 °C to −24 °C and decreasing the air void content from 7% to 3%. A regression analysis was implemented on the test results and it was found that the thickness and air void have the maximum and minimum influences on KIIIc value, respectively. In addition, it was shown that the mode III fracture toughness of tested asphalt mixture is noticeably less than the corresponding value of the same mixture tested under mode I condition with the same testing conditions. The fracture toughness ratio (KIIIc/KIc) that was varied from 0.5 to 0.7 for different testing conditions and specimen sizes was predicted theoretically using some stress/strain based fracture criteria.