Investigation of the fracture resistance of asphalt mixtures at low temperatures with a semi circular bend (SBC) test.

摘要

Low temperature cracking in asphalt pavements, which is defined as transverse cracking resulting from single or few severe temperature drops, is addressed by current specifications with strength and creep tests performed on unnotched specimens. Due to the lack of measurement of fracture resistance of asphalt mixtures, this specification can hardly be used to predict the crack propagation and analyze the pavement response subjected to other types of loads with the existence of cracks.; This thesis investigates the low temperature cracking by experimentally measuring fracture properties of asphalt mixtures and numerically predicting the fracture behavior of asphalt mixtures. A semi circular bend (SCB) test was developed for measuring the fracture toughness and fracture energy of asphalt mixtures. With a circular geometry, the SCB specimen is compatible with a Superpave gyratory compactor (SGC) and can be conveniently machined out from a cylindrical specimen compacted with a SGC or a core taken from the field. The fracture properties of three types of asphalt mixtures were measured at three low temperatures: -20°C, -30°C, and -40°C. Statistical analysis shows that the type of binder and the temperature significantly affect the fracture resistance of asphalt mixtures; however, the density gradient within the cylindrical specimen is not significant enough to result in different fracture resistance. The evolution of the fracture properties with respect to the temperature shows strong temperature dependence of the fracture resistance of asphalt mixtures; while the different patterns of the evolution of fracture resistance among three types of asphalt mixtures indicate a significant interaction between the binder effect and the temperature effect.; The cohesive zone model (CZM) was employed to simulate the fracture behavior of asphalt mixtures using zero thickness interface element. Calibration is needed for achieving simulations close to experimental results. The numerical model was applied to predict the low temperature cracking in a simplified asphalt pavement. The computation results show that the modulus and tensile strength of asphalt mixture are critical for the initiation of crack, while the fracture energy significantly affects the temperature drop necessary for the propagation of a crack in an asphalt pavement.