Fracture parameters and influencing factors of cement asphalt mortar

Cement asphalt mortar (CAM), which is composed of cement, emulsified asphalt, sand and admixture, is an important component material of slab ballastless track of high-speed railway. The fracture resistance of CAM is very important for the ride comfort and stability of high-speed railway. This study was mainly aimed at using semi-circular bending (SCB) test to study the fracture parameters and influencing factors of CAM with high asphalt content. Through SCB test, the fracture parameters such as peak load and fracture energy of CAM were studied. The effects of temperature, loading rate, notch depth and material ratio on fracture parameters were analyzed. The microstructure and pore characteristics of CAM were studied by scanning electron microscope (SEM) and CT scanning. With the increase of temperature, the peak load and fracture energy of CAM decrease. For CAM samples with A/C ratio (mass ratio of emulsified asphalt to cement) of 1.6, when the temperature increases from-15 degrees C to 25 degrees C, the maximum decrease of peak load and fracture energy is 76.5% and 67.2%, respectively. With the increase of loading rate, the peak load and fracture energy of CAM increase. For CAM samples with A/C ratio of 1.2 at 25 degrees C, when the loading rate increases from 0.5 mm/min to 5.0 mm/min, the maximum increase of peak load and fracture energy is 44.0% and 48.2%, respectively. When the temperature is-15 degrees C and 25 degrees C, there is an optimal A/C ratio for peak load and fracture energy. When A/C ratio varies between 1.2 and 1.6, both peak load and fracture energy have the maximum value. When the temperature is-15 degrees C, the fracture occurred in CAM is semi-brittle fracture, and the fracture toughness and fracture energy are suitable to evaluate the fracture resistance of CAM. When the temperature is 5 degrees C and 25 degrees C, the fracture occurred in CAM is ductile fracture, and the fracture energy is more suitable to evaluate the fracture resistance of CAM.