Fatigue performance characterization of styrene-butadiene-styrene and crumb rubber composite modified asphalt binders with high crumb rubber contents

Recycled from waste tires, crumb rubber (CR) is a common additive material using in transport infrastructures to improve the mechanical performance of asphalt mixture. The styrene-butadiene-styrene (SBS) and CR composite modification technology were employed to prepare SBS/CR composite modified asphalt (CMA) binders. To study the effect of CR contents and control modes on the fatigue performance of asphalt binders, the Dynamic Shear Rheometer (DSR) tests, including stress/strain sweep tests and controlled-stress/strain time sweep tests, were conducted to calculate the fatigue crack density as loading cycles. Based on the test data, the fatigue crack density evolution and the modified Paris' law were used to characterize the fatigue performance of SBS/CR CMA binders. A unified fatigue parameter was proposed to evaluate the fatigue resistance and optimize the CR content of SBS/CR CMA binders under two control modes. Results demonstrated that the fatigue crack density only experienced two stages (the crack initiation stage and the steady growth stage) under the controlled-strain loading, while the asphalt binder sample shows obvious structural failure (e.g., stepping into the unsteady growth stage) under controlled-stress loading. The smaller value of the proposed index, ln A /(n + 1), indicated the better capacity of fatigue crack resistance and that of a certain type of asphalt binder under two control modes were almost identical. Furthermore, the value of SBS/CR CMA binder with 40 wt% CR was-6.81 showing the best fatigue performance among these asphalt binders, and the CR contents and the values of proposed index followed a linear relationship.