Fatigue Performance of the Interface between Cement Asphalt Mortar and Concrete Slab for CRTS II Slab Track

The interface between cement asphalt mortar (CAM) and concrete slab (CS) in the China railway track system (CRTS) II slab track is prone to fatigue failure in its service life. However, experimental research on its fatigue performance is still lacking. In this paper, the fatigue performance of the CAM–CS interface was innovatively explored through three-point bending experiments with five stress levels. The fatigue performance was thoroughly evaluated by analyzing its fatigue failure mode, S-N curve, probabilistic fatigue life estimation, fatigue evolution behavior, and fatigue damage model. Results indicated that most of CAM–CS interfaces failed in the mode of mortar failure, i.e., a thin layer of mortar attaching to the CS side. The fatigue life of the CAM–CS interface was evidently lower than that of CAM and CS matrix. The established probabilistic fatigue life estimation model inducing two-parameter Weibull distribution could accurately predict the fatigue life of the CAM–CS interface under various stress levels. The residual strain of the interface evolved from the rapid growth of Stage I to the stable growth of Stage II to the instability of Stage III, accounting for 10%, 75%, and 15% of the fatigue loading process, respectively. As for the fatigue modulus of the interface, three stages of decrease could be recognized corresponding to residual strain. As the maximum stress level rose, the stages with the proportionally highest decrease of the fatigue modulus transformed from Stage III to Stage II to Stage I. Meanwhile, the overall fatigue damage evolution curve rose. Considering aforementioned evolution characteristics of the interfacial fatigue damage, a generalized interfacial fatigue damage model for various stress levels was developed to quantitatively study the fatigue damage process of CAM–CS interface.