Abstract:Research purposes： Now the contact loss between slab and CA mortar is the main damage type of Chinese CRTS II slab track，in order to figure out the damage mechanics of contact loss，the composite specimens of concrete and CA mortar were used to conduct the splitting tensile and shear test. The stress distribution of the interface was obtained with digital image technology ( DIC )， and then the parameters of cohesive model were achieved. The interface mechanical properties and failure mode between slab and CA mortar were obtained through comparing with the cohesive finite element model analysis results and the experiment results. Research conclusions:(1) The DIC technology can clearly describe the stress distribution of the composite specimens interface and its whole failure stage including the interface damage evolution，the formation and propagation of crack. (2 ) The bond failure between track slab and CA mortar is brittle fracture，and the interface normal stress - displacement and tangential stress - displacement are both bilinearity. ( 3 ) The cohesive model parameters between the track slab and CA mortar were recommended as follows： the normal cohesive strength is 1.792 MPa，the normal interface stiffness is 708. 485 MPa/mm，the normal critical fracture energy is 0. 025 2 mJ/mm2，the tangential cohesive strength is 0. 956 MPa， the tangential l interface stiffness is 63.039 MPa/mm，the tangential critical fracture energy is 0.018 mJ/mm2. (4) These results can be used to analyze the interface cracking behavior between slab and CA mortar，and provide theoretical basis for CRTS II slab track design and maintenance.