Mechanical behavior of bonded interface between steam-cured concrete and SCC under direct shear test: Experimental and numerical studies

The interlayer damage of slab ballastless track for high-speed railway has become a weak link that affects the safe operation of track structure. Under the combined action of the train self-weight load and wheel-rail friction, the track plate presents complex stress state. Meanwhile, the interlayer defects and bond state have a great influence on the damage mechanism of track plate. The failure mechanism of concrete-concrete interface under combined stress has been focused on, but it is still not well quantitatively investigated at the grain scale. In this paper, the discrete element method (DEM) combined with digital speckle and acoustic emission monitoring technology is used to conduct the direct shear tests on bonded samples composed of steam-cured concrete and self-compacting concrete (SCC) with different bond interface characteristics. On this basis, it is quantitatively analyzed the effects of interfacial bond strength and interfacial morphological characteristics on the compressive-shear mechanical properties and damage patterns of bonded samples, and the deterioration mechanism of the interface is explained from a mesoscopic perspective. The results show that the compression-shear mechanical response and damage features of the bonded samples are the result of the combined effect of bond strength and morphological characteristics of the interface. The increase of bond strength makes the samples change from shear cracking damage along the interface to tensile cracking damage inside the concrete. The bonded area ratio (BAR) of the interface maintains a good positive linear correlation with the shear strength, and the increase of BAR makes the brittle failure more obvious in the post-peak stage. The increase of interface roughness coefficient (IRC) makes more compressive stress concentration areas form in the interface, which enhances the shear strength of the bonded sample to a certain extent.