Microscopic Deterioration Mechanism and Failure Mode of Rock-Concrete Composites Subjected to Uniaxial Compression and Freeze-Thaw Cycles using ESEM Technology

Abstract: With the continuous advancement of tunnel construction in cold regions, the shotcrete technique has been widely utilized in tunnel support, forming a concrete-rock composite structure. Influenced by the low-temperature climate in the cold region, the freezing of moisture around the tunnel will exert a significant frost heaving force on this structure, resulting in various degrees of freeze-thaw damage to the structure. Hence, investigating the damage characteristics of the rock-mass concrete material under freeze-thaw cycling conditions is of great significance for the protection of tunnel lining. In this study, an environmental scanning electron microscope (ESEM) test was conducted on the rock-concrete composites specimens, and the micro-damage deterioration mechanism and failure mode of the specimens subjected to uniaxial compression freeze-thaw cycling were analyzed from a microscopic perspective. The test results indicate that: (1) The freeze-thaw cycling causes irreversible damage to the interface area between the rock and concrete, with the number and length of micro-cracks continuously increasing, leading to the fracture and separation of some areas at the interface between the two. It directly affects the macroscopic mechanical performance of the specimens. (2) The freeze-thaw cycling weakens the cementation between particles. It can cause the structure between mineral particles to become loose, resulting in mineral shedding and fracture. Some fibrous minerals are damaged, and the size and quantity of pore structures continuously increase, while the integrity and bonding degree of minerals are damaged. (3) The composite specimens mainly experience splitting failure, sliding failure, and the combined mixed failure under uniaxial compression conditions. The splitting failure belongs to the tensile-shear failure dominated by tensile failure, and the sliding failure is a simple shear failure. Additionally, it is found that the interface failure mode of composite specimens (the inclination angle is 90°) is the tensile-shear failure dominated by tensile failure.

Key words: ESEM; freeze-thaw cycles; rock-concrete specimen; uniaxial compression