Abstract
During tunnel construction in cold regions, the good adhesion of surrounding rock-lining interface is one of the important preconditions to evaluate the durability of tunnel lining. However, the repeated fatigue damage between rock and concrete due to the freeze-thaw action leads to debonding at the interface, which significantly affects the protective effect of shotcrete. Accordingly, based on the combination of sandstone-concrete as the object, through the development of sandstone-concrete interface freeze-thaw cycling test, and combining the nuclear magnetic resonance (NMR) test and scanning electron microscopy (SEM) analysis, the mechanism of debonding by freeze-thaw damage at the sandstone-concrete interface was systematically revealed. The conclusions drawn are as follows: (1) With the increase of freeze-thaw times, the content of micropores and macropores at the interface gradually increases, while the content of mesoporous gradually decreases. At the same time, the decrease of freeze-thaw temperature also aggravates the growth of interface cracks, and the freeze-thaw damage of interface is closely related to the minimum freeze-thaw temperature. (2) The damage of the sandstone side becomes more serious under multiple freeze-thaw actions. Concrete as a water retaining plate inhibits the migration of water to its interior, and a pot cover effect exists at the interface to provide better storage space for water accumulation. (3) The C-S-H group is the main source of the bond force of sandstone-concrete interface, and the freeze-thaw effect aggravates the fracture of the C-S-H group, which leads to the interface debonding. This study could provide an experimental basis and theoretical support for systematically recognizing the evolution mechanism of freeze-thaw damage and debonding of shotcrete in tunnels in cold regions.
Highlights
With the continuous progress of cold regions engineering construction, it is the premise to ensure the stability of the project to ensure that the surrounding rock-lining complex has good bonding performance in cold regions [1, 2]
Because it is located in a high altitude cold regions, the repeated action of freeze-thaw may lead to rock-concrete interface cracks, debonding, fracture, and other problems [3,4,5], resulting in the concrete support not being fully effective. erefore, the systematic study of the damage and debonding of rockconcrete interface induced by freeze-thaw and a full understanding of the internal mechanism of interface debonding have good guiding significance and reference
Qian et al [9] studied the tensile strength and damage mode of composites formed by freeze-thaw cycles of 150 times and using splitting tests on two composites formed by ordinary silicate cement mortars, and the results showed that freeze-thaw cycles damage the material itself, and degrade the weak bond interface
Summary
With the continuous progress of cold regions engineering construction, it is the premise to ensure the stability of the project to ensure that the surrounding rock-lining complex has good bonding performance in cold regions [1, 2]. Cheng et al [22] studied the porous damage of rock under freezethaw, carried out SEM and NMR technology tests on siltstone under different freeze-thaw times, and analyzed the distribution characteristics of the pore structure of siltstone. Erefore, in order to systematically understand the bond deterioration performance of rock-concrete interface in freeze-thaw environment, this paper carried out mesoscopic and microscopic studies on sandstone-concrete interface under different freeze-thaw actions to analyze the pore evolution law of interface; the damage deterioration and debonding evolution characteristics of the interface are clarified, so as to better reveal the freeze-thaw deterioration mechanism of interface.
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