Effects of Aqueous and Acid Erosions on the Cracking Behavior of Sandstone Captured by High-Speed Camera During Semi-circular Bend (SCB) Tests

An experimental work is presented that aims to improve our understanding of water–rock reaction, under both neutral and acidic conditions, and its effects on the mechanical deterioration of sandstone in Chongqing, southwest China, where a lot of heritage rock statues are carved in the same strata. SCB tests were conducted to evaluate the weakening of fracture toughness of Chongqing sandstone after water and acid erosions, and a high-speed camera was employed to capture its cracking behaviors under different hydrochemical conditions. Microstructural observation was also carried out to investigate the cracking path at a micro-scale, and the chemical analyses of sandstone soaking water in a duration of up to 120 days allows to reveal the evolving process of water–rock reaction. The results show that compared to acid solutions of pH = 3 and 5, the strength weakening effect of distilled water on Chongqing sandstone is more severe. Crack propagation rates captured by the high-speed camera vary between 20 and 60 mm/s in the SCB tests. There is no significant difference in the data for dry and water-saturated samples, and the same for the samples in the two acid fluids. Yet the crack growth rates of the latter two groups are apparently greater than those of the former two. The chemical reaction between water / acid solutions and Chongqing sandstone is mainly pertinent to the cementation and grain boundaries, which weakens grain contacts and promote crack propagation. This mechanism results in a low K_IC, long crack length, i.e., more tortuosity along grain boundaries, and high crack propagation rate.