Impact of various pore fluids on the mode I fracture toughness of a granite rock

Abstract

[Abstract] The mode I fracture toughness (K IC) of granite samples in deionized water (DIW), hydrochloric acid (HCl), sodium hydroxide (NaOH) and cyclic fluid environments was investigated by pseudo-compact tension (pCT) tests. Specimens were immersed in each fluid for 8 days, with one group subjected to three 8-day cycles (NaOH first, then HCl, and finally DIW). Results show that all fluids reduce the K IC compared to dry samples, most significantly in DIW, due to the smaller kinetic diameter of water molecules that enhances the hydrolysis of siloxane bonds. The cyclic fluid environment shows a higher K IC than DIW alone, possibly due to silica precipitation induced by the pH shift from alkaline to acidic conditions, which may slightly increase strength and reduce the accessibility of hydrolyzing species to the crack tip. For all fluids, about 40% of the mechanical energy is consumed by crack initiation and 60% by propagation.