Experimental study on the effects of hydrochemistry and periodic changes in temperature and humidity on sandstone weathering in the Longshan Grottoes

Abstract

Changes in precipitation, temperature and humidity can lead to the weathering of rock masses in grottoes; these changes are common in sandstone grottoes. To simulate this cyclic process, different salt solutions were designed according to the main precipitated components. Sandstone specimens taken from Longshan Grottoes were soaked in these solutions for 48 h and then placed in a simulated environment with temperature and humidity changes for 5 cycles (50 h) to study the effects of hydrochemical, temperature and humidity changes on the sandstone. Physical indexes, such as mass, wave velocity, surface hardness and tensile strength, of the rock samples were measured every three cycles, and the damage characteristics and mechanisms of the sandstone were discussed based on SEM and XRD test results. The results showed that the macroindicators and microstructures of the samples gradually decreased with increasing number of cycles. The physical indexes of the rock samples in different solutions changed at different rates, the changes in surface hardness and tensile strength were consistent, and the responses were less sensitive to deterioration than to longitudinal wave velocity. In different solutions, the microstructures and mineral compositions of the samples showed different trends with increasing number of cycles. This damage was caused by a combination of various actions, such as feldspar dissolution, chemical erosion, water scouring, clay mineral expansion and disintegration, and salt crystallization, which increased the number of pores, enlarged the holes and expanded the cracks inside the rock samples.