Experimental Study on the Deterioration of Grotto Sandstone under Cooling and Heating Cycles

Grotto temples are important historical relics, and their protection and utilization are becoming increasingly important. However, under the effect of cooling and heating for a long time, the physical and mechanical properties of the grotto rock mass will change in a certain. In this paper, the sandstone of Dazu grottoes in Chongqing was taken as the research object, and the deterioration properties of the grotto sandstone were studied through the mass, longitudinal wave velocity test, CT scanning, X-ray diffraction (XRD), X-ray fluorescence (XRF) analysis. The experimental process involves multiple conditions such as different heating-cooling cycle times, different durations of high and low temperatures, and different cooling methods. These test conditions are designed to analyze the effects of different temperature changes on the quality, longitudinal wave velocity, fracture development, mineral element composition, and internal pores of grotto sandstone. The results show that: (1) The longitudinal wave velocity of sandstone decreased after multiple heating-cooling cycles. The degree of reduction was influenced by the number cycles and the cooling methods. (2) As water cooling method was used during the experiment, soluble salt minerals in sandstone would gradually lose, which leaded to an increase in pore size of the rock sample and the formation of cracks.