Experimental Study on Physical and Mechanical Properties of Gypsum Rock During High-Temperature Dehydration–Hydration Expansion

In order to study the physical and mechanical properties of gypsum rock samples in three states (natural, high-temperature dehydration and hydration time), natural gypsum rock was put into high-temperature condition of 220°C for dehydration treatment, and then the high-temperature dehydrated gypsum rock was treated with different hydration time, and the gypsum rock samples in three states were subjected to ultrasonic test, density test and uniaxial compression test. The results show that the main components of natural gypsum minerals were gypsum dihydrate (71%), dolomite (27%) and potassium chloride (2%). The hydration of high-temperature dehydration samples was an extremely complex physical and chemical process. Hydration had a significant strengthening effect on gypsum rock, and the weak surface of the structure had a significant weakening effect on it during the hydration process. As hydration time increased, the apparent density increased gradually and the longitudinal wave velocity increased. The peak strength of the sample decreased first and then increased, and it generally had a logarithmic relationship with hydration time. The peak strain decreased first and then increased, then decreased and fluctuated, and the elastic modulus first increased and then decreased and then increased again. The expansion rate and limited expansion force of the sample increased with increase in hydration time. After a certain hydration time, the expansion rate of the sample tended to be stable, while the limited expansion force began to decrease slowly after reaching the maximum value.