Macro-micro mechanical properties of building sandstone under different thermal damage conditions and thermal stability evaluation using acoustic emission technology

Abstract Changes in the internal structure and mechanical stability of building sandstone under fire and high-temperature have been the focus of many studies. We aimed to study the macro and micro mechanical properties of building sandstone under different thermal damage conditions and evaluate its thermal stability. Consequently, in this work, changes in mechanical properties of sandstone are evaluated after subjecting the material to heat treatment at different temperatures. Besides, the causes of mechanical deterioration of sandstone after high-temperature treatment are analyzed and the damage evolution of sandstone is characterized by acoustic emission (AE) technology. Following the high-temperature treatment, the macro and micro properties of building sandstone show an obvious change, and the wave velocity decreases as a cubic polynomial. The peak stress of sandstone under load decreases gradually after the action of temperature, and the impact of temperature change on the internal composition of sandstone, especially the decrease of SiO2 content and the increase of porosity, is mainly responsible for mechanical degradation. The AE characteristics of sandstone under unconstrained heating, uniaxial loading at room temperature, and heating loading conditions were tested. The accumulative ring ratio of AE increased linearly with the increase of temperature or deformation, and the correlation coefficient was higher. The correlation coefficient under temperature and loading was more than 0.94. The magnitude of thermal stress in sandstone during the heating process was analyzed theoretically, and static damage factor and dynamic damage factor were calculated quantitatively with wave velocity and AE as characteristic parameters. A compound damage factor is proposed, that is, composite damage includes both thermal damage and loading damage. Our results are of great significance to the stability evaluation of building sandstone subjected to fire and high temperatures.