Changes in surface roughness of sandstone after heating and cooling cycles

The surface roughness of rock directly affects its strength, deformation, and seepage characteristics. Understanding the change of rock surface roughness under the heating and cooling cycles is of great significance for evaluating the damage degree of rock and effectively predicting the instability of rock mass. In this paper, using grayish yellow sandstone as an example, we study the variation in the surface roughness of sandstone after different heating and cooling cycles by the arithmetical mean deviation of the profile (Ra) and the fractal dimension (D). The results show that the surface roughness of sandstone increases with the increase of temperature and cycles after heating and cooling; at above 500 °C, the thermal damage increased significantly due to the expansion and cracking of quartz particles, and the cycle causes the damage to accumulate, which further weakens the adhesion between particles, resulting in a significant increase in Ra and D value after 6 cycles; when the damage accumulates to a certain extent, some minerals fall off from the surface of sandstone, resulting in the decrease of Ra and D value. We also found that there is a correlation between Ra and the D value; that is, Ra increases exponentially with increases in the D value. The research results of this paper are of great significance to the rock mass engineering under the condition of heating and cooling cycles and can be used to monitor the stability of rock mass.