Effect of cyclic heating and LN₂-cooling on the physical and mechanical properties of rocks

In this paper, we mainly aim to investigate the effect of cyclic heating and cooling with liquid nitrogen (LN₂) on rock deterioration, which is a crucial concern in the engineering application of cyclic cryogenic fracturing. P-wave velocity test and uniaxial compressive test were conducted on the marble samples subjected to heating and LN₂-cooling cycles. In each cycle, rocks were first slowly heated to target temperatures, kept for 4 hours then submersed in LN₂for 0.5 hour. The results indicate that P-wave velocity, uniaxial compressive strength (UCS) and Young’s modulus reduce with increasing cycles, while axial failure strain shows an increasing trend. Significant changes in physical and mechanical properties only occur in the initial several cycles, and changing rate drops sharply as cycles increase. By comparing results in 200 C group and results in 400 C group, we found that increasing heating temperature helps intensify the cooling induced damage and improve corresponding property changes. SEM results indicate that the inter-granular cracking is the primary failure mode during heating and cooling cycles. Based on a deterioration model, we calculated the decay constant and half-life value, which can provide some guidance to the engineering applications of cyclic heating and LN₂-cooling.