Experimental Study on the Dynamic Mechanical Properties and Crashing Behaviors of Limestone Under High Temperatures in Real-Time

In this study, a split Hopkinson pressure bar (SHPB) test system with real-time temperature control was developed, and dynamic tests on limestone taken from deep coal mines within real-time temperatures of 25 to 800 degrees C were carried out. Additionally, the scanning electron microscope (SEM), X-ray diffraction (XRD), and energy dispersion spectrum (EDS) tests were conducted to analyze the fracture mechanism of limestone at real-time temperatures. The results reveal that the dynamic compressive strength of limestone linearly declines with increasing temperatures; due to not being affected by thermal shock damage, its strength degradation is not significant after cooling to room temperature, whereas the dynamic elastic modulus exhibits a negative exponential nonlinear decrease with the increase in temperatures. The average strain rate has a positive correlation with the dynamic compressive strength of limestone, while the dynamic elastic modulus exhibits variations in accordance with the Boltzmann function and its relationship with the strain rate. The combined influence of strain rate and temperature on the dynamic compressive strength of limestone can be accurately described by a binary quadratic function. The mechanism of real-time action on limestone can be divided into three stages: when the temperature is between 25 and 200 degrees C, crystal micro-expansion leads to the densification of micropores, which leads to the increase in limestone strength. When the temperature is between 200 degrees C and 600 degrees C, the formation of microcracks induced by thermal stress and intergranular expansion results in a reduction in limestone strength. When the temperature is between 600 and 800 degrees C, in addition to the continued expansion of the intergranular resulting in the increase in the number of micro-cracks, the decomposition of dolomite at high temperatures leads to chemical deterioration and further reduction in the strength of limestone.