Experimental study of the effect of high temperature on primary wave velocity and microstructure of limestone

To study the effect of high temperature on the microstructure and velocity of primary wave (P-wave) propagation in rocks, scanning electron microscope (SEM) experiments, mercury injection experiments and P-wave velocity tests were conducted on limestone samples which had been heated at high temperature (from 25 to 900 °C), and then the variations of P-wave velocity and microstructure were analyzed. Consequently, a P-wave velocity-based damage model was established to evaluate the damage level of limestone. The experimental results showed that: (1) the internal defects of limestone started to develop at 300 °C, and the range of 300–600 °C was the main development stage; (2) the porosity increased slowly with the rising of temperature below 200 °C, and rapidly increased above 300 °C; and (3) the P-wave velocity grew a little below 100 °C and decreased tardily in 100–300 °C, and then sharply decreased in 300–600 °C. The P-wave velocity damage model also shows that damage of the samples occurred above 300 °C. This study suggests that 300 °C should be the damage threshold temperature of limestone, and in 300–600 °C, significant damage of limestone would occur.