Abstract:

After sandstone is subjected to high temperature, the macro and micro properties will change to different degrees. 400 ℃ and 1 000 ℃ are two important nodes in the change of the macro and meso properties of sandstone. In order to further study the influence of heating rate on the physical properties, mechanical properties and internal meso-fracture of sandstone, the uniaxial compression experiment of sandstone under different heating rates was carried out with 350 ℃ and 950 ℃. The whole process of uniaxial compression was monitored by acoustic emission, and scanning electron microscope was used to analyze the meso-morphology of destructed sandstone. After treated at different heating rates, 350 ℃ sandstone has little change in the mass, volume, density and longitudinal wave velocity, while 950 ℃ sandstone decreased significantly in the mass, density and longitudinal wave velocity, and increased remarkably in the volume, and the higher heating rate, the smaller change rate. The stress-strain curve, stress-volume strain curve, compressive strength and elastic modulus of the 350 ℃ sandstone are virtually unaffected due to the heating rate. The stress-strain curve of the sandstone sample at 950 ℃ is upwardly biased with the increase of the heating rate, the compressive strength and elastic modulus first increase and then reach a constant value; the cumulative ring-down counts of acoustic emission of sandstone at 350 ℃ and 950 ℃ have a tendency to decrease with the increase of heating rate. When the temperature is 950 ℃ and the heating rate is 1 ℃/min, the cumulative ring-down counts of sandstone and the sudden acoustic emission area are the largest; scanning electron microscopy analysis of sandstones with different heating rates showed that heating rate has little effect on the mesoscopic morphology of 350 ℃ sandstone; with the decrease of the heating rate, the number of microcracks and micropores of 950 ℃ sandstone will  increase, the volume size of microcracks and micropores will also increase.

Key words: high temperature sandstone, heating rate, mechanical properties, acoustic emission, meso-analysis