Abstract: This research investigated the relationship between temperature (25?900 °C) and the microstructure and mechanical properties of sandstone through the application of nuclear magnetic resonance, electron microscopy, X-ray diffraction and uniaxial compression techniques. The result firstly suggested temperature has a significant impact on sandstone microstructure because an increase in temperature can improve the total porosity. This phenomenon is especially obvious when temperature is higher than 600 °C, in which the high temperature quickly increases the number of medium and large sized pores, which in turn lead to a significant permeability increase. Meanwhile, a temperature rise may also lead to a decrease in elastic modulus, an increase in peak strain and an elongation in pore compaction stage, these can be reflected by a decrease in brittleness and an obvious enhancement in plasticity. In addition, the mechanical strength of sandstone under heat condition may also be impacted by mineral composition. Such impact was not significant when temperature was below 450 °C. That is because low temperature has minor impact on mineral composition, in this way, the rock strength was mainly influenced by porosity. But when temperature raised to 450?600 °C, the dehydration of kaolinite and the formation of new phase minerals increased the rock strength dramatically, this offset the effects of porosity increase, therefore increased the strength of sandstone. However, when temperature exceeds 600 °C, the rock strength decreases again because of a rapid increase in large sized pores.

Key words: sandstone, thermal treatment, microstructure, mechanical properties