Effect of heat treatment on physico-mechanical behaviour of a natural building stone: Laizhou dolomite marble
Yuan Zhang, Xupeng Ta, Shubing Qin
Abstract
To improve our understanding of the physical and mechanical behaviours of building stones after fire, effect of heat treatment on the physico-mechanical behaviour of Laizhou dolomite marbles was investigated under unconfined compressive conditions. Cylindrical samples prepared from the marble were pre-heated to different elevated temperatures of 105 °C, 200 °C, 400 °C, 500 °C, 600 °C, 700 °C and 800 °C, and then cooled down to room temperature. Uniaxial compression, ultrasonic testing and scanning electron microscopy were conducted to measure the mechanical properties, P-wave velocities, and microstructures of these samples thermally treated. Mercury intrusion test and X-ray diffraction analysis were conducted to measure the porosity structure and the mineralogical composition. Results show that Laizhou dolomite marble degrades in strength and stiffness after heat treatment, and the degradation increases with heating temperature rising. After heating, the mass loss and density have no significant changes before 600 °C, but the mass loss increases quickly after 600 °C. Simultaneously, the density decreases significantly. Simultaneous reduction of P-wave velocity happens as heat treatment temperature rises, which illustrates that heating generates microcracks resulting in the strength and stiffness degradation. During the degradation, thermal cracking damage and decomposition of the dolomite are the key factors. Thermal cracking starts about 150–200 °C, and thermal decomposition happens about 600 °C. Above 600 °C, thermal decomposition of the dolomite leads to the significant degradation.