Spalling behavior of metakaolin-fly ash based geopolymer concrete under elevated temperature exposure

Fire-induced spalling is a serious risk to concrete structures, especially for high strength concrete structures. This paper presents results from high temperature spalling tests on geopolymer concrete. The effect of moisture content, concrete strength, heating rate and temperature level on the spalling behavior of geopolymer concrete is studied. The temperature-induced spalling mechanism in geopolymer concrete is investigated through the measurement of residual compressive and splitting tensile strength, variation in permeability (by sorptivity test) and chemical composition (by X-ray diffraction test) of geopolymer concrete after elevated temperature exposure up to 700 °C. The test results indicate that geopolymer concrete exhibit a good spalling resistance as compared to that of OPC concrete. The lower spalling risk in geopolymer concrete under high temperature exposure is facilitated from the highly connected pore structures and lower strength degradation with temperatures. Further results indicate that the pore structure (permeability) of geopolymer concrete gets a significant evolution with the exposure temperature, especially above 500 °C range. This is related to the sintering reaction in geopolymer binders at high temperatures.