Behavior of Metakaolin-Based geopolymer concrete at ambient and elevated temperatures

•Studied behavior of metakaolin-based geopolymer concrete (GPC) at elevated temperatures.•Five GPC mixes with different molar ratios were used. SEM-EDS analysis was performed.•Compressive & tensile strengths, stress–strain, water absorption & weight loss were studied.•Elastic modulus of GPC is affected more by rise in temperature than compressive strength.•Models are proposed for predicting compressive strength and elastic modulus of GPC. Geopolymer or alkali-activated binders are emerging as a potential green sustainable alternative for ordinary Portland cement (OPC). In addition to the environmental benefits of geopolymers, it possesses excellent mechanical properties, including good resistance to elevated temperatures. Although many studies were conducted on the thermal performance of metakaolin-based geopolymer mortar and pastes, the performance of metakaolin-based geopolymer concrete under elevated temperature has been rarely studied. Therefore, the present study investigates the behavior of MK-based geopolymer concrete under ambient and elevated temperatures of 200 °C, 400 °C, and 600 °C. The experimental program of this study comprised five mixes with different formulations to primarily investigate the influence of varying Na2O/Al2O3 and SiO2/Al2O3 molar ratios. The results are discussed in terms of the visual observations for the fresh and hardened specimens, compressive strength development, stress–strain behavior, splitting tensile strength, water absorption, and weight loss percentage due to exposure to elevated temperatures. The residual compressive strength varied from 56% to 63%, 38% to 51% and 28% to 34% after exposure to 200 °C, 400 °C, and 600 °C, respectively. The rate of degradation in the modulus of elasticity with the increase in the exposure temperature is much higher than the compressive strength. Models are proposed for predicting the residual compressive strength and modulus of elasticity of geopolymer concrete after exposure to elevated temperature, which show good correlations with experiments. The SEM-EDS analysis confirms the formation of dense homogeneous geopolymerization gel and corroborate the trends of strength degradation after exposure to elevated temperature.