Comparison of compressive, flexural, and temperature-induced ductility behaviours of steel-PVA hybrid fibre reinforced OPC and geopolymer concretes after high temperatures exposure

•Mechanical properties of GPC and OPCC after high temperature exposure are compared.•Plain OPCC and GPC showed less brittle failure after 500 ℃ and 800 ℃ exposure.•Concrete exhibits strength reduction and ductility increase after 500 ℃ and 800 ℃.•Temperature-induced ductility behaviour is caused by components decomposition. This paper presents a comparison of the performances of geopolymer concrete (GPC) and ordinary Portland cement concrete (OPCC) with and without fibres after exposure to 200, 500, and 800 ˚C. The influences of elevated temperatures on the concretes were investigated by the cracking patterns, residual compressive strength, flexural toughness, failure modes, ductility, and thermogravimetric analysis. The results indicate that steel-PVA hybrid fibre is effective to improve the initial flexural strength, flexural toughness, and equivalent flexural strength ratio of GPC and OPCC. Exposure to temperatures at 500 ˚C and above caused distinct deterioration in mechanical properties of the concrete specimens. Additionally, temperature-induced ductility behaviour, which is quantitatively characterised by equivalent flexural strength ratio and normalized absorbed energy (NAE), is observed in concrete specimens after exposure to 500 and 800˚C. The temperature-induced ductility behaviour having an obvious characteristic of ultimate flexural strength reduction and ductility increase, which is influenced by decomposition of the components at elevated temperatures. The decomposition of calcium compound is the primary factor for the higher mass loss values for OPC than the geopolymer specimens.