Compressive behavior of metakaolin–fly-ash-based geopolymer fiber-reinforced concrete after exposure to elevated temperatures

Portland cement production is responsible for 7% of the total carbon dioxide emissions around the world. Recently, there has been significant focus on developing environmentally sustainable construction products. Geopolymer concrete (GPC) is a sustainable material, and incorporating fibers can mitigate its brittleness while enhancing its overall performance, providing significant potential for various applications. Nonetheless, fire drastically reduces the structural strength and lifetime of reinforced concrete structures. To address this issue, this study investigates the compressive behavior of metakaolin–fly-ash-based geopolymer fiber-reinforced concrete after exposure to elevated temperatures. The GPC mixtures were made of steel fibers (SFs) and a combination of SF and polyvinyl alcohol (PVA) fibers, which were evaluated at exposure temperatures of 300 and 500°C. This investigation experimentally tests a total of 27 cylinders at 28 days, each with a diameter of 100 mm and a height of 200 mm. The results indicate that exposure of the GPC specimens to 300 and 500°C resulted in reductions of up to 24.2 and 45.2%, respectively. The inclusion of fibers had a slight effect on compressive strength, with the use of SF and hybrid fibers (SF + PVA) resulting in improvements of 8.1 and 7.5%, respectively. The addition of fibers significantly improved the post-peak response of both heated and unheated specimens, increasing the toughness index with ratios of up to 22.5 and 26.3% for the heated and unheated specimens, respectively.