Development of a ternary high-temperature resistant geopolymer and the deterioration mechanism of its concrete after heat exposure

A geopolymer paste (GP) synthesised using fly ash, slag, and metakaolin was developed to enhance the heat resistance of industrial by-product-based geopolymers. The GP exhibited a 28-day strength of 60 MPa and maintained at least 80 % of its initial strength and elastic modulus even at temperatures up to 900°C. Subsequently, the GP was blended with aggregates (sands and stones) to produce geopolymer concrete (GPC) with a 28-day strength of 45 MPa. Compressive tests on the GPC after exposure to 100–1000°C revealed that the GPC retained 90 % of its compressive strength up to 500°C, but experienced a 60 % loss in elastic modulus and a fourfold increase in peak strain after 300°C exposure. Stress-strain relation, physical properties, and microstructure were analysed to explore the property evolution mechanisms after heat exposure. The combined effect of geopolymer shrinkage (100–780°C), stone expansion (> 200°C), and stone decomposition (> 500°C) was the primary factor for the GPC property decline. At 800°C, a complete loss of mechanical properties in both the stone and interface transition zones led to significant deterioration of the GPC. These findings offer valuable insights for developing durable construction materials suitable for high-temperature applications, ensuring structural integrity and performance under extreme thermal conditions.