Compressive properties of sustainable geopolymers at elevated temperatures: Strength and elastic modulus evolution

Abstract

Geopolymers, characterised as customisable, environmentally friendly, and thermally robust materials, have yet to receive comprehensive studies on compressive properties in their high-temperature states. In this study, a sodium silicate-activated binary geopolymer with strength and elastic modulus increased in thermal environments above 100 ℃ was developed. Investigation of stress-strain relations, compressive strengths, strains at the compressive strengths, and elastic moduli was performed across temperatures ranging from 100 ℃ to 1000 ℃. The optimal geopolymer product showed substantial strength and elastic modulus enhancements at temperatures below 500 ℃, with elastic modulus decline above 500 ℃, indicating material deterioration. Thermal behaviour investigations and microstructure experiments were conducted to elucidate this mechanism. A positive correlation between hot-state density and mechanical properties was established. The geopolymers showed thermal shrinkage properties, aiding structure compaction with less density loss, which is advantageous for their mechanical properties below 500 ℃. Heightened chemical changes at 500–1000 ℃ led to pronounced property shifts, with product decomposition and ions diffusion causing more deterioration at 500–700 ℃. Initial crystal formation at 800 ℃ played a favourable role in the partial property recovery of the geopolymers. This study broadens the application scope of industrially derived geopolymers, fostering the creation of safer materials for structures vulnerable to heat exposure.