Thermal behavior and post-heating fracture characteristics of polypropylene microfiber-reinforced geopolymer binders

Abstract

This paper investigated the post-heating behavior of fly ash-based geopolymer binders reinforced with polypropylene (PP) microfibers. Geopolymer binders with different fiber contents including 0%, 0.05%, 0.1%, and 0.2% by fly ash weight were prepared and exposed to elevated temperatures of 200 °C, 400 °C, and 600 °C. The effect of fiber reinforcement on the mechanical strengths of unheated binders, residual fracture characteristics of heat-damaged binders, microstructure deterioration, and thermal properties of geopolymer specimens were investigated. The results revealed that PP microfibers had neglected effect on the compressive strength of the binders, but clearly enhanced their flexural strength. Maximum enhancement of 17% was observed in the flexural strength of binders with 0.05% PP fibers. Using PP microfibers enhanced the residual compressive but not the flexural strength of the heat-damaged binders. The fiber-reinforced specimens had higher residual compressive strength compared to the corresponding fibreless ones when heated up to 500 °C. The modulus of elasticity and the toughness of the binders decreased with heating. Fiber-reinforced specimens showed higher reduction in the toughness but lower reduction in the modulus due to heating compared to the fibreless specimens. Using PP microfibers reduced the thermal conductivity of geopolymer binders. The reduction due to the fiber addition was less pronounced for heated specimens compared to unheated ones.