Sustainable and Pseudo-Strain-Hardening Metakaolin and Fly Ash-Based Fiber-Reinforced Geopolymer Composites Activated with Potassium: Development and Carbon Footprint Analysis

The present research investigated the mechanical and physical properties of ambient-cured potassium-activated metakaolin and fly ash (MKFA)-based geopolymer (GP) mortars and composites with varying binder composition, water content, fiber type, and the effect of polyvinyl alcohol (PVA) fiber replacement with polypropylene (PP) or ultrahigh molecular weight [polyethylene (PE)] fiber. Specifically, the compressive strength, density, tensile properties, and global warming potential for the geopolymer materials were investigated. It was found that the geopolymer mortar, comprising an equal mix of 50 wt.% metakaolin and 50 wt.% fly ash, demonstrated a flow spread diameter of 180.38 mm and a compressive strength of 10.81 MPa. Compressive strength and uniaxial tensile tests were conducted to characterize the properties of the developed geopolymer composites, which included 4% by weight silica fume. Generally, replacing PVA fibers with PP or PE fibers resulted in reduced compressive strength, except for the composite containing 1.5% by volume PVA and 0.25% by volume PP fibers. While many composites exhibited pseudo-strain-hardening behavior, the highest tensile strain capacity of 0.54% was achieved by the composite with 1% by volume PVA and 0.75% by volume PP, classifying these composites as pseudo-strain-hardening fiber-reinforced geopolymer composites. Additionally, a life-cycle assessment (LCA) was conducted to evaluate the environmental impact of these geopolymer composites. The carbon footprint of the engineered geopolymer composite (EGC) design mixes was lower than the engineered cementitious composite (ECC) baseline, ranging from 805.71 to 1,277.83 kg CO2-Eq/m3 EGC. The highest contributor to the carbon footprint of geopolymer composites was the production of potassium hydroxide, which can be reduced to improve the environmental performance of geopolymer composites.