Sodium-based, geopolymer foamed composites reinforced with phosphate mine waste particulates and hemp/basalt fibers

This study investigated the mechanical, microstructural, and thermal properties of Na-based geopolymer foams (GPFs) reinforced with varying amounts of two types of reinforcements: raw phosphate mine waste rock (PMWR) as a particulate filler, and natural (hemp) or synthetic (basalt) fibers. The phase composition and microstructural changes of PMWR-reinforced geopolymer have been examined using XRD, TGA/DTG/DSC and SEM/EDS techniques, to assess any possible interaction of these wastes with the alkaline system. Further investigation into the effects of PMWR, alone and in combination with fibers, on the pore structure and morphology of GPFs was conducted and correlated with mechanical strength and thermal properties. The reinforcement mechanisms provided by the PMWR particulates and each fiber type are discussed, along with the synergistic effects of their combined incorporation. Improved flexural properties were identified in composites with higher particulate content (15 wt%) and fiber content (5 wt%), with 3-point flexural strengths ranging from 5 to 13.5 MPa. The effect of fillers on pore structure was most evident at higher loading rates, leading to significant changes in pore size, shape, and connectivity of the GPF matrix, thereby impacting its thermal insulation capacity. The dual reinforcement of geopolymer foams with PMWR particulates and fibers offers a promising approach to enhance the material performance while using low-cost and readily available resources. This approach also presents a sustainable and ecofriendly strategy for repurposing raw PMWRs, supporting circular economy practices.