Mechanical and Thermal Insulation Properties of rGFRP Fiber-Reinforced Lightweight Fly-Ash-Slag-Based Geopolymer Mortar

As a lightweight cementitious material for thermal insulation, the mechanical performance of foamed geopolymer is always compromised by its density reduction. In this study, recycled-glass-fiber-reinforced plastic (rGFRP) fiber was used to reinforce the fly ash-slag based foamed geopolymer, and vitrified micro bubbles (VMB) were applied to further decrease the thermal conductivity and modify the resistance of the lightweight mortar against drying shrinkage. The results revealed that the density, compressive strength, and thermal conductivity of the foamed geopolymer with/without VMB decreased with the increase in foaming agent content. By adding 2~6% of rGFRP fiber, the compressive strength was increased by 25~165%, and the drying shrinkage was reduced the most, by 55%. After the addition of 10% of VMB, the density, thermal conductivity, and drying shrinkage of foamed geopolymer mortar were further decreased, with the highest reductions of 8%, 26%, and 64%, respectively, due to the reduced pore volume and increase proportion of closed pores. With 6% of rGFRP fiber and 25% of foaming agent, the lightweight geopolymer mortar had the optimum performance, with compressive strength of 1.343 MPa, thermal conductivity of 0.134 W/(m·K), and drying shrinkage of 0.095%. This study developed a sustainable lightweight mortar with multiple types of industrial by-products, which benefit both the development of thermal insulation materials and reuse of solid wastes.