Hemp Fiber and Expanded Perlite-Incorporated Lightweight Inorganic Polymer Mortars: Mechanical, Thermal Insulation, High-Temperature Resistance, Microstructural Characteristics, and Life Cycle Assessment

In this study, lightweight geopolymer mortars with low environmental impact, high thermal insulation performance, and strong resistance to elevated temperatures were developed. Fly ash, expanded perlite, and bio-based hemp fibers were employed as the binder, aggregate, and reinforcement, respectively. Hemp fibers were prepared in lengths of 1, 2, and 3 cm and incorporated into the mixtures at dosages of 0.50%, 0.75%, and 1.00% by weight of binder. Sodium hydroxide was used as the activator, and specimens were heat-cured at 90 °C for 24–48–72 h. The workability, unit weight, UPV, flexural, and compressive strength of the geopolymer mortars were determined. In addition, thermal conductivity, high-temperature resistance, microstructural characteristics, and environmental impacts of selected mixtures were evaluated. The results demonstrated that lightweight geopolymer mortars could be successfully produced using expanded perlite aggregate and that hemp fibers significantly enhanced mechanical performance up to 48% at one day. Moreover, fiber reinforcement improved thermal insulation capability by up to 5.5% and high-temperature resistance. FESEM, EDX, elemental mapping, and XRD analyses supported the mechanical and physical findings through detailed microstructural evidence. Furthermore, LCA results revealed that fiber incorporation improved the environmental performance of geopolymer mortars, resulting in approximately a 21% reduction in global warming potential compared with the reference mixture.