The Influence of Sisal and Flax Fibers on the Mechanical Properties, Water Absorption, and Microstructure of Geopolymer Composites

The paradigm of sustainable development, coupled with contemporary inclinations towards green construction, exerts a considerable effect on the evolution of environmentally benign building composites. The main aim of this study is to create geopolymer composites with improved physical and mechanical properties. An examination of the properties of a geopolymer composite (GS), using ground granulated blast furnace slag (GGBFS) and plant fibers, is presented in this paper. Sisal (SF) and flax (FF) fibers, along with their combination (SF + FF), were integrated into the slag at concentrations of 0%, 0.5%, 1.0%, 1.5%, and 2% by weight. Before use, plant fibers were treated with a 5% NaOH solution. The geopolymer composites (GC) underwent evaluation for their density, compressive and flexural strengths, and water absorption characteristics. Scanning electron microscopy was employed to examine the fracture characteristics of the GC. The compressive and flexural strengths of GC were improved by including 1% SF, FF, and their combination, 0.5% SF + 0.5% FF. Compressive strength increases were 11.5%, 8.6%, and 14.5%, while flexural strength increases were 17.4%, 13%, and 19.6%, respectively. Water absorption of GC with 1% SF, FF, and SF + FF decreased by 14.6%, 10.8%, and 20.4%, respectively. The apparent synergistic performance of hybrid sisal-flax reinforcement at a total fiber content of 1% was revealed. GCs at the fracture have a homogeneous rough structure with microcracks and accumulations of geopolymer reaction products. The matrix-plant fiber interface in GC is identified by a rounded region with elongated fibers, indicating the fiber’s performance under mechanical stress. The findings of this investigation suggest the feasibility of utilizing plant fibers in environmentally sound geopolymer construction composites.