Investigative Study and Comparative Factorial Analysis of Natural Sisal Fiber-Reinforced Cementitious and Geopolymer Composites for Sustainable Construction

This study investigates the mechanical and microstructural behavior of sisal fiber-reinforced cementitious and geopolymer mortars using a Design of Experiments (DoE) approach. The objective is to evaluate the combined influence of fiber content and matrix type on mechanical performance and microstructural characterization. The results show that incorporating 4 wt.% sisal fibers affects the mechanical and microstructural properties of the investigated mortar systems. Although fiber incorporation reduces the compressive strength of cement-based mortars, reaching 28 MPa after 28 days, geopolymer composites achieve higher compressive strength (35 MPa) together with a marked improvement in flexural strength, reaching 16 MPa. This enhancement is attributed to efficient crack-bridging mechanisms and greater energy dissipation under loading. Microstructural characterization by scanning electron microscopy and porosity analysis indicates that the addition of fibers primarily modifies the fiber–matrix interface and increases porosity, while the overall matrix structure remains largely unaffected. The findings further suggest that appropriate fiber treatment mitigates interfacial degradation in alkaline environments. Overall, controlling fiber incorporation and matrix formulation is essential for balancing strength and ductility, highlighting the potential of sisal fiber-reinforced geopolymer composites as sustainable alternatives to conventional cement-based materials.