Evaluating the Influence of Alfa Fiber Morphology on the Thermo-Mechanical Performance of Plaster-Based Composites and Exploring the Cost–Environmental Effects of Fiber Content

The construction industry’s escalating energy demands and greenhouse gas emissions underscore the need for sustainable, high-performance building materials. This study investigates the incorporation of locally sourced alfa fibers (AFs) into plaster-based composites to enhance thermal insulation, reduce environmental impact, and lower production costs. Three distinct AF morphologies—small (<5 mm), medium (10 ± 5 mm), and large (20 ± 5 mm)—were incorporated at fixed mass ratios, and their effects on key material properties were systematically evaluated. The results indicate that integrating AFs into plaster reduces composite density by up to 16.5%, improves thermal characteristics—lowering thermal conductivity and diffusivity by up to 52%—and diminishes both CO2 emissions and production costs. The addition of fibers also enhances flexural strength (up to 40%) through a fiber bridging mechanism that mitigates crack propagation, although a general decline in compressive strength was observed. Notably, composites containing medium and large fibers achieved significantly lower densities (~1050 kg/m3) and superior thermal insulation (~0.25 W/mK) compared with those with small fibers, with the largest fibers delivering the greatest thermal performance at the expense of compressive strength. Overall, these findings highlight the potential of AF–plaster composites as environmentally responsible, high-performance building materials, while emphasizing the need to carefully balance mechanical trade-offs for structural applications.