Experimental Investigation of Thermal and Mechanical Properties of Sorghum Stalk Fiber-Reinforced Cement Mortar for Thermal Insulation: Influence of Length, Percentage of Fibers and Water to Cement Ratio

Sustainable building materials development is essential for improving energy efficiency, addressing environmental concerns and optimizing resources use. This study investigates the development and characterization of sorghum stalk fiber-reinforced cement mortar bio-composite for thermal insulation application. Sorghum stalk fiber was added to cement mortar at varying fiber contents (0%, 15%, 30% and 45%), fiber lengths (0.5 cm and 1.5 cm) and varying water–cement ratios (0.4 and 0.6). The composites were characterized for thermal conductivity, thermal diffusivity, density, and compressive and flexural strengths, as well as water absorption and drying kinetics. The result showed that the addition of fiber led to significantly improved thermal insulation performance, accompanied by decreased mechanical strength. The thermal conductivity decreased from 1.57 W/m·K for the control mortar to 0.18 W/m·K (about 88.5% reduction) for 0.5 cm fiber and 0.16 W/m·K (about 89.8% reduction) for 1.5 cm at 45% of fiber. The composite with 15% fiber provided the best balance between thermal and mechanical performance suitable for low load-bearing application, particularly thermal conductivity of 0.90 W/m·K (43% lower) and compressive strength of 10.56 MPa that exceeds the minimum standard to be used in low load-bearing applications; the 30% and 45% fiber composites are suitable for non-structural and thermal insulation applications only. The results obtained demonstrate that the sorghum stalk fiber-reinforced cement mortar is a lightweight, ecological and insulative bio-composite with strong applicability in energy-efficient buildings.