Influence of Wood Fiber on Mechanical and Thermal Insulation Properties of Lightweight Mortar

To advance the development of green building materials and achieve high-value utilization of waste resources, this study investigates the mechanistic influence of incorporating waste wood fibers on the mechanical and thermal insulation properties of lightweight mortar. Five fiber contents were designed—0%, 0.4%, 0.8%, 1.2%, and 1.6%—to systematically evaluate their effects on compressive strength, flexural strength, and tensile bond strength, as well as thermal conductivity, pore structure, and microstructural interfaces. The results demonstrate that at low fiber dosages (particularly 0.4% and 0.8%), wood fibers can significantly enhance both the mechanical strength and thermal insulation performance of mortar. Specifically, at a fiber content of 0.8%, the 28-day compressive strength increased by 10.62%, and the flexural strength by 23.8%; the tensile bond strength reached its peak at 0.4%, with a 14.8% improvement. The lowest thermal conductivity recorded was 0.16 W/(m·K), accompanied by a remarkable 61.9% reduction in porosity compared to the control group. Low-field nuclear magnetic resonance (LF-NMR) analysis revealed that wood fiber incorporation markedly increased the proportion of capillary pores, reduced total porosity, and enhanced mortar compactness; scanning electron microscopy (SEM) observations further indicated that the honeycomb-like morphology and surface roughness of wood fibers substantially improved interfacial bonding performance and microcrack-bridging capacity. The findings suggest that an optimal fiber content—recommended to not exceed 0.8%—can synergistically improve the mechanical and thermal insulation properties of lightweight mortar, providing both theoretical support and practical guidance for its application in green building wall materials.