Influence of Hybrid Glass Fiber Lengths on High Temperature Resistance of Cementitious Composites

Abstract

Fibers incorporated into cementitious composites significantly enhance crack resistance by limiting crack formation and propagation. Short fibers primarily control the initiation and development of microcracks, whereas long fibers contribute more effectively to the bridging of macrocracks. High temperature exposure induces severe damage in cementitious materials, leading to significant microstructural degradation and mechanical property losses. Although the effects of hybrid fiber combinations on composite performance have been extensively studied, their efficiency in mitigating high temperature damage remains an area requiring further investigation. This study investigates the effect of hybrid length glass fibers on the residual performance of mortars exposed to elevated temperatures. Identical fibers of varying lengths (3 mm, 6 mm, and 12 mm) were incorporated to enhance composite design with practical relevance. The specimens were subjected to 400 °C, 600 °C, and 800 °C and evaluated via flexural and compressive strength, mass loss, and ultrasonic pulse velocity (UPV) analyses. Scanning electron microscopy (SEM) was employed to characterize microstructural changes. The results demonstrated that hybrid fiber reinforcement effectively limited both micro and macrocrack formation across all temperature levels, thereby improving the residual mechanical properties of the composite specimens. SEM analysis confirmed that glass fibers exhibited high thermal stability, and the synergistic interaction between fibers of different lengths strengthened the hybrid reinforcement mechanism. Hybrid fibers reduced mass loss and increased UPV values. It was clearly demonstrated that hybrid fibers were quite effective in the durability of cementitious composites.; Short fibers prevent microcracks, while long fibers bridge larger cracks effectively. Hybrid fiber composites outperform single-length fibers in temperature resistance. Glass fibers maintain their integrity, enhancing concrete durability at temperatures. © The Author(s), under exclusive licence to Shiraz University 2025.; © The Author(s), under exclusive licence to Shiraz University 2025.