Comprehensive evaluation of impact strength and microstructural characteristics of geopolymer concrete reinforced with four types of natural fibers of varying lengths.

This study systematically studied the impact strength of Geopolymer concrete (GC) integrating fly ash, slag, and silica fume, reinforced with four natural fibers including sisal, jute, coir, and flax at varying aspect ratios. The primary objectives are to analyze the influence of fiber length on initial cracking number (J1), failure number (J2), crack-bridging mechanisms, and failure modes under impact loading. This study presents a unique contribution by thoroughly examining the impact of fiber aspect ratio in multi-binder GC, offering critical insights into optimizing fibrous GC for improved structural performance and resilience. The impact performance of GC was influenced by both fiber type and length. Coir fibers enhanced J1 by up to 66% and J2 by 171.43%, with optimal energy absorption at 60 mm. Flax and jute fibers showed peak performance at 40 mm, with J2 improvements of 75.82% and 100%, respectively, while longer lengths led to dispersion issues and diminished gains. Sisal fiber at 40 mm offered balanced enhancement (J1: 50%, J2: 117.58%), whereas the highest J2 (135.16%) was achieved with 60 mm, accompanied by a moderate drop in J1, indicating that excessive fiber lengths may hinder bonding efficiency.