Multiscale Reinforcement Strategies in Geopolymers: From Fiber and Nanomaterial Modification to Synergistic Enhancement

ABSTRACT Geopolymers are promising low‐carbon alternatives to Portland cement; however, their inherent brittleness, shrinkage, limited toughness, and workability constraints hinder their broader structural application. Based on a structured Web of Science literature search and keyword co‐occurrence analysis, this review critically examines multiscale reinforcement strategies for geopolymer composites using fibers, nanomaterials, and fiber–nanomaterial hybrid systems. The effects of steel, inorganic, synthetic, natural, and hybrid fibers on fresh‐state behavior, mechanical properties, durability, high‐temperature resistance, and interfacial performance are systematically evaluated. The contributions of nanomaterials, including nano‐SiO 2 , nano‐Al 2 O 3 , and nano‐TiO 2 , to geopolymerization kinetics, pore refinement, matrix densification, and interfacial enhancement are also discussed. Particular attention is given to the synergistic mechanisms of fiber–nanomaterial hybrid systems, including crack bridging and deflection, load transfer across multiple length scales, interfacial modification, and hierarchical microstructural densification. Despite considerable progress, several challenges remain, including nanoparticle agglomeration and fiber dispersion, high material costs, uncertain long‐term durability, insufficient quantitative understanding of cross‐scale interactions, and the lack of standardized evaluation methods. Future research should focus on mechanism‐based material design, interfacial control, long‐term performance validation, and standardized characterization protocols to facilitate the development of high‐performance, durable, and sustainable geopolymer composites.