Fiber–Matrix Interface Engineering in Cementitious Composites: Surface Modification, Durability and Emerging Trends

Fiber-reinforced cementitious composites have become increasingly important in the development of durable and sustainable construction materials, particularly following the replacement of asbestos-based reinforcements. However, the long-term performance of these composites is strongly influenced by the characteristics of the fiber–matrix interface, where moisture transport, interfacial degradation, and stress transfer mechanisms govern durability and mechanical behavior. Consequently, considerable efforts have been devoted to developing surface engineering strategies capable of improving fiber–matrix compatibility and enhancing composite performance. This review examines recent advances in surface modification and interfacial engineering approaches applied to fiber-reinforced cementitious composites. The discussion covers fiber–matrix bonding mechanisms and the main modification strategies, including alkali treatments, hornification, silane coupling agents, polymeric and hydrophobic coatings, nanomaterial-assisted modifications, and carbonation-induced surface engineering. The effects of these approaches on interfacial properties, durability, dimensional stability, and mechanical performance are critically assessed. The literature indicates that treatments combining surface chemistry modification, moisture control, and mineral-based densification provide more consistent improvements in durability than single-mechanism approaches. Future developments are expected to focus on scalable treatment methods, low-carbon cementitious systems, and advanced materials design strategies, enabling the development of next-generation fiber cement composites with enhanced durability, sustainability, and long-term performance.