Study on the Properties and Mechanism of Recycled Glass Fiber–Cementitious Materials Modified with a Silane Coupling Agent

To address the strength degradation of recycled waste glass fiber–reinforced plastics (RGFRP) caused by poor alkali resistance during recycling, this study proposed the surface modification strategy using a silane coupling agent to enable high-value reuse. Four silane coupling agents (KH550, KH560, KH570, and KH792) were used to optimize the interface of glass fiber (GF), successfully constructing a hydrophobic and roughening comodified layer. Experiments results demonstrate that this modification strategy significantly enhanced the interfacial bonding efficiency between fibers and the cement matrix: Specifically, the workability of cement mortar was improved by introducing organic functional groups, while the formation of a rough surface increased fiber pull-out energy and enhanced the mechanical properties of hardened cement mortar (with the maximum expansion degree increased by up to 226.5 mm). The RGF reinforced cementing material modified by KH550 exhibited the best overall performance, with a 28-day flexural strength of 10.79 MPa (a 66.77% increase)and compressive strength of 46.42 MPa (a 12.23% increase)compared to unmodified counterparts. This study revealed the mechanism by which surface engineering regulates the processing-structure-performance in recycled fiber-reinforced composites, providing a critical scientific foundation for establishment large-scale, high-value utilization technologies for RGFRP.