Influence of FRP rebar polymer matrix leachates on cement hydration and bond performance in FRP-reinforced concrete

Fiber-reinforced polymer (FRP) rebars are increasingly used in construction due to their advantages over conventional steel reinforcement. However, well-established standards and design codes for all FRP types remain limited. While most previous studies have focused on the mechanical bond between FRP rebars and concrete, this study provides a detailed investigation of how organic compounds leached from FRP rebars affect cement hydration kinetics and, consequently, bond performance. Ten different FRP rebars—including glass (GFRP), basalt (BFRP), and carbon (CFRP) types—were examined. Analytical techniques such as total organic carbon (TOC), ICP-MS, and FTIR confirmed the leaching of organic compounds from the rebars. Subsequent experiments using isothermal calorimetry, SEM, and mechanical testing assessed how these leachates influence cement hydration in the vicinity of the rebars. The results indicate that specific organic compounds from the polymer matrix can negatively affect hydration in the transition zone, reducing the quality of the interfacial bond between FRP rebars and the cementitious matrix. These findings highlight the importance of chemical interactions at the FRP–concrete interface and suggest that both improvements to the rebar surface and modifications to the concrete mixture should be considered. Given the variability among different FRP rebars, a single universal design guideline may not be sufficient for all products.