Long-Term Durability of UHPECC-Embedded GFRP Bars in Alkaline Environments

Abstract

Novel fiber-reinforced polymer (FRP) bar-reinforced ultrahigh-performance engineered cementitious composites (UHPECCs) have been proposed recently. This innovative composite structure aims to address two critical challenges: (1) the reduced stiffness in FRP-reinforced normal concrete stemming from the lower elastic modulus of FRP; and (2) corrosion concerns faced by steel-reinforced concrete structures. Despite various investigations into the long-term performance of glass fiber–reinforced polymer (GFRP) bars in concrete environments, typically conducted through immersion in simulated concrete pore solutions, the durability of GFRP bars within UHPECCs remains unexplored. The inherently reduced water permeability of UHPECCs raises expectations for the enhanced protection they will provide to internal GFRP bars. Therefore, this study explores the durability performance of GFRP bars embedded in UHPECCs. Three types of GFRP bars made of various matrices (polyester, vinyl ester, and epoxy) were employed. The embedded GFRP bars were immersed in an alkaline solution at room temperature and 40°C for a duration of up to 360 days. Their tensile properties were assessed after specified periods. The results indicated a more pronounced deterioration in GFRP bars made of polyester than bars made of epoxy and vinyl ester. UHPECC covers provided good protection for internal GFRP bars compared with ordinary concrete due to the reduced permeability of UHPECCs. A microstructural analysis revealed that bar deterioration was predominantly due to matrix hydrolysis. This phenomenon resulted in the efficiency of fiber stress transfer. Notably, fibers in UHPECC-embedded GFRP bars exhibited no evident degradation, whereas those in the bars without UHPECC covers displayed slight degradation.