Durability assessment of GFRP bars embedded in UHP-ECCs subjected to an accelerated aging environment with sustained loading

Abstract

Ultra high-performance engineered cementitious composites (UHP-ECCs) have garnered significant attention in the field of civil engineering primarily due to their exceptional tensile strain-hardening performance and excellent compressive strength. To further enhance their tensile strength, particularly in meeting the rigorous environmental and mechanical demands frequently encountered in marine environments, fiber-reinforced polymer (FRP) bars can be employed as the internal tensile reinforcement for UHP-ECCs (referred to as “FRP-UHP-ECC members”). While numerous studies have focused on the durability of FRP bars in concrete environments, the durability of FRP bars embedded within UHP-ECCs, especially with sustained loads, remains unexplored. Glass FRP bars are commonly utilized in civil engineering due to their cost-effectiveness and favorable mechanical properties. Therefore, this paper investigated the durability performance of GFRP bars made from three different matrix resins (i.e. epoxy, vinyl ester and polyester). These bars were centrally embedded in UHP-ECCs and subsequently immersed in alkaline solutions at elevated temperatures while under sustained loads. Their tensile properties over a specified period were evaluated after exposure. The test results revealed a larger degradation in polyester-based GFRP bars compared to vinyl ester-based and epoxy-based bars. In addition, GFRP bars with UHP-ECC covers exhibited less degradation than the bare bars, but this protective effect diminished under sustained loads. Scanning electron microscope (SEM) and X-ray computed tomography (CT) analysis demonstrated that the degradation of GFRP bars was primarily attributed to matrix hydrolysis, which led to a reduction in stress transfer efficiency between fibers, contributing to the tensile strength reduction in GFRP bars.