Experimental study on bond durability of GFRP bar/engineered cementitious composite exposed to freeze-thaw environments

Glass fiber reinforced polymer (GFRP) bars and engineered cementitious composites (ECC) present better structural performance as compared to conventional concrete with reinforcing steel bars. However, the bond behavior of the GFRP bar to ECC matrix under freeze-thaw (FT) cycles in cold climates remains underexplored. Therefore, this study aims to investigate the bond durability of GFRP bars and ECC under FT conditions. An experiment was conducted with 33 pullout specimens, categorized according to concrete types (normal concrete and ECC), compressive strengths (30 MPa and 50 MPa) and the number of FT cycles (0, 100, 150, and 200 cycles). Assessment parameters included surface degradation, failure modes, mean bond strength, weight loss, and the relative dynamic modulus of elasticity. Results indicated ECC specimens exhibited greater durability compared to normal concrete specimens, with no significant improvement in durability observed with increased compressive strength. Specifically, the mean bond strengths of N30 (30 MPa normal concrete) specimens, E30 (30 MPa ECC) specimens, and E50 (50 MPa ECC) specimens decreased by 88.41 %, 38.86 %, and 58.21 % after 150 FT cycles, respectively. Failure modes correlated strongly with concrete type and the number of FT cycles. SEM and composition analyses revealed the effects of FT cycles on the concrete matrix, the bond interface, and the GFRP bars. The ascending branches in the bond stress-slip curves of specimens subjected to FT cycles were effectively modeled using Malvar's model. Based on the declining relative dynamic modulus of elasticity and the correlation between laboratory and natural FT cycles, the estimated fatigue lives for GFRP bar/E30 specimens subjected to 250 FT cycles are 35.7, 71.4, and 46.2 years in Beijing, Detroit, and Vancouver, respectively. This research provides insights on GFRP bar/ECC's longevity in practical engineering contexts.