Investigation on irreversible deterioration mechanism of CFRP–steel adhesive joint based on the hydrothermal aging behavior of resin matrix

Resin-impregnated carbon fiber fabric reinforced polymer (CFRP) is a novel material for steel structure reinforcement, but its performance is influenced by moisture and temperature. This study investigates the irreversible degradation of CFRP–steel adhesive joints in a hydrothermal setting, focusing on resin hydrothermal aging behavior. Moisture absorption tests, Fourier-transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) were conducted to assess moisture's impact on resin matrix's properties. Results indicate that moisture absorption behavior is partially reversible through physical drying, while hydrolysis resulting from moisture absorption is irreversible. The partially reversible aspect of moisture absorption leads to a partial restoration of the thermodynamic properties of the resin matrix. Additionally, the mechanical performance of resin specimens and CFRP-steel adhesive joints in hydrothermal conditions was assessed using tensile and pull-off tests. Findings show that elevated temperatures accelerate the moisture absorption rate of resin while increasing the maximum moisture absorption capacity. The moisture absorption affects the fracture surface morphology of the resin matrix, with aging time negatively correlated with adhesion strength. Compared to the hydrothermally aged state, there is a slight recovery in the mechanical performance of CFRP–steel adhesive joints after drying desorption. The saline environment with no significant promotion aging compared to the distilled water environment. These findings provide insights for evaluating CFRP–steel adhesive joints’ durability in atmospheric or marine environments.