Twenty-Two Years Later: Assessing the Durability Performance of Externally Bonded CFRP Laminates on a Highway Steel Bridge Girder

This study evaluates the long-term durability of carbon fiber–reinforced polymer (CFRP) composites used to strengthen a steel bridge girder on Interstate 95 in Newark, Delaware, 22 years after installation. The original retrofit program combined laboratory and field investigations to validate the structural contribution and fatigue durability of CFRP bonded to the tension flange of steel girders. Approximately two decades later, a follow-up assessment was conducted to examine the condition of the bonded CFRP system under actual service conditions. Field-extracted CFRP samples were tested in tension and compared to control specimens stored under laboratory conditions for 22 years. Compared with control specimens stored under laboratory conditions, field-exposed samples showed 15% lower tensile strength and 26% lower flexural modulus. Corrosion was observed beneath the CFRP at the northern end of the girder, likely due to galvanic coupling between the steel substrate and the carbon fibers in the presence of moisture. Structural health monitoring was performed on the retrofitted girder, and newly collected strain data were compared to original measurements. Differential scanning calorimetry revealed that the glass transition temperature of both field-cured adhesives was below the 66°C minimum recommended by AASHTO guidelines. Fourier transform infrared spectroscopy indicated minor chemical changes in the field-exposed CFRP. The CFRP system has maintained its bond integrity over two decades; however, in regions where corrosion developed beneath the CFRP, the bond integrity was compromised. This study provides rare, long-term performance data on CFRP–steel retrofits in field conditions and supports their continued use to extend the life of aging steel infrastructure.