| Externally bonded glass fiber-reinforced polymer (GFRP) fabrics are being increasingly used for seismic retrofit and rehabilitation of concrete structures. Glass fibers exhibit high strength to weight ratio and low cost in comparison to carbon and aramid fibers. However, previous studies have shown that glass fibers are vulnerable to attack caused by harsh environmental weathering agents such as freezing-thawing, wetting-drying, and exposure to alkaline and acidic environments. Concerned with durability, this study is based on a fracture mechanics approach to evaluate the interface durability of GFRP bonded to Normal Concrete (NC) and High-Performance Concrete (HPC), subjected to two types of weathering protocols: (1) freeze-thaw cycling under calcium chloride, which is used to simulate the deleterious effect of the deicing agents used on highways in wintry weather; and (2) alternate wetting and drying in a sodium-hydroxide solution, which is used to simulate the naturally occurring alkalinity due to the presence of concrete pore water, that can cause degradation due to a combination of mechanisms such as leaching and pitting of the glass fibers, and cracking and spalling of the resin matrix. Durability of the GFRP-concrete interface is characterized based on the critical strain energy release rate, under Mode-I loading, and weight and strain measurements. Unconditioned companion specimens are fractured alongside their aged counterparts to provide baseline-feedback and also enable comparative analysis of the fracture surfaces. Considerable degradation of the interface bond integrity is found to have resulted, with increasing cycling period. Recommendations are given for establishing standardized durability testing protocols, and the Single Contoured-Cantilever Beam specimen developed in this research is proposed to be adopted as a standard test method for interface evaluations. |
