Effect of Different Constituent Fiber, Resin, and Sizing Combinations on Alkaline Resistance of Basalt, Carbon, and Glass FRP Bars

When used as an internal reinforcement, fiber-reinforced-polymer (FRP) composite bars are exposed to a highly alkaline (pH > 12.5) concrete environment. This study evaluated the durability of 24 types of FRP bars in a simulated alkaline concrete environment, specifically with respect to reinforcing-fiber type (carbon, basalt, and glass), fiber sizing, resin chemistry, and manufacturer. A total of 10 types of glass fibers, including two types of E-glass fibers and eight types of electrical corrosion resistance (ECR)-glass fibers, four types of basalt fibers, two types of carbon fibers, six types of resin systems based on vinyl ester, polyurethane, and epoxy resins, and five types of proprietary fiber sizings were used in manufacturing the bars. The study focused on assessing the tensile, transverse-shear, and interlaminar-shear properties of FRP bars subjected to 3 months of accelerated alkaline conditioning at 60°C, as per Canadian Standards Association (CSA) and American Society for Testing and Materials (ASTM) standards. The strength retention and failure of these bars were evaluated as a measurement of the durability and long-term performance of the FRP bars currently available on the market and for quality control by manufacturers. Statistical analysis using independent samples t-test and one-way analysis of variance revealed that the manufacturing parameters have a significant effect on the mechanical characteristics and alkaline resistance of FRP bars. In particular, the results show that the FRP bars manufactured with the same parameters and fiber types but by different fiber manufacturers with different fiber sizings and resin systems produced bars with totally different strength properties and durability performance in an alkaline environment. Vinyl ester resin and silane-sized fiber was the most compatible resin system and produced a more durable glass-FRP bar, while the epoxy resin yielded more durable basalt- and carbon-FRP bars. This paper also describes a procedure for and a criterion of the optimum manufacturing parameters to achieve specific mechanical properties and durability performance with FRP bars.