Concrete Bond Durability of CFRP Sheets with Bioresins Derived from Renewable Resources

Abstract

Bond strength durability of carbon fiber–reinforced polymer (CFRP) to concrete is investigated for two bio-based resins and compared with conventional epoxy (E). The first is an epoxidized pine oil blend (EP) and was used for wet layup installation. The second is a furfuryl alcohol resin derived from corn cobs and sugar cane (FA), and was used to prefabricate CFRP plates, which were installed using an epoxy paste. A total of 137 concrete prisms with a midspan half-depth saw cut were tested. Specimens were conditioned in a 3.5% saline solution at 23, 40, or 50°C for up to 240 days before testing for bond strength. Short-term bond strengths were 3.9, 4.3, and 5.5 MPa for the E, EP, and FA resins, respectively, using a 33 MPa concrete. Reductions in bond strength over the 240 days of conditioning did not exceed 15%. Bond failures of E-CFRP (EC) and EP-CFRP (EPC) were predominantly adhesive-based, where a thin layer of cement paste remained attached to CFRP, while that of FA-CFRP (FAC) was cohesive-based, where there was a thicker layer of concrete remaining on the CFRP. This suggests that bond between the furfuryl alcohol resin and epoxy paste is excellent and remained intact. ANOVA showed that the difference between EPC and EC strengths were insignificant, while that between FAC and EC were statistically significant. Only FAC at 40°C after 240 days showed a statistically significant difference from its unconditioned counterpart. Finally, the 40 and 50°C conditioning was not statistically different from the 23°C.