Thermomechanical Relaxation of CFRP Sheets Bonded to Concrete Substrate: Fid-Bau Portal

Thermomechanical Relaxation of CFRP Sheets Bonded to Concrete Substrate

Yail J Kim

This paper characterizes thermomechanical relaxation for carbon fiber-reinforced polymer (CFRP) sheets bonded to a concrete substrate. A total of 144 CFRP-concrete interface specimens are tested under monotonic mechanical (18 specimens) and thermomechanical (126 specimens) loadings to examine their interfacial capacities and relaxation behavior at elevated temperatures from 25 to 175°C (77 to 347°F). Test parameters are CFRP-bond width (0.25B, 0.50B, and 0.75B, where B is the substrate width) and bond length (1.0L^sub e^, 1.25L^sub e^, and 1.50L^sub e^, where L^sub e^ is the effective length of the CFRP). When mechanically loaded (without thermal loading), the bond width influences the interfacial capacity; however, the bond length does not affect the capacity, owing to progressive CFRP-debonding. Under thermomechanical loading, the mixed glassy and rubbery state of the adhesive causes interfacial stress to decay exponentially, which is particularly noticeable beyond 150°C (302°F). A characteristic demarcation period is observed in thermomechanical relaxation of the interface. Temperature alters the degree of a Pearson product-moment correlation between the interfacial stress and CFRP-bonding schemes. Temperature-dependent multipliers are proposed to estimate the capacity of the CFRP-concrete interface subjected to thermomechanical loading, which is intended to replace the design provision of ACI 440.2R-08.