Thermomechanical Relaxation of CFRP Sheets Bonded to Concrete Substrate

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Title: Thermomechanical Relaxation of CFRP Sheets Bonded to Concrete Substrate

Author(s): Yail J. Kim and Abdulaziz Alqurashi

Publication: Structural Journal

Volume: 114

Issue: 2

Appears on pages(s): 555-564

Keywords: carbon fiber-reinforced polymer (CFRP); interface; relaxation; temperature; thermomechanical

Date: 3/1/2017

Abstract:
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 (1.0Le, 1.25Le, and 1.50Le, where Le 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.