Out-of-Plane Peeling of Carbon Fiber-Reinforced Polymer- Concrete Interface at Elevated Temperatures
Yail J. Kim and Christopher F. Horwitz
Appears on pages(s):
carbon fiber-reinforced polymer (CFRP); debonding; peeling; thermomechanical loading
This paper presents the implications of out-of-plane loadings on the behavior of carbon fiber-reinforced polymer (CFRP) sheets bonded to a concrete substrate at elevated temperatures. These loading schemes are intended to represent variable boundary conditions for a strengthened beam (properly insulated) when a fire takes place in a building. A total of 54 specimens are tested under angled peel-off conditions, 30 to 60 degrees, combined with thermal distress incurred by temperatures ranging from 25 to 150°C (77 to 302°C). As the peeling angle increases, the load-carrying capacity of the CFRP-concrete interface dramatically decreases, which is expedited when elevated temperatures are associated. The characteristic load, determined from energy dissipation, reaffirms that the interface is vulnerable to the angular loadings. On the load-displacement responses, stick-slip motions along the bond line result in locally fluctuating interfacial resistance after the onset of CFRP debonding, which creates traction-free fracture surfaces. The debonding rate in a prepeak load stage differs from that in the postpeak stage, and this observation becomes prominent at elevated temperatures owing to a change in the energy release of the interface. The angular loading is more engaged with the shear component of interfacial fracture energy (GII) than with the opening component (GI); nonetheless, their ratio (GI/GII) is not affected by the thermal loading. With an increase in temperature over 125°C (257°F), the angular loading’s influence on the fracture energy diminishes because the applied load is distributed along the softened interface. Among the three constituents in the interfacial energy, the deformation component is least dominant, followed by the fracture and debonding components. A statistical assessment supports the significance of the thermomechanical loadings at a confidence level of 5%.