Experimental study on CFRP-concrete dynamic debonding behaviour

Carbon fibre reinforced polymer (CFRP) is widely used in strengthening structures against dynamic loading. However, debonding is one of the primary failure modes in CFRP strengthened reinforced concrete (RC) structures. This phenomenon is controlled by the interfacial shear bond-slip behaviour between the two materials, viz. CFRP and concrete. Although the quasi-static bond-slip response has already been extensively investigated, studies on their dynamic behaviour are rather limited, especially those under high loading rate regime. Limited knowledge of the interface behaviour will affect high-fidelity simulations of FRP strengthened RC structures under dynamic loading regime. To shed light on the FRP bond-slip behaviour under high loading rates (above 800 mm/s), the authors proposed a novel experimental method for high loading-rate impact tests using a modified Split Hopkinson Pressure Bar (SHPB) set-up. Based on this set-up, slip rate could be derived through single-lap shear tests under impact loading regime. Dynamic enhancing effect on ultimate load, shear bond stress and fracture energy could be quantified for a wide range of loading rates varying from 0.02. mm/s to 2150 mm/s. It was found that the bond-slip properties showed remarkable dynamic enhancing effect under high loading rate (above 800 mm/s). However, at the loading rate around 2000 mm/s, dynamic effect could be limited by CFRP load capacity in which the CFRP sheet might directly fractured rather than debonded from the concrete surface. The effect of parameters on the bond behaviour was better understood from a detailed experimental parametric study. Constitutive equations were proposed to model the dynamic bond-slip behaviour of the CFRP-concrete interface.