Experimental and theoretical study on ECC-CFRP jointly flexural reinforcement of pre-damaged reinforced concrete beams

The use of engineered cementitious composites (ECC) can greatly reduce or even entirely prevent premature debonding of externally bonded (EB) fiber-reinforced polymers (FRP). This study examined the flexural behavior of pre-damaged reinforced concrete (RC) beams reinforced by carbon fiber reinforced polymer (CFRP) sheets. Ten beams were created and constructed for four-point bending test. The main testing parameters were the degree of pre-damage, the thickness of the ECC layer, and the reinforcing method. According to the test results, CFRP rupture occurred in the undamaged specimens, while CFRP debonding occurred in all of the pre-damaged specimens. The pre-damaged specimens' flexural stiffness and load-carrying capability can be effectively increased. Best flexural performance and a maximum CFRP utilization of 83.2% can be achieved by pre-damaged concrete beams when the thickness of the ECC layer entirely surrounds the longitudinal tensile reinforcement. For pre-damage specimens, the increased ECC layer thickness contributed to increased ductility and had little effect on the ultimate load. A mathematical model based on the plane section assumption is proposed to predict the flexural capacity of ECC-CFRP jointly reinforced beams, and the effect of different failure modes is taken into account. The error between the predicted and measured values is within +/- 10%.