Experimental study of reinforced concrete beam-column joint retrofitted by CFRP grid with ECC and high strength mortar

The failure of a reinforced concrete (RC) beam–column joint during an earthquake can lead to the progressive collapse of the entire structure. This type of failure, which has been mainly observed among structures built prior to the 1970s, occurs due to poor design and inadequate detailing of rebars. Recently, a number of researchers have conducted numerous experiments to improve the overall performance of beam–column joints in terms of strength, ductility, and failure mode using the externally bonded fiber-reinforced polymer technique. However, because epoxy is employed, this method encounters problems, such as debonding and inadequate performance under flammable and moist environments. To resolve the foregoing, a cementitious matrix is utilized to replace the epoxy. Four RC beam–column joints are retrofitted using two different techniques employing carbon fiber-reinforced polymer (CFRP) grid covered with engineered cementitious composites (ECC) and high strength mortar. The dimensions of the retrofitted specimens are retained by removing the concrete cover of the joint where the cementitious matrix is applied. The results show that the failure mode of specimens can be modified by shifting the load concentration from the joint to the beam. Furthermore, the overall performance of specimens in term of strength improves. The specimens also exhibit greater ductility; hence, they are capable of delaying failure.