Enhancing the EB-FRP strengthening effectiveness by incorporating a cracking-control layer of ECC with different thicknesses

Abstract

The multiple and tight cracking nature of engineered cementitious composite (ECC) under tension can significantly mitigate or eliminate the premature debonding of externally bonded (EB) fiber-reinforced polymer (FRP). This paper systematically investigates the flexural performance of concrete beams that were jointly strengthened by hybrid carbon FRP (CFRP) and ECC. The ECC layer realizes the dual-function of maximizing the strengthening effectiveness and contributing additional flexural strength. The test results indicate that the inclusion of an ECC layer changed the CFRP strip from debonding to rupture at the ultimate state, which in turn remarkably increased the member flexural capacity, the energy consumption capacity and ductility, compared to the EB-CFRP strengthened counterpart. The CFRP rupture occurred even though the ECC thickness was only half that of the concrete cover. Further increasing ECC thickness contributed marginally to the member load capacity and ductility until when the ECC total enwrapped longitudinal reinforcement. The optimal thickness of ECC was discussed. The crack width of the concrete block was considerably narrowed after applying the ECC layer. Finally, a model was developed to predict the flexural strength of CFRP-ECC jointly strengthened beams, providing good agreement between the predicted and experimental results.