Experimental study on compressive behavior of damaged normal- and high-strength concrete confined with CFRP laminates

• The effect of pre-existing damage is significant on the compressive performance of confined NSC with small amounts of CFRP.
• The effect of pre-existing damage is smaller on CFRP-confined HSC than on CFRP-confined NSC.
• Pre-existing damage causes higher lateral strain for CFRP-confined NSC and HSC resulting in earlier failure.
• Increasing confinement pressure can eliminate the negative effect of pre-existing damage.

In recent years, it has become increasingly common to strengthen concrete structures by bonding carbon fibre reinforced polymer (CFRP) laminates to the external surfaces of the members. Extensive studies on the mechanical behavior of CFRP-confined concrete have been conducted. However, most of these studies focused on the use of CFRP sheets to confine intact normal strength concrete (NSC), while the behavior of CFRP-confined high strength concrete (HSC) is much less understood. An experimental study was conducted to investigate the axial compressive behavior of CFRP-confined damaged concrete containing NSC and HSC in this study. A total of 60 cylindrical specimens with the dimensions of 150 mm × 300 mm (diameter × height) were tested under axial compression. The test parameters included two types of concrete, two levels of damage to the specimens and three amounts of CFRP wrapping. The effects of these parameters on the failure mode, the ultimate conditions, the energy dissipation capacity and the stress–strain relationship of the CFRP-confined specimens were analyzed. The existing ultimate strength and axial strain models were assessed against the experimental datasets and the performance of these models were discussed. The results showed that CFRP confinement can greatly improve the ultimate strength and axial strain of both intact and damaged concrete specimens. For small amounts of CFRP reinforcement, the pre-existing damage had a significant effect on the compressive performance of CFRP-confined NSC but a smaller effect on that of CFRP-confined HSC. Greater amounts of CFRP considerably improved the ultimate strength and axial strain of the specimens and eliminated the effect of the pre-existing concrete damage. In addition, the results of this model assessment indicated the need to develop more accurate stress–strain models for FRP-confined damaged NSC or HSC.