Comparative study of failure mechanism of CFRP partially confined normal strength concrete (NSC) and UHPC cylinders under axial compression

Ultra-high performance concrete (UHPC) holds significant potential in marine structures due to its superior compressive strength and enhanced durability in comparison to normal strength concrete (NSC). Carbon fiberreinforced polymer (CFRP) confinement has been proven to improve these properties further. However, the compressive behavior of CFRP-confined UHPC, especially for partial confinement, presents complexities arising from the intricate interaction mechanism between UHPC and wrapped CFRP strips. To address this issue, the present study conducted axial compression tests accompanied by digital image correlation (DIC) analyses. Failure modes, stress-strain behavior, hoop strain distribution, and cracking evolution of CFRP partially confined NSC/UHPC were elucidated, thereby uncovering the underlying load transfer mechanism between NSC/UHPC and wrapped CFRP strips. Research outcomes show that the enhancement in compressive strength fcc/fco (0.99 1.43) and strain ecu/eco (1.51 2.59) of CFRP partially confined UHPC is relatively lower than the NSC counterparts (1.28 2.98 and 3.82 15.14, respectively). Moreover, lower hoop strain efficiency eh,rup/efrp can be found for CFRP partially confined UHPC compared to NSC (0.61 vs. 0.86). These phenomena were primarily attributed to the localized shear-cracking pattern and low dilation behavior of confined UHPC. Based on the experimental results, the elucidation of the underlying load transfer mechanism between UHPC/NSC and wrapped CFRP strips provides valuable insights into comprehending the compressive behavior of CFRP partially confined UHPC. Finally, the "arching effect" is found to exhibit limited effect on the ultimate condition's prediction of partially confined UHPC according to the failure mechanism and Li et al.'s model can reliably predict the ultimate conditions among the existing models.