Compressive behavior of ultra-high performance concrete confined with FRP

This paper presents an experimental study on the compressive behavior of ultra-high performance concrete (UHPC) confined with fiber-reinforced polymer (FRP) composites. A total of 18 cylindrical specimens were prepared from UHPC containing 2.5% of micro steel fibers by volume, among which 6 were unconfined and 12 were confined with carbon FRP (CFRP). They were tested to investigate the experimental compressive behavior of unconfined or CFRP-confined UHPC. The external confinement was provided by two to six plies of CFRP wraps with the confinement ratio ranging from 0.11 to 0.54. The test results obtained from this study were presented and compared with those from existing studies on unconfined and FRP-confined UHPC specimens in the form of concrete-filled FRP tubes or FRP-wrapped cylinders. Predictive equations were proposed for the compressive strength and ultimate strain of FRP-confined UHPC, based on the interpretation of test results from the present study and from the existing literature. An existing stress-strain model for FRP-confined conventional concrete has been recalibrated for FRP-confined UHPC. While the recalibrated model predicted the test results of FRP-confined UHPC reasonably well, the inadequacy of a parabolic curve for describing the stress-strain relationship of unconfined UHPC is noticed, as a result of the higher strength and more brittle behaviour of UHPC in compression.