Compressive behavior of FRP-confined ultra-high performance concrete (UHPC) and ultra-high performance fiber reinforced concrete (UHPFRC)

Due to its superior mechanical properties and durability, ultra-high performance concrete (UHPC) or ultra-high performance fiber reinforced concrete (UHPFRC) has emerged as a promising alternative to conventional materials in both strengthening of deficient structures and building of new structures. Contrast to the ductile tensile behavior of UHPFRC, the compressive behavior of both UHPC and UHPFRC is much more brittle. To tackle such demerit, the use of fiber-reinforced polymer (FRP) to provide confinement is an efficient method. This study aims to investigate the stress–strain behavior of FRP-confined UHPC/UHPFRC through axial compression tests of 40 FRP-confined UHPC/UHPFRC cylinders, with the confinement mechanism being carefully analyzed and explained. The test variables included the type and thickness of FRP jacket, the compressive strength of UHPC/UHPFRC, the volume fraction of steel fibers, and the specimen size. The test results showed that FRP-confined UHPC/UHPFRC exhibited a large deformation capacity and generally a bilinear axial stress–strain curve. Axial stress reductions or fluctuations occurred after the first ascending branch for the UHPC specimens; however, such axial stress reductions or fluctuations became less obvious after steel fibers were added. Finally, existing models for the ultimate condition of FRP-confined UHPC/UHPFRC were evaluated using the test results in the present study.