Study on the active confinement of GFRP-confined expansive concrete under axial compression

Abstract

Glass fiber reinforced polymer (GFRP) based tubes provide good passive confinement to enhance structural capacity and ductility. Literature has demonstrated that introduction of the expansive agent in the concrete mixture provides the active confinement on the structures. Thus, this study is to explore the axial compression behavior of GFRP-confined expansive concrete cylinders. Eighteen GFRP-confined concrete cylinders, including nine expansive concrete (EG) and nine conventional concrete (or called ordinary concrete, OG) as a reference were cast and then loaded by axial compression. Compared with conventional concrete mixture, the expansive concrete produces a certain active confinement on the peripheral FRP tube due to expansion of concrete and confinement of GFRP. Experimental results indicate that, due to the confinement effect of FRP and expansion of core concrete, the hoop strain reduction factor, normalized stress at inflection points, the compressive strength and ultimate axial strain of the EG specimens were all improved compared with OG specimens. Moreover, the axial stress-strain model was formulated based on the modification of the unified equations in the literature to account for active confinement effects generated by expansive agent. A comparison indicated that the analytical model captured well with the whole load history, and the predicted data were well consistent with the experimental data.