Stress-strain behavior of FRP-confined concrete containing recycled concrete lumps

A novel method to recycle concrete is to crush demolition concrete into large pieces and then to directly mix the resulting recycled concrete lumps (RCLs) with fresh concrete to produce a new kind of recycled concrete referred to as “compound concrete”. This method avoids the complexity of recycling concrete into aggregates and enables the achievement of a higher recycling ratio and a lower recycling cost. However, due to the large sizes of RCLs and the weak interfaces between fresh concrete and RCLs, compound concrete is much more heterogeneous than normal concrete. A new technique has recently been explored to improve the properties of such compound concrete, in which the compound concrete is provided with a substantial amount of confinement from an external fiber-reinforced polymer (FRP) confining tube. This paper presents the results of an experimental program of axial compression tests on compound concrete-filled FRP tubular columns in which the FRP tubes were prefabricated using the wet lay-up method with fibers only in the hoop direction. The tubes had a negligible axial stiffness, which allows the stress-strain behavior of FRP-confined compound concrete to be clearly revealed. The test results show that, when a significant level of FRP confinement is provided, the behavior of FRP-confined compound concrete is similar to that of FRP-confined normal concrete with a strength equal to that of the fresh concrete. An existing stress-strain model previously developed for FRP-confined normal concrete is evaluated in the paper using the test results of FRP-confined compound concrete.