Behavior of FRP-confined compound concrete containing recycled concrete lumps
A recently proposed technique for the recycling of concrete is to directly reuse large pieces of coarsely crushed demolition concrete (referred to as recycled concrete lumps or RCLs) with fresh concrete in new construction. This novel recycling process is simpler and more cost-effective than the traditional way of recycling concrete as aggregates. The resulting concrete, referred to as compound concrete in this paper, features greater heterogeneity, especially when the fresh and the recycled concretes have rather different strengths. The interfaces between RCLs and fresh concrete, as internal weaknesses, may also compromise the performance of the compound concrete. One possibility to improve the properties of this compound concrete is to supply it with a substantial amount of confinement as may be available in concrete-filled FRP tubes, which are attractive as columns in corrosive environments. This paper therefore presents and interprets the results of an experimental study on the compressive behavior of FRP confining tubes filled with compound concrete. The influences of various parameters, such as the mix ratio and the strength ratio between the old and the fresh concretes as well as the FRP tube thickness, are investigated. The test results indicate that with a significant level of confinement, the ultimate axial stress and the ultimate axial strain of the compound concrete containing RCLs are comparable with those of the fresh concrete, regardless of the strength of the old concrete. This conclusion is important as it means that the weaknesses of compound concrete containing RCLs can be largely eliminated through lateral confinement. The applicability of an accurate stress-strain model previously developed for FRP-confined normal concrete to FRP-confined compound concrete with RCLs is also examined.