Axial compressive behavior of seawater coral aggregate concrete-filled FRP tubes

The use of seawater coral aggregate concrete (SCAC) instead of ordinary aggregate concrete (OAC) in concrete-filled FRP tube (CFFT) members is highly attractive due to the beneficial effect of fiber reinforced polymer (FRP), which has good resistance to salt and can effectively counteract the greatest shortcomings of the chloride-containing ions in SCAC. In the development of marine construction, SCAC-filled FRP tubes are a potential attractive alternative for pile and column applications in corrosive marine environments. The axial compressive behavior of SCAC-filled FRP tube (SCFFT) was first experimentally investigated and compared with OAC-filled FRP tube (OCFFT) in this study. The chosen coral aggregates (CAs) and SCAC were systematically prepared and tested, including classification and materials testing on CAs, uniaxial load testing on SCAC and microstructure analysis of SCAC. The porous nature and low strength of CAs led to a different and brittle failure mechanism of SCAC under uniaxial loading, and result in SCAC experiencing a compacting behavior before the development of its rapid expansion and the activation of confinement in SCFFT. As a consequence, the axial loading of SCFFT displayed a slight drop in the transition zone for the range of axial strains between approximately 0.002 and 0.004. The non-homogeneity and brittleness of SCAC led to a non-uniform hoop strain distribution in SCFFT under compression and thus discounted the effect of confinement. The ultimate load of SCFFT was approximately 60% of that of its OCFFT counterpart. The key elements and basic framework used to develop a detailed analysis-oriented model for predicting FRP-confined SCAC under axial compression was illustrated. Furthermore, the model developed originally for FRP-confined lightweight concrete with ceramsite aggregates was extended to cover FRP-confined SCAC, and the extended model was confirmed to be capable of producing reliable predictions. (C) 2017 Elsevier Ltd. All rights reserved.