Behavior of BFRP-confined geopolymer-based coral aggregate concrete columns under axial compression: Effects of specimen sizes

Fiber-reinforced polymer (FRP) confined concrete significantly enhances the axial compressive behavior and durability of the internal core concrete, demonstrating promising applications in marine environments. However, this strengthening effect is highly influenced by the number of FRP layers and the size of the specimens. Additionally, the use of ordinary Portland cement (OPC) in traditional concrete preparation is associated with high energy consumption and substantial carbon emissions. This study explores the utilization of sustainable geopolymers as an alternative to OPC to develop geopolymer-based seawater coral aggregate concrete (GPCAC) in marine engineering. This approach contributes to the increased utilization of marine resources, reduced greenhouse gas emissions, and saved construction costs. Furthermore, basalt-FRP (BFRP) jackets were employed to wrap GPCAC, aiming to develop an innovative BFRP-confined GPCAC composite column for marine construction. The axial stress-strain behavior of BFRP-confined GPCAC cylinders with different BFRP jacket layers and specimen sizes was investigated. The studied results revealed that the BFRP jacket confinement was an effective means in strengthening the load-bearing capacity and deformability of GPCAC and cement-based CAC cylinders. The failure modes observed in the BFRP-confined GPCAC were analogous to those of BFRP-confined CAC. In addition, as the BFRP confinement stiffness strengthened, the slope of the stress-strain curves at the rising branch, axial compressive strength (fcc), and ultimate axial strain (ecc) of BFRP-confined specimens exhibited enhancement. Compared with un-confined GPCAC cylinders, the fcc and ecc values of 6-ply BFRP-confined GPCAC cylinders with a diameter of 100 mm were enhanced by about 2.09 and 4.55 times, respectively, whereas those with a diameter of 150 mm were improved by about 0.94 and 6.11 times, respectively. This increased effect in fcc and ecc was linearly related to the ratio of BFRP layer thickness to the diameter of the cylinders (T/D). Finally, the expressions in fcc and ecc for BFRP-confined CAC and GPCAC were developed, and the applicability of these proposed models was assessed by comparing them with experimental values of FRP-confined CAC reported in the literature.