Axial compression performance of reinforced concrete encased seawater sea sand concrete filled PVC/GFRP tube columns

To enhance the practical application of sea sand without desalination, a novel type of reinforced concrete encased non-desalinated seawater sea sand concrete filled polyvinyl chloride (PVC) or glass fiber reinforced polymer (GFRP) tube column was proposed in this study. The axial compression performance of the proposed composite columns was investigated by testing of 26 specimens. The test parameters included the concrete strength, seawater sea sand concrete replacement ratio, the configuration of CFRP strips, and other relevant parameters. Results indicate that the failure initiated with cracking concrete at the bottom of the column, followed by the propagation of cracks longitudinally through the middle and bottom sections, and concrete cover spalling at the base. In comparison to specimens with PVC and CP inner tubes, specimens with GFRP inner tube demonstrated increases of 41.1 % in peak bearing capacity and 44.8 % in peak strength index (SIp), respectively. Increasing the number of CFRP layers wrapped on PVC inner tube showed increases of 6.0 % in SIp, 58.7 % in K, and 215.8 % in ductility of specimen, respectively. Compared with PVC inner tubes and CP inner tubes, GFRP inner tubes had significant hoop constraint effect, which enhanced both the ductility and bearing capacity of the specimens. Furthermore, an analytical model for predicting the axial compression load bearing capacity of the composite columns with various inner tube type was developed.