Durability assessment and behavior under axial load of circular GFRP-RC piles conditioned in severe simulated marine environment

This study concerns the feasibility of using innovative glass fiber-reinforced polymer (GFRP) bars, spirals, and hoops in constructing sustainable marine reinforced concrete structures. The experimental investigation aimed at assessing the durability and structural performance of GFRP-reinforced concrete (RC) circular piles exposed to two simulated marine environments in the laboratory. A total of 15 GFRP-RC circular piles measuring 304 mm in diameter and 1000 mm in height were longitudinally reinforced with GFRP bars and transversely with GFRP spirals or hoops. Five specimens were fabricated as references (unconditioned). The remaining 10 specimens were continuously immersed in simulated marine environments (conditioned) for 12 months: five were kept in seawater at room temperature (22 degrees C), while the other five were stored in a large chamber that produced hot waves at high temperature (60 degrees C). After conditioning, all the specimens were tested under axial compression loads. Two structural variables were considered: the transverse reinforcement configuration (spirals versus hoops) and the confinement level (spiral spacing). The durability assessment included microstructure examinations (i.e., differential scanning calorimetry (DSC) and scanning electron microscopy (SEM)) were performed on GFRP bars and spirals taken from the conditioned piles. Furthermore, the bond between concrete and bars or spirals was checked by optical microscopy (OM). The microanalysis observations indicate no visible damage in the contact surface between concrete and GFRP bars or individual fibers and the resin matrix. The compressive test results pointed out that the GFRP-RC piles subjected to severe marine environments experienced 19% enhancement in their axial capacities compared to their reference counterparts. The GFRP spirals and hoops performed well in severe marine environments. The nominal axial capacities of the columns were predicted with the available design equations and are presented and discussed herein.