Study on the Hygrothermal Aging Behavior of Polypropylene‐Based <scp>GFRP</scp> Bars Served in Marine Engineering

ABSTRACT Glass fiber reinforced thermoplastic polymer bars exhibit promising potential for marine infrastructure, yet their hygrothermal durability remains insufficiently understood. This study systematically investigated the macroscopic mechanical degradation and microstructure evolution of polypropylene‐based GFRP (GF/PP) bars under saline and coupled saline‐alkaline environments with a comparable analysis against thermosetting counterparts. Water diffusion behavior, thermomechanical response, and interlaminar degradation evolution were evaluated by water absorption, dynamic mechanical analysis (DMA), and interlaminar shear strength (ILSS) testing. 0.37% of the equilibrium water absorption rate ( M ∞ ) and 79.3% ILSS retention were found under saline–alkaline exposure at ambient temperature. The distinct bimodal relaxation around −6.1°C–5.3°C in DMA curves indicates fiber–matrix interfacial damping, molecular chain mobility, and energy dissipation related to microcrack development. The sunken surface ribs serve as primary water ingress pathways, and saline–alkaline exposure induces more severe chemical deterioration than saline exposure, including linkage bonds fracture driven by hydroxyl ions and fiber etching. Moreover, the conservative life prediction by accelerating aging shows their ILSS retention less than 70% within 1.07–2.0 years in coastal cities. Compared to thermosetting counterparts, the much lower M ∞ , close ILSS retention, and projected service life in GF/PP bars demonstrate their reliable application prospect in marine engineering.