Influence of Long-Term Marine Fluid Ingress and Ion Transport on Properties of 30-Year-Old Reinforced Concrete

Reinforced concrete structures in marine environments deteriorate over time due to the hydrodynamic effects of seawater exposure and the transport of salt-laden, humid air. In particular, fluid-driven permeation and diffusion of chloride and sulfate ions into the porous matrix lead to chemical reactions that cause reinforcement corrosion and strength degradation, thereby shortening the service life of structures and threatening seismic safety. In countries such as Türkiye, which are both coastal and located in an active earthquake zone, evaluating the performance of these structures under prolonged fluid ingress is of great importance. This study investigates the mechanical and microstructural properties of a reinforced concrete structure exposed to long-term marine fluid conditions under real field conditions. Core compressive strength tests, Schmidt hammer tests, and tensile tests on reinforcement steel were conducted on samples taken from the structure. In addition, X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were performed to determine the microstructural characteristics altered by fluid-solid interactions. According to the findings, both the concrete and the reinforcement exhibited strength and durability losses driven by continuous moisture and ion transport. The compressive strength of the concrete did not satisfy regulatory requirements, and microstructural analyses indicated that the C-S-H gel underwent decalcification due to the influx of sulfate and magnesium-rich fluids, Portlandite was largely depleted, and the binder matrix exhibited chemical degradation. Advanced corrosion, cross-sectional loss, and pitting -facilitated by the presence of an aqueous electrolyte- were observed in the reinforcement, leading to reductions in yield strength, ductility, and bond performance. Furthermore, unsuitable aggregate properties and a weak Interfacial Transition Zone (ITZ) created preferential flow paths that accelerated deterioration, significantly reducing the structure's load-bearing capacity.