Comparative Assessment of Conventional and High-Performance Concrete for Marine Structures Along Nigeria’s Atlantic Coastline

Marine infrastructure along Nigeria's Atlantic coastline, including jetties, pile-supported wharves, and sea walls in the South South and South West geopolitical zones, is subjected to the most aggressive structural durability environment in the country, combining tidal wetting and drying, direct chloride exposure, biological fouling, and abrasion from wave action and vessel berthing. This study comparatively assesses the performance of conventional Grade C30 concrete and three high-performance concrete formulations, a reactive powder concrete, a silica fume-supplemented concrete, and a blended fly ash-ground granulated blast furnace slag concrete, exposed to simulated and actual marine conditions along the Lagos and Delta State coastlines. Companion specimens of each mix were subjected to accelerated marine exposure in a salt spray chamber and to real tidal zone exposure at a coastal jetty in Lagos. Durability indicators assessed at 6 and 18 months include chloride diffusion coefficient, carbonation depth, water sorptivity, and compressive strength retention. Results indicate that the reactive powder concrete achieved the lowest chloride diffusion coefficient at 0.14 x 10-12 m2/s, representing a 91 percent reduction relative to the conventional C30 control at 0.84 x 10-12 m2/s. The blended fly ash and GGBS concrete showed the most cost-effective durability improvement, achieving a 76 percent reduction in chloride diffusion at 58 percent of the reactive powder concrete material cost premium. Microstructural analysis confirmed a denser interfacial transition zone and lower pore connectivity in all high-performance formulations. The study recommends adoption of the blended supplementary cementitious material formulation as the standard specification for new marine structural concrete along Nigeria's Atlantic coast. Keywords: high-performance concrete, marine structures, chloride diffusion, Atlantic coastline, durability.