Empirical Analysis of the Effect of Corrosion Inhibitor Admixtures on the Durability of Reinforced Concrete in Coastal Structures, Lagos

Chloride-induced reinforcement corrosion is the dominant durability challenge facing reinforced concrete structures along the Lagos coastline in the South West geopolitical zone, where marine aerosol, tidal splash, and salt-laden construction water accelerate the initiation of corrosion and reduce structural service life. This empirical study investigates the effectiveness of three commercial corrosion inhibitor admixtures, a calcium nitrite-based inorganic inhibitor, an amine and ester organic inhibitor, and a combined inorganic-organic formulation, in extending chloride corrosion initiation time and reducing corrosion rate in simulated coastal exposure conditions. Reinforced concrete specimens of C30 and C40 mixes were cast incorporating each inhibitor at manufacturer-recommended and double dosages, alongside plain concrete controls. Specimens were subjected to cyclic wetting and drying in a 3.5 percent sodium chloride solution over 18 months. Chloride profiling by chemical analysis, half-cell potential mapping, and linear polarisation resistance measurements were conducted at 3, 6, 12, and 18 months. Results indicate that the combined inorganic-organic inhibitor at double dosage achieved the largest improvement, delaying corrosion initiation by 40 percent and reducing steady-state corrosion current density by 58 percent relative to control specimens at 18 months. Calcium nitrite showed strong performance in the C40 mix but diminishing benefit in the C30 mix, suggesting interaction with mix water-to-cement ratio. Half-cell potential distributions confirm active corrosion in all uninhibited control specimens by 12 months. The study provides empirically grounded dosage guidance for inhibitor use in Lagos coastal structural applications and recommends the combined formulation as the preferred product. Keywords: corrosion inhibitors, chloride, coastal structures, reinforced concrete, Lagos durability.