Evaluation of Concrete Durability Characteristics in Structures Exposed to Coastal Environment in Lagos State

Reinforced concrete structures in coastal areas of Lagos State, South West Nigeria, experience accelerated deterioration due to chloride-induced reinforcement corrosion driven by marine aerosol exposure, tidal effects, and high humidity. This study evaluates the durability characteristics of concrete elements from eight coastal structures in Lagos Island and Lekki, ranging from 5 to 25 years in age. Core samples were drilled from structural columns and slabs at above and below tidal zone positions. Durability tests included chloride content by potentiometric titration, carbonation depth by phenolphthalein indicator, half-cell potential corrosion activity assessment, and compressive strength. Concrete cover depth was measured using a covermeter. Results indicate that chloride concentrations exceed the threshold for corrosion initiation (0.4 percent by cement weight) in all below-tidal-zone samples from structures older than 10 years. Half-cell potential measurements indicate active corrosion in 67 percent of tested locations on 15-year or older structures. Mean concrete cover is 32 mm, inadequate for the coastal XS3 exposure class requiring 50 mm cover. Carbonation depth exceeds steel reinforcement depth in 23 percent of above-tidal samples from older structures. The study concludes that current concrete durability practice in coastal Lagos is inadequate and recommends minimum 50 mm cover, low water-cement ratio concrete of 0.40 maximum, and epoxy-coated reinforcement for all new coastal structures.

Keywords: concrete durability, chloride corrosion, coastal structures, Lagos State, marine exposure