Effect of Fly Ash Addition on Compressive Strength and Durability of Concrete in Hot and Humid Conditions of Lagos

This study investigates the effect of coal fly ash addition on the compressive strength and durability of concrete mixes designed for the hot and humid exposure conditions of Lagos State, South West Nigeria. Fly ash from Egbin Power Station, Lagos, is the principal locally available industrial by-product with supplementary cementitious potential, and its optimised use in concrete can reduce OPC consumption and improve durability in the aggressive coastal exposure environment of Lagos. Fly ash is characterised by XRF, XRD, and particle size analysis. Concrete mixes are designed at a target 28-day strength of 30 MPa with fly ash partial replacement of OPC at 0, 15, 25, 35, and 45 percent. Compressive strength is measured at 7, 28, 56, and 90 days. Durability indicators measured include rapid chloride permeability, water sorptivity, and carbonation depth after 28 days of accelerated carbonation. Results show that fly ash replacement retards strength development at 7 days, with 25 and 35 percent replacement mixes requiring 56 and 90 days respectively to match 28-day control strength. At 90 days, 25 percent fly ash concrete exceeds control strength by 12 percent. Chloride permeability and sorptivity decrease significantly with fly ash content, demonstrating improved durability in the long term. Keywords: fly ash, concrete durability, compressive strength, chloride permeability, Lagos State.