Strength and Durability Characteristics of Steel Fibre–Reinforced Fly Ash Concrete Exposed to Aggressive Chemical Environments

Abstract

Concrete structures exposed to aggressive environments often suffer from premature deterioration due to chemical attacks, particularly sulphate and acid ingress, leading to loss of strength and durability. In this study, an experimental investigation was carried out to evaluate the mechanical and durability performance of steel fibre–reinforced fly ash concrete of M20 and M30 grades. Ordinary Portland cement was partially replaced with fly ash at levels ranging from 0% to 35%, while hooked-end steel fibres were incorporated at dosages of 0–2.0% by volume of concrete. The mechanical performance was assessed through 28-day compressive strength and non-destructive evaluation using the rebound hammer test. Durability characteristics were examined by measuring residual compressive strength after 28, 56, and 90 days of immersion in sulphate (Na₂SO₄) and sulphuric acid (H₂SO₄) solutions. The results indicate a strong correlation between rebound hammer numbers and compressive strength, confirming the suitability of non-destructive testing as a supplementary assessment tool. Sulphate and acid exposure caused progressive strength degradation in all mixes, with acid attack producing more severe deterioration than sulphate attack. Moderate fly ash replacement levels (15–20%) improved durability by reducing permeability and refining pore structure, whereas higher replacement levels resulted in increased strength loss. The incorporation of steel fibres significantly enhanced both mechanical strength and durability by improving crack control and limiting aggressive ion ingress. Mixes containing 1.5–2.0% steel fibres with 15–20% fly ash exhibited the highest strength retention under aggressive environments. Overall, the study demonstrates that the synergistic use of steel fibres and optimized fly ash replacement can significantly improve the durability and service life of concrete structures exposed to chemically aggressive conditions.