Effect of cracking in fly ash concrete on chloride diffusion rate

Abstract Reinforced concrete structures in coastal and marine environments are particularly vulnerable to chloride ion damage from seawater, leading to reinforcement corrosion. Chloride ion penetration is a key factor in this process, with the problem becoming more pronounced when cracks develop in the concrete. Cracks significantly influence the rate of chloride penetration, with wider cracks allowing easier access for chloride ions, thereby accelerating the corrosion process. This experimental study investigates how cracks impact chloride diffusion in reinforced concrete, elates the chloride concentration and crack width. The research involves testing concrete samples from both actual structures and laboratory-cast cylinders. Nine concrete cylinders with different compressive strengths were prepared, including K-250 and K-400 grades, both with and without 30% fly ash. Fly ash is known to enhance concrete’s resistance to chloride penetration. Concrete cylinders are cut into a 50 mm thick discs and subjected to a steady state migration test in line with NT BUILD 355 standards. Chloride diffusion rates were calculated using the Nernst-Planck formula. Cracks were introduced into the discs with splitting test, with crack widths of 200, 400, 600, and 800 μm. The results demonstrate a clear correlation between crack width and content of chloride in the concrete. As crack width and area increase, chloride concentration within the concrete rises. This trend was particularly evident in K-400 concrete, where the presence of fly ash significantly reduced chloride concentration compared to K-400 without fly ash, especially when crack widths exceeded 0.6 mm. The study underscores the importance of crack management and the utilisation of fly ash in mixtures of concrete to mitigate chloride-induced corrosion in marine environments.