Chloride resistance of concrete with metakaolin addition and seawater mixing: A comparative study

•Chloride resistance of concrete with seawater and metakaolin was assessed.•Combination of seawater and metakaolin increased chloride resistance of concrete.•There is a correlation between total charge passed and chloride diffusion coefficient.•Chloride in seawater and NaCl curing was immobilized by Friedel’s salt.

Chloride resistance of concrete with seawater mixing and metakaolin (MK) addition was evaluated by analytical techniques. With the combination of seawater mixing and NaCl solution curing, the compressive strength of concrete increased with MK content, which prevented the decrease of strength at 56 days. Both MK and seawater improved the chloride resistance which increased with MK content. The chloride ingress distance was reduced through the refinement of pore structure and immobilization of chloride by formation of Friedel’s salt. The minerals after chloride attack were characterized. The microstructure analysis along ingress direction confirmed the improvement of chloride resistance by MK and seawater.