Effect of Chloride Ions on Concrete with Geopolymer Coatings in Coastal Area

Abstract

This paper presents the effects of chloride ions on OPC (Ordinary Portland Cement) concrete coated with fly ash-based geopolymer mortar. The coating was applied to protect concrete in coastal areas. The mortar was a mixture of fly ash and alkali activator with a mass ratio of 65:35. The alkali activator was a mixture of Na₂SiO₃ and NaOH 12M with a mass ratio of 2.5:1. The coating thickness varied at 2.5 cm, 4 cm, and 6 cm. All specimens were exposed to a marine area with seawater curing for 90 days. The mechanical properties of the specimen were determined by compressive strength. Chloride penetration was assessed for durability. A series of tests were carried out after 0, 30, 60, and 90 days of immersion. Compressive strength after a 90-day immersion increased by 34.16%, 39.81% and 31.38% for thickness 2.5 cm, 4 cm, and 6 cm respectively. Compressive strength with a thickness of 4 cm reached 52 MPa, which was the highest strength. The binding capacity of the chloride in geopolymer coatings was more than 80% and could reduce the free chloride content in concrete. Geopolymer mortar coating on OPC concrete showed good results in compressive strength and resistance to chloride attack from sea water. The recommended coating thickness for optimum results suitable for application is 4 cm.