Effect of sodium hydroxide concentration on chloride penetration and steel corrosion of fly ash-based geopolymer concrete under marine site

•The long term durability of geopolymer concrete under marine site was investigated.•The findings provide valuable data for a practice guide line of geopolymer concrete.•The findings could help select for fly ash geopolymer concrete used in marine site.

In this research, the effect of sodium hydroxide (Na(OH)) concentrations on chloride penetration, steel corrosion and compressive strength of fly ash-based geopolymer concretes under marine environment were studied. The geopolymer concrete were prepared from class C fly ash with sodium silicate (Na2SiO3) and sodium hydroxide (Na(OH)) solutions. The concentrations of Na(OH) of 8, 10, 12, 14, 16 and 18 molar, and the constant molar ratio of SiO2/Al2O3 were used. The 200 × 200 × 200 mm3 concrete cube specimens with steel bar embedded at coverings of 20, 50 and 75 mm were investigated. The specimens were air-cured in laboratory for 28 days and then were exposed to tidal zone of marine environment in the Gulf of Thailand. After 3-year exposure, the specimens were tested for compressive strength, chloride penetration and corrosion of embedded steel bar. The results showed that the chloride penetration and corrosion of embedded steel decreased with the increasing of Na(OH) concentration. The steel corrosion was related to the compressive strength of geopolymer concrete. The corrosion is high with the concrete of low compressive strength. In addition, increasing the Na(OH) concentration in geopolymer concrete resulted in a decrease in the chloride binding capacity.