Evaluation of Sulfate Resistance of Fly Ash-Based Geopolymer Concrete

Abstract

This research, the effect of sodium hydroxide (NaOH) concentrations and Si/Al ratios on compressivestrength of geopolymer concretes exposed to magnesium sulfate solusion were studied. The geopolymerconcrete were prepared from Mae Moh fly ash with sodium silicate (Na₂SiO₃) and sodium hydroxide(NaOH) solutions. In the first group, the concentration of NaOH was varied at 8, 10, 12, 14, 16 and 18molar and the Si/Al ratio was kept constant at 1.98. In the second group, the concentration of NaOH waskept constant at 14 molar and the Si/Al ratio was varied at 2.2, 2.4, 2.6 and 2.8. The concrete cylinderspeciments of 100 mm in diameter and 200 mm in height were prepared for compressive strength test ofconcrete. The hardened geopolymer concretes were air-cured and immersed in 5%-magnesium sulfateconcentration. The compressive strength of geopolymer concrete was tested after being exposed tomagnesium sulfate solution for 90 and 180 days. In adddition, the compressive strength of air curing concretewas also investigated at the age of 7, 14, 28, 60, 90 and 180 days. The results showed that compressivestrengths of geopolymer concrete significantly increased with the increase of a concentration of NaOH.The strength loss of geopolymer concrete due to magnesium sulfate solution increased with the increaseof a concentration of NaOH and Si/Al ratio

Keywords : Geopolymer Concrete / Fly Ash / Compressive Strength / Magnesium Sulfate / NaOHConcentration / Si/Al Ratio