Effect of Admixture on the Properties of Fly Ash Geopolymer

Abstract

The research studied the effect of admixtures on properties of fly ash geopolymer. The geopolymer was synthesized by a reaction among fly ash, sodium silicate (Na₂SiO₃) and 10 M sodium hydroxide (NaOH) solutions. Admixtures were mixed in geopolymer paste at dosage of 1-2% by weight of fly ash. The mass ratio of Na2SiO3/NaOH was 1.5 and geopolymer was cured at 65 C for 48 hr. Admixtures were selected based on concrete knowledge comprising of calcium chloride, calcium sulphate, sodium sulphate and sucrose. Their effects on setting time, degree of reaction and compressive strength were studied. In addition, microstructure examination was conducted by SEM while morphology was studied by XRD. Results showed that accelerating admixtures can be shortened the final setting time of geopolymer including to calcium chloride and calcium sulphate; while sucrose increased the final setting time. For sodium sulphate, it had little effect on final setting time. In addition, admixtures at dosages of 1% by weight of fly ash increased the compressive strength higher than 2% dosage. In addition, SEM and EDX techniques showed that the resulted geopolymer has reformed the microstructural and morphological structures relevant to the degree of reaction.

Keywords : Geopolymer / Fly Ash / Admixture / Setting Time / Degree of Reaction