Properties of fly ash geopolymer paste containing Portland cement

Abstract

Abstract

This article presents the effect of ordinary Portland cement (OPC) replacement on low calcium fly ash (FAF)
and high calcium fly ash (FAC) geopolymer paste. Fly ash was replaced with OPC at the rate of 5, 10 and 15% by weight
of binder. Sodium silicate (Na2SiO3) and 10 molar sodium hydroxide (NaOH) solutions were used as the alkaline solution
in the reaction. The Na2SiO3/NaOH ratio of 0.67 and the liquid/binder (L/B) ratio of 0.50 and the curing at ambient
temperature were used for all of mixtures. The results found that the level replacement of OPC increase showed the
compressive strength tended to increased. The compressive strength of low calcium fly ash (FAF) and high calcium fly
ash (FAC) geopolymer paste at 7 days with 15% OPC replacement were 22 and 34 MPa, respectively. In addition, the
microstructure analysis indicated that the increase of OPC replacement resulted in the addition formation of calcium
silicate hydrate co-exists with the aluminosilicate geopolymer products. This results lead to overall increase in the
compressive strength of fly ash geopolymer products.