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.
Keywords : Geopolymer, Low calcium fly ash, High calcium fly ash, ordinary Portland cement, Compressive strength, Microstructure
