Final Setting Time and Compressive Strength of Fly Ash and GGBS-Based Geopolymer Paste and Mortar

Geopolymer binders are attracting the attention of researchers as substitution to cement binder in conventional concrete. In manufacturing 1 ton of cement, 1 ton of CO2 is released into the atmosphere. Thus, replacement of cement by geopolymer material in construction industry reduces pollution by two ways: reduction in carbon dioxide emission into atmosphere by reducing the consumption of cement and utilization of fly ash, which is another waste product piling in huge quantities in thermal power plants. To examine the use of geopolymer as a replacement to cement, it is essential to investigate normal consistency, final setting time and compressive strength of geopolymer which are routine tests generally conducted for cement. The procedure adopted for determining the normal consistency, final setting time and compressive strength of geopolymer is same as the procedure adopted for cement. In these tests, cement is replaced by geopolymer material and water is replaced by alkaline activator solution. The parameters considered in this investigation are geopolymer source material (fly ash and GGBS) and alkaline activator consisting of sodium meta silicate and sodium hydroxide of different molarities (8, 12, 16 M). The ratio of sodium meta silicate to sodium hydroxide considered in this study is 2.5. The test results indicated that combination of fly ash and GGBS results in decreased final setting time and increased compressive strength. It was also observed that increase in sodium hydroxide increases compressive strength of geopolymer mortar.