Microstructure Studies on the Effect of Alkaline Activators to Flyash Ratio on Geopolymer Concrete

Abstract

Abstract: Fly ash-based geopolymers are new binding materials produced to replace the ordinary Portland cement used in concrete. In this research, the effect of alkaline activators to flyash ratio on the compressive, split tensile, flexural strength and microstructural study of fly ash-based geopolymers were studied. Alkaline activators to fly ash ratios of 0.30, 0.35, 0.40 and 0.45 and ratio of sodium silicate (Na2SiO3) to sodium hydroxide (NaOH) maintained constant throughout the study. The alkaline activator solution was prepared by mixing sodium silicate (Na2SiO3) with a 12M NaOH solution. The samples were casted and cured at a temperature 60° C for 24 hours in Dry oven and kept at room temperature till the testing (7days and 28 days). The test results indicated that the compressive, split tensile and flexural strength increased when the ratio of alkaline activator to fly ash was decreased. The ratio of 0.30 produced the maximum compressive strength, which was 68.02 MPa at 28 days curing. SEM (Scanning Electron Microscope) test conducted on geopolymer concrete samples and observed that alkaline activators to fly ash ratio of 0.30 and 0.35, geopolymer samples has the continuous, homogenous matrices and less porous structure because of the high dissolution of the fly ash particles in the alkaline activator solution.