Investigation on effects of fineness of flyash and alkaline ratio on mechanical properties of geopolymer concrete

Geopolymer is a new development in the world of concrete in which cement is totally replace by pozzolanic material like fly ash and activated by highly alkaline solutions to act as a binder in the concrete mix. Experimental investigation has been carried out to find the effect of fineness of fly ash and alkaline solutions ratio on the mechanical properties of fly ash based geopolymer concrete. Geopolymer concrete is produced by activating fly ash with a highly alkaline solution of sodium silicate containing 16.32% Na2O, 32.75% SiO2 and 50.93% H2O and sodium hydroxide solution having 13 molar concentrations is maintained constant throughout the study. Compressive strength, split-tensile strength and flexural strength are obtained using three samples of fly ash with fineness of 364, 442 and 610 m2/kg. Alkaline ratio (i.e., Na2SiO3/NaOH ratio) of 1, 1.5, 2, 2.5, 3 and solution to fly ash ratio of 0.35 is considered. The specimens are cured in an oven for 110 oC for 7 hrs and tested after 7 and 28 days rest period. It is observed that the fineness of fly ash in terms of specific surface area (m2/kg) increases the strength of geopolymer concrete and optimize at alkaline solution ratio at 1.5.