Experimental Investigation on the Effect of Modulus and Concentration of Alkaline Solution on properties of the Alkali-Activated Slag Concrete

Alkali activated slag (AAS) binders can be used as a replacement to Portland cement. AAS concrete is made by slag activation with alkalis without the use of Portland cement. Due to the effect of alkalis on the properties of AAS concrete, in this study the effect of alkali concentration and sodium silicate modulus of alkaline solution on the setting time, slump, compressive strength and drying shrinkage of AAS concrete were investigated experimentally. For this purpose, 20 mix designs with different ratios of alkali concentration and sodium silicate modulus were cast and the setting time of paste and slump were tested in fresh state and in addition, concrete compressive strength of 7, 28 and 90 days and drying shrinkage of concrete samples up to 400 days, were measured. In most mixes, with increasing the alkali concentration and the sodium silicate modulus of the activator solution, the slump of fresh concrete was increased and the rate of the initial compressive strength development of the mixtures was enhanced but the setting time was lowered. However, in high alkali concentrations and silicate moduli, a decrease in compressive strength and an increase in setting time were observed with increasing the parameters of activator solution. However, with increasing the sodium silicate modulus and the concentration of the alkaline solution, the initial shrinkage rate was increased, but it was observed that the effect of the sodium silicate modulus is much higher than the alkali concentration on the final amount of the drying shrinkage of the samples.