Effect of Silicate Content on the Properties of Alkali-Activated Blast Furnace Slag Paste

The effect of silicate content (SiO2/Na2O) of an activator on physical and mechanical properties of alkali-activated blast furnace slag paste has been investigated. The paste was produced by activating blast furnace slag with sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solution. The SiO2/Na2O ratio varied from 0.2 to 1.2. The test specimens were cast and cured in water (fully immersed condition) at room temperature and the direct compressive strength at the age of 3, 7, 14, 21, 28 days were obtained. It has been observed that the compressive strength and ultrasonic pulse velocity of test specimen increases with the increase in silicate content up to a silicate ratio of 0.8. Compressive strength is found to be a maximum 44.53 MPa at 28 days. It is noticed further that the compressive strength increases with age. It is also observed that the silicate ratio has a significant influence on porosity, water absorption and water sorptivity. The mineralogical and micro-structural changes were studied using XRD and SEM/EDX, while porosity, total pore volume, pore-size distribution, etc., were studied using mercury intrusion porosimetry.