RESISTANCE OF ALKALI ACTIVATED WATER-COOLED SLAG GEOPOLYMER TO SULPHATE ATTACK

Ground granulated blast furnace slag is a finely ground, rapidly chilled aluminosilicate melt material that is separated from molten iron in the blast furnace as a by-product. Rapid cooling results in an amorphous or a glassy phase known as GGBFS or water cooled slag (WCS). Alkaline activation of latent hydraulic WCS by sodium hydroxide and/or sodium silicate in different ratios was studied. Curing was performed under 100% relative humidity and at a temperature of 38 C. The results showed that mixing of both sodium hydroxide and sodium silicate in a ratio of 3:3 is optimum, giving better mechanical as well as microstructural characteristics compared with cement mortar with varying cement content (cement:sand ratios of 1:3 and 1:2). Sodium hydroxide:sodium silicate (3:3 by weight) activator showed superior resistance to attack by 5% MgSO4 as compared with other mixes. Strength reduction ratios after 6 months of immersion relative to the strength of 28 days cured specimens are 52, 49 and 21% upon using 2% NaOH, 6% NaOH and sodium hydroxide:sodium silicate (3:3).