Ground granulated blast furnace slag is a finely ground, rapidly chilled aluminosilicate melt material 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 6% sodium hydroxide was studied. Nano silica is an ultrafine material that can modify mechanical, microstructural and thermal properties of geopolymer products and added to the geopolymer mix in the ratio of 0, 0.50,1 and 1.5% of the dry weight. Curing was performed under 100% relative humidity and at a temperature of 38 o