VOL. 2, NO. 3, April 2012 ISSN 2225-7217 ARPN Journal of Science and Technology ©2011-2012. All rights reserved. http://www.ejournalofscience.org 170 Effect of Nano-Silica on Alkali Activated Water-Cooled Slag Geopolymer 1 H.M.Khater, 2 B.A.El-Sabbagh, 3 M.Fanny, 4 M.Ezzat, 5 M.Lottfy Housing and Building National Research Centre (HBNRC) 87 El-Tahrir St., Dokki, Giza, P.O. Box 1770 Cairo 1 Email: Hkhater4@yahoo.com ABSTRACT 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 Keywords: Nano- silica, Geopolymer, Slag, Microstructure, Thermal properties. C. Gelenium Ace super-plasticizer was added in the ratio of 4% from the dry weight to ensure best dispersion of the nano silica. The results showed that increasing in the percentage of nano silica results in enhancement in the mechanical properties as compared to the control mix up to 90 days. The study of thermal properties is taken place for the different ratios by experimental and mathematical evaluation. The study showed that the thermal properties as well as thermal insulation property are improved with the increase of ratio of nano silica. 1. INTRODUCTION Geopolymers are inorganic polymeric materials, firstly developed by Joseph Davidovits in 1970s. Geopolymerization involves a chemical reaction between alumino-silicate oxides and alkali metal silicate solutions under highly alkaline conditions yielding amorphous to semi-crystalline three-dimensional polymeric structures, which consist of Si–O–Al bonds [1], and gave a fresh insight into this class of inorganic polymer. Geopolymerization is being considered for replacing traditional structural materials and offers a possible solution to the immobilization of toxic and radioactive wastes as well as the treatment of industrial wastes to produce value added construction materials. Therefore, there is an increasing need for multiple source materials to be jointly geopolymerised to maximally exploit the respective properties of the individual sources regarding compressive strength, stability and durability [2]. Geopolymer can be thought of as a new generation binder as a substitute for the calcium silicate hydrate which are essential components of Portland cement. Ordinary Portland Cement (OPC) is the main ingredient used in the production of concrete-the most widely used construction material in the world. In the past, concrete was simply a composite of OPC paste with aggregates, however, modern-day concrete incorporates other cementitious materials, which act as partial replacements of OPC. The manufacturing of OPC requires the burning of large quantities of fuel, and decomposition of limestone. Both, burning of fuel and decomposition of limestone, result in significant emissions of carbon dioxide. For every ton of OPC manufactured, nearly one ton of CO 2 is produced depending on the production process adopted [3]. Cement plants are reported to emit up to 1.5 billion tons of CO 2 into the atmosphere annually [4,5]. Hence, environmental preservation has become a driving force behind the search for new sustainable and environmentally friendly composites to replace conventional concrete produced from OPC. In 1978, Davidovits [6] introduced the word ‘geopolymer’ to describe an alternative cementitious material, which has ceramic-like properties. As opposed to OPC, the manufacture of aluminosilicate-based geopolymer does not consume high levels of energy, as water cooled slag (WCS), known also as ground granulated blast furnace slag, is already an industrial by- product. This geopolymer technology has the potential to reduce emissions by 80% [3] because high temperature calcining is not required. It also exhibits ceramic-like properties with superior resistance to fire at elevated temperatures. Geopolymer can be produced by combining a pozzolanic compound or aluminosilicate source material with highly alkaline solutions [7].