IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE) e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 11, Issue 2 Ver. I (Mar- Apr. 2014), PP 73-79 www.iosrjournals.org www.iosrjournals.org 73 | Page Durability Study of Geopolymer Paste Blended with Blast Furnace Slag Debabrata Dutta 1 , Somnath Ghosh 2 1. Research Scholar, Department of Civil Engineering, Jadavpur University, Kolkata- 700032, W.B, India., 2. Professor, Dept. of Civil Engineering, Jadavpur University, Kolkata- 700032, W.B, India. Abstract: In this program consequence of incorporating blast furnace slag on mechanical properties and durability of resulting fly ash geopolymer paste sample was investigated. The program consisted immersion of geopolymer samples having percentage blast furnace slag ranging from 10 to 20 of fly ash in a 10% magnesium sulfate solution up to a period of 15 weeks and evaluation of its resistance in terms visual appearance, change in weight and compressive strength at regular interval. Addition of blast furnace slag considerably improved mechanical properties and durability of geopolymers paste. Keywords: Fly ash, Blast Furnace Slag, Geopolymer, Apparent porosity, Sorptivity, Compressive Strength, Durability. I. INTRODUCTION Geopolymeric binders [1, 2, 3] are a types of inorganic binding agents whose common feature is alkaline activation of clinker or substances with latent hydraulic properties. Geopolymer shows potential more than ever in a few aggressive situations where Portland cement concretes are vulnerable [4]. The presence of zeolite-type substances is accountable for improving the properties of the alkali-activated binders, for example by rising their resistance to acids [5] or refining their ability to immobilize heavy metals [6, 7]. Geopolymer materials are reported to exhibit high early strength, better durability and have almost no alkali-aggregate reaction [8]. These materials are therefore expected to be cement for the future [9]. Low calcium fly ash based geopolymer prepared with different activators have shown higher compressive strengths and excellent performance under different acidic and sulphate exposure [10-16]. It has also been reported to be highly resistant to elevated temperatures [17-19]. Geopolymer activated by a mixture of sodium hydroxide and sodium silicate solution shows higher compressive strength [10, 16, 17]. The addition of reasonable amount of minerals to a geopolymer can have significant enhancement on the geopolymer structure and properties. Temuujin et al. [20] recommended that the addition of calcium compounds CaO and Ca(OH)2 improves mechanical properties of the fly ash-based geopolymers cured at ambient temperature. It was investigated that lime through pozzolanic reaction form a strong inter particle bond with amorphous silica and alumina [21]. Positive effect in conventional cement concrete by adding blast furnace slag has already been studied [22]. In this study blast furnace slag was used as a source material of calcium carbonate. The aim of the study was to predict the effect of addition of blast furnace slag as a supplementary material on mechanical properties and durability of fly ash based geopolymer pastes. Blast furnace slag by weight of 10% and 20% by fly ash was added to the fly ash based geopolymer paste. The assessment regarding durability of geopolymer materials was done by regular monitoring of its physical appearance, weight changes and compressive strength changes on exposure to 10% magnesium sulphate solution. Effects of apparent porosity and water sorptivity on weight and strength changes have also been predicted. II. EXPERIMENTAL A. Materials For this research purpose low calcium Class F fly ash was collected from Kolaghat Thermal Power Plant near Kolkata, India. It had chemical composition as given in table-1. About 75% of particles were finer than 45 micron and Blaine’s specific surface was 380m 2 /kg. The blast furnace slag used was in powdered form having specific gravity 2.8, bulk density 1236 kg/m 3 , consisting of 39.07% CaO. The average particle size of blast furnace slag was varied between 35μ to 65μ. The chemical composition of blast furnace slag is given in Table- 2. Laboratory grade sodium hydroxide in pellet form (98 percent purity) and sodium silicate solution (Na 2 O= 8%, SiO 2 =26.5% and 65.5% water) with silicate modulus ~ 3.3 and a bulk density of 1410 kg/m 3 was supplied by Loba Chemie Ltd, India. The alkaline activating solution was prepared by dissolving required quantity of sodium hydroxide pellets in water. The activator solution (sodium hydroxide and water) was left for 24 hours after that predetermined quantity of sodium silicate solution was added 3 hours before being used to manufacture geopolymer specimens. This activator solution had Na 2 O content equal to 8.0% of fly ash and