PREPARATION AND STUDY OF GEOPOLYMER CONCRETE AS AN ALTERNATIVE TO CONVENTIONAL CEMENT CONCRETE

Current concerns about global warming due to the buildup of greenhouse gases in ouratmosphere have prompted the cement industry to investigate alternatives to ordinary Portland Cement (OPC). One ton of carbon dioxide is produced for every ton of OPC cement. A sustainable alternative to this OPC is low CO2 producing Geopolymer cement.Geopolymers produce no CO2 in chemical reactions and less emitted carbon dioxide due to manufacturing techniques. Hence, GPC’s have emerged as a promising alternative to conventional cement concrete in the view of sustainability.

What is Geoplymer Concrete (GPC)?

Davidovits (1988; 1994) proposed that an alkaline liquid could be used to react with silicon (Si) and aluminum (Al) in a source material of geological origin or in by-product materials such as fly ash and rice husk ash to produce binders. Because the chemical reaction that takes place in this case is a polymerization process, he coined the term 'Geopolymer' to represent these binders. The primary difference between Geopolymer concrete and Portland cement concrete is the binder. Unlike ordinary Portland/pozzolanic cements, geopolymers do not form calcium- silicate-hydrates (C-S-H gel) for matrix formation and strength, but have an inorganic polymer of alumino-silicates as the binder to bind the loose coarse aggregates, fine aggregates, and other un-reacted materials together. This is the fundamental concept of Geopolymer Concrete.

Preparation of Geopolymer Concrete

There are two main constituents of GPC, namely the source materials and the alkaline liquids. The source materials for geopolymer concrete should be rich in silicon (Si) and aluminium (Al). These could be natural minerals such as kaolinite clays or by-product materials such as fly ash, silica fume, slag, rice-husk ash etc. The alkaline liquid consists of an alkaline activator solution (AAS) which is a combination of solutions of alkali silicates and hydroxides (eg: Sodium silicates and Sodium hydroxdes),besides distilled water. The role of AAS is to activate the geopolymeric source materials and conduct the polymerization.

The following materials are generally used to produce GPCs:i. Fly ash (low calcium ASTM class F)ii. GGBS,iii. Fine aggregatesiv. Coarse aggregatesv. Alkaline activator solution (AAS) : The most common alkaline liquid used in

geopolymerisation is a combination of sodium hydroxide (NaOH) or potassium hydroxide (KOH) and sodium silicate (Na2SiO3) or potassium silicate.

Aggregates + Flyash + alkaline activator (Na silicates and NaOH) = GPC

The sodium silicate solution A53 with SiO2-to-Na2O ratio by mass of approximately 2 ( i.e., SiO2 = 29.4%, Na2O = 14.7%, and water = 55.9% by mass)The sodium hydroxide with 97-98% purity, in flake or pellet form, is commercially available. The solids must be dissolved in water to make a solution with the required concentration in the range between 8 Molar and 16 Molar.Distilled water is used to make these solutions.The ratio of Sodium silicate to sodium hydroxide is usually kept 2.5 and several mix proportions can be used in getting the desired properties. An industrially available super plasticizer water retardant can be used to increase workability.

The test samples (cubes of 15*15*15cm or 10*10*10cm) are steam cured or dry cured and tested for various properties as per standard procedures and compared to those that of OPCC.

This paper deals with the detailed preparation method of Geopolymer concretes and comparison of GPC with Ordinary Portland Cement Concrete in terms of 3 day, 7day, 28 days Compressive strength, Durability, Creep and Drying shrinkage, Sulphate resistance and Sulphuric Acid resistance. Various mix proportions used in this comparative study are given and discussed in detail. It lists down the major advantages and disadvantages of GPCs in comparison with ordinary Portland cement. The behavior of geopolymer concrete under various laboratory tests is explained. There is also a brief mention of the various applications of geopolymer concrete in the modern day construction industry.