Development of Fly Ash and Slag Based Geopolymer Concrete

Abstract

Concrete is one of the widely used material all over the world. Ordinary Portland cement (OPC) is used as the primary binder to produce concrete. The demand of concrete is increasing day by day for the need of development of infrastructure facilities. However, it is well known that the production of OPC not only consumes significant amount of natural resources and energy but also releases substantial quality of carbon dioxide to the atmosphere. The global cement industry contributes around 2.8 billion tons of the greenhouse gas emissions annually, or about 7% of the total man-made greenhouse gas emissions to the earth’s atmosphere. It is essential to find alternatives to make environment friendly concrete. One of the alternatives to produce more environmental friendly concrete is to replace the amount of portland cement in concrete with by-product materials such as fly ash and ground granulated blast furnace slag. Another alternative to make environmental friendly concrete is the development of inorganic alumina-silicate polymer, called Geopolymer, synthesized from materials of geological origin or by-product materials such as fly ash that is rich in silicon and aluminum. By exploring use of the fly ash based and slag & fly ash based geopolymer concrete two environment related issues are tackled i.e. the high amount of CO2 released to the atmosphere during production of OPC and utilization of fly ash and slag. Experimental work in this major project comprises preliminary investigation on the fly ash based and slag & fly ash based geopolymer concrete. Class F unprocessed fly ash from thermal power station and Class F processed fly ash from Dirk India Private Limited has been used for fly ash based geopolymer concrete. Ground granulated blast furnace slag from JSW steel has been used for slag & fly ash based geopolymer concrete.The effect of good quality fly ash as well as slag on the mechanical properties like - Compressive Strength, Split Tensile Strength , Flexural Strength and Modulus of Elasticity of geopolymer concrete has been investigated. Results are compared for ordinary portland cement concrete, fly ash based geopolymer concrete and slag & fly ash based geopolymer concrete for M25 normal grade and M45 medium grade, respectively. For developing the mix proportion of geopolymer concrete, parameters like alkaline liquid to fly ash ratio 0.4, rest period 1 day, curing temperature 900°C, curing period 48 hours and concentration of NaOH solution 14 M are kept constant. The parameters such as alkaline liquid ratio 2 & 2.5, addition of super plasticizer 1.5% & 2.0%, extra water content 15% & 20% etc have been varied throughout investigation. The parameters giving highest results are selected for making fly ash based and slag & fly ash based geopolymer concrete. The density of geopolymer concrete was found equivalent to that of control concrete for both grades. For M25 grade geopolymer concrete, cement content is fully replaced by combination of unprocessed and processed fly ash (50:50) proportion in case of fly ash based geopolymer concrete and combination of slag & unprocessed fly ash (80:20) proportion for slag & fly ash based geopolymer concrete. For M45 grade concrete, cement content is fully replaced by combination of 25% unprocessed fly ash and 75% processed respectively for fly ash based geopolymer concrete and combination of 40% slag & 60% unprocessed fly ash respectively for slag & fly ash based geopolymer concrete have been used. The cubes, beams & cylinders are prepared as per IS provisions and tested for the Compressive strength, Split Tensile strength Flexural strength and Modulus of elasticity, respectively for all concrete mixes. Samples have been tested at 3, 7 and 28 days, respectively.Non destructive test such as Ultrasonic Pulse Velocity test and Rebound Hammer test are performed for checking the quality of concrete. The results have indicated that the geoplymer concrete gives good results for various mechanical properties as compared to control concrete. Very less amount of variation in mechanical properties have been observed in geopolymer concrete as compared to that of control concrete. The geopolymer concrete is a good alternative as a construction material from strength considerations.