Strength and Durability Study of Fly ash 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 signi cant 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 nd alternatives to make environment friendly concrete. One of the alternative to produce more environmentally friendly concrete is to replace the amount of Portland cement in concrete with by-product materials such as

y ash. An important investigation in this regard is the development of high volume

y ash concrete that utilizes up to 60 percent of y ash, and yet possesses excellent mechanical properties with enhanced durability performance. Another alternative to make environmentally friendly concrete is the development of inorganic aluminasilicate polymer, called Geopolymer, synthesized from materials of geological origin or by-product materials such as y ash that is rich in silicon and aluminum. Fly ash, one of the source materials for geopolymer binders, is available abundantly worldwide, but to date its utilization is limited. Currently, 90 million tonnes of y ash is being generated annually in India. By exploring use of the y 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. Experimental work comprises preliminary investigation to nd the e ect of salient parameters on y ash based geopolymer concrete. Total ten parameters i.e. composition of alkaline liquid, ratio of alkaline liquid to y ash, concentration of sodium hydroxide, ratio of sodium silicate to sodium hydroxide, curing time, curing temperature, dosage of superplasticiser, rest period, additional water content in the mix, replacement of

y ash by metakaolin have been investigated and results of these parameters is used for developing mix design process. Three concrete mixes i.e. mix-1 with the y ash based geopolymer concrete, mix-2 with y ash replaced by 10% of metakaolin, mix-3 with OPC concrete having equivalent amount of OPC to that of y ash in concrete mix-1 have been designed for investigation the mechanical and durability properties. Class F y ash is used as a source material. Geopolymer concrete has been heat cured for 24 hours at 750C temperature. Sodium silicate and Sodium hydroxide solution is used as alkali activators. A small amount of water and naphthalene based superplasticizer also has been incorporated for maintaining consistent workability for all concrete mixes. Mechanical properties like Compressive strength, Split Tensile strength and Flexural strength of geopolymer concretes is investigated and results are compared for all concrete mixes. A standard size cubes, beams and cylinders as per IS provisions are used for evaluating the Compressive strength, Split Tensile strength and Flexural strength. Specimens have been tested at the age of 3, 7, and 28 days, respectively. Sulfate resistance and acid resistance test is conducted for durability study. The performance of concrete mixes evaluated based on visual appearance, change in mass, and change in compressive strength after the exposure period of 42 days. UPV test is performed for checking the quality of concrete after the specimens of durability study. 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. Geopolymer concrete is quite e ective in terms of providing e ective resistance to sulphate and acid exposures. Geopolymer concretes have exhibited minimum change in mass and good strength retention capacity after the designated exposures. The geopolymer concrete is a good alternative as a construction material from both strength and durability considerations.