An experimental study on fly ash based geopolymer concrete

Abstract

Concrete is the most abundant manmade material in the world. One of the main ingredients in a normal concrete mixture is Portland cement. However the production of cement is responsible for approximately 5% of the world’s carbon dioxide emissions. In order to create a green world it is needed to develop the replacement of cement as a green building material. It is estimated that the production of cement will increased to 3.2 billion tons from 2.2 billion tons till 2018. On the other hand, the climate change due to global warming and environmental protection has become major concerns. The global warming is caused by the emission of greenhouse gases, such as carbon dioxide to the atmosphere by human activities. The production of Portland cement and the mortar preparation involves the emission of carbon dioxide, thus by replacing the Portland cement there can be reduction in the carbon dioxide emission. The thermal power plants produce fly ash in a very large amount. More than 175 million tonnes of fly ash is produced every year; this would require 40000 hectares of land for disposal. The Ministry of Power, Govt. of India estimates 1800 million tonnes of coal to be used every year and 600 million tonnes of fly ash generated by 2031-2032.Now the problem arises for its disposal. Continuing on working in direction to find the alternative for the cement, the concept that the fly ash is also having binding property has been employed. This leads to the direction to work on the replacement of cement from the concrete by fly ash.
Therefore the focus to work in this direction acquainting with the idea that the replacement of cement is possible with fly ash and this alternative to regular concrete is known as Geopolymer Concrete (GPC). In this paper full replacement of cement with fly ash to produce the Geopolymer concrete was studied in detail. To produce the Geopolymer concrete, the constituent materials used are fly ash (which is a bye product obtained from thermal power plants) and the alkaline activators. The alkaline activators used in this study for the polymerization are sodium hydroxide (NaOH) in flakes form and sodium meta-silicate (Na2SiO3) in gel form. The objective of the present work is to compare the strength parameters of the Geopolymer concrete with Concrete made with Ordinary Portland cement (OPC) and also to see the effect of various conditions such as the curing time, curing temperatures on the strength of geopolymer concrete by the replacement of the cement with Fly Ash and Alkaline Activators. For this cube specimens are casted of size 150mm x 150mm x 150mm for compressive strength test & the cylinder specimen of size 150mm dia., 300mm height for split tensile strength test. The casted specimens were kept in the oven at 60°C and 120°C for 24, 48 and 72 hrs to ascertain the behaviour of geopolymer concrete, and to know the maximum strength we can achieve by Geopolymer concrete.