Prediction of compressive strength of geopolymer products using central composite design

Abstract

Geopolymer products are formed by mixing of raw materials in the presence of activator solution of sodium hydroxide. The raw materials such as fly ash & bottom ash are by-products of power plants and granulated blast furnace slag (GBFS) is a by product of steel production units. Environment friendly disposal of these by products are a challenging problem because of the cost involved. This paper deals with the development of eco-friendly geopolymer products by using these industrial by- products. For effective use of these products it is important to know how the composition, concentration of activator solution and exposure to adverse environment affects the compressive strength of the product. In order to develop mathematical models to predict the effects of proportion of different raw materials, exposure time in various atmospheres (such as air, acetic acid, magnesium sulphate, sodium sulphate and sodium chloride) and concentration of activator solution on compressive strength of geopolymers, the statistical technique of Central Composite Design is chosen. The maximum compressive strengths predicted by the models for the cases, when samples are exposed to 1%, 2%, 3% NaCl solution are 12.79Mpa, 10.91 MPa and 11.38 MPa respectively, at the end of 140 days. Compared to that, the predicted compressive strength of the sample exposed to airis 14.33 MPa at the end of 140 days. The other important observation is that, in both the cases, the compressive strengths are increasing with the length of exposure time. This assumes importance as NaCl solution is highly corrosive. The peak values in both the cases are yet to reach. These are the most significant results that are obtained in this study.