Optimizing the Properties of Metakaolin-based (Na, K)-Geopolymer Using Taguchi Design Method

Geopolymer paste is an innovative construction material which shall be produced by chemical action of inorganic molecules. It is a more environmentally friendly alternative to conventional Portland cement which is abundantly available worldwide. In this study, the influence of different alkaline activators (Na and K) on the mechanical and thermal behaviors of metakaolin-based geopolymer was investigated. The aims of this study is to find out the mixes and their process parameters, which are appropriate to produce Geopolymer paste with one of the highest compressive strength, highest - lowest porosity and highest- lowest initial and final setting time. Taguchi method is used in the design of the experiments for the metakaolin-based Geopolymer. Five factors were selected as process parameters that are more likely to affect the Geopolymer characteristics. These are the amount of Si, alkali type, alkali reagents ratio, mixing time, and water content. The effect of these parameters on the setting time, density, porosity, compressive strengths at 7 and 28 days. The results of study found that the Geopolymer paste with high compressive strength of (107.2MPa) can be obtained with the formula (0.2K2O.0.8Na2O. Al2O3. 3.6SiO2.xH2O) using proper processing condition in which the alkali silicates to the alkali hydroxides molar ratio should be kept in the range of 2.26. The results revealed that the use of alkali solution of K-ions and Na-ions improves the compressive strength of the geopolymer remarkably as compared with the use of Na-ions solution along. In addition, it has been noticed that the setting time is reduced, for geopolymers with silica content of less than 3.8, when K-ions is used. Similarly, the bulk density of geopolymers is found to be reduced by adding K-ions.