Design Mix Formulation and Optimization of Metakaolin Based Alkali Activated Geopolymer Concrete with the Taguchi Method

Abstract

Concrete mix formulation is the science of deciding relative proportions of ingredients of concrete, to achieve desired properties in the most economical way. Formulation of concrete mix requires adequate knowledge of the properties of its constituents. Aluminosilicate materials have recently found applications in construction industry due to their unique and flexible properties. The metakaolin used for this study was the locally sourced kaolin calcined at 750oC. The alkali activating reagents include a fixed concentration of sodium silicate solution and sodium hydroxide solutions of three different concentrations. Strength development of metakaolin – based geopolymer concrete is quite different from that of ordinary Portland cement concrete due to differences in their constituents, hence, the need for special formulation, most especially when high strength is required. Taguchi method was adopted in this study to formulate mix proportion for high compressive strength of geopolymer concrete at ambient curing condition. Four parameters were selected that are more likely to influence the compressive strength of metakaolin – based geopolymer concrete, these include aggregate content, alkali – binder ratio, alkali reagent ratio and alkali reagent concentration. The effect of these parameters on the density, workability and compressive strength at 3, 7 and 28 days are determined. The result showed that an optimum mix obtained from a formulation formula (2.75SiO2 * Al2O3 * 0.55Na2O * 6.8H2O) produced a compressive strength of 62MPa at 28 days of open air curing. It was revealed that the molar concentration of the alkali reagent (sodium hydroxide) should be kept within 10M range for an open air curing, the alkali reagents to binder ratio should be kept at 0.7 or less with no addition of water to achieve reasonable workability. Also, it has been observed that the bulk density of metakaolin – based geopolymer concrete that yielded substantial strength fall within 2250kg/m3 and 2350 kg/m3.