Modeling and optimization of compressive strength and bulk density of metakaolin-based geopolymer using central composite design: A numerical and experimental study

Geopolymers have received considerable attention due to their properties and applications as environmentally friendly alternatives to ordinary Portland cement. This paper reports the use of a central composite design technique to model four synthesis parameters (curing temperature, SiO2/Al2O3, Na2O/SiO2, and H2O/Na2O ratio) to optimize the compressive strength and bulk density of metakaolin-based geopolymer bodies. Thirty-one geopolymer paste compositions, derived by applying central composite design software, were prepared and their compressive strengths and bulk densities were measured. The experimental data were then modeled by the method of analysis of variance and the effect of the interactions between the four chosen variables parameters on the compressive strength and bulk density was studied by surface plots. The optimum values of the four variables, determined in this way, were a curing temperature of 67 degrees C, SiO2/Al2O3=2.90, Na2O/SiO2=0.20, H2O/Na2O=13.75. The measured strength and density of this sample was 62.4 MPa and 1.59 g/cm(3) respectively, and the amorphous character of this sample was demonstrated by XRD.