Application of the Taguchi approach for the composition optimization of alkali activated fly ash binders

• Hellenic fly ash is converted to structural material having cement-competitive strength.
• Taguchi method permitted the simultaneous optimization of several factors by conducting the minimum number of experiments.
• The alkali to aluminum ratio has the highest impact on the strength development.
• The interrelation of precursor composition, microstructure and strength is reported.

This paper presents an experimental study carried out to optimize the mix proportions of fly ash based geopolymers, in order to achieve the maximum compressive strength. The Taguchi design methodology was applied and the experiments were designed using a L16 orthogonal array with three factors varying at four levels each. The effect of alkali content, alkali kind and silicon content in the activation solution is analyzed using mean response data and ANOVA technique. The final products were examined using XRD, FTIR and SEM. According to the results, the optimum values of the process parameters are sodium to aluminum ratio of 0.85 in the starting mixture and silicon to sodium oxide of 1.35 in the activation solution. The mean value of optimal strength is predicted as 42.6 MPa, with a tolerance of ±3.1 MPa, for a 95% confidence interval. Confirmatory experimental result obtained for the optimum conditions is 43.1 MPa.