Computational design of fly ash geopolymer mortar using experimental and attribute evaluation approaches

Abstract

Geopolymer is a ceramic-like inorganic material synthesized at room temperature and is a potential sustainable replacement of Portland cement. In the present work, a comprehensive experimental program was designed to evaluate the relative importance of mix design factors controlling the strength of fly ash geopolymer mortar. Restrained factors, namely, temperature of curing; alkaline solution to fly ash (L/FA) ratio; sodium silicate to sodium hydroxide (SS/SH) ratio; sodium hydroxide molarity; and fly ash to sand (FA/Sand) ratio, and unrestrained factors, namely, H2O/Na2O; SiO2/Al2O3; SiO2/Na2O; and Al2O3/Na2O molar ratios, were considered for evaluation. Feature subset selection and multivariate adaptive regression splines (MARS) techniques were used to determine the significance of these factors. Results show that temperature of curing is the most significant factor. FA/Sand and L/FA are found to affect compressive strength more significantly than sodium hydroxide molarity and SS/SH. Except for H2O/Na2O molar ratio, other molar ratios were observed to be very less significant. It is noted that mix design of geopolymer mortar should not be based on the molar ratios, instead mix design must be prepared by controlling the restrained factors. The findings of this study should be helpful in optimization of design factors leading to a robust geopolymer mix.