Compressive strength optimization of the ambient-cured metakaolin-based geopolymer mortar using the Taguchi design approach

Abstract

This study utilized raw natural kaolinite sourced along Pugu hills, Tanzania, as the aluminosilicate source. To optimize the compressive strength, nine (9) metakaolin geopolymer formulations were activated using the Taguchi technique at various Na2SiO3/NaOH mass ratios, NaOH concentrations, and alkaline/binder ratios. The ideal parameters were 12 M, 2.5, and 0.8 Na2SiO3/NaOH mass ratios, NaOH concentration, and alkaline/binder ratios, respectively, resulting in a compressive strength of 70.38 MPa. When the optimized geopolymer was exposed to a higher temperature, its compressive strength increased by 15.57 % at 200°C compared to room temperature. Compressive strength decreased with exposure over 200°C, and weight loss and water absorption were directly correlated with this. The SEM results show that the former lacks a well-linked geopolymer network when comparing weak and superior formulations. High-strength formulations are verified to include higher levels of orthoclase and albite, according to Rietveld refinement and XRD research. The XRD patterns showed the development of sanidine, chrysotile, and nepheline crystalline phases at temperatures higher than 200°C, which may have contributed to the decrease in strength of the geopolymer specimens