Superplasticizers (cement concrete water reducers) are applied to improve the flowability of calcium-rich, alkali-activated materials, with inconsistent results. However, superplasticizer applications are limited in metakaolin-based geopolymers. The possibility of using polycarboxylate superplasticizers and methyl isobutyl carbinol (MIBC) to ameliorate the flowability of metakaolin-based geopolymers was investigated. The ratio of metakaolin, fumed silica, NaOH or KOH, and water in geopolymers at a Na2O or K2O:Al2O3:SiO2:H2O ratio = 1:1:4:10 or 1:1:4:11 was maintained in the formulations. In this study, ether- or ester-based polycarboxylate superplasticizers did not improve the workability of fresh metakaolin-based Na-geopolymers. A low MIBC dose (0.5 wt.% of metakaolin) improved the flowability by 19% and additionally increased the 7-day compressive strength by 22% from 68 to 83 MPa for plain Na-geopolymers. The entrained fine froths produced by adding MIBC during mixing likely reduced friction between metakaolin particles, and the slurry became more workable. Hence, the geopolymer mixture with an improved flowability became more homogenous, which ensured more extensive metakaolin dissolution and hydrolysis. A low MIBC dose could be effective for Na-geopolymers with dual benefits of improved workability and enhanced compressive strength.
Keywords: compressive strength; flowability; metakaolin-based geopolymers; methyl isobutyl carbinol.