Mix design formulation range for metakaolin-based geopolymer synthesis

Abstract

This article presents a range of mix design formulations to obtain metakaolinbased geopolymer synthesis. Geopolymer samples were synthesized from metakaolin, a 10 M sodium hydroxide solution, and alkaline sodium silicate. These three components were mixed in different proportions to form a paste which was molded in a cylindrical shape, set at room temperature for 24 hours, and demolded. The workability of the paste, the integrity of the samples, development of efflorescence, and the presence of undissolved metakaolin particles in the microstructure of the geopolymer matrix were observed. Since sodium and water play a vital role in the geopolymerization and were added at fixed proportions, a mix design was employed based on the molar proportions of aluminum, silicon, and sodium plus water. The simplex design plot was able to separate the regions of a mix of the components that showed different behaviors according to the observed responses. The dissolution of metakaolin, condensation of orthosialate and silicate species, which are expected to interact with each other according to the model of geopolymerization of Davidovits, can explain the observed results. "Good results" (no release of white powder, no efflorescence, no shrinkage, and no cracks) after 28 days of curing at room conditions were observed for the molar proportions 0.097 < Al < 0.112, 0.120 < Si < 0.178, and 0.711 < Na+H 2 O < 0.775 (Na/H 2 O = 0.185).

Entrapment of Acridine Orange in Metakaolin-Based Geopolymer: A Feasibility Study

“…Metakaolin, MK (Al 2 Si 2 O 7 ), the product of thermal dehydroxylation of kaolinite (Al 2 Si 2 O 5 (OH) 4 ), has been widely used as a model aluminosilicate precursor in the evolution of alkali-activated solids [ 1 , 2 , 3 ]. The extremely fine grain size of such a mineral assures an extended dissolution of Al 3+ and Si 4+ ions in strong alkaline media where they generate hydrated moieties, Al(OH) 4 −1 and Si(OH) 4 [ 4 ].…”