Alkaline activation of metakaolin and calcium hydroxide mixtures: influence of temperature, activator concentration and solids ratio

Abstract Metakaolin is a highly reactive metastable clay that reacts with alkaline solutions forming a cementitious material with high mechanical performance. This material fixes alkalis as structural components. When metakaolin activation is carried out with highly concentrated alkaline solutions in the presence of calcium hydroxide, the main reaction product is a sodium aluminosilicate similar to that obtained when metakaolin is activated in the absence of calcium hydroxide. Additionally, the formation of CSH gel as a secondary product is also observed. The rate of polymer formation is influenced by parameters such as curing temperature, alkali concentration, initial solids content, etc. When the activator concentration increases, a delay in polymer formation is produced, whereas temperature accelerates its formation. The solids ratio (metakaolin/Ca(OH)2) does not influence the rate of aluminosilicate formation, but it is demonstrated that larger product precipitation is produced when the solids ratio increases.