Alternative binders based on lime and calcined clay

Abstract

Alternative binders are in this study defined as binders without Portland cement. In this particular project it will be based on calcined clay or fly ash as a source of reactive silica and alumina in combination with lime and calcium sulphate (e.g. gypsum) and/or calcium carbonate to stabilize special calcium aluminate phases like ettringite and/or calcium monocarboaluminate hydrate, respectively. Gaining strength is all about maximizing the transformation of liquid water to hydrates with hydraulic properties as fast as possible. Hence, admixtures speeding up the reaction kinetics can be part of the formulations as well. Two synergy principles have been described for making improved binders based on slaked lime and pozzolanic SCMs. One showing how neutral salts may accelerate by forming strong alkaline solutions in situ and another one how calcium carbonate can play a role when alumina containing SCMs are used by leading to an even higher conversion of liquid water into solid hydrates leading to lower porosity and higher strength. Calcined marl may substitute for calcined clay, but then the calcium carbonate content should be reduced in accordance with the remaining calcium carbonate content after calcination.