Influence of lime, calcium silicate and portlandite on alkali activation of calcined common clays

Abstract

The application of calcite rich common clays has marked impact on the formation of alkali-activated binders. Experiments have shown that the carbonate decomposition can be well controlled via the calcination procedure, whereby the majority of the decomposition and the subsequent CO2 release occurs above the calcination temperature of 750 ​°C. The decarbonation of the calcite can mostly be separated from the dehydroxylation of the layered silicates. Depending on the composition of the raw clay material, the CaCO3 decomposition leads either to the formation of lime or other Ca rich minerals. The mechanical properties of the alkali-activated binders were investigated and despite the very low amounts of layered silicates of the clay raw materials and the high content of unreactive minerals, compressive strengths of above 20 ​MPa of the mortars could be obtained. The presence of lime in calcined clays up to an adequate amount has a positive effect on post-solidification and the carbonation resistance of the mortars.

Keywords

• Alkali activation
• Geopolymers
• Alkali-activated binders
• Common clays
• Calcium oxide