Reaction kinetics of calcined smectite in a clinker-free model and a synthetic cement system in comparison with selected calcined phyllosilicates

Abstract

The investigations of clinker-free model and synthetic cement systems reveal deeper insight into the behavior of metasmectite during early hydration. The use of metasmectite accelerates the aluminate clinker reaction and influences the degree of hydration of alite. Its chemical reactivity can be demonstrated in clinker-free as well as model cement systems by direct quantification of the metasmectite, its portlandite consumption and C-S-H formation. The influence on sulfate balance reveals an interaction of metasmectite's negatively charged surfaces with ions from the pore solution and demonstrates that sulfate adsorption does not solely take place on surfaces of C-S-H. Overall, it can be concluded that the impediment of the alite hydration during early hydration due to metasmectite is rather insignificant compared to metakaolinite and is within the range of metaillite. These findings provide a significant contribution to the expected widespread use of calcined clays with a low metakaolinite content in cementitious systems.