Kinetics of Al uptake in synthetic calcium silicate hydrate (C-S-H)
Yiru Yan, Ellina Bernard, George Dan Miron, Daniel Rentsch, Bin Ma, Karen Scrivener, Barbara Lothenbach
Abstract
The effect of equilibration time on the composition, structure and solubility of calcium aluminate silicate hydrate (C-A-S-H) was investigated in 0.5 M NaOH solutions at Al/Si = 0.1. Longer equilibration time led to longer silica chains, to less Na and, to more Ca in C-A-S-H, as well as to an increased fraction of tetrahedral Al(IV) charge-balanced by Ca2+. Aluminium, calcium and silicon concentrations in solution changed rapidly during the first day, while after 14 days only minor changes were observed. The long-term concentrations could be reproduced well by the thermodynamic CASH+ model. Over a longer time span of up to 10 years, a slow redistribution of Si and Al in C-A-S-H as well as the partial replacement of Na+ by Ca2+ in the interlayer space was observed. This study highlights the importance of considering the effect of time on C-A-S-H structure.