Dissolution phenomena of CaO-SiO2-H2O gel at Ca/Si>1 coexisting with ettringite system

We have studied the influence of interaction between CaO-SiO2-H2O (C-S-H) gel and ettringite (AFt) on their dissolution regarding the initial chemical feature of degraded cement pore water. In this work, firstly dissolution experiments were performed in C-S-H gel at Ca/Si=1.0, 1.2 and 1.47 coexisting with AFt of which amount was 5% of mol corresponding to each C-S-H gel. Secondly, assuming the congruent dissolution of AFt, dissolution of the same system was calculated by combining with the dissolution model of C-S-H gel at 1<Ca/Si≤1.5, considering without interaction between C-S-H gel and AFt. Measured and calculated results of Ca, Si Al and S total concentrations and pH values of C-S-H gel coexisting with AFt system were investigated. Discrepancies between experimental and calculated Ca, Si, Al and S total concentrations and pH values suggested the importance of interaction phenomena in C-S-H gel coexisting with AFt system. By considering the substitutions of Al(OH)4- and SO42- with Si tetrahedra in the structure of C-S-H gel, these discrepancies are discussed in this study. (author)