Dissolution Phenomena of Ca0-Si0₂-H₂0 Gel at Ca/Si>l Coexisting with Ettringite System

Abstract

We have studied the influence of interaction between CaO-Si02-H20 (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=l.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 l<Ca/Si:Sl.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 so~with Si tetrahedra in the structure of C-S-H gel, these discrepancies are discussed in this study.