Impact of carbonation on chemical and mineralogical properties of stabilized and solidified matrices

ABSTRACT: The purpose of this study is to determine the impact of carbonation, the reaction of atmospheric CO2 with the cementitious matrix, on the chemical and mineralogical properties of stabilized and solidified (S/S) matrices. The evolution of carbonation with time was followed using thermogravimetric analyses (TGA). X-ray powder diffraction (XRD) allowed the mineral phases of S/S matrices to be identified before and after carbonation. The results showed that carbonation causes the complete and partial transformation of portlandite and C-S-H respectively to calcium carbonate. Geochemical modeling of long-term carbonation of monoliths using PHREEQC showed a decrease in monolith pH, an increase in the calcium, silicon and aluminum concentrations in solution because of the dissolution of the portlandite and the anhydrous tricalcium aluminate and the decalcification of C-S-H. Calcium concentration decreased with acidification of the solution because of precipitation of calcium carbonate. Silicon concentration has been stabilized in acidic medium because of the formation of silica gel by the C-S-H carbonation. The immobilization of lead by carbonation was also shown.