Hydration products in two aged cement pastes

The hydration products in two aged cement pastes (DTA/DTG/TG) were compared with those in fresh ones (static heating, SH) and were also studied by mass spectrometry (MS), IR and thermo XRD-analysis. The products considered here were: the sorbed water, the CSH gel including hydrates, portlandite, calcite, aragonite and vaterite. Except carbonates their content was higher in the stronger paste C-43, than in C-33, but lowered with ageing (only the CSH gel water remained approximately unchanged). The sorbed water content became with time lower and similar in both pastes (it evaporated up to 155-185DGC in TG); the escape of the rest moved to higher temperatures (500-700DGC). The three DTG peaks at 200-400DGC indicated jennite-like phase in the CSH gel; the mass loss (155-460DGC) was higher on ageing due to development of organic matter, especially in C-43 (DTA, TG, IR). Portlandite content changed little and carbonate content increased considerably. They decomposed in air at 470 and 720-740DGC, in argon at 450 and 680-710DGC and in vacuum at 400 and 630DGC, respectively (DTG peak, XRD). Between 500 and 700DGC the simultaneous evolution of H2O and CO2 was observed by MS, which is attributed to dehydroxylation of jennite-like phase and/or to decomposition of some carbonate hydrate and/or hydrocarbonate (three peaks on CO2 evolution curve, MS). The d(001) peak of portlandite exceeded the nominal value and will be analyzed separately.