13C chemical shift anisotropies for carbonate ions in cement minerals and the use of 13C, 27Al and 29Si MAS NMR in studies of Portland cement including limestone additions

• 13C chemical shift anisotropies for inorganic carbonates from 13C MAS NMR.
• Narrow 13C NMR chemical shift range (163–171 ppm) for inorganic carbonates.
• Anhydrous and hydrated carbonate species by 13C MAS and 13C{1H} CP/MAS NMR.
• Limestone accelerates the hydration for alite in Portland – limestone cements.
• Limestone reduces the amount of aluminium incorporated in the C-S-H phase.

13C isotropic chemical shifts and chemical shift anisotropy parameters have been determined for a number of inorganic carbonates relevant in cement chemistry from slow-speed 13C MAS or 13C{1H} CP/MAS NMR spectra (9.4 T or 14.1 T) for 13C in natural abundance. The variation in the 13C chemical shift parameters is relatively small, raising some doubts that different carbonate species in Portland cement-based materials may not be sufficiently resolved in 13C MAS NMR spectra. However, it is shown that by combining 13C MAS and 13C{1H} CP/MAS NMR carbonate anions in anhydrous and hydrated phases can be distinguished, thereby providing valuable information about the reactivity of limestone in cement blends. This is illustrated for three cement pastes prepared from an ordinary Portland cement, including 0, 16, and 25 wt.% limestone, and following the hydration for up to one year. For these blends 29Si MAS NMR reveals that the limestone filler accelerates the hydration for alite and also results in a smaller fraction of tetrahedrally coordinated Al incorporated in the C-S-H phase. The latter result is more clearly observed in 27Al MAS NMR spectra of the cement–limestone blends and suggests that dissolved aluminate species in the cement–limestone blends readily react with carbonate ions from the limestone filler, forming calcium monocarboaluminate hydrate.