Aluminium-27 solid state NMR spectroscopic studies of chloride binding in Portland cement and blends

Alumina-rich pozzolanic and latent hydraulic binders such as pulverised fue l ash, metakaolin, and ground granulated blast furnace slag, together with silica fume, are frequently added to Portland cement concrete to improve pe rformance and to retard chloride ingress and thereby inhibit chloride-induc ed corrosion of the carbon steel reinforcement. Al-27(H-1) MAS and CP/MAS N MR spectroscopies have been used to follow both the hydration processes of the cement blends and the interactions of chloride ion with the hydrated al uminium species. The spectra of the hydrated aluminate phases were interpre table on the basis that the AFt (Aluminate Ferrite tri-) phase ettringite, C(6)AS(3)H(32)(3CaO . Al2O3. 3CaSO(4). 32H(2)O, or C(3)A . 3CaSO(4). 32H(2) O), and the AFm (Aluminate Ferrite mono-) phases calcium mono-sulphoalumina te, C(4)ASH(12) (3CaO . Al2O3. CaSO4. 12H(2)O, or C(3)A . CaSO4. 12H(2)O), and the lamellar tetracalcium aluminate hydrate, C(4)AH(13) (3CaO . Al2O3. Ca(OH)(2). 12H(2)O,or C(3)A . Ca(OH)(2). xH(2)O) were present as the only h ydrated species containing octahedrally-coordinated aluminium. Inall cases, only the AFm phase Friedel's salt (3CaO . Al2O3. CaCl2. 10H(2)O, or C(3)A . CaCl2.10H(2)O) could be identified as the major chloroaluminate phase pro duced by the interactions of the cement pastes with chloride ion, (C)2000 K luwer Academic Publishers.