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 fuel ash, metakaolin, and ground granulated blast furnace slag, together with silica fume, are frequently added to Portland cement concrete to improve performance and to retard chloride ingress and thereby inhibit chloride-induced corrosion of the carbon steel reinforcement. Al-27(H-1) MAS and CP/MAS NMR spectroscopies have been used to follow both the hydration processes of the cement blends and the interactions of chloride ion with the hydrated aluminium species. The spectra of the hydrated aluminate phases were interpretable 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-sulphoaluminate, 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 hydrated 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 produced by the interactions of the cement pastes with chloride ion, (C)2000 Kluwer Academic Publishers.