Substituted Hydrated Calcium Silicates Obtained in Autoclave Hydration

Hydrated calcium silicates containing Al^3+] or Fe^3+] were prepared by autoclaving C₃S and β-C₂S in the presence of C₃A or C₂F at 190°C. Al^3+] and Fe^3+] diffuse into the crystal lattice of α-C₂SH and C₃SH_1.5. Solid solutions containing Al^3+] and Fe^3+] were placed in contact at 25°C with sources of sulfates, either in aqueous stirred suspensions or as pastes. Al^3+] and Fe^3+] remain stable in the solid solution, inhibiting the formation of ettringite. This absence of ettringite can explain the resistance of autoclaved cement pastes and concretes to sulfate attack.