Tricalcium silicate is the major component of ordinary Portland cement and the hydration products are responsible for the high strength of cementitious products. It is known that the crystal structure of tricalcium silicate depends on the kind and amount of foreign oxides incorporated into the lattice. In this study the influence of multiple doping with MgO, Al2O3 and Fe2O3 on the hydration characteristics was analysed by isothermal heat-conduction calorimetry. The hydration products were characterised by differential scanning calorimetry, X-ray diffraction Si-29 solid-state nuclear magnetic resonance spectroscopy and scanning electron microscopy. The hydration is dominated by the kind and concentration of foreign oxides, independent of the influence of the doped oxide on the crystal structure of C3S. Combined doping with MgO + Al2O3 or MgO + Fe2O3 shows no interactions between the foreign oxides on their influence on hydration. In the case of combined doping with Al2O3 + Fe2O3, the retarding effect of Fe2O3 on the main reaction is much stronger in the presence of Al2O3. (C) 2008 Elsevier B.V. All rights reserved.