Influences of alkali oxides doping on the crystal structure,defects and hydration behavior of tricalcium silicate C3S were investigated by X-ray powder diffraction with the Rietveld method,inductively coupled plasma optical emission spectroscopy,thermoluminescence and isothermal calorimetry.All the samples were stabilized as T1 form C3S.Changes in the crystal structure of C3S could mainly be monitored by changes in lattice parameters,which were closely correlated with the incorporation concentration and substitution types of alkalis.Although alkalis were incorporated at trace level in C3S,the thermoluminescence and hydration behavior of C3S were significantly influenced.Initial hydration activity was dramatically increased and highly related to the intensity of the irradiation-induced thermoluminescence peaks at low temperatures due to their direct correlation with defects.The oxygen vacancy sites resulting from the substitution of alkalis for Ca could readily account for the acceleration of the initial hydration of C3S.