Belite-rich cements with enhanced reactivity have been long pursued, due to the benefits of the low sintering temperature and CaCO3 demand compared with alite-rich cements.In this work, the physi-and quimisorption of water molecules on the β-C2S (100) surface have been studied using the first-principles calculations based on Density Functional Theory.Energy and structures have been investigated, as well as energy barriers and reaction paths for water dissociation using the Nudged Elastic Band method.Our results indicated that the first step of hydration is molecular adsorption with a binding energy between-0.78 to-1.24eV.It is followed by dissociation of the adsorbed H2O molecule to form a hydroxyl pair, with binding energy between-1.07 and -l.29eV.The reaction barriers and reaction paths for the H2O molecule from chemical adsorption to dissociation on oxygen and calcium atoms are significantly distinct, and the activation energy of O1 type oxygen atoms (labeled by their symmetry) is the lowest.This is consistent with the published results that O1 is the active oxygen points in the β-C2S bulk.With a water dissociation energy barrier of 4-414meV on β-C2S (100) surface,the exothermic reaction can take place spontaneously, as corresponds to the fact that β-C2S reacts with water at normal temperature.