This work presents a comparative study of the hydration and carbonation reactions of three calcium silicate phases.Triclinic tricalcium silicate and γ-dicalcium silicate were synthesized in laboratory from stoichiometric mixtures of CaO and fumed silica (SiO2).The reactivity of the synthesized calcium silicate systems were then monitored during both carbonation and hydration reactions.Along with the synthesized calcium silicates, the reactivity of natural wollastonite was also investigated in this work.For carbonation reaction, calcium silicate samples were first mixed with deionized water and then exposed to CO2.After 24 hours of reaction the samples were analyzed using Fourier Transform Infrared (FTIR) Spectroscopy, thermo gravimetric analysis (TGA) and scanning electron microscopy (SEM) techniques.The presence of Ca(OH)2, CaCO3 and calcium silicate hydrates (C-S-H) was identified in case of both hydrated and carbonated tricalcium silicate and dicalcium silicate specimens.For wollastonite specimen, polymerized silica and CaCO3 were identified as the main reaction products.