The present study investigates the preparation of Portland cement powders with various particle sizes and degrees of crystallinity, prepared by High Energy Ball Milling, and their use as a binder material addition.The structural, the microstructural and the morphological transformations of the processed powders during the milling process were studied.The electrical conductivity and the ion concentrations of the pore solution of cement pastes prepared with the processed cement were measured to understand how prolonging milling duration affects the early stage of setting reaction.The effect of using the activated cement powders as a binder material addition on mechanical properties of the resulting cement pastes was studied. Results have shown that for an addition percentage up to 10%, the flexural strength, and the young modulus were improved as a function of the milling duration of the addition materials. Results have suggested that, besides of the particle size reduction, the formation of the amorphous fraction within the processed cement contributes to the acceleration of the early stage of hydration and improves the mechanical properties of the cement paste.