The present invention relates to a novel cementitious product produced from steelworks slag additivation to obtain material having properties suitable for use in the partial or total clinker replacement for the production of different types of cement. The process, which is also object of this invention, aims to adapt the properties of steelworks slag, by means of thermochemical treatment, including and preferably, but not only, still in the liquid steelworks slag pot, taking advantage of the thermal input of steel processing, to form a greater amount of alite (essential compound to increase pozzolanicity), under controlled conditions. After additivation, preferably, but not exclusively, the additivated steelworks slag is subjected to quenching, comminution and concentration to stabilize the alite fraction, to release the present phases and to remove any excess contaminants, such as metallic iron.