The carbonation of waste cement and the use of the products in cement formulations can open a way for the mitigation of cement production environmental impact (~6% of global emissions of CO2) and for a circular economy, reducing mineral resource depletion. Upon carbonation conditions (i.e. time, humidity, composition), CaCO3 polymorphs as calcite, vaterite, aragonite and amorphous polymeric silicoaluminates (PSA) are formed. Mixed in a cement, they can contribute to strength development and durability. The mechanism and kinetics for CaCO3 and PSA formation and their behaviour during clinker hydration need to account for the role of both crystalline and amorphous species. This is a two step proposal based on s3DXRD/PCT measurements; fist step focuses on the gas-solid carbonation in CO2 atmosphere, monitoring model phases and hydrated cements in different humidity conditions, while step 2 investigates hydraulic reactivity of the products in water/cement mixtures for 48 hours.