The foremost objective of this research is to improve the fundamental knowledge of the early hydration mechanisms of Portland cement and the carbonation of the hydration product portlandite by the combinational approach of computer modeling and laboratory experiments. The approach started with an in-depth understanding of the dissolution mechanism of C3S and C2S immediately in contact with water and followed by the polymerization mechanism of silicates (the building block of C-S-H) under the influence of external parameters (i.e. temperature, Ca/Si ratio etc.), as a representative initial step of cement hydration kinetics. The model (ReaxFF combined with MetaD) enables an optimization of the C3S and C2S reactivity, which will allow an even further reduction of the clinker content in cementitious binders without loss of hydration performance. The proposed model will provide new insight into the initial hydration mechanism with an in-depth understanding.