Crystalline cement hydrates such as Alumina Ferrite-mono and-triphases (AFm and AFt) show different hydration states depending on the exposure temperature and relative humidity.Varying hydration states of cement hydrates may have a direct impact on the specific density/volume of cement paste, e.g.the volume of some hydrates can change as much as 20% during drying.The present paper describes the outcomes of a newly developed experimental multi-method approach used to investigate the impact of relative humidity (RH) and temperature on structural and thermodynamic properties of crystalline cement hydrates with different hydration states (i.e.varying molar water contents).