Understanding the sulfate balance mechanism of cement is needed for an effective use of sustainable blended cements. Pure phase systems allow to study the interaction between sulfate and each of the phases involved in early age hydration separately. This paper explores the effect of different factors on sulfate requirement in C3S/C(3)A systems. It was observed that reaction rates of both C3S and C(3)A have an influence on the overall sulfate balance, as they affect the amount of sulfate adsorbed on C-S-H and the amount of ettringite formed, respectively. Furthermore, the type of sulfate source used (gypsum or hemihydrate) can also significantly change the position of the aluminate peak for the same total sulfate in the system.