This lecture explores the formation and properties of aluminate hydrates in cement chemistry, focusing on ettringite and AFm phases. It discusses the thermodynamic simulation of hydration, the decomposition of ettringite and C-S-H, and the solid solutions of AFm phases. The lecture also covers the effect of limestone addition on AFm phases and the characteristics of hydrogarnets. Aluminate hydrates play a crucial role in the hydration process, contributing to strength development and space filling in cementitious materials.