The cement powder that is produced by ball milling the clinker consists of fine multiphase particles ranging in size from about 1 to 100 mm. The hydration reactions that occur when the cement is mixed with water are complex and interdependent. In order to simplify the investigations most studies have been carried out on the hydration reactions of the individual phases in the cement, but it should be noted that the phases present in the cement clinker are not chemically pure and extensive solid solubility can occur. For example, tricalcium silicate (C3S) formed in the clinker, can contain up to 2 wt% MgO as well as some A120 3, Fe20 3, T i02 and other oxides in solid solution. Dicalcium silicate can form solid solutions with Na20 , K20 , A120 3, Fe20 3 and F. Tricalcium aluminate can incorpo­ rate over 5 wt% Na20 and K20 in its structure and the composition of the ferrite phase is variable and can contain MgO (Kohlhaas, 1983).