Compositions of the aluminate phase in clinkers

Because of the close admixture with other phases, which is often on a scale of lOpm or less. X-ray microanalysis of the aluminate phase in clinkers is frequently difficult or unreliable. Data have been reported for cubic, orthorhombic, pseudotetragonal or unspecified forms of the aluminate phases in ordinary clinkers (R1,K1,B2,H3) and for aluminate phase (G3,G4,S1,B3) and glass (B3) in white cement clinkers. Tables 1.2 and 1.3 include, respectively, average compositions based on these somewhat scanty data, and suggested site occupancies based on them. The values in both tables take into account both the experimental data and the requirement of reasonable site occupancies. 

Pure C,A contains 62.3 /o CaO and 37.7 /o AIjO,. Substantial proportions of both calcium and aluminium are thus replaced, the total content of impurity oxides being typically around 13% for the cubic and up to about 20% for the orthorhombic modification. The content of equivalent Na,0 (Na,0 -I- O.66K2O) appears to be around 1% for the cubic form and 2-4% for the orthorhombic form. None of the analyses indicates alkali contents as high as that required by the formula NC A, even though considerable amounts of silicon arc present. 

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