Evidence from X-ray microanalysis

For lower ARs, the interstitial material consists essentially of ferrite of higher iron contents, and in white cements it consists of aluminate very low in iron, possibly together with glass. In each case, small amounts of silicate phases are probably also present. 

The reason why mixes with AR 1.7 do not yield any CjjA, on independent crystallization is that the solid phases are not pure CjA, QAF and CjS. For AR = 2.71, the quaternary liquid in equilibrium with C,S, C S and CjA at 1400X contains 55.7% CaO, 27.1% AljOj, 10.0% FcjOj and 7.2% SiOj (S8). This composition can be closely matched by a mixture of aluminate (63%), ferrite (30%) and belite (7%) with the normal compositions given in Table 1.2, the bulk composition of this mixture being 54.4% CaO, 26.4% AI2O3, 9.7% Fe Oj, 5.6% SiO and 1.8% MgO, with 1% each of TiOj, Mn20j, NajO and KjO. Independent crystallization can thus yield a mixture of the three phases. The liquid composition cannot be matched by a mixture of pure CjA, C AF and CjS, which is relatively too high in CaO, so that if no ionic substitutions occurred, some C,2A7 would also be formed. A strict comparison would be with the actual composition of the clinker liquid, which is modified by minor components, but lack of adequate data precludes this. 

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