K₂O-Containing Phase in Portland Cement Clinker

Abstract

In the previous paper concerning with Na₂O-containing phase in portland cement clinker, it was indicated that the X-ray diffraction pattern of the ternary compound of Brounmiller and Bogue to which the composition NC₈A₃ is assigned, is not correct, and the prismatic dark phase in clinker of the systems C-A-F-S-M-N-(SO₃) is the metastable phase of NC₈A₃, containing small amount of SiO₂.
Successively, some studies of K₂O-containing phase in portland cement clinker have been made. From the microscopic observation and powder X-ray diffraction, the following results have been obtained.
a. KC₂₃S₁₂ is not a ternary compound, but a stabilized α′-C₂S by the formation of substitutional solid solution of K₂O in C₂S.
b. The prismatic dark phase in preparation of the systems C-A-(F)-S-K is the metastable phase of KC₈A₃, containing small amount of SiO₂ as solid solution or an integral part of the unit cell structure.
Accordingly, the fact that the addition of increasing amounts of K₂O to a raw mixture results in progressively increased amounts of free CaO in clinker is not only due to the formation of substitutional solid solution of K₂O in C₂S, but also the following reaction:
3C₃A+K₂O=KC₈A₃+CaO
Furthermore, the manner in which K₂O is combined in portland cement clinker has been discussed.