Polymorphic types of belites in clinkers

XRD powder evidence shows that in the majority of clinkers the belite is predominantly or entirely of P-CjS structure (GI,YI), though some peaks are broadened (Gl) and the presence also of both a and a (presumably u l) forms has been reported (GI,Yl,RI,OI). Characterization of the polymorphic form is rendered difficult by the similarities between their powder patterns (Fig. 1.5) and by overlaps between the peaks and ones of other phases, especially alite, but has been aided by examination of fraetions in which the belite has been concentrated by chemical (Rl) or heavy liquid (Yl) separation. 

The striations in the common. Type I grains of belite are zones into which impurity ions rejected during the transition from a to a have been concentrated (Y1,01,C1). In some cases, they appear to have retained the a-CjS structure (Y 1,01,FI). In contrast, a study on synthetic belites showed that the material exsolved between the lamellae or at grain boundaries was often 

Studies on synthetic belites suggest the possible occurrence of modulated structures, i.e. ones in which compositional or structural variations occur with a statistical periodicity that is not a rational multiple of that of the basic structure (H5). Such effects might occur in clinker belites. 

---