Alite dendrites

Fig. 4.2 Reflected light micrograph of a polished and etched section of a Portland cement clinker, showing crystals of alite (dark, angular) and belite (less dark, rounded) embedded in a matrix of interstitial material, itself composed mainly of dendritic ferrite (light) and aluminate (dark). Courtesy Materials Science Department, British Cement Association.

Fig. 4.3 Backscattered electron images of polished sections of (A) a Portland cement clinker and (B) grains of a Portland cement in a fresh paste. In both sections, alite is the predominant clinker phase. In (A), the relatively large, darker areas are of belite, and the interstitial material consists of dendritic ferrite (light) in a matrix of aluminate (dark) cracks and pores (black) are also visible. In (B), the belite forms well-defined regions, which are rounded, striated and darker than the alite the interstitial material, present, for example, in a vertical band left of centre within the larger grain, consists mainly of ferrite (light) and aluminate (dark). Scrivener and Pratt (S28).

When examining a polished section or thin section, the viewer must constantly think in three dimensions, not merely in terms of the nearly two-dimensional view seen in the microscope. Dendritic periclase, therefore, should be considered as a three-dimensional, branching, treelike or skeletal crystal, typically growing within a liquid matrix, the surface of the section revealing only part of the tree. Alite, the most abundant phase in portland cement clinker, tends to form a somewhat discontinuous, open, three-dimensional framework of linked and stacked crys-... 

Tiny belite crystals formed as a surficial decomposition of the alite during slow cooling have always been clear in the writer s observations secondary belite (formed out of the matrix during cooling) is also clear, perhaps because these crystals have little to exsolve. Research is needed on this point. Amoeboid crystals are rarely colored dendritic crystals have never been observed to be colored in the writer s experience. Ono s belite color interpretation seems most applicable to properly formed crystals. 

Surficial deterioration of alite, amoeboid ragged belite, dendritic and lake periclase, loss of alumina brick Overturning from delayed petroleum coke, producing longer burning zone (Jefferson and Kruse, 1987)... 

Photograph 7-85 Dendritic periclase forming substrate for belite overgrowth (center left). Alite crystals exhibit facial extensions into matrix of very finely microcrystalline aluminate and ferrite. Slowly cooled from high temperature. (S A6703)... 

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