Tricalcium Silicate and Alite Phase

Tricalcium silicate is the most important component of Portland cement clinker. Its share as a rule is overpassing 55% and reactivity with water has the decisive effect on paste hardening. At room temperature CjS is triclinic. The structures of different polymorphic phases of tricalcium silicate was determined by Jeffery [99], The basis was the rhombohedral pseudo-stracture with hexagonal unit cell [99]  

The stmcture of Jeffery is only simplified [100]. Studying the pseudo-hexagonal ciystals Regourd [35] found the superstmcture peaks, in case of which a= 1400 pm. 

Handke et al. [101] on the basis of inlia-ied and Raman spectroscopic studies advanced the hypothesis that the stractuie of triclinic C3S seems to be laminar and is composed of the layers of Cla2[SiOJ and CaO. The symmetiy of single layer being close to the R3m symmetiy, proposed by Jeffeiy. This laminar C3S stmcture could explain its non-Hstoichiometiy and easy decomposition into C2S and CaO. In C3S stmcture proposed by Belov et al. [102] the oxygen coordination number (CN=6) non belonging to SiO tetrahedra is also close to octahedral coordination, existing in CaO crystals. 

The stability range of individnal C3S polymorpliic phases can be somewhat different depending on the method nsed for their establishing. 

With temperature decrease three hexagonal planes 201 , 204 and 220 give on X-ray pattern doublets and triplets, instead of single peak. At the studied temperature range peak 009 is not splitted. It means that the distance between the planes per- 

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