Effect of the Special Features of Clinker on the Formation of Cement Stone.

The transition from the trigonal to the monoclinic modification of the alite phase in the clinker is accompanied by a reduction of the initial heat of hydration and the degree of hydration. Consequently, the composition of the initially formed crystalline hydrate phases changes. In this case the preferential formation of portlandite, which is characteristic of distinctly crystallizing clinkers with dominant alite crystal sizes up to 40 mu m, is regarded as most favorable for hydraulic activity over a 28-day period. During the later stages of hardening (3 to 28 days), when the primary crystallization skeleton is already formed and secondary hydrates are appearing, a smoothly occurring crystallization of the hydrate phases is required to attain a high hydraulic activity.