Dehydrated forms of gypsum dissolve in water faster than dihydrate. This can be both advantageous and disadvantageous. The advantage is that the ready supply of soluble calcium sulfate can control the reaction rate of finely ground C3A reactive forms. The disadvantage is that, if there is too much dehydrated gypsum present, a supersaturated solution is produced, from which gypsum crystals can be formed that produce a so-called false setting. The different solubilities of the different forms of calcium sulfate are illustrated in Figure 5. The formation of solids in the experiment with an initial concentration of 50 mmol l-1 of CaSO4 and equilibrated at 12 ° C; (I): formation of small primary entities / dispersers as evidenced by the change in I (q) ∞q – 1 for q> 1 nm – 1 and I (q) ∞q0 for q <1 nm – 1 (pink and orange dotted lines); (II) development of a structure factor; (III) the formation and development of large dispersion characteristics evidenced by the increase in intensity at q <1 nm-1; this change followed a dependency on I (q) ∞q – 3> a> −4 (where a is the exponent: green dashed line); (IV) the growth of the primary species is manifested aq> 1 nm – 1 by the displacement of the dispersion curves towards lower q values and the gradual decrease of the intensity towards I (q) ∞q – 4 (blue dashed line ); The box shows a selected dispersion curve and indicates the meaning of the dependence I (q) of the dispersion exponents q (dashed pink, orange and blue lines) that indicate the characteristic features of the dispersion as described in Figure 5.

In order to obtain the optimum properties of the cement with a minimum demand for water and a controlled setting behavior, it is necessary to match the level of easily soluble (dehydrated) calcium sulfate with the reactivity of the clinker. This approach is illustrated in Figure 6. The SO3 present in the cement as hemihydrate (CaS041/2H20) and the soluble anhydrite are called D.SO3.