Water Demand of Cement

Water demand and its variation is usually associated with changing forms of the calcium sulphate in the cement, i.e. the proportions of gypsum, hemihydrate, anhydrite. Dependent on the temperature and residence time in the cement mill the degree of dehydration to hemihydrate or soluble anhydrite will change. These minerals have different solubilities and therefore can affect the water demand of the cement as the balance between the soluble sulphate and C3A reactivity changes.

hello Michael,

I have the same problem in my grinding station as our friend.

my WD was around 38% and by increasing the speed of the ventilator we sucked a bigger percentage of fines that there circulating inside our ball mill.

this way we dropped the WD from 38% to 36%, which is still high.

Doesnt gupsum influense just the setting time ?

By the way the temperature of the cement in the ball mill outlet is about 80 deg. celcius.

Thoughts and comments are highly appreciated.

Regards,

Pavlos 

Correct observation. Hemihydrate gypsum and anhydrite soluble in dry conditions may occur only at temperatures above 100  ^oC. When I studied this question, I found, that under intense grinding and high level of pressing this temperature can be reduced through education defects in the crystal lattice. (see http://www.izvuzstr.sibstrin.ru/fulltext/ 2010  № 2 p. 22 -26 in Russian lang.). It is possible that this phenomenon can occur when grinding cement. That you could recommend. I somewhere read that as a regulator setting of cement, you can use a mixture of 50% CaSO₄ 2H₂O/50%/CaCO₃.