What do we define as free water content?
In practice, the determinations of humidity levels are carried out by drying anhydrite screeds at 40˚C. This technique is tried and proven and for that specific binder-type state of the art.The using of higher drying temperatures is refrained from, as this binder-type tends to give off more and more crystalline bound water. This crystalline bound water is from calcium sulphate and is released in two steps at 70˚C and at 105˚C (depending on the finesse of the temperature steps). In literature you find that in cementitious systems apart from anhydrite also ettringite is produced as hydrate phases. Read more