Factors affecting the hydration process and properties of expansive cement .2.

The same shrinkage processes which are familiar from Portland cements can also be observed when expansive cements harden. For this reason, it is theoretically and practically impossible to achieve a volume which remains constant during the course of hydration. However, a controlled increase in volume can be achieved provided the effects of external constraints on, the swelling process (temperature, moisture, mechanical restraint of the swelling) are taken into account. This improves the properties of concretes based on expansive cements. The processes taking place during the hydration of expansive cement depend to a great extent on the temperature, temperature behaviour pattern and holding period. At temperatures slightly above 0 degrees C the swelling value that can be achieved is larger than at normal temperature or with heat treatment. Mechanical restraint during the swelling process is necessary depending on the swelling potential. Concretes made with expansive cements react more sensitively to drying out than do normal cements, so moisture treatment is absolutely essential during the hardening process. Protective storage or moist storage at 100 % r.h. is to be preferred to storage in water.