The critical degree of saturation is a function of the nature of the material and is a consequence of the distance between a freezing site and the nearest air-filled space. During freezing, the build-up of expansive pressures and potentially damaging stress in the concrete matrix increases with increasing distance between the freezing site and the nearest air-filled space. It may therefore be postulated that there exists a critical distance, denoted DCR, in respect of freeze- thaw damage. In practical terms, it is equivalent to the thickest possible water saturated cement paste zone around an air-filled void, such as a sphere, that can exist prior to initiation of damaging micocracks. This leads to the concept of a critical spacing factor, denoted LCR. These two parameters are related by the following equation (Fagerlund, 1997):
