There is little agreement as to how to minimize damage to concrete from freezing and thawing. The only agreement that exists is that it is the action of ice crystals compressing unfrozen water that has the disruptive effect on the structure of concrete. To get around this damaging effect, researchers have come up with air entrainment. The average bubble to bubble distance in concrete containing 3% air is not more than 1/100 of an inch. In effect, this divides the paste into thin layers. Then, when freezing and expansion occur, there is room into which unfrozen water being compressed by the ice crystals can flow without destroying the structure of the paste. Other suggestions shown by practical experience are: (1) use a well balanced, rich concrete mix; (2) entrain air; (3) use only sound aggregate; and (4) protect the concrete until it has gained sufficient strength to withstand freezing and thawing.