When engineers weigh results of numerous studies on disruption of concrete by corrosion of steel where chlorides are present, some of them conclude that calcium chloride admixtures can contribute to this serious problem. In the structures that have suffered severe distress mainly bridge decks and parking structures large amounts of chloride ion have been found near the top surface, and less further down. The amounts within several inches of the top surface are very large compared with the amount that could have originated from a calcium chloride admixture (if it were used) in the usual amounts of 2 percent or less by weight of cement.
In 1977 H. K. Cook and W. J. McCoy noted general agreement that, when the amount of commercial calcium chloride is limited to 2 percent by weight of cement, the degree of corrosion in ordinary reinforced concrete is insignificant if the concrete is reasonably dense and there is adequate cover over the steel.
The soluble chloride contributed to concrete by admixtures decreases as a result of chemical combination with the cement paste. Studies by Monfore and Verbeck showed a rapid decrease during the first 10 days after mixing for concretes containing 2 percent calcium chloride by weight of cement. Even greater reductions took place where the cement contained a significant amount of tricalcium aluminate. Verbeck later said that as much as 75 to 90 percent of the chloride from the admixture becomes part of the chloraluminate of the hydrated cement, through he noted that the chloride is also combined in other ways, since it becomes combined even in cement that contains no tricalcium aluminate. Concrete made with 2 percent calcium chloride or less should not be corrosive to reinforcing steel provided the usual recommendations are followed for adequate concrete cover over the steel and good densification of the concrete.