A number of cases have been reported in which excessive corrosion of aluminum conduits has resulted in cracking and spalling of the concrete in which it was embedded. In cases of corrosion where the concrete cover was too thick to result in concrete failure, the conduit collapsed inwardly. The consequences of these isolated experiences have been the banning of aluminum conduit in concrete by such groups as the Army Cops of Engineers and the District of Columbia Building Department.
Aluminum industry researchers and some other investigators believe that serious aluminum corrosion problems occur only when a galvanic reaction is set up; in other words, when chloride salts are present in appreciable quantities in the concrete along with aluminum and steel. The Aluminum Association and its members have investigated virtually every report of aluminum deterioration in concrete and they state that in all cases soluble chlorides were found to be present in appreciable quantities in the mix. Therefore, their recommendations are that soluble chlorides of any type, including calcium chloride, must not be used in concrete in which aluminum is to be embedded or that, since this is difficult to guarantee, a protective coating be provided for the aluminum. Their investigations show that there is no case of corrosion of aluminum in concrete in which an adequate protective coating has been applied to the aluminum.
Some other independent studies indicate that calcium chloride alone has no harmful effect on aluminum. These studies were made on aluminum specimens embedded for 18 months in concrete blocks containing a calcium chloride mix and they concluded that "the atmospheric specimens from concrete with added calcium chloride were not corroded any more severely than those from the standard mix." This, too, would seem to support the theory that the three elements- steel, aluminum and a soluble chloride- are needed before serious aluminum corrosion will occur.
The aluminum industry suggests protecting the conduit with bituminous or asphalt-base paint or other inert or insulating coatings.