Q.: Our company sold a 10x20-foot sign for use in southern California. This is mounted on legs made of 12-inch-square steel tubes. Another company contracted to set the sign in place. With the legs in 2-foot-diameter holes 7 feet deep, they mixed some concrete and dumped some flake calcium chloride into the mix directly from the bag. Then they placed the concrete in the holes around the steel legs. Are the legs going to corrode quickly, break up the concrete and make the sign fall down?
A.: It probably seems attractive to cause concrete in sign postholes to set rapidly, and it is possible that your subcontractor may even have added an overdose of calcium chloride. That would permit getting off the job quickly after placing the concrete.
Whether there was an overdose or not, it is always considered bad practice to add solid calcium chloride to the mix. ACI 212.2R, "Guide for Use of Admixtures in Concrete," says that "calcium chloride should be added to the concrete in solution form" and it explains how to make up the solution.
The presence of chloride ion can contribute to corrosion of steel in concrete if both oxygen and moisture are available. Consequently, corrosion could begin where the steel enters the top of the concrete or at some place where the concrete becomes cracked. One cannot say for certain that you will have quick, disastrous corrosion or even slow disastrous corrosion. If your environment is very dry it could greatly prolong the life of the legs. You might just keep an eye on the bases of the legs to see what is happening to them; or you might demand that the work be redone on the basis that the concrete was not mixed according to acceptable procedures.