Q.: I know that there are cements for sulfate resistance. Has anyone ever developed or marketed a cement that reduces corrosion of reinforcing steel in concrete?

A.: There is no standard cement or cement specification for this purpose. Nevertheless, there is good evidence that some portland cements do permit less corrosion of steel than others. Cements high in tricalcium aluminate (C3A) have been found to be beneficial. There has now been enough experience with such cements in building 16 major platforms for oil storage structures in the North Sea that a recommendation appears in "Guide for the Design and Construction of Fixed Offshore Concrete Structures," ACI 357R-78, which says, "The tricalcium aluminate content (C3A) should not be less than 4 percent to insure durability of the reinforcement." The effect is greatly improved by use of a low water-cement ratio, which should be kept below 0.4 if possible.

If you need more information for design purposes we suggest you get in touch with the Portland Cement Association, 5420 Old Orchard Road, Skokie, IL 60077. In addition to providing technical information they may be able to tell you what portland cement companies manufacture a portland cement with a C3A content of 4 or more.