There are several ways contractors can build or retrofit concrete parking structures to ward off the effects of chloride-induced corrosion. J. E. Dunn Construction Co., Kansas City, Missouri, demonstrated two of these methods on separate projects:
CATHODIC PROTECTION SYSTEM: Corrosion is the electrochemical process of reinforcing steel losing electrons and decomposing to iron oxide. Reinforcing steel that loses electrons acts as an anode. Cathodic protection systems stop the loss of electrons, thus stopping corrosion, by reversing the current flow and turning the steel into a cathode. J. E. Dunn installed a cathodic protection system in a 59,000-square-foot parking garage in the Crown Center office, hotel, and retail complex in Kansas City. Titanium ribbons having a mixed precious metal oxide coating were chosen as the artificial anode. The system performed with 100 percent effectiveness when tested.
SILICA FUME CONCRETE: J. E. Dunn used silica-fume concrete to build the Kansas City International (KCI) Airport Terminal A parking garage. This was the first project in the country that had written specifications for the use of dry compacted silica fume in a ready mix batch plant. To produce a concrete with the desired corrosion resistance, the silica fume had to meet certain chemical composition requirements. For each load, the supplier of the dry compacted silica fume had to provide the exact chemical makeup of the product. Project specifications also required a second test on every third or fourth load.