What is the best procedure to control rebar corrosion in bridge decks?
It is not certain that there is yet any "best" procedure but a Reinforced Concrete Research Council study of the subject is being made at Purdue University. The work has mostly taken two general directions: (a) preventing steel from corroding and (b) preventing penetration of salt into the deck by sealing the deck surface. (a) Galvanizing the steel or coating it with epoxy have been the principal methods in the first approach. Galvanizing delays corrosion of the steel until the zinc coating has been consumed by corrosion but does not protect the steel permanently. It is necessary to insulate galvanized bars electrically from any nongalvanized bars in the same concrete. Galvanized rebars cost 30 to 50 percent more than plain rebars. Epoxy coatings increase the cost of rebars 100 percent or more. Although epoxy coatings do not corrode, they have the potential disadvantage of leaving the rebars unprotected if they contain pinholes or holidays or if they become chipped off by rough handling. Some epoxy coatings do not develop a good bond to the concrete. Cathodic protection of steel by applying a small electrochemical counter current to the steel in a deck specially constructed for the purpose is effective. A disadvantage is that electrical power must be supplied continuously to each such bridge for its whole life. (b) Preventing the penetration of salt into decks has been attempted with many materials. Bridge decks have been impregnated with a variety of polymers to make them impermeable. Others have been covered with membranes such as a bituminous overlay. If such membranes break, however, the salt solutions that find their way in through the cracks are more damaging because the concrete is likely never to dry out. Furthermore, the deterioration is hidden by the membrane and may not be detected until far advanced. There is a third approach which has not received much attention previously: self-protecting steels, which develop in service a tightly adhering layer of their own corrosion products. This method is also being studied in the project at Purdue .