CHLORIDES AND BRIDGE DECK DETERIORATION

SIXTEEN BRIDGE DECKS WITH VARIOUS DEGREES OF DETERIORATION WERE SUBJECTED TO DEICING SALTS AND CORED AND ANALYZED FOR CHLORIDE CONTENT. A BASIC MATHEMATICAL RELATIONSHIP WAS FOUND WHICH DESCRIBED THE DISTRIBUTION OF CHLORIDE WITH DEPTH. THE LOG OF CHLORIDE CONTENT IS INVERSELY RELATED TO THE DEPTH BELOW THE SURFACE. A MATHEMATICAL EXPRESSION WAS DERIVED OF THE CHLORIDE ANALYSIS OF THE CONCRETE OBTAINED FROM PILES THAT WERE CONTINUOUSLY SUBMERGED IN BAY WATER. THIS MATHEMATICAL EXPRESSION WAS FOUND TO BE THE SAME FOR BRIDGE DECKS OR PILING WHICH INDICATED THAT FOR EACH ADDITIONAL INCH, THE CHLORIDE CONTENT WOULD BE REDUCED BY APPROXIMATELY 1/2. THE DISTRIBUTION OF CHLORIDE IN THE CONCRETE WAS FOUND TO BE HIGHLY VARIABLE. THE REINFORCING STEEL FROM ONE DISTRESSED BRIDGE DECK WAS REMOVED AND IT WAS FOUND THAT THE MEAN OF THE MAXIMUM CORROSION LOSS WITHIN EACH FOOT OF STEEL WAS 29 MILS. BASED UPON THE MECHANISM AND DESIGN LIMITATIONS, DETERIORATION OF A NOMINALLY CHLORIDE-FREE CONCRETE DECK DUE TO CORROSION CAN BE PREVENTED BY USING A NON-CORROSIVE DEICING CHEMICAL OR A MEMBRANE BARRIER ON THE CONCRETE SURFACE. THE HALF-CELL POTENTIAL OF THE REINFORCING STEEL IN SECTIONS OF TWO BRIDGE DECKS WAS MEASURED AND IT IS SHOWN THAT DETERIORATION IS ASSOCIATED WITH CORROSION OF THE STEEL AS INDICATED BY THE ELECTRICAL MEASUREMENTS. THE MEASUREMENTS CAN BE USED TO LOCATE ACTIVE CORRODING REINFORCING STEEL IN BRIDGE DECKS AND COULD SHOW PROMISE IN EVALUATING REPAIR TECHNIQUES THAT ARE CONSIDERED TO BE ARRESTING THE CORROSION OF THE STEEL.