Motorists traveling on Interstate 64 near Charlottesville, Virginia, are likely puzzled by the plastic wrap covering the columns and piers of the Route 631 bridge that spans the highway. It might look low tech, but the plastic wrap is the protective outer layer of a state-of-the-art process for removing chloride ions from reinforced concrete structures. The process, called electrochemical chloride extraction (ECE), gives highway agencies a new tool for bridge maintenance and repair.
The ECE process removes chlorides from concrete structures by applying an anode and electrolyte to the surface of the concrete and then passing direct current between the anode and the reinforcing steel, which acts as a cathode. Since anions (negatively charged ions) migrate toward the anode, ECE makes it possible to move the chloride ions toward the anode and out of the structure.
The Charlottesville bridge was built in the 1960s. Three years ago, the deck and piers underwent minor repairs. Joints in the deck allowed chloride ions remaining from winter deicing treatments to leak onto the pier caps and columns below. Once the chloride ions penetrate the concrete cover, they produce a corrosive environment that causes the reinforcing bars to corrode, which in turn causes delamination in the concrete.
The ECE process offers a noninvasive alternative to the conventional options of replacing the damaged concrete, applying a jacket of fresh concrete, or installing a cathodic protection system. The ECE process takes about 6 to 10 weeks, and it requires that water and electricity be available at the site. By removing the offending chloride ions and thus halting the corrosion, the process can make major repair and rehabilitation work unnecessary. It can be used on bridge decks and substructures, but it is particularly suited for substructures, where it will not interfere with traffic.
The goal of the Charlottesville project is to determine how practical the ECE process is for full-scale concrete structures and to identify any improvements that could be made to the technology.
"There's really no doubt that ECE works," says Gerardo Clemena, principal research scientist at the Virginia Transportation Research Council (VTRC). "The only question is, how practical is it for full-scale structures and how long does the beneficial effect last."
|
|
|
|
|
|
|
|
|
|
|
|
|
|
