The use of brackish water in the original concrete mix has led to extensive and complex concrete repairs to Sweden's combined Svinö and Öland Bridge. Crumbling piers have been covered with reinforced concrete shells and the affected foundations strengthened. Repairs are now focusing on the deck, including replacing some of the parapets, joints, and bearings by contractor Nordic Construction Company (NCC) for client Swedish National Road Administration, Vägverket.
One of the latest Conjet Robot 363 MPA high-pressure water jetting hydrodemolition machines is playing a key role assisting in repairs to the bridge deck. Contractor Waterjet Entreprenad AB, working as the specialist hydrodemolition contractor for NCC, is using hydrodemolition to selectively remove concrete from the edge of the deck and clean and expose reinforcement for NCC to cast on new sections of parapet.
“This is probably the world's most extensive concrete bridge repair project, and hydrodemolition has been the only approved and specified method of removing concrete from bridge decks and other sensitive structures in Sweden for the past 20 years,” says Vägverket bridge repair project manager Jan-Olof Bolin. “This technique of using very high-pressure jets of water to remove the concrete does not cause any damage to the healthy concrete left behind. It also removes concrete from above or below any reinforcement, which is cleaned of any rust. Hydrodemolition also produces a very rough and uneven surface, which provides a strong bond at the interface for the new concrete to key onto. In my opinion it is the only concrete removal method that meets the required adhesive bond strength.”
The owner approved the use of brackish water in the original concrete mix instead of more expensive fresh water. Construction of Europe's then longest road bridge has been plagued with concrete chloride attack ever since it was completed in 1972. “The bridge was charged with salt and fated right from the start,” says Bolin. Severe chloride attack of bridge piers above and below sea level was first noticed in the early 1980s. Some piers had deteriorated so badly that only half the cross sectional area of reinforcing steel remained. Extensive repair was the only option for the vital crossing, which now carries an average of 5 million vehicles a year, compared with an originally forecast 350,000 a year. Repairs started in 1990, and NCC completed pier restoration in 2000. At the end of 2002, NCC started on the third phase to restore an initial 2300 meters of parapet and replace 19 joints and some of the bridge's bearings.
After Waterjet has removed a length of the deck edge and exposed and cleaned the original steel reinforcement, NCC follows, casting a new section of reinforced deck and integral parapet edge beam. NCC and Waterjet stagger these repairs from side to side of the bridge to avoid the risk of any chloride cross contamination from the old concrete being removed to the new concrete.
“The current third phase of repairs to the parapet, joints, and bearings should be finished by May 2005,” says Jan-Olof Bolin. “This will bring the total overall cost of inspections, testing, and renovation so far to nearly twice the cost of the original bridge at today's prices.”