Aggressive decay threatens hundreds of bridges

Many of Denmark’s flyovers suffer from a concrete deficiency that will incur massive future maintenance costs

September 1st, 2012 8:08 am| by admin

New statistics from the national road authorities indicate that a large number of the country’s flyovers are suffering from an aggressive form of concrete degeneration that could require them to be replaced long before expected.

Up to 600 road and railway bridges — about 15 percent of the nation’s total — face substantial maintenance work in order to prevent the alkali-silica reaction (ASR) from eroding the concrete structures from the inside out. 

“Already today there are numerous bridges affected by ASR and we expect a considerable rise in cases during the forthcoming year,” Erik Stoklund, the maintenance chief for Vejdirektorated, told science and technology weekly Ingeniøren. “The flyovers are the hardest hit because the penetrative road salt creates a perfect platform for ASR.”

Stoklund said ASR is limited to smaller constructions such as highway and railway flyovers while larger bridges are unaffected.

The ASR problem stems from the concrete building boom that occurred in the 1960s and 1970s, when concrete was produced using sand with a high content of porous reactive flint, a type of stone that reacts intensively when penetrated by moisture. Road salts used in the winter contribute significantly to the trouble.

Use of this type of concrete was only ended in 1987, when quality demands were enhanced and the ASR issue was solved.

But before then hundreds of structures were built, and the state railway stretch to Køge, south of Copenhagen, offers a prime example of at-risk bridges, as many were constructed in the early 1970s.

As many as 300 of the structures nationwide dating from the 1960s are in immediate danger of being affected by the condition.

There have already been a few instances where it was more cost-efficient to tear down bridges affected by ASR, and according to Bent Grelk, ASR specialist with consultancy group Rambøll, the issue could become a lot worse in the future.

“The dilemma can easily be described as a ticking bomb. A large number of bridges from that era will decay as soon as the moisture insulation is breached,” Grelk told Ingeniøren.

Grelk also estimated that moisture insulation in bridges constructed in the 1960s typically has a life expectancy between 30 and 50 years, meaning ASR could potentially become a serious problem in the coming years.

Vejdirektoratet expects that in 2020 the problem will be so dire that over 200 million kroner will be needed annually to maintain the stricken bridges, up to 50 percent more than today’s upkeep costs.

The new information has Dansk Vejforening, an interest group whose members include road maintenance and transport companies, urging the government to dedicate more funds to combatting ASR.

“The government has just proposed a budget that allocates so little road maintenance funds for 2013 that we cannot keep up with the infrastructure wear as it is,” Søren Bülow, the head of Dansk Vejforening, told Ingeniøren. “This new information should be a cause for alarm for politicians.”

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