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Coating Will Remedy Faulty Concrete in Metro Project

Monday, April 30, 2018

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A silane coating will be used to help treat several flawed concrete panels found on the $2.7 billion Silver Line Metro extension in Northern Virginia. The concrete issue stems from different sources, including an incorrect cement-to-water ratio and insufficient leeway for water to expand and contract within the building material.

According to NBC4 Washington, project leaders found 1,750 panels, produced by Pennsylvania-based Universal Concrete Products, to be an issue. These panels have been installed in every station along the second phase of the project, excluding the Dulles International Airport station.

The U.S. Department of Transportation inspector general is currently looking into the issue.

Flawed Concrete

The equipment Universal Concrete used in the creation of these panels was later found to be improperly calibrated. Changing the water-to-cement ratio to an automatic machine-based method from a manual method caused the problem, resulting in the concrete containing too much water. The air entrainment—which allows freezing water to expand into the air bubbles to help keep the concrete from cracking—was also found to be insufficient.

Overall, 115 concrete panels will be completely replaced. Those remaining will be treated with the silane coating, which will help prevent water from entering the concrete, though the coating will have to be reapplied every 10 years.

"This is about to begin—the contractor will coat all of the station panels with the silane," said Charles Stark, the head of Metropolitan Washington Airports Authority’s Dulles Corridor Metrorail Project. "It's our responsibility as the Airports Authority to make sure that the facility we turn over to the Washington Metro will last 100 years."

The contractor will carry the additional costs of the repair, noted the Associated Press.

Other issues found include 110 locations where connections to concrete support beams for stations were cracking, which was caused by insufficient protection against freezing water. These areas will be treated with pressurized grout. Lead contractor Capital Rail Constructors is required to fix the issue.

The second phase of the Silver Line will extend 11.4 miles, noted NBC4 Washington, with six stations planned. Despite the concrete issues, a significant delay is not anticipated: the date for substantial completion is still set for Aug. 7, 2019.

   

Tagged categories: concrete; Contractors; Failure analysis; Government; Infrastructure

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