HERNDON, VA. -- Inspectors have found issues with some of the materials being used in the construction of Phase 2 of Metro's Silver Line.
Specifically, concrete panels that form the basic structure of the Metrorail stations have been found to have durability issues.
"We have noticed a number of problems with the durability with some of the concrete panels that we use to build the Metrorail stations," said Charles Stark, senior vice president of the Dulles Corridor Metrorail Project (DCMP). "None of these problems affect the structural strength of the panels, but they will affect the ability of the system to make it to the hundred year life that’s required by the contract."
The Metropolitan Washington Airports Authority (MWAA) has been contracted to complete the DCMP by the Washington Metropolitan Area Transit Authority (WMATA), which will take over control when it is completed. However, as part of contract, the structure must be durable for 100 years. The durability issues place the life of the concrete panels, if left untreated, at ten years.
"There’s three issues. One, is there’s slightly too much water in some of the cement of some of the panels. Some of the panels have insufficient entrained air, that is microscopic air bubbles that are in the concrete that help the concrete withstand freeze-thaw cycle which we experience at this latitude," explained Stark. "And the final one is that we noticed that during the manufacture, some of the panels, a few of them, have their steel mesh, which is the reinforcing inside the panel too close to the outside surface of the panel which makes them more susceptible to salty water from the highways getting into the concrete, rusting the reinforcing mesh and causing cracking."
MWAA contracted Capital Rail Constructors (CRC) to complete the DCMP, which subcontracted United Concrete Products (UCP) to create the concrete panels in question.
Stark said that investigators tested over 1,700 panels installed at five of the six stations that are a part of Phase 2 (only the Dulles Airport Station was excluded) and found that 60 of them will have to be replaced. The remaining panels can be salvaged to meet the 100 year requirement by applying a silane coating every ten years.
"We intend to coat the stations with a coating called silane which will prevent the salty water from entering the concrete and causing the problems I referred to," said Stark. He added the costs of the initial fix and the ongoing treatment will be paid for by the contractors.
The main contractor, CRC, released this statement on the issue:
Capital Rail Constructors (CRC), is serving as the contractor for Phase II of the Metrorail Silver Line project. As is customary with a project of this size and scope, a rigorous quality control program is established and maintained throughout construction. During this process, CRC identified a quality control issue with some of the architectural precast panels (designed and fabricated by Universal Concrete Products of Pottstown, Pennsylvania). Working closely with representatives for the Metropolitan Washington Airports Authority and independent testing professionals, CRC determined that these panels do not present a safety risk to workers or the public; however, some of the panels require corrective action. The corrective plan includes sealing to improve durability and replacing precast when durability requirements cannot be met through sealing.
The cost of the precast panel repairs will be paid for by CRC and the supplier Universal Concrete Products, and not by MWAA or WMATA. The corrective work on the affected architectural precast concrete panels will not impact the overall project schedule. Most of the corrective work is complete. The work to replace any remaining panels will be conducted at night.
WMATA General Manager Paul Wiedefeld said they will review the work when the time comes to take over the project.
"We want to make sure that it meets all of our needs and we’ll do that and that’s the process, but they will not turn it over to us for another year plus, so when we get to that point we’ll work through those issues," added Wiedefeld.