Contractors on the $2.7-billion Silver Line Metro extension in northern Virginia will protect or replace 1,569 precast concrete panels used on five stations after multiple issues were discovered on hundreds of the panels.

在混凝土面板的质量控制测试中，Capital Rail构造仪，Clark Construction Group和Kiewit基础设施南部的合作伙伴关系，发现水泥 - 水比在早期生产过程中的规格不足。面板是由宾夕法尼亚州Stowe的通用混凝土供应制造的。

资本铁路建设者项目总监基思·库奇（Keith Couch）说，对混凝土工厂的调查错误地读取了骨料的水分含量。他说：“要么探针工作正常，要么无法正确校准。”

Couch说，通用混凝土供应最初使用标准的手动方法来“燃烧”水分来测试总水分含量。他说，在秋天，该工厂切换到自动探测器。

The problem was discovered in April 2017, after more than six months of production using the automated probe. At that point, the plant had cast a total of 578 panels, including 309 panels while the probe was in place. Couch says quality control inspectors were alerted by data anomalies. “The batch tickets said the water ratio was within spec,” he says. “When you went in and compared the math, the math didn’t make sense.”

CRC tested the aggregate using a manual burn-off method and discovered that the water content was reading too low, which led the system to add too much water to the final mix.

Don Faust, president of Universal Concrete Products, did not respond to calls for comment.

CRC launched a deeper investigation into the panels. Couch says that petrographic analysis revealed a low-air-entrainment issue in some panels.

Additionally, engineers with the Metropolitan Washington Airports Authority, which is overseeing Silver Line construction, discovered issues with rebar placement during a plant inspection, says Charles Stark, vice president of the Dulles Corridor Metrorail Project. “One of our engineers was in the subcontractor’s plant and noticed that as they were casting the panels, the steel reinforcement could end up too close to the surface,” he says.

然后，CRC在所有1,569个面板上进行了磁共振成像，并发现了65个面板，覆盖钢筋的混凝土覆盖不到3/4英寸。其中，五个面板是内部面板，不暴露于元素。工程师建议应更换其余60个面板。库奇说，已经安装了42个，并且工作人员希望在六月之前取代所有这些。

由于高水含量和低空气夹带可能导致未来的耐用性问题，因此CRC和MWAA同意应使用带有腐蚀抑制剂的硅烷涂层来密封所有安装的面板。斯塔克说，银线在10车道的杜勒斯收费公路的中间路线，因此外部面板在冬季可能会暴露于可能的盐喷雾中。

Couch说，顾问建议每15年重新申请密封剂，而Silane制造商愿意去20年的保修。Couch说，出于谨慎的态度，CRC选择了每10年的预期寿命每10年重新涂抹密封剂。CRC将建立一个基金来支付未来的申请。Couch说，CRC尚未达到有关问题和未来补救的通用混凝土产品的财务解决。他补充说：“首先，我们必须正确地完成工作，然后我们将与Universal解决。”

Couch says the partnership’s quality control plan did its job. “We found an issue, we elevated the issue, we did an immediate investigation and we put corrective action in place.”