The firm hired by Montgomery County to perform field inspections on the Silver Spring Transit Center improperly tested the strength of concrete, apparently failed to measure its thickness and didn’t raise sufficient concerns when the concrete started to crack, according to independent engineers and county officials.

Montgomery officials are also investigating whether all of the inspectors from the Robert B. Balter Co. who signed off on the project were certified to work with high-strength concrete and other materials, as required by county regulations.

Concrete not strong enough to sustain the daily strain on the transit center is one of multiple design and construction failures identified by engineering consultants last week in a report on the $112 million train-and-bus hub, which is $80 million over budget and two years behind schedule. It was found to be unsafe and in need of significant repairs because of cracking and a lack of supporting steel in key locations.

Balter, an Owings Mill, Md., firm, handles field inspections and materials testing on all of the county’s capital construction projects, including the Silver Spring Civic Building, the Mid-County Community Recreation Center and the Grosvenor-Strathmore Metro garage. All were completed without questions about the firm’s work, according to county officials.

At the transit center, one of Balter’s key responsibilities was to test concrete as it was trucked to the construction site in 2010 and 2011. According to the study, by KCE Structural Engineers, the samples tested by Balter showed that the concrete met the required strength. But when the consultant tested samples taken from the finished slabs of roadway late last year, the concrete was found to be below the strength required by designers.

Concrete issues at the Silver Spring Transit Center

The report said the quality of the concrete was a factor in the facility’s excessive cracking. As built, the transit center has a useful life of about 12 years rather than the 50 years specified by the county’s contract with the builders, consultants said.

Balter, which was paid nearly $1  million for its work on the transit center, is not the only contractor called to account for deficiencies. The report cited the engineering firm Parsons Brinckerhoff for flaws in the building’s complex design, an ellipse-shaped structure of concrete beams, girders and slabs reinforced by a network of steel tendons and cables that were “stressed,” or wound too tightly, contributing to the cracking. The general contractor, Foulger-Pratt, did not follow contract documents and neglected to install critical supporting cables in concrete roadway slabs, the report said. Their absence would have created a safety hazard if not discovered.

Both of those companies have declined to comment on the study’s findings.

KCE concluded that Balter, as the field inspection firm, “did not raise sufficient concern regarding numerous issues that were known and/or became visible in the concrete during construction, apparently did not follow up on solutions to those issues, and did not perform their services in accordance with Industry Standard.”

KCE also noted that it could find no record showing that Balter measured the thickness of the slabs, as required. At several points, the concrete is less than the contract’s specification of 10 inches thick. Phone calls to Lori Balter, president of the firm, were not returned.

The apparent lack of rigorous inspection has sparked discussion about the county’s practice of outsourcing the critical task to independent contractors.

General Services Director David Dise likened the county’s role to that of a homeowner commissioning a renovation or addition.

“Like any owner, we try to hire the best people we can,” Dise said. “When they don’t work out, like any owner, we have to deal with that.”

But not all localities take the same approach. Fairfax County said it uses staff inspectors. Contractors are free to hire their own third-party engineers before county inspections. “But bottom line, we do not contract out the inspections,” said spokeswoman Merni Fitzgerald.

Montgomery County Council member Valerie Ervin (D-Eastern County), whose district includes the transit center site, said the county may want rethink how it manages inspections.

“It seems to me there was a missing link and that it was that the county did not have its own inspectors on that project. And I think we’re going to pay for it somehow.”

Among KCE’s findings was that “apparently not all of the [Balter] inspectors had the certificates required of them by the county,” although it also noted that they were “apparently very experienced in construction in general.” The report did not elaborate.

The issue sent county officials scrambling last week to check the résumés and qualifications of Balter staff working on seven active projects: new libraries in Silver Spring, Gaithersburg and Olney; the Plum Gar Neighborhood Recreation Center in Germantown; the Travilah fire station; the Third District police station in Silver Spring; and the Animal Services and Adoption Center in Derwood.

Dise said Friday that all credentialing of personnel on the sites checked out.

But the transit center is a far more specialized and complicated project than the others, county officials said, far more than just a “parking garage.” The three-level building must handle heavy and constantly shifting loads created by large passenger buses. Concrete was used in ways that steel is usually employed, for load-bearing beams and girders.

According to county regulations, the Department of Permitting Services is supposed to hold a preconstruction meeting with all major contractors on a project. One purpose is to verify the credentials of the inspection team, “including evidence of laboratory accreditation and technician certification from recognized authorities.”

County officials said all attendees at the meeting had appropriate credentials, but they acknowledged that those there may not have been the ones working at the site. “We don’t know whether all credentialed people actually reviewed the post-tensioning on the job site,” said Deputy County Attorney John Markovs, who is leading the county’s legal response to the troubled project. “I can’t take an official position until we hunt it down and look at it.”

Balter was tasked with taking samples of concrete from every fifth truck that arrived at the construction site. The samples, taken before they were poured, were in cylinders and “cured,” or allowed to harden, according to the report.

They were left to set for varying lengths of time before they underwent compressive testing to determine the strength.

It isn’t clear how Balter ended up with test results showing that the concrete was stronger than required by design specifications while KCE’s subsequent testing of the finished slabs showed them to be below contract requirements. But the KCE report offered a couple of possible scenarios.

The hardening of concrete is driven by a chemical reaction between cement and water, a process known as hydration. KCE said it was possible that the samples taken by Balter were cured in a “more hospitable environment” than the existing slabs themselves, possibly at temperatures between 60 and 80 degrees, accelerating hydration and allowing hardening to occur more rapidly.

At the same time, according to KCE, portions of the concrete were poured in cold weather, which slows hydration. The report suggests that the concrete poured into place may not have been properly warmed. The difference in concrete strength, KCE said, is “suggestive of insufficient and inconsistent quality control in cold weather conditions.”

Also, KCE said it is impossible to determine from documentation submitted by Balter how much water was added to the transit center concrete. Moreover, when KCE examined Balter’s analysis of cylinder samples, they all showed the same water-cement ratio — which is statistically impossible.

Balter’s test results showed that the concrete was stronger than the contractually required 8,000 pounds per square inch. But samples pulled from the site by KCE showed a strength of 6,970 psi on five of 18 major pours on the second and third levels of the building. Overall, portions of the building “contain unacceptable concrete” that will have to be strengthened with new overlays, the consultants said.