Testing showing weaker-than-expected concrete in the main floor of Denver International Airport’s terminal has slowed construction on a massive renovation project and could delay completion by up to 10 months, according to a new report produced by the contracting team.

The extent of the delay — and the severity of problems with the 25-year-old structure’s original concrete — won’t be known until at least April, DIA spokesperson Stacey Stegman said. That’s when intensive testing of the concrete that is now underway is expected to be complete.

DIA expects that testing will shed light on the concrete’s load-bearing ability before contractors bring cranes onto the main floor of the terminal and begin erecting steel.

But a preliminary estimate by Great Hall Partners, the private consortium carrying out the $650 million renovation project, is that the concrete issues could delay the project by 209 work days.

That would equate to roughly 300 days when weekends and holidays are added in — or nearly 10 months beyond late 2021, the original target for completion.

DIA and the contracting team say work is continuing on other parts of the project, but the delays affect a walled-off portion of the lower level beneath the airport’s tented roof. It’s the same main floor that includes the two main security checkpoints.

The contracting team, led by Madrid-based Ferrovial Airports and Centennial-based Saunders Construction, disclosed the potential delay due to the concrete problems in a monthly project report filed on Thursday. That report was first covered by CBS4.

“The projected schedule represents their estimates but does not include the airport’s review and analysis or ways to mitigate” the problem, said Stegman, DIA’s vice president of communications, in a statement. “The issue cannot be fully known or realized until April when the testing is completed and the airport is able to review and analyze the results with Great Hall Partners.”

It’s possible, she said, that adjustments to project plans or construction will be required, but engineering experts “have informed us that the airport is safe and can support the construction.”

Great Hall Partners CEO Ignacio Castejon reiterated in a statement provided by a spokesperson that the contractors and DIA will need to analyze the coming test results before they can determine the impact of the concrete issue on the project.

“Our recent construction update report projects an estimated and preliminary delay based on the current status of the project and the information we have as of today,” Castejon said.

“Compressive strength” of concrete is the issue

The root of the issue, according to both DIA and the Great Hall Partners report, was that the “compressive strength” of the concrete, or its ability to bear heavy loads, was found in early testing last fall to be lower than what the airport’s project plans specified. Stegman said the inconsistency with plans “isn’t uncommon” in such a large project — but it has paused some work until it the problem’s full extent is known.

Another issue on the radar is the potential for deterioration within the concrete, which caused the replacement of concrete in a DIA runway more than a decade ago. But Stegman said recent testing of concrete samples from the terminal “show no indication” that deterioration has occurred.

The renovation is part of a $1.8 billion public-private partnership deal with the Ferrovial team that also covers three decades of private oversight of expanded terminal concessions.

As part of the contract, Ferrovial agreed to a set cost for the renovation project, but with a big caveat: new requirements imposed by DIA and unforeseen construction challenges were to be covered by a $120 million contingency fund filled by the airport.

A recent accounting provided to The Denver Post by DIA shows that it has approved $7.2 million in additional costs, leaving a $112.8 million balance in that fund.

Work began last summer, and significant change is planned for much of the terminal. By the end of the project, the main floor security will move upstairs to expanded spaces on the north ends of each side of the terminal. Consolidated airline check-in areas that occupied the length of the upper floor are being consolidated in the south and middle portions of that level.

Downstairs, the south end of the main floor will become a welcome plaza. The north end will have new shops and other concessions that are walled off in a secure area that travelers will pass through as they descend from the new security checkpoints to the underground train that goes to the concourses.

Document: Great Hall Partners’ recently filed construction report

Discussion of the concrete issues is on page 14 (the final page in the digital version).