As Denver International Airport waits for an assessment of weak concrete in the terminal to wrap up, its contractors are delivering increasingly startling forecasts of the potential impact on a renovation project’s timeline.

May 2023 is the most recent projection made by Great Hall Partners for completion of the final phase of the $650 million-plus project, as disclosed this week in a monthly project report for bondholders.

That would be 18 months beyond the original target of November 2021. And the estimate has grown from a forecasted 10-month project delay in February.

DIA won’t confirm the contractors’ latest projected delay. A spokeswoman says it’s too soon for a solid estimate of extra time or cost resulting from the concrete problems on the main floor, under the terminal’s tented roof. That’s because an outside firm’s assessment of core-sample testing, along with potential adjustments to the project — including some that might save time — is still underway.

The assessment had been expected in April but likely will be delivered by early May, said Stacey Stegman, DIA’s senior vice president of communications.

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Great Hall Partners, led by Madrid-based Ferrovial Airports and Centennial-based Saunders Construction, has not submitted a formal claim to DIA to extend the project’s timeline or recoup more costs from the project’s $120 million contingency fund, Stegman said.

But it has gone quiet in the face of media inquiries.

“GHP isn’t commenting or answering questions at this time,” spokeswoman Alana Watkins wrote Wednesday in an email to The Denver Post, referring questions to DIA.

Some work has resumed in a walled-off area on the main floor where the weak concrete was discovered. Spider cranes — a type of crane that distributes weight better — are now at work setting steel. Elsewhere, work has continued on other parts of the project.

The contracting team won a $1.8 billion public-private partnership deal that covers the renovation and three decades of private oversight of expanded terminal concessions.

The terminal renovation plans include moving the two main security checkpoints from Level 5, which is the main floor of the terminal, up to Level 6, along with the consolidation of the airline check-in counters there to make room. More concessions spaces and a welcome plaza are planned on the main floor.

Formal notice of problem last fall

On Nov. 2, Great Hall Partners sent DIA a formal notice that initial testing had shown that the “compressive strength” of the main floor’s concrete — its ability to bear loads — was lower than what project plans specified from the airport’s original construction 25 years ago.

Caroline Clevenger, the assistant director of the University of Colorado Denver’s construction engineering and management program, said both DIA and the contractors were right to take the issue seriously before getting too far along on the project.

“If it’s a load-bearing issue, those are game-stoppers,” she said of the concrete problems. “Because you don’t want the building to fall down. They need to take extra caution.”

Results of recent testing confirm issues

The Post has reviewed several more recent engineering and material investigation reports after obtaining them from DIA through a public records request.

Some of the dozens of concrete core samples tested since the initial disclosure have been found to meet or exceed the strength levels indicated in the project plans, but many did not. A variety of factors were faulted, including excess air pockets, uneven settling of the chunky aggregate that’s mixed in and variations in concrete mixtures.

But worries about deterioration of the cement mostly were unfounded, the firms found.

Great Hall Partners said in its new bondholder report, filed April 15, that the schedule impact of 551 additional calendar days was preliminary. It could be adjusted as the contractors and DIA explore potential changes to project sequencing or construction methods, the report said, and such changes potentially could save the project time.

The report also notes that Great Hall Partners is in discussions with DIA over other potential “compensation events” that include the discovery of unknown utilities and material containing contaminated lead.

Document: Great Hall Partners’ most recent project report: