Former employees are accusing the company of mixing crushed stone into high-quality concrete, the newspaper reported, potentially reducing the lifespan of the concrete from 50 to as little as 17 years.

The newspaper did not name the company, identifying it only as a mid-sized firm in the Stuttgart area. Citing the regional public prosecutor’s office and affidavits filed by former employees, the newspaper reported that authorities are investigating the firm’s 40-year-old owner.

The company is accused of including poor-quality concrete in its delivery of 35,000 cubic metres of concrete used to build an underground nuclear storage facility at the Neckarwestheim plant in 2004. The Süddeutsche quoted one of the manufacturer’s former mixing overseers as saying that where the sub-par concrete was used, “expensive renovations or even the wrecking ball are likely to be necessary within the anticipated lifespan of the concrete.”

Employees also accused the company of supplying sub-par concrete to other major building projects in the German state of Baden-Württemberg, including medical facilities, kindergartens, the Stuttgart Arena and museums built by automakers Mercedes-Benz and Porsche.

The company that operates the Neckarwestheim plant, energy group EnBW, told the newspaper that strict controls would have made it impossible to manipulate the concrete.

Investigators from the Ministry of the Environment in Baden-Württemberg found that quality control tests were conducted twice as often as required during construction of the Neckarswestheim facility. None of the tests showed problems with the concrete, the ministry reported on Friday after sending investigators to the facility on Thursday.

A spokesman for the concrete company declined to comment on the investigation, saying the firm was unfamiliar with the affidavits.

“It’s totally incomprehensible that such obviously false statements would be made,” said the spokesman, who was not named in the newspaper report. He added that the firm “does not sell or distribute sub-par concrete.”

A spokeswoman for the public prosecutor’s office in Stuttgart confirmed that the firm has been under investigation since last year on suspicion of fraud for delivering inferior quality concrete. Investigators searched the owner’s private home and office in November, she told the paper.

A former company employee told the Süddeutsche that his employers used a remote-control system to dilute the cement with cheap crushed stone and waste products.

“I could watch the manipulation on my screen, but I couldn’t stop it,” a former employee told the paper.