Aggregate Industries NE Inc. also agreed to plead guilty to a criminal charge of conspiracy to defraud the federal government.
Six employees of Aggregate, which supplied concrete used in tunnels and roadways in the Big Dig project, were indicted last year on federal charges that they falsified records to hide the substandard quality of 5,000 truckloads of concrete.
The company itself was not charged, but prosecutors at the time said their investigations continued.
The indictment charged the men with recycling concrete that was too old or did not meet contract conditions and, in some cases, double-billing for the loads. The company was paid $105 million for 135,000 truckloads of concrete, and more than 5,700 of those truckloads did not meet specifications, according to the indictment.
The deal announced Friday will end the case against Aggregate, which has since been bought by Holcim Ltd., a concrete company based in Switzerland. The six employees still await trials on charges of conspiracy to defraud the government, making false statements and mail fraud.
Under the plea agreement, Aggregate will pay $42 million to settle the civil investigation and $8 million in criminal fines. It will pay $27 million for a fund that will be used to finance future maintenance and repair costs on the project, and the other $15 million will be divided by the state and federal government.
Under the agreement, Aggregate also will sell its largest asphalt plant in Boston and pay for a monitor to track its legal compliance. The company also agreed to provide as much as $75 million in insurance for potential structural maintenance costs and pay $500,000 to state highway officials to check regularly where they suspect substandard concrete was poured.
The agreement allows Aggregate to avoid debarment by the Federal Highway Administration, letting the company continue receiving federal and state highway contracts.
"Today's effort is an extremely good result," state Attorney General Martha Coakley said.
The deal was crafted over two years, and the government agreed to it after the concrete met specifications for strength, durability and porosity, said company attorney Robert Popeo.
"But it wasn't a walkaway; as you know, it came with a criminal penalty and it came with a substantial civil penalty," Popeo said. "The company is glad to have it behind it."
The case was investigated by state and federal officials after a whistleblower who worked on the Big Dig sued in 2005.
"He is proud to have helped recover a very substantial amount of money for the taxpayers. He's very proud of having tried to do something to stop and correct a problem," said Andrew Rainer, an attorney for Timothy Chase Jr., a truck driver who filed the first lawsuit.
He and three others who later filed whistleblower lawsuits will share nearly $2.8 million from Friday's civil settlement, their attorneys said.
Meanwhile, state and federal prosecutors were determining whether to charge or settle with various Big Dig contractors in the tunnel ceiling collapse in July 2006 that killed a Boston woman.
Coakley said she may announce within a few weeks whether she'll press criminal charges in connection with the ceiling collapse.
Aggregate's attorney said the company did not supply concrete in that area and was not involved in investigations.