Two plead guilty to delivering bad concrete to the “Big Dig”

The case against a group of men who are being accused of throwing substandard concrete into the walls of Boston’s “Big Dig” project is beginning to stick. Two of the six former managers of Aggregate Industries NE Inc. that were indicted in 2006 have pleaded guilty of delivering faulty product.

Gerard McNally, a former quality control manager of Aggregate, and Keith Thomas, a former dispatch manager, admitted to 12 charges, including two conspiracy counts, five mail fraud counts and five counts of filing false reports in connection with the “Big Dig” project.

McNally and Thomas have agreed to cooperate with the prosecutor’s case against the four remaining and former Aggregate employees: John Farrar, a former dispatch manager; Robert Prosperi, a former general manager; Marc Blais, a former dispatch manager; and Greg Stevenson, a former district operations manager.

Sentencing for McNally and Thomas is scheduled for Oct. 1. In 2007, Aggregate pleaded guilty to fraud and agreed to pay a $50 million settlement to end civil and criminal investigations into the substandard concrete that was delivered to the “Big Dig.”