Two former employees of Aggregate Industries NE Inc., Saugus, Mass., pleaded guilty on July 8 to 12 charges involving a conspiracy to deliver substandard concrete to the $15-billion Central Artery/Tunnel project. Four more employees are scheduled to go to trial this week in U.S. District Court in Boston. Gerard M. McNally and Keith H. Thomas pleaded guilty to two counts of conspiracy, five counts of mail fraud and five counts of filing false reports stemming from a 2006 indictment alleging that, between 1996 and 2005, the six defendants delivered at least 5,000 10-yd truckloads of “non-specification” concrete to the project. The indictment charged the concrete was over 90 minutes old, had been adulterated and not batched to CA/T standards. Aggregate paid a $50-million settlement in 2007. The trial of the other defendants will begin July 15, says a spokeswoman for the U.S. attorney for the District of Massachusetts.