BOSTON -- Six men who worked for Aggregate Industries, the Big Dig's largest concrete supplier, have been charged with falsifying records to hide substandard concrete used on the project.

NewsCenter 5's Janet Wu reported that the defendants, all current or former employees of the company, were named in a 135-count indictment.

The men are accused of covering that subpar cement was used on vital parts of the Central Artery Project, including in ramps, tunnels, roads, slurry and seawalls.

"The conduct alleged in today's indictment is illegal and is an affront to hardworking Americans whose tax dollars fund projects like the Big Dig," U.S. Attorney Michael Sullivan said.

Prosecutors claim that from 1996 to 2005, more than 5,000 truckloads of concrete delivered by Aggregate Industries were either watered-down, recycled from other projects or were so-called old concrete, or concrete that had been mixed for longer than 90 minutes before it was poured.

"This was pretty bad. They were caught red-handed. Essentially, what happened here, folks, is the taxpayers from both Massachusetts and the taxpayers of the United States did not get what they paid for," Attorney General Tom Reilly said.

Five of the six men indicted appeared in court Thursday to face charges they submitted false records to cover their alleged crimes. One man living in Pennsylvania and no longer employed by the company and did not appear in court.

"On many occasions, when loads were rejected by inspectors because the concrete did not meet project specifications, the trucks were simply routed back to the Central Artery Project, again by the defendants and their co-conspirators," Sullivan said.

Prosecutors could not link any of the leaks in the tunnels to any of the alleged substandard concrete.

"The best information I can give you at this point is that we do not have any evidence that the structural integrity of the tunnels has been compromised," Reilly said.

Attorneys for the defendants said their clients were under intense pressure to deliver large amounts of concrete quickly and did only what they were told to do. They also said prosecutors are ignoring certain facts.

"The failures of the Turnpike Authority, the failures of the state and federal governments, the failures of Bechtel -- and all of a sudden the company supplying the concrete is responsible for it all? I think sometimes in politics instead of accepting responsibly, the tendency is to blame the little guy," said defense attorney Stephen Delinksky.

Sullivan agreed that those managing the project should have known about the alleged substandard concrete. Four of the six men are still employed by Aggregate Industries, but they have been suspended with pay.

The Central Artery and Third Harbor Tunnel project or Big Dig buried Interstate 93 in tunnels beneath downtown Boston connected the Massachusetts Turnpike to Logan Airport with a tunnel beneath Boston Harbor.