Hamm Compactor Does Work Of Two At Midway Airport
The first 3000 Series base compactor delivered in the United States – a Hamm Model 3412 owned by Walsh Construction – was doing the work of two machines in bringing stone base to 100 percent compaction to meet Federal Aviation Administration (FAA) specs on a major airfield project. The Hamm was hard at work preparing bases for concrete runway, taxiway and apron structures for the airfield reconstruction and terminal expansion of Chicago Midway Airport. "The contract calls for 7 inches of CA 6 Grade 8 stone base on top of a dirt subbase," said Tony Charielle, project superintendent, heavy/highway, for Walsh. CA 6 is a 3/4-in. crushed limestone aggregate with fines. "So we prepared the subbase with our dozer, at which time the Hamm roller would come behind it and get compaction on the soil."
Cut
to subgrade
For the soil subgrade, Walsh would cut to subgrade and perform a proof
roll by driving a loaded truck on it under the gaze of FAA inspectors.
"If the soil deflects more than a half inch, we are directed to either
undercut it anywhere from 6 inches to 2 feet," Charielle said. "If
we do undercut it, we call for PGE [porous granular embankment, 6-inch
stone down to fines] material for the hole, compact it with the Hamm 3412,
and put CA 6 on top of that."
That material is 8 inches of stone, to be compacted to 7 inches. Then
6 inches of cement treated permeable base [CTPB] would be placed, followed
by 17-inch-thick portland cement concrete structures above. "We're
mandated to have 100 percent compaction so we water our stone constantly,
and we've had no problems at all achieving compaction with the Hamm,"
Charielle said. A competing roller had been used earlier in the project,
he said. "We could get 100 percent with it, but it took a lot more
effort than the Hamm," Charielle said. "With the Hamm, we hit
it a few times and it would be there."
In fact, the Hamm 3412 was doing the work of two other units on the Midway
project. "We got rid of all the other rollers we had," Charielle
said. "It replaced two compactors." That's because it only would
take two or three passes with the Hamm 3000 Series unit to reach 100 percent
compaction, Charielle said. "We could do that with high frequency
running on the roller," he said. "With the other machine, it
all depended on what the subbase was underneath. If we didn't have a really
good subgrade and dirt, we had a lot more difficult time. With the Hamm,
it really didn't matter."
Boosting productivity
Being able to greatly reduce the compaction time with a product like
the Hamm 3412 means a lot to a contractor like Walsh, which was undertaking
the Chicago Midway airfield reconstruction on a very tight schedule. "Last
year they did an area as large as the 5-acre concrete area in front of
us, and it took them all fall to do it," Charielle said. "We
did an area twice that big in a month, and it had a lot to do with the
Hamm roller." Gesturing behind him, Charielle said "We did this
2-acre area back here in about a month, because the Hamm helps,"
he said. "I've never achieved compaction as easily with another machine
as with this one."
Unpredictable subsurface conditions also complicate construction, but
the Hamm compactor helps keep the project on schedule. "Seventy-five
percent of one area we hit on the north side required a 2-foot undercut,"
Charielle said. "Having this roller definitely helped for that work,"
he said. "We took the Hamm® down to better ground, and we started
putting the PGE in and hitting it with the Hamm roller," Charielle
said. "We were getting compaction on the subbase which we didn't
even need, but could attain with the Hamm. That made the owners – the
City of Chicago – pleased with the product."
Scuttlebut leads to Hamm
For Walsh's Charielle, Hamm's reputation in asphalt compaction had preceded
the 3000 Series. "I had seen them with asphalt crews, but I didn't
know they made one for stone," he said. "One of my superintendents
had come across the brand and asked me to start inquiring to find someone
who carried it, and see if we could get someone out here." Walsh
wound up with the 3412, an 84-inch-wide, single-drum vibratory compactor
with operating weight of 12 tons. "Our dealer said it was the top-of-the-line
model, what you should have in this situation," Charielle. "We
didn't argue; they know their product better than we do."
Once in its hands, Walsh Construction had no qualms about purchasing the
new 3000 Series model. "The reason we purchased it was that we were
getting compaction with it, and it didn't matter what it cost," Charielle
said. "If this was going to get us what we needed in this time frame,
that's what we wanted."
