Oscillation Conquers Changed Density Specs

Columbus specifications have changed from "tons per hour per roller", Smith says. "A certain roller would have so many tons per hour that it could compact, according to their science. Then they went to a density specification, where you had to get a minimum of 92 percent of the laboratory density, up to 97 percent, but with no number-of-passes requirement. We couldn't guarantee that we could do that every time, especially as the weather got colder, in the fall of the year, when it seems we do most of our work."

That's because Decker is called by developers to quickly pave subdivision streets before the season shuts down before winter. "As people start to panic, and realize it's almost winter, we're out there getting the last few subdivisions in before the season closes up, and conditions aren't suited for compaction."

The penalty in Columbus for not meeting the spec is that the contractor must supply an extended warranty. "That's something we didn't want to have to get involved with," Smith says. "And we were on the cusp of failure all the time, right at 92 percent. But we wanted to get up higher than that, up into the middle range."

Today, the mix specification remains in flux. "The whole specification is evolving as we speak," Smith says. "They are trying to come with a spec that will give them more longevity for their streets and highways. They're experimenting — sometimes at our expense, it seems — but we're working our way through it. And the HD O90Vs help assure that we won't have a problem."

Exacerbating the situation is the Portland cement concrete (PCC) pavement lobby, which is pushing the city to look more critically at HMA paving in its borders. "The lobby claimed HMA was not being tested enough, so the city decided to do compaction testing," Smith says.

Nonetheless, the high technology of the oscillation system in its twin HD O90Vs are helping Decker meet the challenge from PCC. "They do the job," Smith says. "We're happy with them. They are good machines and they have saved us money by not having to have another extra roller on the job."

In the process of changing specifications, the city went from a single spec of concrete base with a couple of inches of asphalt, to five different kinds of potential mat designs, Smith says. "On concrete, asphalt was a single lift of an inch and a half thick, on a variable surface. Before the oscillation rollers we had a tough time because we had variable lift thicknesses. It's not that we failed; it's just that we were on the edge of failure, too close to be safe."

Thin mats need oscillation

Other design specs include composite with stone and aggregate base and 1 1/4-inch surface course. "If you roll it too many times, it just breaks over and starts to destroy the mat," Smith says. "We were just getting to the 92 or 93 percent level, and then it would go the other way. With the conventional rollers, half a pass might be too much, but with the oscillating rollers, they seem to stop compacting the mat at the right time. When it gets as hard as it needs to get, it doesn't go in the other direction.

Don't ask me why, but I've seen it, and it's remarkable. We're also getting compaction in fewer passes, which means less time on the job."

Another danger of overcompaction is crushing of the aggregate within the mat, with telltale white streaks on the mat surface. "That can happen," says Snoke, asphalt superintendent. "But what we are having more of is our edges breaking off on us as we try to roll too much out. For that we will use an 8- to 12-ton straight roller on the last 6 to 8 inches."

More than just paving

Decker was started in Columbus in the 1950s by Ed Decker. It was acquired in the 1960s by Marble Cliff Quarries, and later by Medusa Aggregates. In 1981, Roger Apple and Fritz Smith — both employed by Marble Cliff — purchased the assets from Medusa and reincorporated in the name of Decker Construction Company.

Today, Decker operates within a five-county area in central Ohio, and specializes in a remarkable number of construction niches, including asphalt paving, asphalt maintenance, cold milling, roller-compacted concrete pavement, concrete construction, and new construction related to road widening, excavation and storm sewers. The firm completes approximately 350 commercial and public projects per year.

During the peak of the season, Decker employs approximately 150, with four paving crews, four stone crews, six maintenance crews, six concrete crews and four excavation crews.