Keeping Void Rates Low

June 25, 2014

A high percentage of air voids in hot mix asphalt projects ultimately contributes to flaws in roadways. The ability to consistently keep air voids to a minimum is where Thompson, GA–based C&H Paving excels. Whether repaving existing county roads or building new highways, C&H Paving has found the right combination of compacting equipment with two double-drum vibratory rollers and a pneumatic tire roller. C&H Paving attributes much of the successful void rates to the performance of the pneumatic tire roller—a PT240 from Case Construction Equipment—and its ability to alter its operating weight through a combination of ballasts to meet the requirements for each individual job.

The Georgia Department of Transportation (DOT) requires air voids to be less than 6% of the final mix. Prior to implementing the new Case roller train, it was not uncommon for the company to pass the tests with ratings in the range of 5%. C&H Paving now regularly passes those tests with ratings in the 3% to 4% range—some of the best ratings in the state of Georgia.

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Controlling Quality
C&H Paving serves a range of customers in the public and private sector throughout Georgia, and works in conjunction with its own asphalt plant (BCI Inc.) to ensure quality and productivity. C&H Paving also handles road-building projects in turnkey fashion, providing everything from site clearing and preparation to the finished roadway. C&H Paving owner Benji Cranford attributes much of the successful void rates to the performance of the pneumatic tire roller—a PT240 from Case Construction Equipment—and its ability to alter its operating weight through a combination of ballasts to meet the requirements for each individual job.

“Benji is not like many others, because he’s vertically integrated,” says David Johnson, sales representative, Border Equipment Co. “He has full control over the product from beginning to end. He has full confidence in the quality of the asphalt, so he can focus on the laying technique onsite. And he has full control over scheduling and asphalt production, which makes him extremely flexible to respond to the needs of his customers.”

After exploring new compactor options in 2012, C&H Paving added a Case DV210 (99 horsepower, 22,928 pounds) double-drum vibratory roller to its equipment fleet. Based on the compactor’s performance, it later added the PT240 pneumatic tire compactor (99 horsepower, 20,525 pounds unballasted) and a Case DV213 (130 horsepower, 28,718 pounds) double-drum vibratory roller. Cranford uses all three on most projects in a sequence designed for optimal compaction. The process typically begins with the DV213 serving as a “breakdown roller” and performing the initial vibratory compaction with two passes. The PT240 then compacts the mat, and the DV210 rounds out the process to achieve the final smooth finish of the roadway.

The PT240 roller plays an important role in helping achieve consistent asphalt density. The tire configuration (four in front, four in back) with 2-inch tire overlap provides 78 inches of compaction width. Cranford says the rubber-tired roller essentially “kneads” the hot-mix asphalt gently at the surface as it rolls across it with its weight. The result is greater asphalt density and fewer possibilities for voids that can lead to flaws and deterioration.

“The DOT is rough on you for having voids,” says Cranford. “They want to make sure your voids are below 6%. It seems to me that the big rubber tire roller is what helps more than anything.”

Pneumatic tire rollers rely on sheer weight to perform compaction and, in the case of the PT240, that weight can be altered to tailor performance to the job at hand. When setting up the machine, operators can adjust the ballast and the inflation of the tires to allow the roller to conform to the surface being paved. This flexibility also helps simplify Cranford’s equipment needs (and associated owning/operating costs), as he can now perform tasks with one machine that previously took two or three different pneumatic tire rollers.

“If you’re paving an airport runway, you want to be as heavy as you can be,” says Cranford. “You fill it (the PT240) full of water, and with the plate it’s about 52,000 pounds. If you knock the water out of it, then you’re down to 40,000. If you’re on a city street and you don’t need that much weight, you can take the water out and the plate off of it and now you’re down below 30,000 pounds. It just helps because, before, you might have two different rollers. You’d have a smaller rubber tire roller and a bigger one. Now you don’t have to have that, you just have one to do it all.”

That ability to tailor the weight also helps Cranford improve productivity and reduce excessive traffic on the hot asphalt (which could lead to overcompaction and deterioration). By ballasting the machine to heavier weights, he can complete compaction in fewer passes compared with performing a greater total number of passes with a lighter machine.

“You can speed up production and you can roll it, and you don’t have to beat it as much (with excessive passes),” he says.

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Testing Rates Prove Quality
The Georgia DOT performs regular testing to ensure that voids are typically kept below 6%.

For C&H Paving, this has recently included the construction of 3 miles of passing lanes on State Route 47 near Lincolnton, GA, and a wide variety of resurfacing jobs as part of Georgia’s Local Maintenance and Improvement Grant (LMIG) project, a state-run program that helps local governments keep up maintenance on state roads.

Georgia DOT testing samples showed that C&H Paving was able to consistently keep air voids below 6%, often showing void ratings between 3% and 5%. According to Cranford, the PT240 roller played a key role in maintaining low void percentages and others in the industry are taking notice.

The DOT was surprised by the low averages, says Cranford. “The inspectors [were saying to other contractors], ‘Well, Benji’s getting them,’ and the other paving contractors [were asking] ‘What’s he using?’ Everyone wants to know. Sooner or later they’ll have one because it just eases your mind.”

“When you go home at night and don’t have to worry about voids, because you won’t know until the next day if you passed or not, you sleep a little bit better.”