Both types of compactor do the same thing in different ways. We asked Dale Starry, marketing manager for compaction at Ingersoll-Rand, to shed some light on the pros and cons of each.
Tandem-drum vibratory compactors offer contractors a high productivity solution for finishing asphalt, although single-drum machines, because of their superior traction and slope-climbing ability, are used frequently in soil and gravel compaction on roadway sub-bases as well as asphalt. In the vibratory mode, steel-drum rollers quickly increase the density of fresh asphalt and are usually the preferred machine for the initial breakdown pass in most applications.
After the breakdown pass you can use either a steel-drum or a pneumatic-tire compactor to continue compaction. But tandem steel-drum machines, with their ability to vibrate the surface, achieve the required level of density in roughly half the number of passes as a pneumatic-tire machine in the intermediate rolling applications, Starry says.
The key difference is that steel drums leave behind a surface that is more permeable and open textured. Many state departments of transportation are using permeable asphalt pavements designed to let rain migrate through the top asphalt layer to drainage channels underneath. In areas with high rainfall amounts, the open texture is often spec’ed because this type of road surface is better at reducing standing water and spray from passing vehicles. Open-texture asphalt pavements also give vehicles better traction and skid resistance.
Pneumatic-tire machines create a smooth, impermeable wear layer.
As a general rule, pneumatic-tire compactors are only half as productive as tandem-drum vibratory compactors in the intermediate applications, but for two key reasons they still play an important role in almost every contractor’s asphalt compaction strategy.
First, pneumatic-tire machines create a smooth, impermeable wear layer. While the textured wear layers that steel drums create are gaining favor in some states, Starry estimates only about 15 percent of roadways are designed with this criteria in the specs. Smooth, impermeable wear layers drain water to the sides and prevent it from weakening the sub-base.
Second, pneumatic-tire machines are much preferred when compacting naturally occurring soils, crushed stone and chip-seal surfaces because steel drums tend to fracture these types of stone, Starry says. The working speed of pneumatic compactors, many of which can run from 4 to 8 mph, is well matched to a chip spreader.
Steel-drum compaction is essential in today’s asphalt paving. Every project requires at least one vibratory compactor in the roller train and most projects have at least two. Whether or not you also include a pneumatic-tire compactor in your compaction fleet will be largely dictated by regional requirements.
Paving trains are moving at faster speeds than ever before and rollers must, by design, keep up with pavers for efficiency. There have been significant improvements in compaction equipment during the past decade, especially with vibratory rollers. Pneumatic-tire compactors have also evolved, Starry says, to include productivity enhancing features such as hydrostatic drive systems and improved tires.