Dual design/performance can benefit pavement contractors of all sizes.
Asphalt compaction practices vary from contractor-to-contractor and region-to-region — larger asphalt paving projects generally rely on some combination of double-drum vibratory and pneumatic tire rollers to complete the work. The double-drum vibratory compactor provides the brute force of compaction while the pneumatic tire roller provides varied weight through ballasting, and a kneading action that results in excellent density, fewer voids and a well-sealed finish.
The continued adoption of combi rollers — a vibratory steel drum on the front and a sequence of pneumatic tires on the back — has provided another option for paving contractors that ultimately delivers the best attributes of each standalone design.
Achieving Greater Density/Smoother Finish in Residential and Commercial Paving
Paving contractors who work in residential and commercial applications may not have the capability of owning multiple rollers that provide unique benefits/capabilities. A combi roller provides those residential and commercial contractors with the ability to own a single machine that provides the compaction power of a vibratory drum, and the finishing ability and density of a pneumatic tire. This can be extremely beneficial in northern climates where asphalt is subject to more rain and snow, and the inevitable heave of freezing and thawing cycles.
Contractors who currently rely on standalone vibratory drum compactors will see an immediate benefit. The pneumatic tires knead the asphalt in a way that results in greater density and fewer voids, and ultimately allows more of the bitumen to rise toward the top of the finish – providing a better seal. This results in a stronger product that will last longer and is less susceptible to water incursion and the affects of it freezing/expanding/thawing.
Manufacturers offer a number of sizing options to fit varied applications — some of which have never had the benefit of a pneumatic tire roller before due to size/scale — from walkways and golf cart paths up to parking lots and roadways. For instance, CASE offers a range of both small- and large-frame combi options, from one unit that compacts at just over three feet in width up to a larger roller that compacts at a width of five feet, six inches.
Greater Productivity/Fewer Passes
Large-frame combi rollers provide the benefit of high-frequency steel drum compaction. This allows for greater control of compaction performance based on the type of asphalt being compacted, and the thickness and density requirements of each lift. This, followed by the finish of a pneumatic tire, allows for paving projects to be completed faster and in fewer total passes. This provides obvious benefits in productivity and profitability (completing more work, in less time), but it also improves quality. Completing a paving job in fewer passes reduces the opportunity for over compaction, which can lead to faster deterioration of the new asphalt.
Compatible with Intelligent Compaction Technologies
While different in design than standalone machines, combi rollers are fully compatible with intelligent compaction and infrared technologies required by many asphalt contractors. These technologies improve compaction quality during the initial passes, require fewer passes to reach target specs, and result in savings in time, fuel costs and machine maintenance – as well as avoiding pitfalls related to under- or over-compaction.
We talk a lot about intelligent equipment utilization, and combi rollers provide fleet owners an opportunity to simplify their fleet outlay. While every contractor is different (large-scale highway contractors will always rely on the multi-unit setup, for instance) some will be able to swap out multiple standalone units and standardize on a combi roller, ultimately resulting in lower carrying costs, greater simplicity in transporting equipment to jobsites, and a lower total cost of ownership for that asset.
The major structural difference an equipment owner will notice when comparing a combi roller to a double drum compactor is that it replaces the rear water tank with a tank and distribution system for an emulsifying agent that prevents the asphalt from sticking to the pneumatic tires — water alone doesn’t work with the rubber tires. Similarly, large thermal aprons can be added to encase the pneumatic tires and further prevent asphalt sticking.
Combi rollers ultimately provide contractors with a great opportunity to increase productivity, make fewer passes over the finished product, and achieve greater densities and quality compared to standalone units. Contractors who work in residential construction and commercial development should explore these options before making their next compaction purchase.