Important Note: The information and techniques presented herein are general guidelines for the compaction of asphalt. Contractors are advised to select their compaction equipment and adapt their compaction strategies based on the specific requirements, site conditions, and material characteristics of every project to ensure the best results.
Specialty Compaction: Rolling on Airports, Bridges, Chip Seal, & Thin Lifts
Specialized asphalt paving applications require a tailored approach to compaction. While the fundamental goals of achieving density and a smooth finish remain the same, factors like the paving environment, material properties, and specific quality standards demand a different strategy. Selecting the right asphalt rollers and implementing a precise compaction plan are critical for the success and longevity of these projects.
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- Compaction on Airport Runways and Taxiways
- Paving on Bridge Decks
- Chip Seal Compaction
- Paving Thin Lifts
Compaction on Airport Runways and Taxiways
Paving on airport runways and tarmac involves much higher standards than typical road work due to the extreme loads and consistent stress from aircraft. The Federal Aviation Administration (FAA) sets strict specifications that contractors must meet to ensure safety and the long-term integrity of the pavement.
One of the most notable differences is the use of echelon paving, where two pavers work side-by-side to lay down parallel mats. This technique is used to create “hot joints,” ensuring that the seams between the lanes are compacted while both mats are still hot and pliable. For other areas where cold joints are unavoidable, it is common to cut back the unsupported side of the joint by a few inches to ensure a good level and confined connection to help achieve better cold hot joint densities. Advanced joint systems, such as VRAM (Void Reducing Asphalt Membrane) and RPE (Reinforced Polyethylene), are also used to improve joint integrity.
On airport jobs, double drum vibratory asphalt rollers and tandem oscillatory asphalt rollers are often used. Pneumatic tire rollers can also be effective but require careful management. The tires must be coated with an adequate release agent and their ideal temperature must be within 40°F of the mat’s temperature to prevent the asphalt picking up. In addition, vibratory pneumatic tire rollers, a proven technology only made by SAKAI, have been used to increase the kneading effect and density through a combination of vibratory action with the pneumatic tires.
Paving on Bridge Decks
Paving up to and over bridge decks is a specialty application that requires a careful compaction plan to prevent structural damage to the bridge’s foundation and deck. Unlike standard roadways, the underlying structure of a bridge is not a continuous subgrade. The application of standard vibratory force could cause unintended damage to the bridge itself.
For this reason, heavy static 3-wheel compactors or double drum oscillatory asphalt rollers are the preferred machines. While a static roller relies solely on its weight for compaction, an oscillatory roller utilizes a back-and-forth motion that dissipates force horizontally into the asphalt mat, effectively limiting the vibration transmitted to the bridge deck below. These rollers are chosen because they apply a more gentle and controlled force.
Chip Seal Compaction
Chip seal is a cost-effective paving treatment used for less-travelled country roads, driveways in some southern US regions, and to restore and extend the life of a road in many regions. Unlike traditional asphalt paving, rollers on a chip seal job are not compacting a thick asphalt mat. Instead, their primary function is to embed the loose aggregate chips into a hot emulsion.
For this application, pneumatic tire rollers or combination rollers are the best choice. The staggered rows of rubber tires on a pneumatic asphalt roller apply a consistent kneading effect that helps to orient the chips, push them into the binder, and create a uniform surface. A combination roller uses the drum to knock over the chips followed by the tires kneading them into the emulsion. The rollers on a chip seal job often operate at a faster speed than on standard road work to keep up with the high production rate of the chip spreader and emulsion distributor.
Paving Thin Lifts
A thin lift is a layer of asphalt that is typically less than two inches thick. Compacting thin lifts presents a challenge because the asphalt roller’s dynamic force can easily fracture the aggregate in the mat if not properly applied.
Double drum oscillatory rollers are considered the ideal roller for thin lifts as their back-and-forth motion provides a consistent, gentle force without damaging the aggregate. Double drum vibratory rollers can also be used, but they must be set to a high frequency (to keep impacts per foot consistent) and low amplitude to avoid fracturing the aggregate. In some cases, to prevent any risk of damage, a static compactor can be used as a finishing roller.