- Use a bio-degradeable release agent to clean the affected tires. Apply more release agent to the tires before resuming the compaction process.
- Be sure the distribution mats and tire scrapers are properly positioned and in good working condition.
- Move the pneumatic compactor on the asphalt layer in an area where the surface temperature is relatively low.
- Heat the tires by operating on the warm mat before moving ahead to a higher temperature zone.
Heating the rubber tires and keeping them at the correct temperature are very important. Wheel covers help keep heat confined around the front and rear axles. Caterpillar recommends using wheel covers on pneumatic compactors for all asphalt compaction applications. Covers are especially important when compacting asphalt that contains modified asphalt cement. If wheel covers are not installed, the tires are exposed to the ambient conditions and can lose heat rapidly.
Release agents are sometimes used to help prevent hot asphalt from sticking to rubber tires. Always confirm with the public works department what release agents are permitted. Most compactors have a tire spray system that is often filled with water and an additive. Common additives include detergents, water softeners or purpose-designed additives that increase the film thickness of the water sprayed on the tires.
In some areas, natural vegetable oil is substituted for water in the spray system reservoir. Do not use petroleum distillates as they are harmful to asphalt and the environment. To prepare the pneumatic compactor for placement in the desired position behind the paver, plan your approach to heating the tires. Apply a release agent (if needed), and keep the tires hot.
- Before the start of the paving and compaction process, operate the pneumatic compactor on a paved surface behind the starting point. Operate at high speed to build up heat in the rubber tires by flexing them.
- When using a release agent, wet the tires thoroughly just as the compactor is ready to start its first pattern.
- Check the temperature of the asphalt layer and guide the pneumatic compactor operator into the correct temperature zone.
- Be alert for any sign of excessive asphalt pick-up on the tires. Especially watch for asphalt clumps falling off the tires when the compactor stops and reverses.
- If you see excessive asphalt pick-up, immediately clean the tires. Move the compactor back to a cooler temperature zone. Gradually move the compactor forward, allowing the tires to heat up prior to reaching the desired temperature zone.
- Once the tires are heated, keep them heated. If there is an interruption to the paving and compaction process, do not park the pneumatic compactor. Move the compactor to a place on the asphalt layer where it can continue to roll in order to keep the rubber tires heated.
Deep pneumatic tire marks
Using a pneumatic compactor on hot asphalt layers, especially layers three inches thick or thicker can result in deep tire marks that are difficult to clean up, particularly behind vibratory screeds.
Ordinarily, a pneumatic compactor is used during the intermediate phase of compaction on an asphalt layer that is already close to final target density. The tire marks it leaves in the mat are normally shallow and can be smoothed out by the finish-phase compactor.
However, if the compactor is used during the initial compaction phase or if the pneumatic compactor rolls an area where the mat is thicker and hotter than normal, the rubber tires can leave deep marks that do not clean up easily during finish compaction.
Using a pneumatic compactor during the initial phase is usually done when compacting a base or binder layer that is going to have another layer laid on top of it. In that instance, the tire marks and loss of smoothness are less of an issue.
Using a pneumatic compactor during the initial phase on the final layer (wearing layer) of asphalt is not common because the final layer is often measured for smoothness. A pneumatic compactor is normally in the intermediate position when compacting the final asphalt layer.
If deep tire marks appear during the compaction of the final layer:
- Move the pneumatic compactor farther behind the paver where the asphalt layer is cooler, or …
- Decrease tire pressure to flatten the tires somewhat and reduce the tire contact pressure.