Placing asphalt is only a single battle in the war to reach project specifications. What comes after paving — breakdown, intermediate and finish compaction — is where bonus checks are often earned (or not).
How can you ensure your crew can avoid and, if necessary, overcome compaction problems? The following excerpt from The Cat Paving Products “Guide to Asphalt Compaction” highlights a few common compaction challenges, along with solutions your crew can implement today.
Asphalt pick-up on dry drum surfaces
The most common cause of downtime on double drum, asphalt compactors is a malfunctioning drum spray system.
If any part of the steel drum does not have a water film on the surface, hot asphalt is likely to stick to the drum. The stickier the asphalt mix, the more severe the problem. A small amount of asphalt pick-up on the drum quickly becomes a large problem. With each drum rotation, the amount of pick-up increases and the mat will begin to show divots.
When asphalt begins to stick to a drum surface, operation of that compactor must be terminated until the drum is completely clean and any problem with the drum spray system is repaired. Continuing to operate the compactor will result in severe mat damage that will require extensive handwork to fill in and level divots left in the mat.
The primary cause of dry areas on the drum surface is a plugged spray nozzle. Good maintenance and clean water supply are the keys to preventing plugged spray nozzles.
- Use clean water. Whenever possible, fill water spray reservoirs with water from approved sources. If you have to use pond water, for example, increase the frequency of maintenance steps.
- Change main spray system filters. Follow the filter change interval shown in the machine’s Operation and Maintenance Manual. When the main spray system filter is plugged, water bypasses the filter and unfiltered water goes to the spray bars. Unfiltered water is more likely to cause spray nozzles to plug. Always have a spare filter stored on the compactor or in the maintenance vehicle.
- Maintain inlet filters. Most water reservoirs have an inlet filter inside the reservoir fill port. The inlet filter is the first stage of water filtration. Do not discard the inlet filter. Place the water supply hose inside the inlet filter.
- Clean spray nozzles. The spray nozzles have internal brass or plastic screens. Nozzle screens should be examined daily for contamination. Clean nozzle screens thoroughly as needed. If you use contaminated water, increase the frequency of nozzle maintenance. If only one side of the nozzle is plugged, the spray pattern will be smaller and can cause the dry strip on the drum and start the asphalt pickup.
- Maintain water distribution mats. The drum will have some type of water distribution mat to help spread the water film evenly on the drum surface. As the distribution mats wear, you may have to adjust them to maintain good drum contact. Replace distribution mats according to wear indicators.
- Understand spray system capabilities. Most water spray systems offer full-time or intermittent spray. Never sacrifice water coverage in an effort to conserve water. It is better to stop more frequently for water refills than to stop for drum cleaning.
- Protect the water spray system during cold weather. An optional water spray system antifreeze kit is available. It includes a separate reservoir for antifreeze. At the end of the shift, the operator can circulate antifreeze through the system to prevent overnight freezing.
Asphalt pick-up on rubber tires
Asphalt also can stick to rubber tires. The severity of asphalt sticking to rubber tires depends primarily on the stickiness of the asphalt. Tire pick-up is also affected by the difference in temperature between the surface of the asphalt layer and the rubber tires.
When asphalt begins to stick to the rubber tires of a pneumatic compactor, the operator must immediately stop and correct the problem.