Smooth pavement is the goal, but there are many factors that play a role in the end result of your blacktop. It can be difficult to achieve optimal density of your asphalt mix, but by changing one or multiple facets of your daily operations, you’ll be on your way to smoother, denser asphalt.
To assist contactors in attaining high quality compaction, Todd Mansell, Product Application Specialist for Caterpillar, offers insights on the best practices for asphalt compaction.
What is Compaction?
Compaction in its most basic form is the act of getting the air out of your asphalt mix in order to reach peak performance of your mix. Compaction starts behind the screen – both tamping and vibratory. Operators only have a limited amount of time to get the best density from your asphalt mix. Smoothness of the road is directly impacted by the compaction efforts.
Here are a few practical tips to help your paving crew achieve both density and production:
1. Keep an Eye on Your Mix Temperature
To reach optimal compaction, you need to hit the optimal temperature for your mix. This is achieved when the mix is still hot, regardless of the type of mix you use. Creating density is easiest when you’re at the highest temperature for the type of roller you’re using. The chart below reflects the temperature to hit for each specific roller. If you’re working with a heat that’s too intense for your roller, you run the risk of bulging.
2. Establish an Effective Rolling Pattern with the Correct Roller
The rolling pattern used directly affects compaction. First, you have the breakdown roller, which develops the majority of the density in an asphalt layer. It works immediately behind the paver where the asphalt is the hottest and it must match the production and speed of the paver. Breakdown rollers can be of any type but are most often vibratory steel wheel or pneumatic tire. Second, you have the intermediate roller, which comes into play immediately after the breakdown roller. The goal here is to develop final target density of 100 percent. Pneumatic tire rollers are occasionally used as intermediate rollers because they provide a different type of compaction than a breakdown steel wheel vibratory roller. Lastly, there are finish rollers whose goal is to clean up marks left by previous rollers. This state may achieve additional density gain. Static steel wheel rollers are primarily used as finishing rollers because they can produce the smoothest surface of any roller type.
3. Use Test Strips to Ensure Compaction Quality
If you’ve done everything right up to this point, your next step is to check your work. Start by confirming your equipment and patterns developed the required density for the project. Check screed laid density and monitor the temperature of the asphalt layer. Document the start and stop of your tender zone, if any, directly on the road. Check the density across the width of the asphalt layer and after each breakdown pass so you can outline the gauge placement and pull the core out as soon as possible. Verify the accuracy of onsite testing gauge and determine the number of roller passes. Trial and error will lead you to the ideal roller pattern to achieve optimal density and compaction.
4. Communicate with Your Team
Preparation, planning and training are key components of achieving optimal asphalt compaction, but they mean very little if nothing is being communicated. Smooth asphalt roads are paved when the paving operator is in tune with the roller operator who is in sync with the quality control team who is working closely with the hot plant.
With these tips, site managers and their teams can achieve the optimal asphalt compaction keeping customers and drivers safe and happy.
About the Expert
Todd Mansell is a Product Application Specialist for Caterpillar. Todd has been in the asphalt paving and construction business for over 25 years, working as an asphalt laboratory and field technician, laboratory manager, field inspector, paving quality manager and quality control manager for both government and private employers in both Canada and the United States. Todd has written articles and developed and delivered several paving and compaction training courses in the classroom and on the job site. Todd has also spoken at World of Asphalt 2018 and CONEXPO-CON/AGG 2017.
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Compaction: The Key to Asphalt Pavement Performance