How much pavement is needed?

Palmer course paving

When sizing and pricing a paving job, it’s always important to consider compaction. Compaction is what happens when you compress the asphalt material, thus reducing its volume. In other words, it’s how thick the asphalt is after it settles and is finished.

Properly compacting hot-mix asphalt will result in about a 25 percent reduction in the material thickness. So, we lay 1.25 inches of asphalt for every inch of finished thickness. Pavement thicknesses always should be specifically stated in finish compacted thickness. Do not just say “install XX inches of asphalt.”

Advantages of properly compacted asphalt include:

  • Reduction in air voids that make asphalt permeable
  • Increased durability
  • Material longevity
  • A smooth and uniform surface

How do we compact asphalt? We use mechanical, vibrating rollers. The rollers are driven across the pavement while at the highest temperature to compact the pavement. As a general rule, the higher the temperature of the mix being paved, the better the compaction. The ideal temperature depends on the mix composition, the pavement thickness and the type of binding agent used.

By keeping the pavement rollers in the proper pattern – or zone – you can reach your target compaction density. Cross rolling will ensure that you get uniform surfaces, particularly when paving parking lots and drive lanes.

You can run into a number of problems when proper compaction is not achieved:

  • Over-compacting can cause the pavement to segregate and become unstable. This can lead to premature cracks and failure.
  • Not enough compaction can lead to raveling of the pavement. This is when the asphalt mix begins to separate, which leads to reduced longevity.

If the asphalt is not compacted correctly to begin with, correcting it is extremely complicated and expensive. More times than not, you’ll need to replace the asphalt entirely.

The goal in compacting hot-mix asphalt always is to provide a smooth, structurally sound, durable and long-lasting pavement.