10 Fundamentals of Compaction in Construction and Roadbuilding

Yet compaction isn't as simple as rolling material flat — it's a scientific process involving force, frequency and material behavior. By understanding the core principles of road compaction, soil compaction and so on, you can work more efficiently, reduce material displacement and achieve density targets with fewer passes. 

If you've been in the industry for decades, you likely already know a lot of this — but I've been in this industry a long time too, and I'm always learning something new. I also appreciate a good refresher to stay at the top of my game, and I hope you do too. And in case any of you run Volvo asphalt rollers or soil compactors, I’ve also included some key advantages you’re getting with the products we provide. Take a look.

1. How Vibration Works In Soil and Asphalt Compaction

• Vibration is the motion of the drum created by rotating an eccentric weight inside, which transmits energy to the material being compacted. Densification begins at the bottom and continues to the top of the layer. Vibration applies repeated impacts to the surface of the pavement or soil realigning aggregate and removing air voids. For asphalt, this must be done while the mixture temp allows for reduced viscosity.
  
  Volvo Advantage: Volvo vibratory drums offer high dynamic force and frequency, so you reach densities faster.

2. The Role of Centrifugal Force in Achieving Proper Density

• Centrifugal Force is the force generated by the eccentric weight rotating inside the drum, calculated as (mass × radius of eccentricity) × frequency². Greater centrifugal force at the appropriate amplitude allows you to reach compaction density targets in fewer passes.
  
  Volvo Advantage: Maximized dynamic force at each amplitude setting means you can achieve efficient compaction results in fewer passes while minimizing excessive wear to the machine.

3. Optimizing Impact Spacing for Efficient Compaction

• Each vibration cycle creates an impact with the mat. Ideal impact spacing should be between 10 and 14 impacts per foot, depending on drum diameter, for optimum smoothness. Too few impacts can lead to poor compaction results, while too many impacts may cause damage to the mat or material displacement. Bigger drum diameters have more contact area and require fewer impacts per foot.
  
  Volvo Advantage: High frequency allows operators to travel faster while maintaining proper impact spacing. All Volvo large tandem rollers are equipped with an impact spacing meter to help operators maintain ideal impact spacing.

4. Setting the Right Amplitude for Optimal Compaction

• Amplitude is the total vertical distance the vibrating drum is displaced from the neutral position by the mass of the rotating eccentric (“nominal amplitude” is the industry term used to specify drum movement). Higher amplitude is required for thicker lifts or difficult-to-compact mixes, while lower amplitude is needed to compact thinner layers or mixes with softer aggregates.
  
  Volvo Advantage: Eight selectable amplitude settings offer precise adjustments based on lift thickness and material type.

5. The Importance of Adjusting Compaction Frequency

• Frequency is the number of complete cycles of the vibrating mechanism in a vibratory compactor per minute (VPM) or second (Hz). Higher frequencies allow faster rolling speeds without compromising compaction quality.
  
  Volvo Advantage: Our vibratory drums are designed for the highest frequencies possible based on amplitude setting, including our DD128C asphalt compactor with the industry’s highest frequency at 4,800 VPM.

6. How Dual Amplitude Impacts Compaction Performance

• Dual amplitude eccentrics change amplitudes by reversing eccentric rotation. In high amplitude, the lead drum’s eccentric rotates in the direction of travel, while the trailing drum rotates opposite. This design allows the machine to be used on thin and thick lifts and permits higher frequency in low amplitude. The trailing drum tends to create a bow wave of material ahead of it.
  
  Volvo Advantage: We offer dual-amplitude drums with dual frequency, 8-amplitude drums with a fixed frequency and 8-amplitude drums with multiple frequencies. Most OEMs offer only dual-amplitude drums.

7. How Oscillation Works In Compactor Drums

• Oscillation drums create a compaction motion using two eccentrics connected by belts or chains to a shaft in the center of the drum. The eccentric is rotated in the same direction, but 180° out of phase. The two eccentrics cancel the vertical element of vibration and create a rocking motion that applies a force for compaction without impact. This energy is effective in sensitive applications.
  
  Volvo Advantage: The drums offered on our Ultra-Pac compactors have been specially designed to meet or exceed the results produced by oscillation drums without the complexity or maintenance and wear concerns.

8. Why Auto-Reversing Eccentrics Create Smoother Compacted Surfaces

• An eccentric that rotates in the direction of travel. Each time the machine changes direction, the eccentrics reverse to match. Auto-reversing eccentrics reduce the bow wave in front of the drums (shown in the illustration below), minimize material displacement and ensure consistent compaction results. This feature delivers industry-leading smoothness.
  
  Volvo Advantage: Volvo 8-amplitude drums use movable weights connected to the eccentric weight to change amplitude, so eccentric rotation can automatically reverse to match the direction of travel for smoother results.

9. Why Drum Diameter Matters with Asphalt and Soil Compaction

• Larger drum diameters have proven advantages on quality and performance. They have less tendency to displace material and cause ripples in the mat. Larger diameter drums have a greater area of contact than drums with smaller diameters. This improves compaction performance and reduces drum edge markings and material displacement.
  
  Volvo Advantage: We lead the industry with large drum diameters on tandem rollers. Some manufacturers’ rollers come with small-diameter drums for a lower production cost, but they typically sacrifice performance and quality.

10. The Value of Intelligent Compaction (IC) Systems

• An improved compaction process using rollers equipped with GPS antennas, sensors for vibration and temperature (for asphalt) to provide data to guide the operator and generate reports. Intelligent Compaction provides operators with guidance on pass coverage, compaction measurements and mat temperature (for asphalt) so they can make corrections in real time.
  
  Volvo Advantage: Compact Assist on Volvo rollers includes our touchscreen Co-Pilot display and exclusive real-time density estimates when equipped with Density Direct™ (for asphalt compactors).

Mastering these fundamentals goes beyond operating a machine — it's about understanding how vibration, force and material behavior work together to create a solid, lasting foundation. When you apply these principles with precision, the results aren’t just smoother surfaces, but longer-lasting roads and structures that withstand the test of time. Investing in both knowledge and the right compaction equipment ensures your crew can consistently meet density targets with efficiency and confidence.

We’ve written several other blog posts that include both asphalt and soil compaction tips and tricks. Be sure to check them out!

Justin Zupanc
Product Manager – Compaction

Justin started with Ingersoll-Rand in 2003 and has continued his career with Volvo Construction Equipment as an electrical engineer working in various roles from design and systems engineering to cab engineering manager and more.