For driveways, parking lots, patch work, and other small tonnage jobs

By SAKAI America

Compaction is a critical aspect of asphalt paving that directly impacts the long-term performance and durability of the finished surface. While many contractors understand the basics of compaction, optimizing this process requires a deep understanding of the factors involved and the potential consequences of mistakes.

Before You Begin: Selecting the Right Asphalt Compaction Equipment
Choosing the appropriate asphalt roller for a small-tonnage project like a residential driveway, small parking lot or patchwork is essential for achieving optimal compaction results. Consider the following factors:

• Project size and scope: For small-tonnage jobs, a lightweight, maneuverable roller is typically sufficient.
• Asphalt mix type: The type of asphalt mix will influence the required compaction effort. Dense-graded mixes may require more aggressive compaction than open-graded mixes.
• Equipment type: Consider the advantages and disadvantages of different equipment types, such as:
  – Double-drum vibratory rollers: Vibratory action punches at a higher weight class than the equivalent ton static roller.
  – Combination rollers: Combine the benefits of a front vibratory drum and static rear tires. Tires knead the mix, reducing voids and boosting density. They’re trickier to learn on  but reduce the need for multiple rollers for many applications.
  – Pneumatic tire rollers: for finish rolling and chip seals.
  – Walk-behind rollers (fixed or steerable): easy to load/unload for quick patch jobs, maneuverable.
  – Plate compactors: for around manholes, curbs and joints.
  – Hand tools: for narrow and tight spaces.

Drum size and weight: The drum size and weight of the roller are crucial factors in achieving proper compaction. For residential driveways and small parking lots, a vibratory roller with a drum width of 36-51 inches and a weight of 1.5-5 tons is typically sufficient. For larger parking lots a double-drum roller with a drum width of 54-58 inches and a weight of 4-8 tons may be necessary.

General roller weight guidelines for common lift thicknesses:

• Residential driveways: 1.5-3 tons for 1-2” lifts, 3-5 tons for 2-3” lifts
• Small-to-medium parking lots: 3-5 tons for 2-3” lifts, 8 tons for 4” lifts
• Patchwork: 1.5-3 tons for 1-2” lifts

Note that these are general recommendations, and the optimal drum size and weight may vary depending on the specific project requirements, such as asphalt mix density and compaction conditions.

Like Everything in Life, a Proper Foundation Underlies Success:
Before compaction of the asphalt mat itself comes into play, the sub-base/base must be dry and properly compacted with no visible water or movement under repeated pressure of equipment. An asphalt mat is only as good as what lies beneath it. Base material is the support structure for the asphalt surface, distributing loads and providing stability. Poorly, nonuniformly compacted base material can permit rutting, crack propagation, uneven wear, potholes, frost heave from water intrusion, and at worst, base failure resulting in the need for complete tear out. Mix moisture is under the plant’s control but contractors should control moisture in the base before laying the mat, as well as ensuring that the mix isn’t subjected to rain before application. Ensure that the base design accounts for the anticipated loads. For example: no amount of compaction will prevent pavement failure under a heavy truck for which the base is not prepared.

Beyond the Basics: Temperature Considerations
Beyond the standard practices of selecting the right roller and following recommended pass patterns, experienced contractors should consider not only the temperature of the mix before beginning but during compaction. Monitoring asphalt temperature is crucial for achieving optimal compaction. Rolling at too low or too high temperatures can affect compaction quality and the long-term performance of the pavement. Rolling should cease in the “tender zone” and finish before the mix cools. Rolling in the “tender zone” can cause shoving of the mat and checking. Rolling at too cool a temperature will be ineffective and damage the mat. Temperature ranges will vary with your local plant mix. A general guideline for the tender zone of hot mix asphalt (HMA) would be 250F-140F. Don’t rely solely on a temp gun; use a probe to check the internal temperature of the mat.

Assessing Density Success
While formal density testing may not be common for smaller paving projects, experienced contractors can use observations and practical techniques to assess compaction quality:

• Visual inspection: Look for signs of aggregate segregation, unevenness (smoothness), depressions around stop-and-start areas, roller edge marks, shoving, checking and cracking. Are joints smoothly compacted and minimally detectable?
• Operator feel: After the fifth to seventh pass, an operator may detect the vibrating drum changing from bounces to random vibrations as compaction progresses. However, the easiest way to achieve uniform compaction from the operator perspective is to accurately count the number of passes (equally covering the entire job).
• Tools: Where a density target is required, electromagnetic density or non-nuclear gauges (i.e. Transtech) are simpler, less expensive and require no licensing compared to nuke gauges. Intelligent Compaction is usually reserved for larger projects and larger rollers due to the investment expense. Core samples and nuke gauges are more commonly used on larger projects.

Common Symptoms of Compaction Issues & How to Prevent Them
The following are symptoms of improper compaction. To deliver a long-lasting finished product, contractors should become familiar with these and take preventative measures for the next job:

• Washboarding:
  – Cause: over-speeding a vibratory roller (space between impacts)
  – Prevention: slowing roller, turning up vibratory frequency or a mix of both
  • Rutting, depressions and potholes:
  – Causes: improper base compaction, incomplete mat compaction, lift too thin
  – Prevention: ensure an even, compacted base for proper support of the mat. Ensure proper compaction of the mat by utilizing temperature-based rolling with a sufficiently weighted roller for the lift thickness.
• Alligator cracks:
  – Causes: improper or non-uniform base compaction, insufficient lift thickness
  – Prevention: ensure thorough and uniform compaction of the entire base, select a mat thickness appropriate for the intended load
• Raveling:
  – Cause: aggregate not bonded well with the binder
  – Prevention: compaction should begin at hot temperatures (290F+ but depends on the mix type) to ensure proper binding
• Crushed surface aggregate (white capping):
  – Cause: vibratory force too high
  – Prevention: reduce the roller’s amplitude setting

Additional Considerations

• Equipment maintenance: Regular maintenance of compaction equipment is essential for ensuring optimal performance and longevity. Follow the manufacturer’s recommended maintenance schedule and address any issues promptly.
• Operator training: Ensure that operators are properly trained on the use of compaction, implementing best practices and addressing common challenges, experienced contractors can deliver high quality work that meets or exceeds client expectations. Delivering projects with proper compaction will ensure long term performance of the mat, which is crucial to the reputation of an asphalt paving contractor.

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