Among the heavy machinery that the construction industry is heavily dependent on for almost any kind of project involving earthworks are roller compactors. However, there are various kinds of rollers that are readily available for hire within the construction equipment rental market, and it due to this reason that it becomes important to choose the right type of roller compactor for the right kind of compaction job.
Some of the more important factors that contractors or project managers should take into consideration prior to taking a compactor for hire include budget limitations, size of compaction area, project site layout (open space/ restricted space) and even the route to the project site. These considerations will ultimately decide not just what type of roller is needed, but also the size of the roller and the required duration that the roller will be needed on a rental basis.
Soil compaction is without doubt one of the more important aspect of stability of roads or structures being built. It is a norm for surfaces or foundations to be compacted before any sort of construction can begin. For soil compaction involving new stretches of roads being laid or structures being built, smooth drum rollers are suitable.
Generally, smooth drum rollers are fitted with large, smoothened heavy steel drums that apply weight over large surface areas to compact soil as the rollers ‘rollover’ these surface. Some smooth drum rollers have vibratory capability and these rollers vibrate as they move over surfaces which enable the machine to achieve a higher level of compaction due to combination of impact and vibration.
Vibratory smooth drum rollers are perfect for compacting material/ soil that are sandy or silty with lesser passes compared to other types of rollers. In essence, adequate compaction of silty or sandy surfaces could be achieved much more quickly using these rollers which keep project budgets in check and on schedule.
Overview of Vibratory Rollers for Asphalt
Vibratory rollers are generally associated to smooth drum rollers with the only difference being the vibrating component that is fitted to these machines. The vibratory roller compactor is among the most frequent type of roller compactor that is taken for hire by project owners. The reason for this that as the roller passes over a target surface the compaction and flattening coupled with the vibration enhances the compaction.
To achieve optimal compaction of asphalt double drum vibratory rollers are generally assigned to move close behind a paver whilst the asphalt mix is still hot. In essence the vibratory roller should move over the asphalt whilst the surface temperature of the mix remains above 240º F with the vibratory roller should be set at the highest possible frequency level and an amplitude setting that matches the thickness of the asphalt concrete.
The latest models of roller compactors available for hire also feature oscillation technology that was developed specifically to enhance compaction of asphalt even further. Oscillation technology in essence provides more compaction force compared to static rolling which reduces the number of passes required to achieve optimal compaction.
Achieving maximum soil density is critical for construction projects (roads, foundations, embankments). Roller compactors are key—here’s how to optimize their use:
1. Key Factors for Optimal Compaction
- Soil Type
- Granular (sand/gravel): Vibratory rollers work best (frequency: 25–40 Hz).
- Cohesive (clay/silt): Sheepsfoot/padfoot rollers (high kneading pressure).
- Mixed soils: Combination rollers (vibration + static weight).
- Moisture Content
- Target ±2% of Optimum Moisture Content (OMC) (per Proctor test).
- Too dry: Poor particle bonding. Too wet: Liquefaction risk.
- Lift Thickness
- Granular soils: 8–12 inches per layer.
- Cohesive soils: 4–6 inches per layer.
2. Roller Selection Guide
| Roller Type | Best For | PSI Range | Passes Needed |
|---|---|---|---|
| Vibratory Smooth Drum | Sand, gravel | 50–100 psi | 4–6 |
| Sheepsfoot | Clay, silt | 200–400 psi | 6–8 |
| Pneumatic | Asphalt, mixed soils | 60–80 psi | 8–12 |
| Grid Roller | Rocky soils | 150–250 psi | 5–7 |
3. Compaction Process Optimization
- Pre-Test
- Conduct Proctor (ASTM D698/D1557) for OMC and max dry density.
- Use nuclear density gauge or sand cone test for field verification.
- Roller Settings
- Frequency: 25–40 Hz (granular) / 20–30 Hz (cohesive).
- Amplitude: 0.5–2.0 mm (high for deep layers, low for finish).
- Speed: 3–6 km/h (slower = better compaction).
- Pass Strategy
- First passes: Static mode to seat the layer.
- Middle passes: Vibratory mode at high amplitude.
- Final passes: Static mode for smooth finish.
4. Real-Time Monitoring Tech
- Intelligent Compaction (IC)
- Sensors (e.g., Bomag’s Variocontrol, Caterpillar’s Compaction Control) track:
- Stiffness (MPa) via accelerometers.
- Pass count mapping (GPS).
- Alerts for under/over-compaction zones.
- Sensors (e.g., Bomag’s Variocontrol, Caterpillar’s Compaction Control) track:
- Drones + AI
- Multispectral imaging detects moisture variations.
5. Common Mistakes & Fixes
- Problem: Low density in cohesive soils.
- Solution: Increase kneading action (sheepsfoot), reduce lift thickness.
- Problem: Segregation in granular soils.
- Solution: Use vibratory rollers with smaller amplitude.
- Problem: Over-compaction (crushing aggregates).
- Solution: Limit passes to 8–10 (verified with IC).
6. Industry Standards
- ASTM D1557: Modified Proctor test.
- AASHTO T 99: Standard Proctor.
- FHWA HIF-16-002: Intelligent Compaction guidelines.
Pro Tip: For critical projects (e.g., runway construction), use continuous compaction control (CCC) systems for real-time feedback.