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1. Introduction to Asphalt Millings
Asphalt milling refers to the recycled material produced when deteriorated asphalt pavement is removed and reclaimed through a process called milling. The milling process uses a machine to grind off the top layer of asphalt down to a desired depth. The removed material, or reclaimed asphalt pavement (RAP), can then be reused in various construction applications. Asphalt millings provide an economical and sustainable pavement material option.
| Fact | Details |
|---|---|
| Other Names | Reclaimed asphalt pavement (RAP), milled asphalt |
| Production Method | Milling with specialized equipment |
| Typical Size | 1/2 to 2 inches |
| Composition | Milled old asphalt |
| Appearance | Black aggregates with some fine material |
| Primary Uses | Base course, driveways, shoulders, trails |
2. Benefits of Using Asphalt Millings
Asphalt millings offer many advantages that make them a prime recycled material choice:
Economical
Provides substantial cost savings over virgin aggregate
Reuses waste
Recycles existing asphalt that would otherwise go to landfills
Versatility
Can be used in many applications with proper preparation
Performance
Compacts into a strong, stable finished surface
Low Dust
Binds together better than gravel, minimizing dust
Availability
Produced in large quantities by numerous milling projects
Sustainability
Conserves natural resources and landfill space
Driveway Sealer Calculator Determining Required Materials for Asphalt Driveway Sealcoating Projects
3. Potential Uses of Asphalt Millings
Due to their versatile properties, asphalt millings can serve a range of construction functions:
| Use | Details |
|---|---|
| Driveways/Parking Lots | Durable, low dust surface; needs grading |
| Road Base | Stabilized millings make an excellent flexible base course |
| Shoulders | Can build up and reinforce soft shoulders |
| Trails/Paths | Smooth, solid surface for walking, biking, horses |
| Landscaping | Decorative mulch around trees and beds |
| Temporary Roads | Quick access over unpaved areas |
Gradation of Miller Asphalt
The particle size distribution, or gradation, of milled asphalt, can vary substantially depending on the properties of the original pavement. Here are typical size fractions:
| Sieve Size | % Passing |
|---|---|
| 1 inch | 95-100% |
| 3/4 inch | 70-95% |
| 3/8 inch | 60-85% |
| #4 | 45-70% |
| #100 | 5-25% |
Controlling the gradation by screening helps create better-performing finished surfaces. Removing excess fines prevents dust and instability.
5. Compaction Recommendations
Proper compaction of milled asphalt is crucial for strength and durability:
- Target density of 95% Proctor density for stability
- Use a pneumatic tire roller for breakdown
- Finish with a vibratory steel drum roller
- Add moisture if needed to reach an optimum level
- Compact in 6-inch lifts until the desired depth is reached
Higher densities greatly improve the performance of traffic surfaces constructed with asphalt millings.
6. Uses Over Gravel
Compacted asphalt millings provide far superior surfacing compared to gravel roads and drives:
| Factor | Millings | Gravel |
|---|---|---|
| Strength | Higher | Lower |
| Dust Control | Excellent | Poor |
| All-Weather | Excellent | Poor |
| Smoothness | Good | Fair |
| Cost | Low | Medium |
Asphalt millings can readily be placed directly over an existing gravel surface. This caps the gravel and binds it together into a stronger stabilized layer.
Asphalt Batch Size Calculator for Efficient Production Planning
7. Best Practices for Use Over Gravel
To successfully use asphalt millings over gravel:
- Ensure gravel substrate is compacted and stable
- Grade and crown gravel for proper drainage
- Spread a 3-4 inch uniform layer of millings
- Compact with roller to lock millings together
- Add 1-2 inch fresh layer and recompact
- Fill potholes with additional millings as needed
- Re-grade periodically to maintain shape
Proper preparation and installation procedures create a durable, long-lasting surfacing.
8. Environmental Benefits
Utilizing recycled asphalt millings provides noteworthy environmental advantages:
- Conserves virgin aggregates like crushed stone
- Provides an outlet for reclaimed asphalt rather than landfilling
- Reduces trucking needs and associated emissions
- Recycling extends the service life of raw materials
- Reuses existing pavement rather than new mixes
- Lower energy inputs than the creation of new hot mix asphalt
9. Common Concerns and Considerations
Some common concerns when using asphalt milling include:
| Issue | Mitigation |
|---|---|
| Stockpile Segregation | Use best practices to minimize segregation |
| Excess Fines | Screen and remove fines as needed |
| Contaminants | Ensure millings are free of debris before use |
| Lack of Binders | Add emulsion or foamed asphalt to increase cohesion |
| Dust Control | Use water, compaction, and surface sealing |
Typical Asphalt Milling Equipment
| Equipment | Description |
|---|---|
| Cold Planer | Large milling machine rotates grinding drum to remove asphalt |
| Skid Steer | Smaller mill attachment for skid steers in tight areas |
| Front End Loader | Scoops and loads milled material into trucks |
| Dump Truck | Hauls millings from project site to storage or reuse site |
| Pneumatic Roller | Compacts millings with rubber tires for breakdown |
| Steel Drum Roller | Provides final compaction of millings with vibratory drum |
12. Milling Production Rates
| Milling Depth | Production Rate |
|---|---|
| 1 inch | 600-800 square yards per hour |
| 2 inches | 400-600 square yards per hour |
| 3 inches | 300-500 square yards per hour |
| 4 inches | 250-400 square yards per hour |
| 5 inches | 200-350 square yards per hour |
Rates depend on machine size, material properties, and site conditions.
13. Asphalt Milling Emission Reduction
Asphalt milling produces substantially lower emissions compared to alternative removal methods:
| Method | Relative Emissions |
|---|---|
| Cold Milling | Low Emissions |
| Hot In-Place Recycling | Moderate Emissions |
| Full-Depth Removal | High Emissions |
Milling produces little heat or fumes since it operates at ambient temperatures.
14. Uses as Stabilized Base Layer
Mixed with emulsified or foamed asphalt, RAP makes an excellent stabilized base:
| Feature | Benefit |
|---|---|
| Strength | Provides structural support for pavement |
| Flexibility | Resists cracking better than cement |
| Water Resistance | Maintains strength when wet |
| Affordability | More economical than virgin aggregate |
Stabilized RAP provides excellent pavement base properties.
15. Seasonal Considerations
| Season | Effects |
|---|---|
| Summer | Higher temperatures aid compaction. Dust control is needed. |
| Winter | May not compact well when frozen. Can be used below freezing if protected. |
| Wet Periods | Water spray aids compaction. Drainage is important. |
| Dry Spells | Water application prevents segregation during handling and laydown. |
10. Sourcing Asphalt Millings
There are several options for sourcing asphalt millings at reasonable cost:
- Check for local ads or listings for free/cheap milling
- Contact paving companies directly about excess RAP
- Connect with municipalities and transportation departments
- Time requests for early summer when most milling occurs
- Be willing to transport millings or pay nominal hauling fees
- Request clean, screened material for the best quality
With some research and outreach, quality recycled asphalt millings can be acquired to suit almost any project need. Their versatility and advantages make them a prime “green” pavement material.
