What is Asphalt Compaction?
Asphalt compaction is the process of compressing freshly laid asphalt to reduce air voids and achieve the desired density. During compaction, the asphalt thickness decreases from the initially poured thickness to a final compacted thickness.
Formula
The asphalt compaction calculation uses this formula:
$$\text{Compacted Thickness} = \text{Poured Thickness} - (\text{Poured Thickness} \times \text{Compaction Factor})$$
This can be simplified to:
$$\text{Compacted Thickness} = \text{Poured Thickness} \times (1 - \text{Compaction Factor})$$
Where:
- Poured Thickness is the initial thickness of the asphalt when laid (in inches)
- Compaction Factor is the proportion of thickness lost during compaction (typically 0.20-0.30)
- Compacted Thickness is the final thickness after compaction (in inches)
Example Calculation
Let's calculate the compacted thickness for a typical asphalt layer:
Given:
- Poured Thickness: 12 inches
- Compaction Factor: 0.25 (25% compaction)
Calculation:
$$\text{Compacted Thickness} = 12 - (12 \times 0.25)$$
$$= 12 - 3$$
$$= 9 \text{ inches}$$
Result: The compacted asphalt thickness will be 9 inches.
Common Compaction Factors
Different asphalt mixes and conditions result in varying compaction factors:
- Dense-graded mixes: 0.20-0.25 (20-25% compaction)
- Open-graded mixes: 0.15-0.20 (15-20% compaction)
- Stone matrix asphalt: 0.10-0.15 (10-15% compaction)
- Porous asphalt: 0.05-0.10 (5-10% compaction)
Why This Matters
Understanding asphalt compaction is critical for:
- Accurate Material Estimation - Ensures you order the right amount of asphalt
- Achieving Design Thickness - Helps meet structural requirements
- Cost Control - Prevents over-ordering or under-ordering materials
- Quality Assurance - Ensures proper pavement performance
- Project Planning - Allows accurate scheduling and logistics
Best Practices
- Always account for compaction when calculating asphalt quantities
- Use manufacturer-recommended compaction factors for specific mixes
- Conduct test sections to verify actual compaction rates
- Consider temperature and weather conditions that affect compaction
- Ensure proper roller weight and number of passes for adequate compaction