Technical Guide · 2024-06-10 · 7 min read
The quality of reclaimed asphalt pavement (RAP) is one of the most important factors determining the success of cold in-place recycling (CIR) projects. Poor-quality RAP can lead to mix design failures, poor compaction, and premature pavement deterioration. Thorough RAP quality assessment before project design is essential.
Why RAP Quality Matters
RAP quality affects CIR performance in several ways:
- Gradation: The gradation of the RAP affects the mix design and the properties of the recycled mixture
- Asphalt content: The existing asphalt content in the RAP contributes to the total binder content of the recycled mixture
- Binder properties: The properties of the aged binder in the RAP affect the performance of the recycled mixture
- Contamination: Contamination (soil, organic material) can reduce the strength and durability of the recycled mixture
RAP Sampling
Proper sampling is essential for representative RAP quality assessment:
- Core sampling: Take cores from the existing pavement at regular intervals (typically every 500m)
- Sample size: Minimum 5kg per sample for laboratory testing
- Depth: Sample the full depth of the asphalt layers to be recycled
- Documentation: Record the location, depth, and visual condition of each sample
Laboratory Testing
The following tests are typically performed on RAP samples:
Gradation Analysis (ASTM D5444) Determines the particle size distribution of the RAP after extraction. The gradation affects the mix design and the properties of the recycled mixture.
Asphalt Content (ASTM D2172 or ASTM D6307) Determines the percentage of asphalt binder in the RAP. This is used in the mix design to calculate the total binder content of the recycled mixture.
Recovered Binder Properties (ASTM D1754, D36, D5) Tests the properties of the recovered asphalt binder:
- Penetration: Indicates binder hardness/softness
- Softening point: Indicates high-temperature performance
- Ductility: Indicates low-temperature flexibility
Moisture Content (ASTM D2216) Determines the moisture content of the RAP, which affects the mix design water content.
Contamination Assessment Visual inspection and testing for:
- Soil contamination
- Organic material
- Concrete or other non-asphalt materials
RAP Quality Acceptance Criteria
| Parameter | Acceptable Range | Notes | |---|---|---| | Asphalt content | 3–8% | Higher content reduces required new emulsion | | Penetration (recovered binder) | 10–100 | Very hard binder may require rejuvenator | | Moisture content | < 3% | Higher moisture requires adjustment | | Contamination | < 5% | Higher contamination may require rejection |
Mix Design Implications
RAP quality test results are used in the CIR mix design:
Emulsified Asphalt Content The required emulsified asphalt content depends on the existing asphalt content in the RAP:
- Higher existing asphalt content → lower required new emulsion
- Typical range: 2–4% by weight of RAP
Rejuvenator If the recovered binder is very hard (penetration < 20), a rejuvenating agent may be added to restore binder flexibility and improve low-temperature performance.
Cement or Lime If the RAP has poor cohesion or high moisture sensitivity, cement or lime may be added to improve early strength and moisture resistance.
Documentation
All RAP quality test results should be documented and used in the mix design report. The mix design report should include:
- RAP sampling locations and depths
- Test results for each sample
- Average and range of each parameter
- Mix design calculations
- Recommended mix proportions
Thorough RAP quality assessment and documentation is essential for designing a CIR mix that will perform well throughout its service life.
Discuss Your Project
Contact Bridgent for equipment specifications and a project-specific quotation.
Topics
- RAP quality
- reclaimed asphalt pavement
- CIR quality control
- pavement recycling