Compaction density is a core indicator of roller construction quality, and different materials (earthwork, asphalt, base layers) require specific testing methods. Below are 6 common field testing techniques and their applications:

1. Destructive Testing Methods

Sand Cone Test

• Standard:

• Expressway subgrade ≥95%, Class-I roads ≥93%.

• Materials: Earthwork subgrade, gravel base layers.

• Procedure:

1. Excavate a 15cm-diameter pit (depth = compacted layer thickness).

2. Fill the pit with standardized sand to calculate volume.

3. Weigh the excavated material (wet), then oven-dry to determine dry density.

Ring Knife Test

• Materials: Clayey subgrade.

• Procedure:

1. Press a ring knife (typically 200 cm³) into the soil layer.

2. Extract and weigh the soil sample, then oven-dry to calculate dry density.

• Pros: Simple, low-cost.

• Limitations: Not suitable for gravelly soils.

2. Non-Destructive Testing

Nuclear Density Gauge

• Standards:

• Asphalt surface ≥96% (*JTG F40-2004*), cement-stabilized base ≥98%.

• Materials: Asphalt layers, stabilized bases.

• Principle: Measures density and moisture via γ-ray absorption.

• Procedure:

1. Place the gauge flat on the test point.

2. Emit rays and record data (density/moisture) in 30 seconds.

• Pros: Fast (1 min/point), allows continuous testing.

• Note: Requires calibration and radiation safety protocols.

Non-Nuclear Density Gauge (PQI)

• Materials: Asphalt pavements.

• Principle: Uses electromagnetic waves to estimate density via dielectric constant.

• Advantage: No radiation; ideal for urban roads.

3. Dynamic Testing

Portable Falling Weight Deflectometer (PFWD)

• Application: Rapid subgrade/base layer验收.

• Procedure:

1. Generate impact load with a falling weight.

2. Record deflection (μm) via sensors.

• Standard: Dynamic modulus ≥40 MPa (design value).

Continuous Compaction Control (CCC)

• Principle: Real-time compaction monitoring using roller-mounted sensors (CMV values).

• Use: Large-scale digital subgrade construction.

4. Asphalt-Specific Tests

Core Drilling

• Standards:

• Surface layer ≥96%, intermediate/binder layers ≥95%.

• Procedure:

1. Extract a 100mm-diameter core.

2. Lab-test bulk density.

3. Calculate compaction (core density / Marshall density).

• Note: Fill drill holes with hot asphalt.

Infrared Thermography

• Purpose: Identifies uneven compaction (temperature variations >20°C require re-rolling).

5. Testing Frequency Requirements

6. Troubleshooting

• Low compaction:

• Earthwork: Increase passes or adjust moisture.

• Asphalt: Raise initial temperature or reduce speed.

• Data anomalies:

• If nuclear gauge deviation >3%, verify with sand cone.

7. Summary

• Earthwork: Sand cone/ring knife + PFWD Assistance.

• Asphalt: Nuclear gauge screening + core drilling verification.

• Smart construction: CCC for real-time monitoring.
  Follow the principle: "Process control + final validation" to ensure reliability!