Current US state DOT compaction specifications
Current state DOT compaction specifications often follow one or more of the following approaches:
- Ordinary Compaction: A specified roller makes a specified number of passes, or makes continuous passes until no further compaction can be observed.
- Stiffness Control: Each lift is compacted to reach a target stiffness value, which is often measured with a Dynamic Cone Penetrometer (DCP), Light Weight Deflectometer (LWD), or GeoGauge (Soil Stiffness Gauge). In Europe, a Plate Load Test (PLT) is sometimes used.
- Density Control: Each lift is compacted until a target density value is met through direct or indirect measurements; often accompanied by an acceptable range in moisture content. Field QC/QA options usually include a direct measurement of density/moisture content or an indirect measurement using a nuclear density gage. This is the most common specification currently in use.
Current specifications also commonly dictate size and weight characteristics, allowable roller patterns, and allowable lift thicknesses in either a loose or compacted state.
Soils IC Specifications
The first intelligent compaction specifications were established in Europe in the early 1990s, and the US first adopted IC specifications in the mid-2000s.
Current IC specifications for these material types generally follow one of the following two approaches:
- Field calibration of IC roller measurements to either stiffness or moisture/density test data using test beds.
- Identification of weak areas for assessment with conventional QC/QA methods (e.g. moisture/density or stiffness).
The following is a timeline of specification development for IC of soils. They are also applicable to aggregate subbase.
United States National Guidelines
- FHWA Generic Soils IC Specification
- AASHTO PP81-14 IC specification (for both soils and asphalt)