Compaction
Compaction is the process by which the volume of air in an HMA mixture is reduced by using external forces to reorient the constituent aggregate particles into a more closely spaced arrangement. This reduction of air volume produces a corresponding increase in HMA density (Roberts et al., 1996).
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Intelligent Compaction
Intelligent compaction is a roller-mounted system of sensors, GPS and software that measures, maps and records compaction in real time.
Introduction to Compaction
Compaction Importance
The volume of air in an HMA pavement is important because it has a profound effect on long-term pavement performance. The exact nature of that effect is nuanced, and likely not linear.
Factors Affecting Compaction
HMA compaction is influenced by a myriad of factors; some related to the environment, some determined by mix and structural design and some under contractor and agency control during construction (Table…
HMA Compaction
It has been said that the top three factors in real estate are “location, location, location”. It can also be said that the top three factors in HMA pavement construction are “compaction, compaction, compaction”.
Compaction Equipment
There are three basic pieces of equipment available for HMA compaction: (1) the paver screed, (2) the steel wheel roller and (3) the pneumatic tire roller. Each piece of equipment compacts the HMA by two principal means:
Tender Mixes
A tender mix is an internally unstable mix that tends to displace laterally and shove rather than compact under roller loads. Internal mix stability is a function of asphalt binder viscosity and aggregate gradation and shape.
Temperature Differentials
Construction-related HMA temperature differentials are large mat temperature differences resulting from placement of a significantly cooler portion of HMA mass into the mat.
Cold Weather Paving
Compaction is of special concern during cold weather paving because as ambient temperatures decrease, HMA cool-down rates increase and the time available for compaction (before cessation temperature is reached) is reduced.
Permeability vs. Aggregate Size and Lift Thickness
It is generally believed that HMA densities between 3 and 8 percent air voids will result in a pavement that would not be susceptible to water damage, oxidation, raveling, and cracking.
Compaction Measurement and Reporting
Compaction reduces the volume of air in HMA. Therefore, the characteristic of concern is the volume of air within the compacted pavement.
Nuclear Density Gauge
A nuclear density gauge measures in-place HMA density using gamma radiation. Gauges usually contain a small gamma source (about 10 mCi) such as Cesium-137 on the end of a retractable rod.
Electrical Density Gauges
An electrical density gauge, like TransTech’s Pavement Quality Indicator (PQI™), measures pavement density indirectly by measuring its dielectric constant.