Use of Nuclear Gauge for Construction Quality Control of Unbound Base Course Containing Reclaimed Asphalt Pavement

About the report:

A recent study determined that the Virginia Department of Transportation (VDOT) can use up to 30% reclaimed asphalt pavement (RAP) in a pavement base aggregate layer without adverse effects on pavement performance. However, an effective quality-control protocol to monitor construction is needed to implement the use of RAP in the base course. The study recommended using a lightweight deflectometer device to perform quality-control and quality-assurance monitoring of RAP-aggregate base construction. VDOT does not currently use a lightweight deflectometer device for any of the unbound layer construction, rather a nuclear density gauge is commonly used for compaction control. Major modification of existing VDOT practices and significant resource allocations would be required to implement the use of lightweight deflectometer devices for compaction control. As an alternative, this study evaluated the use of a nuclear gauge to monitor the construction quality of a base course containing RAP. Although several state departments of transportation currently use nuclear density gauges for such construction monitoring, accurate moisture measurement using a nuclear device is challenging because of the presence of hydrogen atoms in RAP that comes from both asphalt and compaction water.

The study’s research team conducted a laboratory trial using wooden boxes filled with RAP aggregate blends at different proportions and a field test section. The team measured densities using a nuclear density gauge and verified them by the sand cone method. Nuclear moisture content measurements were compared with the oven-dry test method and a Speedy® moisture tester. The team determined that the nuclear gauge measured the wet densities accurately irrespective of RAP content in the base aggregate. On the other hand, the presence of RAP affected moisture measurements, which is directly proportional to the increasing content of RAP. The team concluded that a nuclear gauge can be used to monitor RAP aggregate compaction but an offset value (or correction) for moisture measurement needs to be incorporated. Although the presence of asphalt did not affect the Speedy moisture tester’s moisture measurements, a relatively small sample size affected the measurement accuracy, especially at higher RAP contents because more hydrophobic particles contributed to nonuniform moisture distribution.

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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