For the past several decades, density of freshly laid hot mix asphalt (HMA) mats has been measured by contractors, consultants or governmental agencies using nuclear density gauges. However, use of these devices requires the user to maintain an inordinate amount of records on the use of the equipment. These requirements include calibration and recalibration records, certification records of the operators, records on radiation badges, and periodic testing of the operator’s badges for radiation exposure. In addition, there is always the concern about possible accidents with the gauges that might expose the radiation source to the operators or other bystanders. Because of these issues and concerns associated with using the nuclear gauges, the contractors in Kentucky were interested in the feasibility of using other methods of measuring density for process control.

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