[en] The report documents an evaluation of the state-of-the-art capabilities of nuclear density gauges to monitor the density of asphalt concrete. In particular, providing immediate information on compaction by the use of roller-mounted gauges and measuring the densities of thin layers were addressed. The study included three phases: literature search, laboratory tests, and field trials. The first phase included a review of current literature on the theory and operating characteristics of commercially available equipment and a review of State highway agency procedures and specifications for monitoring asphalt concrete density. The second phase included a series of laboratory tests to verify factory calibrations and to determine the depth sensitivity, chemical composition errors, and thin-lift capabilities of the various gauges under laboratory conditions. The third phase consisted of five sets of field trials. The data show that, within limitations, static nuclear gauges can be used for acceptance testing of thin-lifts, but only when all parameters affecting the measurements are precisely known. The dynamic gauges can be effectively used to monitor relative density growth