Improper mix designs and amounts of asphalt cement are major causes of premature failure in pavement structures. There are three major methods for determining asphalt content: solvent extraction, nuclear asphalt content gauge, and metering methods. This article discusses one specific indirect test, the nuclear test, in an effort to provide accurate information on its abilities and its limitations and to encourage its use. It describes the equipment and its operation, in addition to licensing, safety, and economic factors that support its use. It also addresses the gauge's more favorable environmental operation over traditional methods. There are three gauges currently on the market, consisting of a control unit, sample chamber, and specimen pan. Neutrons are transmitted into the asphalt mix, and their movement through the material is influenced by the hydrogen composing or surrounding the aggregate. During the calibration process, the nuclear gauge "counts" the neutrons influenced by the hydrogen as they pass through the sample, establishing the hydrogen versus neutron count relationship. Correlating these counts to asphalt content using mathematical regression techniques permits the evaluation of asphalt content for any sample having the same mix design. Environmental concerns are making chemical methods increasingly costly and imposing additional regulations on solvents. The nuclear gauge method is accurate, cost-effective, environmentally clean, and quick to perform.


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  • Accession Number: 00781712
  • Record Type: Publication
  • Files: TRIS, USDOT
  • Created Date: Jan 16 2000 12:00AM