Electrical Density Gauges

Pavement Quality Indicator (PQI)

PQI™ from TransTech.
Figure 1. PQI™ from TransTech.


An electrical density gauge, like TransTech’s Pavement Quality Indicator (PQI™), measures pavement density indirectly by measuring its dielectric constant. The PQI™ passes a small current through the pavement, which creates an electrical sensing field. Density is measured by the response of this electrical sensing field to changes in the pavement’s complex impedance (consisting of the pavement’s composite resistivity and dielectric constant). This response is then calibrated to pavement density (TransTech, 1997[1]).


Troxler’s PaveTracker™ is lightweight, small, and measures sub-surface pavement properties. The device uses a micro power-probing field to determine density and can be used in a number of different applications. It can be used to take instantaneous direct density readings or can be pulled along the mat allowing for density profile determination. Because of the ease of use, a moderately skilled operator can evaluate paving quality rather quick and not have to be specially trained and certified.

Advantages and Disadvantages

Using non-nuclear density devices are advantageous because:

  1. Readings can be obtained in seconds vice one to four minutes for a nuclear gauge.
  2. They contain no radioactive source and are therefore not subject to radiological controls. Since a nuclear density gauge contains one or more radioactive sources, it is subject to various federal and local controls such as operator certification, security requirements, and periodic leak detection and contamination surveys.

To date, most studies seem to indicate that electrical density gauges are not as consistently accurate as nuclear density gauges.

Footnotes    (↵ returns to text)
  1. TransTech Systems, Inc.  (1997).  Pavement Quality Indicator instruction manual.  TransTech Systems, Inc., Schenectady, NY.