U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590

Skip to content U.S. Department of Transportation/Federal Highway AdministrationU.S. Department of Transportation/Federal Highway Administration



Publication Details

An Input for Moisture Calculations - Dielectric Constant From Apparent Length Research/Reference: useful for researchers doing further work in the pavement area as well as those developing improved testing and design procedures. Includes documents of historical value.

Primary Topic: Materials-General

Description: Time domain reflectometer (TDR) probes are used in the Long Term Pavement Performance (LTPP) Seasonal Monitoring Program to obtain the moisture content in unbound base and subgrade materials. The TDR technique is based on the measurement of the travel time by an electromagnetic wave induced into a waveguide, in this application, a moisture probe. The apparent length is the length between the beginning and end points on the waveform that correspond to the beginning and end of the metal tube portion of the moisture probe. This apparent length of the probe can be used to calculate the dielectric constant of the material surrounding the probe. The dielectric constant is an input to the calculation of moisture content.

FHWA Publication Number: FHWA-RD-99-201

Publication Year: 1999

Document Links: PDF (file size: 0.2 mb)

View Pavement Publications

PDF files can be viewed with the Acrobat® Reader®
Updated: 10/21/2015
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000

All Federal Highway Administration (FHWA) information technology systems will be unavailable, Friday, October 28, at 10:00 p.m. to Sunday, October 30, at 11:59 p.m., EDT, while work is being performed on the network. During that time, users will not be able to access any FHWA systems.

If you have any questions or problems, please contact the 5-Help Service Center @ (866) 466-5221 or 5-HelpServiceCenter@dot.gov.