ASTM D4748-98

1.1 This test method covers the nondestructive determination of thickness of bound pavement layers using short-pulse radar.

1.2 The accuracy and applicability of this test method is a function of these components: radar-system penetration, radar-system resolution, and the dielectric constant.

1.2.1 As the electromagnetic wave generated by radar propagates through the bound pavement layers, the wave is attenuated and contaminated. At some depth, this attenuation and contamination becomes so severe that accurate layer-thickness determination cannot be made by the radar. This maximum penetration depth is a complex function of radar system parameters such as transmitted power, receiver sensitivity, and signal processing, as well as the electromagnetic properties of the pavement materials and environmental factors such as moisture content. A typical system for this application should have a minimum penetration depth of 20 in. (508 mm).

1.2.2 Radar system resolution is determined mainly by the transmitted pulse width of the radar. A typical system for this application usually has a resolution sufficient to determine layer thicknesses of 1 in. or greater, to an accuracy of +0.2 in. Radar-derived layer-thickness information without prior knowledge, or core verification, of dielectric constants, is an estimation.

1.3 This test method may not be suitable for application to extremely moist or wet (saturated) pavements due to the increased attenuation of the electromagnetic signal caused by such moisture.

1.4 The values stated in inch-pound units are to be regarded as the standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific hazard statements are given in Section 6.