Paving fabric interlayer systems have been used in more than 230,000 lane-kilometers (142,000 lane-miles) of pavement in the U.S. Paving fabrics are a special class of geosynthetics which provide the generally acknowledged functions of a stress absorbing interlayer and a waterproofing membrane.1 The stress related performance has been easily verified by the observed reductions of cracking in pavement overlays. The waterproofing benefit is not easily verified; yet improved overlay performance can also be attributed to a lower moisture content in a pavement base and subgrade.

This Engineering Bulletin presents a compilation of studies that collectively verify and quantify the waterproofing effectiveness of the paving fabric interlayer system. The waterproofing effectiveness of an asphalt cement saturated fabric layer has been investigated both in the laboratory and in pavements in the field. Results of the moisture barrier system testing from various laboratories are presented. Next, this document reports on field evaluations of the moisture barrier in pavements. These evaluations utilized some interesting measures including large scale pavement permeability testing and ground penetrating radar.