Guidelines on the Use of Underseals As a Pavement Moisture Barrier (0-4391-1)

The placement of an asphalt seal coat under an asphalt concrete has been used to provide an impervious membrane to stop the intrusion of surface or subsurface moisture. It is also specified to enhance the bond of subsequent applications asphalt concrete pavement. However, underseals have contributed to premature cracking, rutting, stripping, and flushing or bleeding. The objective of this study was to develop the criteria needed to determine when and where to place an underseal. Researchers reviewed the literature, surveyed and interviewed engineers in Texas Department of Transportation (TxDOT) districts to determine the current practice, experiences, and problems around the state regarding the use of underseals. Case studies of forensic investigations of pavements where underseals or lack of underseals have contributed to pavement failures and presented. A decision tree and criteria were developed and evaluated to determine when and where to place an underseal. Guidelines and training materials were developed on the use of underseals as a moisture barrier.