Develop Guidelines for Placing an Under Seal

Project Description

Research and experience have shown that placing an asphalt seal coat, or underseal, between layers of asphalt mixtures is necessary to stop the intrusion of surface or subsurface moisture. However, some engineers feel that premature failures have occurred on highway pavements because an underseal was installed.

The Texas Department of Transportation (TxDOT) requested that TTI study the mechanisms that make a seal beneficial, evaluate when a seal may lead to a premature failure of the pavement layers, and develop the criteria needed to determine when and where to place such an underseal.

Based on the results from a literature review, a district survey, and forensic documentation, researchers developed decision-making criteria, guidelines, and instructional materials.

In addition, they concluded that:

• When pavements contain large amounts of free water, the rates of deterioration range from 10 or 20 to hundreds or thousands of times greater than rates during times when they contain little or no free water.
• When base materials that contain more than 5 to 10 percent fines (which are most of the flex base materials in Texas) become saturated, these bases will not drain freely due to capillary forces.
• In most cases, water that enters a pavement¿s structure comes through the pavement surface, as opposed to seepage from groundwater.
• The infiltration of water through pavement surfaces depends on the overall permeability, which is affected by the mixture type, density, and degree of cracking for asphalt concrete pavements (ACP).

Project Publications

Guidelines on the Use of Underseals as a Moisture Barrier 0-4391-S

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

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