PAVEMENT DESIGN FOR MOISTURE

Most pavements built in the United States have been constructed without pavement underdrains, or porous base or subbase. Since most of these pavements are apparently performing adequately, this would indicate that subdrainage is not necessary on most pavements. Many pavements have, however, fail because of excessive moisture. For these pavements, a recognition of the particular conditions causing excess moisture would allow a design to be developed that would either eliminate the excess moisture or assure that the pavement is structurally adequate to overcome the weakened condition caused by the moisture. Almost every pavement failure can be blamed on moisture, and a reduction of that moisture content would almost always result in higher strength and a longer life. While pavements that perform adequately without subdrains can be said to be adequately designed for the particular moisture conditions, improved moisture conditions would allow less pavement structure for the same performance or longer life with the same pavement structure. It is recommended that overall performance of a pavement to carry the design loads for a long period of time, to maintain a satisfactory serviceability index, and to have very little maintenance be evaluated. To accomplish this with the best cost benefit, tradeoffs such as additional structure for frost penetration, more permeable bases and subbases, effective sealing of cracks and joints in portland cement concrete pavements, and subsurface drainage should be considered. Examples of the results of frost action in northern Illinois are provided.