SOURCES OF, EFFECTS OF, AND MINIMIZING ENTRY OF, WATER IN PAVEMENTS

Most of the water occurring in pavements originates as precipitation. Some of this precipitation gains direct access to the pavement through surface infiltration, while other water takes a more round-about route and eventually reaches the pavement as groundwater. Surface infiltration occurs almost everywhere in the United States. Groundwater seepage most often occurs in areas where rainfall exceeds evaporation. Water can cause very large changes in properties of pavement materials and in the pavements' structural response to loads. Free water in granular base courses can easily reduce their strength 25% or more under dynamic loads. Other effects of water on pavements include degradation of aggregates, stripping of asphalt from aggregates, pumping, blow-ups, frost heave, reduced strength during spring thaw, swelling of subgrade soils, and weakened subgrades and bases. Thus, it is important to rapidly drain free water from the pavement system. It also follows that there should be some benefits to keeping out as much water as possible. Keeping the water out is not easy because pavement surfaces are not completely impervious; and cracks, joints, and other structural discontinuities are continually moving under load and temperature stresses. In time, these movements tend to open even the best sealed systems. However, sealing joints and porous surfaces does reduce the infiltration of water for awhile. Other means for minimizing the enter of water includes design changes to reduce differential movements between different pavement components and paving areas adjacent to the pavement. Brief discussions are provided on reflection cracking of overlays on jointed concrete pavement, jointless pavements, edge joints, and drains to minimize entry of water.