Effects of Subgrade-Compaction Moisture Content on Performance of Asphalt Roads in Minnesota

Abstract

To identify ways to better design and construct asphalt pavement roads in Minnesota, this study examines the effects of excess moisture in the subgrade layer of road cross-sections in Minnesota through modelling. The subgrade layer of a road is the bottommost layer and consists of the existing soil. This layer's importance is sometimes neglected since it is farthest from the driving surface and is not imported as a construction material. However, it is the layer of a pavement cross-section that is most susceptible to a reduction in strength due to excess moisture. Using pavement modelling software, the effects of an increase in subgrade moisture and consequently a decrease in relative compaction on pavement design life were tested. A set of six road cross-sections were designed to exemplify the broad categories of asphalt paved roads seen in Minnesota. In each of these test cross-sections, a small increase in subgrade moisture content yielded an increase in the damage ratio and a decrease in the design life of the road. These results indicate that the moisture content in the subgrade layers of roads is influential in the driving surface performance. Additionally, achieving proper moisture levels in the subgrade during construction and maintaining the proper level of moisture over the life of a road is crucial to achieving that road's design life.