Seal courses for a soft asphalt pavement with semi-rigid base in cold regions

As a typical structure of roads, asphalt pavement with base course of cement stabilized aggregates, which is usually called semi-rigid base course can be found everywhere in China. Research experiences show that the semi-rigid base course is often more susceptible to moisture and frost or less sufficient for moisture and frost stability. Such designs more frequently lead to reflected cracks, with more extensive low temperature cracking. As more water is penetrating down into the base course through the cracks, the bearing capacity will decrease and deterioration of the road increase. To make an improvement, especially in developing a soft binder asphalt pavement with larger void content of the mix for low volume roads, the author tries to use seal coat as a functional course. This course, in between wearing and base courses, and around 10 mm thick of mixture of asphalt binder and fine aggregates, is specially designed for moisture separation and/or mitigation of reflected cracks. In recent years, test roads consisting of seal courses were constructed in north China's Heilongjiang and Gansu Provinces, where environmental conditions differ largely in temperature, precipitation, geology and others. Some details of design, construction and performance of the seal course based on laboratory and in-situ experiments as well the test roads constructed are presented in this paper.