Polish Experience with Testing of Selected Shales as Material for Road Base Courses

Abstract

Base courses are important layers of road structures and their basic role is to reduce forces produced by service loads. The compaction process as well as climatic conditions influence materials used in base courses. In Poland, laboratory and field experiments were performed with five burnt coal shales as materials for road base courses. The tested shales were originally coarse-grained aggregates susceptible to compaction and frost. The laboratory tests focused on the influence of compaction and frost cycles on shale properties. It was identified that compaction and frost cycles significantly changed shale properties, i.e. grading, sand equivalent, passive capillarity and hydraulic permeability. Crushing of the stone fraction and increase in the silt-and-clay fraction resulted in a tendency to increase passive capillarity as well as reduce the sand equivalent and hydraulic permeability of the tested shales. Long-term field tests were carried out on an experimental road section with a shale base course. After 5 years’ operation of the road, the load capacity of the base course did not decrease. It was proved that burnt coal shales may be used in base courses but changes of their properties should be predicted.