Effects of Gradation, Composition, and Degree of Compaction on the Mechanical Characteristics of Recycled Unbound Materials

Recycling is a hot topic in the Netherlands. This implies also the recycling of waste resulting from the demolition of buildings and civil engineering structures. Since the late 1970s, reuse of old concrete and masonry as base course materials for roads is common practice in the Netherlands. Although such materials have been successfully used for more than two decades now, relatively little information is available on the effects of factors such as gradation, composition, and others. Knowledge about these factors is required, because the quality of the recycled materials varies from location to location and is fairly difficult to control. To gain this knowledge, a large research program was started at the Delft University of Technology into the behavior of unbound base course materials made from recycled concrete and masonry rubble in relation to factors such as gradation, composition, and others. The results indicate that indeed such factors have an influence on the mechanical characteristics. However, it is shown that the degree of compaction (DOC) is the most important of the influence factors. This is an important result for practice, because the DOC is far easier to realize and to control than are factors such as gradation and composition. The results have shown that good-quality road bases can be built from recycled concrete and masonry rubble.