Durability testing of basic crystalline rocks and specification for use as road base aggregate

One of the most important materials for the construction of high quality pavement layers in roads in South Africa is the Basic Crystalline group of rocks. The major deposits of these materials are associated with the dolerites and basaltic lavas of the Karoo Supergroup. Problems related to the in-service deterioration of road aggregates produced from the crushing of these materials, despite their conforming to the necessary specifications, have been experienced in southern Africa for many years. This has usually resulted in the use of more expensive materials being transported further to the road project. Twelve such materials were collected from various parts of southern Africa and tested for their durability using the standard specified tests as well as a range of non-standard and new tests. Based on the results, new test methods and tentative specification limits have been proposed for assessing and predicting the durability of basic crystalline materials obtained by crushing unweathered material sources.