8th International Conference on Managing Pavement Assets CHARACTERIZATION OF UNBOUND BASE MATERIALS FOR ROADS USING A NEW DEVELOPED REPEATED LOAD CBR TEST

It is well accepted that the mechanical characteristics of unbound granular materials should preferably be determined by means of repeated load triaxial testing. This testing method is however, not readily available and not an easy test to be done especially in developing countries. This is a major drawback for using mechanistic methods for the design of low-cost roads in developing countries that for their bearing capacity heavily rely on granular base and subbase layers. Currently, the design of such pavements is still mainly done using empirical design methods but such methods have reached their limits given the fast increasing traffic volumes and axle loads in such countries. Application of mechanistic based methods has become a necessity but this implies a need for proper characterization of unbound materials. Given the fact that the characterization of the unbound granular base and subbase materials for low-cost roads is still done using empirical methods such as the California Bearing Ratio test (CBR), a relatively simple testing technique is developed which is based on the widely practiced CBR test. The repeated load CBR test presented in this paper provides a realistic estimate of the stress dependent resilient modulus of unbound granular materials, which can be used for mechanistic design analysis of low-cost pavements. Furthermore, the effect of degree of compaction and moisture content on the resilient modulus and permanent deformation is investigated for different unbound granular materials, ranging from the high quality crushed rock (G1) base material from South Africa to rather marginal materials such as Ferricrete from South Africa and weathered basalt from Ethiopia