Effects of quantity and plasticity of fine particles on the workability and resilient behaviour of aggregate-soil mixtures for granular pavement layers

The paper presents the results of a laboratory investigation seeking to quantify the effects of fine quantity and type on the workability and resilient response of aggregate-fine soil mixtures for subbase formation. Laboratory devices were used to simulate in-field conditions and compact samples and evaluate their resilient response under pulsing loads. Four different types of fines passing through a 63 µm sieve (one non-plastic silt and three silty-clays exhibiting plastic behaviour) in three different quantities (5.4, 10.8 and 16.2%) were combined with coarser aggregates while maintaining the same grading distribution. A variant of the generalized model proposed in the Mechanistic Empirical Pavement Design Guide was calibrated to distinguish the contribution of fine type to resilient modulus from that of moisture content and suction. The results evidenced an improvement in mixture workability during the compaction process when using plastic fines instead of non-plastic ones. However, the quantity of plastic fines should be limited (lower than 10.8% within the aggregate skeleton) in order to achieve a high compaction level and to attain a hardening resilient behaviour rather than the softening one observed in the case of granular materials containing non-plastic fines.