Mix design of bitumen-stabilised materials – South Africa and abroad

The need for sustainable road infrastructure maintenance has led to a significant growth in pavement recycling and bitumen-stabilisation technology. This, in turn, has created a need for robust mix design and pavement design procedures for bitumen-stabilised materials (BSMs), using either foamed bitumen or emulsified bitumen binders.This paper outlines the research developments in the field of BSM technology and testing and their link to a standardised mix design. At the same time, the link between mix design and structural design is established, creating a platform for laboratory test results to be used in the evaluation of the life of the pavement structure. In particular, the challenging areas of mix design are highlighted, namely: Development of a laboratory compaction method for BSMs that effectively simulates field compaction,Improvement of laboratory curing procedures to simulate the dry-back phenomenon that occurs in the road, after construction,Development of triaxial testing equipment and procedures that enable evaluation of the shear properties of BSMs during standard mix designs, in order to provide a link to field performance and structural designThe paper describes the mix design procedures that have been developed over five years, based on experience with full implementation in practice, based on more than global 200 mix designs. This is followed by implementation of the new design method via two case studies that use the triaxial information from mix design for performance analysis and structural design of BSMs. Based on field performance, the holistic design approach works. Finally, the added benefits of monotonic triaxial testing in terms of determining flexibility parameters are explored. The dissipated energy parameter has been found to provide potential in evaluating the flexibility of BSMs