Foamed bitumen mixes = shear performance?

Abstract

Road rehabilitation technology is currently under the global spotlight. Considering that cold bituminous binders, e.g. emulsion and foamed bitumen, have become more commonly used in cold recycling operations, there is a need to understand the performance properties of these materials. Great strides have been made in the modelling of foamed bitumen treated materials in recent years. Performance functions that may be used in the design of pavements incorporating these materials become increasingly important.

The challenge of modelling the behaviour of these mixtures is complicated by the variety of foamed mixtures that are produced and the range of mix variables that prevail. Binder content (BC), active filler content, parent rock type, aggregate gradation, plasticity, moisture content, etc. can vary significantly from mix to mix. A unified approach to designing with these materials that accounts for all of these variables is exceptionally challenging.

This publication investigates the shear and dynamic properties of foamed bitumen stabilised mixes and their role in the performance modelling of these materials. Latest research findings are synthesized with the relevant aspects of the mix evaluation and classification procedures. Correlation of different testing protocols and mix compositions is made with a view to providing synergy to the research results and direction to their application in mix design and pavement design.

Keywords:

• Foamed bitumen
• Cold mix
• Triaxial testing
• Permanent deformation
• Shear properties
• Resilient modulus

Acknowledgements

The authors extend their gratitude to the Gauteng Department of Transport and Public Works (Gautrans) in allowing data from research projects financed by Gautrans to be included in this publication.