A Review of Crumb Rubber Modification in Dry Mixed Rubberised Asphalt Mixtures

This paper provides an overview of crumb rubber modified asphalt mixtures with particular reference to the dry process. The dry process involves the blending of crumb rubber with hot aggregates prior to mixing with bitumen. In comparison to the wet process (process of incorporating crumb rubber into bitumen prior to mixing with aggregates), this mixture type has a number technical issues. The lack of standards and inconsistent performance have resulted in scepticism among practitioners and researchers in accepting the dry process for rubber modification even though it has the potential to recycle more crumb rubber compared to the wet process. This has resulted in the overwhelming majority of asphalt paving projects involving crumb rubber using the wet process. Therefore, to better understand the mixture, details pertaining to dry mixed rubberised asphalt are discussed in this paper with sufficient information from previous research. The discussions highlight several critical issues regarding its modification concept (the function and behaviour of rubber particles within the mixture), mixture design criteria and mechanical performance of this mixture type. This is necessary in order to identify the factors that play a significant role in improving the mixtures properties for future studies. Additionally, the review will be a positive step in the direction of achieving an appropriate design standard for dry mixed rubberized asphalt mixtures.