Investigating the in situ Properties of Crumb Rubber Modified (CRM) Bitumen



The heterogeneous nature of crumb rubber modified (CRM) bitumen makes it impossible to extract from asphalt as a single component. It is recovered as two separate entities, namely the rubber crumbs and the solvent soluble fraction containing the base binder. Additionally, the solvent recovery process destroys the chemical equilibrium of the CRM bitumen blend; this makes it impossible to re-blend the separated components to reproduce a CRM bitumen of the same properties as the in situ binder. Hence no means exist of extracting and testing the recovered CRM binder in order to determine the properties of the in situ binder.

The increased use of CRM bitumen in South African road pavement surfacings in the last few years has coincided with major highway distresses throughout the country. This has brought about a need to investigate the binder as a possible contributory cause of the observed distresses. This has led to indirect means of investigating the state of the in situ binder. This paper aims to show how tested properties of the original CRM bitumen with ageing can be correlated to the in situ binder in order to determine the performance of the binder in road pavements.

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