A Brief Analysis of Over-Digested Crumb Rubber Modified Bitumen

Authors: Georges A.J. Mturi, Johan O’Connell, Herman Marais, Nomashaka Hawes



In South Africa, crumb rubber modified bitumen is produced according to viscosity specifications. As the crumb rubber is digested, the viscosity of the CRM bitumen eventually falls below the minimum recommended requirement and as such the binder is contractually  unacceptable. This paper aims to show that although digestion viscosity curves have successfully been used as a production tool, they cannot be used as an indicator of performance at lower in-service temperatures. Rheologically, the disintegrated rubber polymers from the de-vulcanization of the rubber crumbs due to the over-digestion process are still capable of imparting elastic properties. The over-digested CRM binder remains useful for re-blending or application in alternative products requiring lower viscosity binder.

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