Cohesion in crumb rubber modified bitumen

This article reports on a study of crumb rubber-mediated improvement in bitumen cohesion, analyzed with the UCL method. UCL, a procedure developed to characterize bituminous binders, evaluates the cohesion obtained by adding a certain amount of bitumen or bituminous mastic to a standard mix aggregate. This method was chosen because it can be used to assess bitumen containing crumb rubber added by either the wet or the dry mix process. In the dry mix process crumb rubber is combined with the mix as if it were a fine aggregate; i.e., crumb rubber and binder are blended during mix manufacture, laying and compaction. In the wet mix process, the binder is blended with the crumb rubber prior to mixing with the aggregate; i.e., when added to the mix, it has already been modified. The effect of digesting this dry mixed material prior to use was also analyzed in the present study. A comparison of the dry (with and without digestion) and wet mix processes showed the latter to be more effective, particularly when the crumb rubber was blended with the binder via microscopic dispersion.