Modification of binder with tyre rubber and polymeric networks for usage in road asphalt mixes

Hybrid modification is a relatively new concept of incorporating two or more polymeric modifiers of different nature to a bitumen, in order to take advantage of their complementary features. However, the problem of its inherent storage instability is a major concern that limits the industrial application. Hybrid Systems (HSs) were formulated by the addition of different copolymer (reactive and non-reactive) to a model rubberised binder (Crumb Tyre Rubber Modified Bitumen). The resulting HSs were evaluated by means of thermos rheological analysis, technological characterisation, fluorescence microscopy and modulated differential scanning calorimetry. The results obtained pointed out that both, in-service properties and storage stability were notably enhanced by the development of a complex multiphasic structure of: polymer-rich and asphaltene-rich phases, non-degraded rubber particles and digested rubber chains. This enhancement is attributed to the development of a multiphasic system composed of non-dissolved CTR particles, a polymer-rich phase and an asphaltene rich-phase. In the case of non-reactive HSs, droplets of swollen ethylene copolymer form a well-defined dispersed phase. By contrast, reactive HSs display a different morphology, almost invisible by optical techniques, as consequence to the development of a chemical network that yields by far the highest degree of modification.