Abstract

GTR(ground-tyre rubber)-modified binders or CRMB (crumb rubber-modified binders), by the so-called wet process, represent a particular case of PMB (polymer-modified binder), due to the specific features of this recycled-to-be rubber: a mixture of natural and synthetic vulcanized rubbers, carbon black and plasticizers among others. When the GTR is incorporated to the bitumen, the strong structure created through vulcanization and the strong
bond between carbon black and rubber (carbon gel or bound rubber) hinder the swelling of the rubber and the extensive dispersion within the bitumen. Crumb rubber particles tend to settle towards the bottom of the storage tanks.
The use in many formulations of co-additives may hide or cover up to some extent the results of PMB-criterion stability, showing as stable binders with high concentration of decanted fine solid particles. Therefore, a more severe assessment is proposed, based on solubilisation, in order to quantify the concentration of “non-assimilable” rubber particles, allowing thus for a sedimentation extent and profile kinetics evaluation, as well as an assessment of the
extent of digestion of the rubber. This method was applied to several binders manufactured with different concentration of GTR, different additives and different processes, to support the solubility approach. When these portions of the stored samples were analyzed through rheological measurements, a good agreement was in most cases found with the solubility tests. The prediction of stability was also evaluated at the industrial production site as well as the asphalt plants storage tanks.

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