Influence of Bitumen Chemistry and Crumb Rubber Pre-Treatment on the Storage Stability and Rheological Performance of Modified Binders

Vollständiger Abstract

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The incorporation of crumb rubber (CR) into bitumen offers significant performance and sustainability advantages, yet its widespread adoption is impeded by poor storage stability caused by thermodynamic incompatibility. To address this fundamental challenge, this study investigates the role of bitumen chemistry, specifically the balance of fractions determined via SARA analysis, and the efficacy of crumb rubber pre-treatment in creating a stable binder system. Two base bitumen with distinct chemical compositions (PG 58-28 and PG 70-22) were modified with 10% and 15% CR, comparing two distinct modification philosophies: a palliative approach using styrene-butadienestyrene (SBS) and a fundamental approach employing devulcanized CR : a conventional stabilization approach using low dosages of styrene-butadiene-styrene (SBS) (1-3%) with untreated CR, and employing pre-treated, devulcanized CR without SBS. Binder performance was thoroughly investigated using storage stability and the Multiple Stress Creep Recovery (MSCR) test. The SARA analysis revealed that the softer bitumen, possessing a higher maltene-toasphaltene ratio, provided a superior solvent medium for polymer swelling. Despite this, all untreated CRMB blends exhibited severe phase separation (ΔSP>7°C), and the addition of SBS at 1-3% dosages proved insufficient to achieve stability, failing to meet the standard specification criterion (ΔSP≤2.5°C). In contrast, pre-treatment of the CR via thermo-mechanical devulcanization resulted in inherently stable blends (ΔSP