Effect of model compounds on stress relaxation in asphalt binders

Recycled asphalt, enriched with asphaltene, wax, and oil modifiers that function as warm mix asphalt additives or rejuvenators, is increasingly utilized in asphalt pavement construction. However, the impact of incorporating these compounds on the stress relaxation behavior, a key factor closely associated with the cracking resistance of asphalt binder, remains largely unexplored. Therefore, this study aims to evaluate the effects of wax, asphaltene, and re-refined engine oil bottom (REOB) additives on the stress relaxation response of bituminous binders under different cooling rates and aging conditions. Key findings indicate that wax accelerates thermal stress relaxation, with aging and cooling rates significantly affecting the asphalt’s behavior; asphaltene shows varied structuring effects based on dosage and cooling rate, particularly notable at a 4 % dosage under slow cooling; and REOB additives exhibit pronounced sensitivity to cooling methods, with differences becoming less evident after aging or at higher dosages. Additionally, the interaction between wax and asphaltene within the binder matrix suggests that wax’s influence is dominant at lower asphaltene levels, whereas high asphaltene content predominantly dictates the binder’s stress relaxation performance, minimally influenced by cooling methods. These insights reveal the complex interactions between binder components and external conditions, providing guidance for optimizing asphalt binder formulations for enhanced cracking resistance. • Wax accelerates stress relaxation in asphalt binders. • Asphaltene increases relaxation modulus significantly at 4 % dosage and slow cooling. • REOB additives show marked sensitivity to cooling methods, less so after aging. • High asphaltene content primarily influences stress relaxation, overriding wax effects.