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For cold regions, combining styrene–butadiene–styrene (SBS) with dioctyl adipate (DOA) provides a promising strategy to improve bitumen’s low-temperature performance. However, most studies emphasize short-term aging, while the role of plasticizers under long-term aging remains unclear. This study employed atomic force microscopy, rheological testing, and FTIR to investigate DOA/SBS composite-modified bitumen after long-term aging. Results show that DOA markedly alters bee-structure morphology: at 2 % DOA, large microstructures increase, but at 3–4 %, large bee structures nearly disappear while small ones become more numerous and aggregated. This microstructural transition reduces interfacial compatibility and narrows the linear viscoelastic range. FTIR results reveal that DOA exerts a dual effect, accelerating both asphalt oxidation and SBS degradation, with a dynamic balance reached at ∼3 % DOA. Performance grading (PG) confirms these effects: SBS-modified bitumen (PG82–22) decreases to PG76–22 at 2 % DOA, remains unchanged at 3 %, and further decreases to PG70–28 at 4 %, where the improvement in low-temperature grade (to −18 °C) arises mainly from SBS degradation. Overall, low to moderate DOA (<2 %) enhances low-temperature performance by regulating asphaltene clustering, while excessive DOA exacerbates SBS degradation. These findings highlight the need for controlled DOA dosages in durability design and suggest < 2 % DOA as optimal for 5 % SBS-modified bitumen, providing guidance for future composite rejuvenator development.
Tian et al. (Wed,) studied this question.