Abstract
The use of methylene diphenyl diisocyanate (MDI)-based additives to prepare isocyanate-modified bitumen (IMB) provides an effective solution for achieving energy savings and performance improvements. However, the thermal-oxidative aging properties of bitumen modified with isocyanate additive have not been well discussed, which limits the fundamental understanding of its durability-related performance. To promote the understanding of the aging mechanism of IMB, experimental investigations and quantum chemical calculations were conducted to investigate the aging properties of IMB. IMB samples were prepared and aged under controlled laboratory conditions. The evolutions of aging behaviors were examined through physical and chemical approaches. The role of noncovalent intermolecular interactions in delaying oxidation was interpreted through density functional theory (DFT)-based theoretical calculation. The results revealed that amide-related bonds can be generated due to the chemical interactions between isocyanate and bitumen compounds. Chemical reactions tend to reduce the potential sites for oxidative attacks, thereby inducing delayed oxidation of IMB. Consequently, lower chemical and rheological aging indexes can be observed in IMB, and chemical crosslinking can provide effective support for the elastic response after aging. In addition, the noncovalent interactions between isocyanate and bitumen molecules can result in a lower tendency towards oxidation, which provides a cooperative effect on the inhibition of aging. The findings of this study offer insights into the aging behaviors of IMB and provide references for the design of chemically modified bitumen.
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