Introducing a Sustainable Bio-Based Polyurethane to Enhance the Healing Capacity of Bitumen

This paper introduces the in-situ formation of biomodified polyurethane in bitumen as a novel strategy to enhance the healing capacity and aging resistance of bitumen. Bitumen is a substance that is known to have the capacity for healing. Self-healing bituminous composites can recover their properties. An increase in bitumen's healing capacity can be facilitated using various modifiers. This study examined the merits of using a biobased polyurethane to both improve the healing capacity of bitumen and to enhance its resistance to aging through in-situ polymerization of polyurethane. The effect of aging on healing capacity was examined by studying specimens before and after aging in the laboratory. To do so, thermomechanical analysis and spectroscopy were used to characterize bitumen containing a biobased polyurethane from castor oil. It was found that the biobased polyurethane was quite compatible with bitumen, and the presence of polyurethane improved the overall thermomechanical properties of the bitumen. To evaluate the extent of healing, a time-sweep rheometry test was used to create samples with specific initial damage degrees. The degree of damage was selected to be a 30%, 45%, or 60% reduction in complex modulus. A healing index was calculated for each of the three damage levels after a 60-min rest period. The study results showed that the introduction of biobased polyurethane not only improved the healing index, it also mitigated the negative effects of aging on bitumen's healing capacity. Compared to samples of unmodified bitumen, the average healing index of samples containing biomodified polyurethane was 1.3 times higher at 16% in the unaged state and 3.5 times higher at 7% in the aged state. In addition, the samples containing biomodified polyurethane showed better resistance to aging as evidenced by average 72% and 50% lower increases, respectively, in carbonyl and sulfoxide (known products of aging in bitumen) when exposed to the same aging protocol.