Influence of hybrid microcapsules on the low-temperature cracking resistance of asphalt binder

To improve the low-temperature crack resistance of asphalt binders, this study incorporates microcapsules hybridized with multi-walled carbon nanotubes (MWCNTs) into asphalt. The low-temperature creep properties, viscoelastic behavior, and crack resistance of the modified asphalt before and after long-term aging were comprehensively evaluated using the Bending Beam Rheometer (BBR), low-temperature Dynamic Shear Rheometer (DSR), and Asphalt Binder Cracking Device (ABCD) tests. Fourier Transform Infrared Spectroscopy (FTIR) was utilized to analyze the chemical structure of microcapsule-modified asphalt both before and after aging and to calculate the characteristic peak indices. Pearson correlation coefficients were established between the asphalt's low-temperature performance indicators and the characteristic peak indices. The results indicate that microcapsule incorporation significantly enhances the low-temperature crack resistance of asphalt by improving its elastic deformation capacity, optimizing interfacial bonding, and releasing the core material to soften the asphalt and fill cracks. As a result, the cracking temperature of unaged asphalt decreases from - 27.3 degrees C to - 32.1 degrees C. However, the enhancement effect reaches saturation when the microcapsule content exceeds 2.5 %. After long-term aging, the release of the microcapsule core material modifies the asphalt composition by increasing the branched alkane content. Meanwhile, MWCNTs can mitigate the oxidation reactions in asphalt and reduce the deterioration of low-temperature performance induced by aging. Moreover, in the unaged state, the stiffness modulus, percentage of residual stress, and cracking temperature strongly correlate with the proportion of branched alkanes and the relative content of aromatic compounds. After long-term aging, correlations among low-temperature performance indicators remain strong, whereas their correlations with microstructural chemical parameters weaken.