Effect of multi-walled carbon nanotubes on the performance of styrene–butadiene–styrene copolymer modified asphalt

The performance of styrene–butadiene–styrene block copolymers modified asphalt (SBS PMA) is heavily degraded in pavement engineering due to the weak interphase and the aging of SBS. In this paper, a type of functionalized multi-walled carbon nanotubes (CNTs) with hydroxyl groups was selected to address the two problems. Brookfield viscometer, dynamic shear rheology, bending beam rheometer, atomic force microscopy, and scanning electron microscopy were used to capture the performance and micro-morphologies of asphalt samples. Results of the performance investigation showed that CNTs decreased the viscosity (100–135 °C) of SBS PMA, performing a better workability. CNTs acted as a barrier to reduce oxygen-uptake amount of SBS, providing a better anti-aging property. The anti-rutting and fatigue resistance of SBS PMA were enhanced by adding a suitable amount of CNTs. All the binders with CNTs had similar stiffness, but that difference between them and the SBS PMA was higher at temperatures above −24 °C. Therefore, CNTs do not affect the anti-cracking property of SBS PMA. Results of morphologies analyses showed that CNTs enriched the interphase of SBS PMA not matrix. The reinforced phase (SBS-phase) of the binder with suitable amount of CNTs performed uniform distribution, and an interlocked structure. A significantly pull-out behavior of CNTs reinforced the interface, formed a dense network, and changed the behaviors of molecular motion in asphalt. Thus, functionalized CNTs with finer dispersion in the matrix provided SBS PMA with better mechanical properties.