Mixing carbon nanotubes with asphalt binder through a foaming process toward high-performance warm mix asphalt (WMA)

This paper investigates mixing carbon nanotubes (CNTs) with asphalt binder through a foaming process to produce high-performance warm mix asphalt (WMA). Two different solvents of ethanol and a water-based surfactant are used to disperse the multi-walled CNTs. Initial morphological assessment of the two CNT solutions showed that a more homogenous dispersion of the CNTs was achieved using the water surfactant solution. The foaming performance, thermal, and rheological properties of the foamed asphalt mixed with different percentages of CNTs are further investigated. The test results showed that a very small amount of CNTs (0.06% similar to 0.1% in weight of the binder) can effectively enhance the foaming performance for bubble stability without tangibly increasing the rheological properties of the foamed asphalt. The specific heat capacity of the foamed samples was smaller than the neat binder, whereas the glass transition temperature of the foamed samples shifted to a lower temperature as compared to that of the neat binder. The thermal conductivity of the 6% CNTs sample (0.24% wt. in asphalt binder) was improved by two-fold compared with the foamed unmodified asphalt, which indicates the potential of using CNTs in the binder for enhancement of thermal properties in asphalt pavements.