Experimental investigation of fracture properties of asphalt mixtures modified with Nano Fe₂O₃and carbon nanotubes

This paper investigates the effect of Nano Fe2O3 and CNTs (carbon nanotubes) on fracture properties of HMA (hot mix asphalt) mixtures subjected to mixed mode I and II loading. Semi-circular bend (SCB) specimens were used for performing fracture experiments. Four different percentages (i.e. 0.1%, 0.4%, 0.8% and 1.2%) of Nano Fe2O3 and CNTs were individually mixed with the same base binder to provide two different nanomaterial modified mixtures (i.e. Nano Fe2O3 and CNTs modified HMA mixtures). Both the Nano Fe2O3 and CNTs were found to improve fracture properties of HMA mixtures remarkably; however, the fracture strength of HMA mixtures was more improved by CNTs than Nano Fe2O3. Generally, the highest improvement in fracture resistance achieved by utilisation of these nanomaterials is observed when the specimens are loaded under pure mode I (i.e. 27% and 46% for the Nano Fe2O3 and CNTs modified HMA mixtures, respectively), and as the amount of shear mode (mode II) at the crack front increases, the improvement effect of Nano Fe2O3 and CNTs on the fracture resistance reduces gradually. The results also demonstrate that the appropriate percentage of Nano Fe2O3 and CNTs for modifying HMA mixtures is 0.8% and 1.2%, respectively.