High- and Intermediate-Temperature Performance of Asphalt Binder Containing Carbon Nanotube Using Different Rheological Approaches

The present research work was undertaken to evaluate the rutting performance of carbon nanotube (CNT)-modified asphalt binders. Additionally, intermediate-temperature performance, aging resistivity potential, and high-temperature storage stability were also evaluated. Reported literature on rutting performance of CNT-modified asphalt binders is mainly based on the Superpave rutting parameter (G*/sin), which does not account for the recovery aspect of binder. The paper first highlights the importance of the elastic response of CNT-modified asphalt binders for better understanding about its rutting performance. Further, different approaches such as the evaluation of zero shear viscosity (ZSV), creep test, and multiple stress creep recovery (MSCR) were utilized to reach appropriate conclusions. A recently developed approach, linear amplitude sweep (LAS), was used for evaluating intermediate-temperature performance. The CNT was varied as 0, 0.4, 0.75, 1.5, and 2.25% by the weight of control binder. The G*/sin value was found to increase until 1.5% CNT content; however, the addition of 2.25% CNT resulted in decreased G*/sin, indicating reduced rutting performance at higher CNT content. Contrary to the G*/sin trend, significant improvement in recovery value was observed for all CNT percentages. Further, based on detailed analysis carried out for different rheological parameters such as ZSV value (evaluated using the steady shear approach), deformation resistivity potential from creep test, recovery (R), and nonrecoverable creep compliance (Jnr) from the MSCR test, CNT addition to the control binder showed significant improvement in rutting resistivity potential for all CNT percentages. Although ZSV value significantly improved with the addition of CNT, the increase in CNT content showed an early transition from Newtonian to non-Newtonian behavior. Further, analysis for stress sensitivity was carried based on the R and Jnr values obtained from the MSCR test, which showed an increase in stress sensitivity with the addition of CNT to the control binder. The need for improvement in the current protocol used for evaluating stress sensitivity of asphalt binder (based on the MSCR test) has also been discussed. Improvement in intermediate-temperature performance evaluated through LAS test was also observed. Also, CNT addition to asphalt binder was found to be stable under high-temperature storage conditions. Overall, improvement in high- and intermediate-temperature performance can be expected with the addition of CNT to the control binder.