Abstract:
The earlier failure of pavement surfaces is often attributed to fatigue cracking and permanent deformation caused by factors such as high temperature, water exposure, and unbalanced axle loads. These distresses result in additional costs due to accelerated Maintenance and Rehabilitation (M&R) activities. To address this issue, extensive research has been conducted to explore the use of additives that enhance the mechanical properties of asphalt mixtures, thereby increasing pavement durability and sustainability by reducing the rate of permanent deformation. This study focuses on the incorporation of nitrile rubber (NR), derived from waste sources like nitrile surgical gloves, as an additive in conventional asphalt mixtures. Five different percentages of NR modified bitumen (0%, 2%, 4%, 6%, & 8%) were used to produce NHA Class B gradation specimens. These specimens were then subjected to Dynamic modulus testing in the Asphalt Mixture Performance Tester (AMPT) at four temperatures and six different frequency sweeps, from which stress-dependent master curves were constructed for each mixture. The results showed that the dynamic modulus values increased significantly at the 4% NR modified mixture, indicating better performance at all combinations of temperature and frequency. Statistical analysis, employing a Two-level factorial design, was conducted to assess dynamic modulus and phase angle. Sensitivity analysis was performed using Design Expert Software, revealing that dynamic modulus is sensitive to temperature and frequency. Specifically, an increase in temperature from (21.1 to 54.4) reduced dynamic modulus, while a decrease in frequency (from 25 to 0.1Hz) also reduced the dynamic modulus. Furthermore, response surface modeling (RSM) was employed to predict the dynamic modulus of NR modified mixtures, achieving a significant improvement by capturing 99% of the variance in the tested data. The RSM demonstrated a strong capability to correlate and represent the interdependencies between various factors, such as dynamic and phase angle, temperature and dynamic modulus, among others. In conclusion, the utilization of nitrile rubber as an additive in asphalt mixtures shows promising in enhancing pavement performance and reducing permanent deformation. The findings of this study provide valuable insights for the development of more durable and sustainable pavement materials.
