Abstract:
Flexible pavements mainly consists of two basic components that are aggregate and asphalt binder. These two components (aggregate and asphalt) in HMA mixtures are optimally mixed in quantity to produce an economical mix design. Flexible pavements are facing serious problem of developing ruts particularly in areas of Pakistan where temperature is high. This is mainly due to the drastic increase in road traffic during the last two decades. This study targets upon the performance evaluation of modified and controlled laboratory prepared HMA mixtures. Wheel tracking and dynamic modulus tests are used to evaluate the performance of HMA mixtures. Two gradations (NHA class-A and NHA class-B) of wearing course, a bitumen penetration grade of ARL 60/70 and an aggregate source of Margalla were used for preparation of mixtures. Bakelite was introduced as modifier for performance characterization of asphaltic mixtures prepared for this study. The test results indicated that with the addition of bakelite, the performance of mixtures improved significantly. The percentage reduction in rut depth at 6% optimum bakelite content was observed to be 29% for HMA mixtures of class-A gradation, while that was 38% for HMA mixtures of NHA class-B, when compared to controlled mixtures. Likewise, the percentage increase in dynamic modulus values was found to be 36% for HMA mixtures of NHA class-A, while that was 46% for HMA mixtures of NHA class-B at temperature of 50°C. The analysis technique of 2n Full Factorial Design of Experiments was used to carry out analysis. Loading frequency was found to be the most effectual factor on the values of dynamic modulus, followed by temperature and percentage of bakelite.
