Investigation of Nanoclay Effect on Fatigue Behavior of Hot Mix Asphalt (HMA) by damage ratio method

Damage of flexible pavement due to cracking and rutting occurs. among these mechanisms, a lot of fatigue crack can be seen in asphalt surface, so many research has been done to improve the fatigue life of asphalt mixtures. The use of different materials in improving the behavior of bitumen characteristics is able to increase the life of asphalt pavement. Today, polymeric nanocomposites are one of the most popular of materials discovered recently and it can successfully improve properties if polymer is modified with small amount of nanomaterial on condition that the nanoparticle is dispersed at nanoscopic level. The tests on asphalt mixture modified by cloisite indicates that nanoclay modification can improve mechanical behavior properties of mixture, such as creep, indirect tensile strength. However, it has not mitigated the fatigue problem and hence, more research is required before it can be utilized on a large scale. In this paper, two types of montmorillonite nanoclay were used: Cloisite 15-A and Cloisite 30-B. For this purpose, control, 2, 4 and 6% of nanoclay mixtures were prepared. Then the fatigue behavior and resilient modulus test at medium and low temperature were evaluated. Four-point bending beam fatigue testing has been used for beam specimens under 10Hz loading frequency and test temperaturesbased on AASHTO T321 standard. Fatigue life, bending stiffness, dissipated energy and damage ratio were calculated using beam fatigue test results. At the end, it is concluded that both additive have great influence on improving fatigue behavior of asphalt mixtures at 25°C. In contrast, nanoclays don’t seem to have a beneficial effect on fatigue behavior at low temperature. Due to extremely high specific surface of nanomaterials, bitumen viscosity goes up and fatigue life will significantly improve. While at low temperatures, because of bitumen plastomer properties, we encounter with cracks problem and reduce in fatigue life.