Application of nano-silica and styrene-butadiene-styrene to improve asphalt mixture self healing

Nanoparticles, due to their physical and chemical characteristics, present an inherent potential to improve the performance of bituminous materials. Presently, the technology of producing nanosized particles is evolving, and their application in various aspects of pavement engineering is becoming more cost-effective. Nanosilica, due to its spherical shape, high specific area, very tiny size and higher density compared to bitumen, presents an inherent potential to accelerate molecular randomisation movements, promote bitumen binder flow into microcracks and evolve healing index (HI) of hot mix asphalt (HMA). Moreover, it has been proved that Styrene–Butadiene–Styrene polymer (SBS) promotes fatigue life of HMA and decreases its temperature sensitivity. It would be interesting to know if the addition of nanosilica to modified binder with SBS will promote the total HI and lead to an enhanced HMA life cycle. In this study, the effects of four parameters, most importantly, the effect of the combination of nanosilica particles and SBS polymer to improve the self-healing of asphalt mixture was investigated using the Taguchi design of experiment (DOE) method. Experiments performed with the Superpave indirect tensile test included repeated loadings (fracture) and healing phases. These experiments showed that the combination of nanosilica and SBS promoted the self-healing of HMA, significantly. Moreover, the optimum condition to attain maximum HI and effect factor of each parameter, based on Taguchi DOE method, was obtained. Furthermore, scanning electron microscope images of fatigued, under healing and healed HMA samples were captured to investigate HMA self-healing mechanism.