Performance Evaluation of Styrene Butadiene Styrene and Nano- Silica Modified Asphalt Concrete Mixtures

Abstract

Asphaltic materials are widely used in the construction of highways throughout the world, due to their technical qualities and low initial cost as compared to other materials. The flexible pavements are mostly affected by meteorological factors in addition to traffic loads, which results in pavement premature failures like rutting and moisture induced damages and necessitates early maintenance & repair. However, Hot Mix Asphalt (HMA) performance has been improved by utilization of polymers and nanomaterial which improves service life and reduce pavement distresses. Previous studies concluded that Utilization of Polymers and nano materials have drastically improved mechanical properties of HMA. This study focuses on the effect of adding various percentages of Nano Silica (NS), i.e, 2,4,6 and 8 % (by weight of bitumen) along with constant 4.5 % SBS. Indirect Tensile Strength (ITS) Test, Resilient Modulus (MR) and Hamburg Wheel Tracking Test (HWTT) were used to evaluate the performance of unmodified and modified mixtures. The MR test was performed at both temperatures i.e 25 ℃ and 40 ℃, which depicts different metrological conditions of this region. Tensile Strength Ratio (TSR) was estimated to check the moisture resistance of mixtures using ITS results for unconditioned and conditioned samples. Moreover, a model was developed for the rutting potential of modified mixtures using Multi Expression Programming (MEP), a sophisticated technique which uses the experimental data and suggests an equation for different input variables. The results indicate that adding NS to SBS modified bitumen enhances the various mechanical properties of asphalt mixtures including Stiffness, moisture and rutting resistance. Temperature has adverse effect on stiffness of mixtures while modifier has direct relation with stiffness. Two-way factorial method justified the effect of temperature and modifier on MR with 95 % precision while MEP model for rutting shows R value (>0.95) which shows good relation between experimental and predicted data. Moreover, the NS and SBS has good impact on mechanical properties of HMA mixtures. It was found that 4.5% SBS with 6% NS (by weight of the binder content) in the mixture performed better than the other percentages of modifier materials assessed in study which improves rut resistance and Resilient Modulus by 56% and 1.55 times while reducing moisture susceptibility by 18%, respectively.