Performance Evaluation of Nano-Materials in Asphalt Concrete Mixtures

Abstract

Nanoparticles are utilized to modify the asphalt binders and improve the pavement mechanical performance against the common distresses of permanent deformation (rutting propensity) and fatigue, manifested on asphalt pavements. This study reviews the existing body of knowledge on Nano-modification of asphalt binder using four different Nano-materials: Carbon Nanotubes (CNTs), Carbon Black, Graphene Nano Platelets (GNPs) and Nano Clay. The motivation behind this in-depth review of Nano-modification of asphalt binder was to synthesize the implications of various Nano-materials on the mechanical properties of asphalt binder. The study concludes by proposing the suitability of each of the Nano-material – its extent/ proportion by weight of asphalt binder, economic suitability, environmental compatibility and availability in Pakistan. CNTs (with optimum percentage of 1%) yielded best results – increases stiffness, rutting performance and resistance against fatigue cracking. Carbon Black improved high-temperature performance, such as rutting resistance, fatigue performance, and stiffness, but had no considerable effect on low-temperature cracking. Subjected to the type of binder and polymers employed, carbon black up to 6% (by weight of binder) revealed to be a potential modifier of asphalt binder. Graphene Nano-platelets (GNPs) produced PG-70 when 4% of GNPs are added to the binder. The wheel-tracking slope (WTS) decreased from 0.58 to 0.35 and this reduction is also suggestive/ attributed to high resistance to permanent deformation. Nano Clay added asphalt binder’s Complex Shear Modulus (G*) increased while the Phase Angle (δ) dropped, indicating enhanced stiffness and elasticity. Enhanced rigidity improved rutting resistance, while increased elasticity provided maximum deformation recovery. 2-4% (by weight of binder) of Nano-clay in asphalt binder yielded optimum results. The results indicate that the addition of Nanoparticles enhanced the rutting performance and strength of asphalt mixtures. Nano-modified asphalt (given the reasonable selection of Nanomaterials for the base binder) can offer many benefits (i.e. improve the durability of asphalt pavements, save energy and cost, decrease maintenance and rehabilitation) requirements in road construction industry of Pakistan.