A study on steady and dynamic viscosity evaluation of bio-rubberized asphalt binders

Abstract

Abstract The use of polymer and rubber-based additives for modification of asphalt binders forms a quite popular approach to achieve enhanced performance in the resultant asphalt binders and pavements. The application of bio-rubberized asphalt binders (BRAB) produced with waste-derived rubber and bio-oil/pyrolytic oil modifiers has recently gained interest in obtaining a synergistic effect across a wider temperature regime. In this study, BRAB was prepared through the modification of base binder with a combination of repurposed non-tire vehicular rubber (dosage: 16%) along with bio-oils derived from the pyrolysis of scrap tires (dosage: 6%). As the preparation process also impacts the performance of BRAB binders, the effect of variable preparation/fabrication approaches are assessed in this study. The production of BRAB was attempted through three approaches: sequential addition, heat pre-treatment, and microwave pre-treatment. Modifiers were added to the base binder one by one in the sequential addition method, whereas modifiers were pre-mixed and subjected to thermal and microwave treatments before being introduced to the base binder in the two pre-treatment approaches. A key engineering property that helps to assess the performance of an asphalt binder is the fluid’s flow resistance or its viscosity. The two most prevalent types of viscosity used in asphalt binder evaluation are the dynamic and steady-state viscosity, classified depending on how they are measured. In the dynamic domain, the viscosity is known as complex viscosity, whereas in the steady state, it is known as steady shear viscosity. The zero-shear viscosity (ZSV) is the viscosity that corresponds to the Newtonian plateau in a flow curve at low shear rates or low frequency domain and has attracted a lot of attention from the asphalt industry as a way to evaluate binders’ high-temperature performance. The ZSV can be determined by two test methods: shear rate sweep (in steady state mode) and frequency sweep (in oscillation mode) using a dynamic shear rheometer. This study examined the applicability of both testing methods to get reliable estimates of the ZSV of BRAB binders. The study also investigated the effects of binder preparation approaches on the flow characteristics and ZSV of BRAB binders. The findings help to understand the high-temperature performance of bio-rubberized asphalt under different testing methods.