Low-content crumb rubber modified bitumen for improving Australian local roads condition

A global trend for developing sustainable transport infrastructure by adopting various sources of recycled material is being promoted by researchers and media daily. Recycling End of Life Tyres (EOLTs) in the form of Crumb Rubber (CR) builds on decades of past tradition. Local councils in Australia welcome recycling practices and sustainability although a general lack of guidelines is commonly acknowledged for low-traffic roads. This paper evaluates the benefits of low-content crumb rubber modified bitumen (CRMB) for its application on Australian local roads, often exposed to very hot summer temperatures. Blending conditions play a vital role in CRMB; these include temperature, mixing duration and applied shear rate or shear mixer speed. In this study, the influence of blending conditions on the physical, chemical, thermal and rheological properties of low-content CRMB is investigated. Two shear mixing rates (700 and 3500 rpm) and three mixing durations (30, 60 and 90 min) were chosen and rubber-modified blends were prepared with 7.5% CR. Rheological tests such as master curve, black diagram, Cole-Cole analysis, and Multiple Stress Creep Recovery were investigated. It was observed that the mixing duration has minimal effect on low-content CRMB, however, the applied shear rate has an impact in the sense that it produces a relatively stiffer - and oxidised - blend at higher mixing speeds. This was also correlated to the outcome from Fourier Transform InfraRed analysis (FTIR). Overall, the use of low-content CRMB in local Australian roads can significantly improve the rutting performance while facilitating the recycling of end-of-life tyres. (C) 2020 Elsevier Ltd. All rights reserved.