Sustainability Assessment of Green Asphalt Mixtures: A Review

During recent decade, the pavement sustainability has received much attention by road agencies, companies, governments and research institutes. The aim of this paper is to introduce and evaluate the sustainability of the technologies developed or underdeveloped to address environmental issues of asphalt mixtures, and the waste materials and by-products that can be recycled and reused in asphalt production. Warm Mix Asphalt (WMA) technology, the most popular waste materials to substitute neat binder (crumb rubber modifier (CRM), recycled plastic (RP), vacuum tower bottoms (VTB)) and/or virgin aggregates (reclaimed asphalt pavement (RAP), reclaimed asphalt shingles (RAs), construction and demolition (C and D) wastes, steel and copper slags), and bio-binders were evaluated with respect to their environmental and economic benefits and engineering performance as the main components of pavement sustainability. The performance evaluation was carried out by examining rutting, moisture susceptibility, thermal and fatigue cracking resistance. Two main environmental impacts, greenhouse gas (GHG) emission, and energy consumption were considered to study the environmental effects of these technologies and materials. Additionally, the economic effect was investigated considering initial cost and long-term benefit. Results of investigation illustrated that although each individual technology and waste material is valuable in terms of performance and/or the environment, specific combinations such as WMA + RAP, WMA + CRM, RAP + CRM, and WMA + CRM + RAP lead to further benefits. Notably, these combinations suffer from a lack of comprehensive economic analysis, thus, their sustainability cannot be fully assessed and is prone to future studies.