Urban mining for asphalt pavements: A review

The increasing consumption of natural resources for road construction and generation of urban waste
materials are two global ecological problems. Urban mining aims to convert waste materials into raw
materials for industrial production, and as a result, address both problems simultaneously. This study
explores the potential of urban mining for asphalt pavement surface courses. In the first part, as each
country/region has its unique challenge with waste materials, a screening method taking the EU and
Switzerland as case studies is employed to select waste materials that potentially qualify for asphalt
surface courses. The second part presents a review of laboratory studies regarding the performance of
asphalt mixtures with selected waste materials. Based on the industrial experience, the third part dis-
cusses the technology, specifications and cost considerations of asphalt surface courses with waste
materials. Furthermore, the technical maturities for using waste materials are estimated in terms of
technology readiness level (TRL). Overall, the paper demonstrates that various categories of waste ma-
terials can be potentially used in asphalt surface courses, revealing urban mining opportunities. The
selected waste materials may improve the performance of asphalt mixtures with optimization of several
factors, such as the fraction size and amounts of waste materials for addition or replacement. The TRL
results showed that using crumb rubber (wet process) and steel slag are currently more mature than
using other waste materials in asphalt surface course.