Mechanical and leaching characterisation of impact-absorbing rubberised asphalts for urban pavements

A new impact-absorbing material is being developed to protect vulnerable road users in urban areas and has been produced and tested, mechanically and environmentally in the laboratory. The main constituent of this innovative material is the rubber recycled from end-of-life tyres to foster a circular use of resources and exploit rubber’s elastic properties. The study aims to provide a complete Uniaxial Compression Test (UCT) and leaching analysis of the material to propose and optimise a mix that is mechanically sound, durable, and respectful of the environment, in view of in-situ applications. Therefore, the UCT and Dynamic Surface Leaching Test (DSLT) were carried out on rubberised asphalt specimens with different mix designs. The 64 days cumulative concentrations of leached heavy metals and trace elements from unit surface of specimens were calculated and quantified, according to the CEN/TS 16637 standard. In parallel, thanks to a specific mechanical characterisation, compressive stress–strain curves were obtained, and the relaxation and elastic modulus were evaluated. The results from the compression tests showed that the A-mixes have the best elastic and absorbing behaviour, especially those made with an SBS-modified bituminous emulsion (A4). The results from DSLT showed that the cumulative concentration of released elements, per unit surface of specimens were lower than the Dutch Soil Quality Decree (SQD) thresholds, taken as a reference. The low and early release of leachant observed for the mixtures, especially A4 as the most promising one, leave the possibility to handle the leaching with several solutions, including rubber coating treatment or water washing before their incorporation into the mix to limit and prevent their leaching while permitting very high injury reduction performances.