Use of Municipal Solid Waste Bottom Ashes in Rubberized Asphalt Mixtures

The increasing need of environment protection and preservation has been stimulating road agencies to progressively adopt sustainable technologies for the design, construction, and maintenance of their assets, with the consequent increasing use of recycled materials, industrial by-products, and wastes. In such a context, the experimental investigation presented in this paper moved from the idea of synergistically combining the use of bottom ashes originating from incineration of municipal solid waste (MSW) and crumb rubber from end-of-life tires. The performance-related properties of rubberized asphalt mixtures containing MSW bottom ashes in partial substitution of natural aggregates were evaluated by means of laboratory tests focused on the determination of workability, viscoelastic characteristics, antirutting potential, and resistance to crack propagation. Tests were carried out by considering an ash-amended rubberized asphalt mixture and, for comparison purposes, a standard gap-graded rubberized mixture (GGRM). Obtained results indicate that the rubberized mixture containing bottom ashes exhibited lower workability (16 % decrease in k parameter), reduced stiffness (decrease of dynamic modulus at 20°C of approximately 40 % and 60 % at 0.1 Hz and 10 Hz, respectively), and decreased anti-rutting potential (17 % decrease in flow number values) with respect to the standard GGRM. Conversely, the addition of bottom ashes was found to provide beneficial effects in terms of resistance to crack propagation (with fracture toughness values five times larger than those of the reference mixture). These outcomes suggest that the use of MSW bottom ashes must be carefully considered because environmental benefits may be counterbalanced by lower performance.