Incorporation of crushed asphalt as a circular economy strategy for de-sealed soil reclamation: case study in Prato, Italy

Sealing severely impairs soil ecosystem services. In addition to preventing further sealing and degradation, soil de-sealing is increasingly promoted as a compensatory strategy, especially in urban environments. However, its implementation is often limited by high costs and the need for imported topsoil. In this study, we evaluated the feasibility of reusing the crushed asphalt generated during de-sealing as a component of constructed urban soils as a circular economy strategy. A field experiment was conducted in Prato (Italy), in a newly de-sealed parking lot. After having verified that the in situ sealed soil was unsuitable for a prompt green recovery of the area, a transported urban soil amended with compost was mixed with increasing proportions of crushed asphalt (0, 10, 25, and 50% w/w). Over one year, we assessed soil physicochemical and biochemical properties, greenhouse gas fluxes, and vegetation establishment and diversity. Asphalt incorporation at the highest asphalt dose (50%) modified soil texture, increasing the sand fraction, reducing bulk density and lowering soil water availability. Soil chemical fertility showed limited and transient changes, with no persistent reductions in nutrient availability. Soil respiration, enzyme activities, and gas emissions were generally unaffected by asphalt addition. Finally, even the highest asphalt addition did not impair vegetation cover or biomass and species diversity, at least in the short-term monitoring period considered in this study. Although further research is needed to strengthen the evidence base on the effects of incorporating decommissioned asphalt into urban green spaces, these findings represent an encouraging step toward supporting the large-scale implementation of this practice, thereby promoting more widespread de-sealing practices in urban areas.