Mix Design of Recycled Asphalt Concretes for Sustainable Rural Mobility: Bicycle and/or Pedestrian Routes

The ever-increasing demand for environmental sustainability in the production of bituminous asphalt concretes requires technical solutions to reduce pollutants emissions into the atmosphere and to reduce the consumption of natural raw materials, encouraging the recycling of secondary raw materials. This paper presents the results of a bituminous asphalt concrete mix design study to be used, in single layer and rural context, for construction of bicycle and/or pedestrian superstructures that are sustainable at the same time, in environmental and economic terms. In particular, Construction and Demolition Waste (CDW) recycled aggregates cold-bonded with bitumen emulsion were used. The first part of the study focused on the mix design of asphalt concretes made up exclusively of CDW aggregate and variable percentages of bitumen (6÷10%). The first results of mixes performance characterization (porosity, Marshall stability, indirect tensile stress, Cantabro index, etc.) showed quite modest results. To improve the mixtures performance, an addition of 2% by weight of artificial filler (pozzolanic cement) was provided. Laboratory performance characterization has made it possible to establish that these recycled asphalt concretes can be effectively used for the construction of bicycle and/or pedestrian superstructures, as well as for the environmentally sustainable construction of a secondary interconnecting road to serve the diffuse building of the territory in the suburban area. Since the obtained recycled asphalt concrete, by its nature, does not exhibit a good surface texture, in order to provide an aesthetically aspect and ensure the road surface regularity and durability, a surface finishing was experimented with a mixture of Portland cement and finely crushed glass that would provide the surface with a light color and a certain degree of refraction and reflectance. The research demonstrates that it is possible to achieve good results in terms of both reducing production costs and environmental impact, in the production of eco-sustainable asphalt concretes with “lower performance”, in absolute terms, but which are fully compatible with those required for cycling and/or pedestrian superstructures.