Use of foamed bitumen in cold recycling: mechanical characterization of materials

The use of recycling in the construction of road pavements in Italy dates back to the end of the 1970s when, due to the first big oil crisis, new working methods that could limit the use of oil and its derivatives were experimented. Among them, the technique of in-situ recycling was set up, developed in a “hot” procedure and a “cold” one. The “cold in-situ recycling” utilises a convoy of recycling, which mills the old pavement, mixes the material with the new binder, water, additives and any new aggregate, lays the pavement layers, levels and compacts. In-situ recycling offers several advantages over off-site recycling: saving in construction times of the road infrastructure; less material to be moved (and related costs); quality of the end product. Cold recycling is particularly profitable from an economic and environmental point of view: it assures a reduction in pollutant emission into the atmosphere, but also an energy saving due to not having to heat the aggregate. The paper describes a study on the mechanical properties of mixtures obtained from cold recycling with the use of foamed bitumen and cement. Different mixtures were analysed for sub-bases, road bases and base courses. All the materials were tested using traditional protocols, but their mechanical properties were also checked by dynamic procedures. Finally a design method was arranged on the basis of a catalogue for pavements, in order to propose constructive solutions compatible with the use of cold recycled materials.