Half-warm mix asphalt with emulsion. An experimental study on workability and mechanical performances

One of the major sustainability-related challenge facing materials for asphalt pavements is the energy consumption and the release of harmful and odorous fumes. Reductions in these emission levels have been progressively achieved by a number of cleaner and low-temperature technologies. Recently, a further step towards an improved road pavement sustainability is represented by the half-warm mix asphalt (HWMA) mixtures, which are produced between 70 °C and 100 °C without negatively affecting their final performances. Among these methodological approaches, a very interesting solution for urban or low volume traffic roads is represented by HWMA mixtures prepared with a conventional warm emulsion and heated aggregates. Although this technique is capable of combining the advantages of hot and cold mixes, limiting some drawbacks, it is still little known and remains confined only to some regional areas (in Spain with the term mezclas templadas). There are no standards or specifications, but only some construction practices resulting from the experience gained in the field. Thus, a laboratory-scale experimental study was set up to analyze in detail the behavior of dense-graded HWMA mixes prepared with emulsion intended for a surface course layer of a low or medium traffic road. The objective was to evaluate the influence of three mix-design variables, such as compaction temperature, binder content and aggregate gradation on the volumetric and mechanical, i.e. indirect tensile strength and moisture susceptibility, properties of these mixtures. The rank comparison between the selected mixtures represented the starting point for improving on the one hand the mix-design process and on the other the operational procedures of production, transportation and placement.