The high production temperatures (about 170°) of bituminous mixtures modified with traditional SBS polymers have as a consequence high energy consumption, which are accompanied sometimes by critical atmospheric emissions, with negative environmental impacts and consequent limitations in the use of the plants, especially near urban areas. Moreover, the use of RAP increases the level of emissions.
On the basis of these limitations, technologies are being developed to lower production temperatures (warm recycling) and the laying of bituminous mixtures.
The study is aimed at identifying the “warm” technology best suited to the production needs of the bituminous mixtures used on the Italian motorway network (use of polymer modified “hard” bitumens, open-graded mixtures) without compromising their performance, also with a view to increasing the RAP percentages currently used.
The next step after hot recycling, therefore, is the so-called “warm” bituminous mixtures also known as Warm Mix Asphalt (WMA), which can be a valid alternative to hot recycling practices for which there are technical problems associated with production with high quantities of milled material. In hot recycling, very high production temperatures are required in order to produce a mix that can be processed properly and with appropriate volumetric and performance properties. The production of warm bituminous mixtures (warm recycling) offers the possibility of overcoming these problems by lowering the working temperatures (mixing and compaction) without compromising the possibility of using high quantities of RAP. These technologies have only been introduced on the market in the last years and therefore not much data are available on the actual effectiveness of the products on the market, especially in the case of mixtures produced with modified bitumen. In order to be able to verify any critical issues related to the use of warm recycled mixes (warm recycling), both in operational and performance terms, a specific experimental task has been developed as part of the ERA project aimed at verifying the potential of bituminous mixtures, both dense- and open-graded, produced with WMA technology.