Asphalt concrete with bottom ash: environmental aspects

As a consequence of the recent scientific knowledge and industrial technologies the use of some recycled materials in construction applications is growing. According to recent studies use of bottom ash coming from Hospital and Municipal Solid Waste Incinerator (HSWI, MSWI bottom ash) is suitable as aggregate in road construction in place of natural stones. The advantages connected to this innovation are well known, but doubts about environmental aspects haven’t been absolutely solved yet. The environmental impact of asphalt concrete with bottom ash has been studied carrying out leaching tests on laboratory specimens according to the Italian law (DM 5/02/1998). Results showed that asphalt concrete containing waste material has the same leachability of the traditional mixes and the concentrations of pollutant elements are within limits set by national rule. Nevertheless, a global evaluation of this secondary materials for re-use andrecycling in asphalt concrete is based on its life-cycle. The critical phase is when the pavement has to be stripped for pavement maintenance operations. Reclaimed Asphalt Pavement (RAP) is an unbound and incoherent material; therefore each aggregate grain is not completely covered by bitumen and so leachability of pollutant substances can be high. On the contrary there are not environmental risks when RAP is reused to produce hot or cold asphalt concrete In this paper, the authors present results of leaching test performed on asphalt concrete containing HSWI bottom ash. This research confirmed use of bottom ash coming from Hospital and Municipal Solid Waste Incinerator as aggregate in asphalt concrete is suitable and environmentally safe. It is not necessary any change in the construction and maintenance operations at the end of its working life.