Utilisation of bottom ash in road construction: evaluation of the environmental impact

France incinerates about 40% of its municipal solid waste (MSW), producing 2.7 million tons of bottom ash annually. Utilisation of bottom ash (BA) is encouraged in France but strictly regulated. Only bottom ash meeting specific criteria and produced in accordance with a quality assurance plan can be used in roadbeds and embankments. In order to evaluate the environmental impact of BA used in road construction under real conditions, two road sections were built: one containing a sub-layer of BA and the other, constructed using only natural gravel to serve as a reference. Water percolating through each roadbed was collected and sampled periodically over three years. Analysis of the samples shows minimal leaching of pollutants from BA. The results are encouraging and indicate that BA utilisation can be safe and can have an environmental impact no greater than that of natural materials.