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.

Utilisation of bottom ash in road construction: a lysimeter study.

The incineration of municipal solid waste (MSW) results in the annual production of 2.7 million tons of bottom ash in France. Utilisation of bottom ash in road construction is encouraged in France but strictly regulated. Because the incinerator residues contain enriched concentrations of metals and salts, particular attention must be focused on the potential environmental problems. In the present study, a laboratory tool (lysimeter) has been developed to reproduce the conditions of bottom ash utilisation and to study their environmental impact via the percolates collected at the bottom of the lysimeter. Four lysimeter experiments were conducted in order to study reproducibility, as well as the influence of water flow rate and pressure on the composition of the percolates. The lysimeter experiments have been then compared with the utilisation of bottom ash under real conditions (two experimental road sections). The comparison of results of lysimeter test and those measured after performing the French standard leach test (AFNOR NF X31-210) shows a recovery of 89% for the chlorides and between 30 and 35% for the sulfates. This indicates that almost all chlorides have been dissolved, contrary to the sulfates, which are less soluble.