Use of residues from the incineration of domestic wastes and other residual matters mixed with cement in road construction

The incineration of household refuse in the Federal Republic of Germany yields up to about 3.5 million tonnes of residual waste per year. About 90% of this consists of grate ash and about 10% of fly-ash, the latter mostly being collected in electrostatic precipitators. The grate ash consists chiefly of sintered combustion residues of different particle sizes. In its properties. this ash resembles natural mineral mixtures, but is generally less strong and often has lower frost resistance. For this reason and because in some cases it contains fly-ash with a high content of harmful matter, chis ash can only tentatively be used in nonstabilized sub-bases and in other road constructional work. The unutilized remainder, as well as the fly-ash containing harmful matter, has to be dumped ondisposal tips, at considerable expense. Preliminary investigations conducted by the Research Institute of the Cement Industry in Germany suggest that the refuse incineration residue (grate ash with and without fly-ash) can be utilized to a much greater extent if it is bound with cement and used, for example, as a road sub-base construction material. With the correct technological procedure, the harmful properties of the grate ash incorporated in concrete and in cement-bound sub-base mixes do not produce any long-term adverse effects. With cement as the binder, the leaching of the harmful substances from the flyash can notably be lessened. By using grate ash in cement-bound sub-bases, the demands upon natural raw material resources are eased and the land areas and cost entailed by disposal dumping are reduced. Extensive favourable experience has also been gained with cement-bound sub-bases constructed with coal fly-ash in the Federal Republic of Germany. In some applications, concrete demolition rubble and asphalt waste stripped from old roads have been successfully utilized in cement-bound sub-bases.