The reuse of solid residues from mass-burning and fluidized-bed reactors for concrete production

The present work concerns the evaluation of MSWI solid residues reuse as partial replacement of natural aggregates for concrete production. The residues studied are: bottom ash derived from two mass-burning kilns (MB(A) and MB(B)) that treat MSW; exhausted sand and bottom ash derived from a fluidized-bed incinerator (FB(C)) that receive MSW-derived solid recovered fuel (SRF). The bottom ash derived from MB(A) were pre-treated by means sieving and iron removal processes; moreover, additional washing was applied. Sieving and iron removal processes with a subsequent ageing (for two months) were performed on the bottom ash derived from MB(B). Natural aggregate was partially replaced (with a weight percentage from 7% to 40%) with different residues for the production of some concrete mixtures, casted adopting different types or dosages of residues and two different type of cement. Regarding the mechanical characterization of concrete mixtures, the use of 400 kg/m3 (corresponding to 23% of natural aggregate replacement) of bottom ash from fluidized-bed reactor (with the use of CEM42.5R) showed the best results: in this case concrete mixtures could be classified in concrete class C16/20, suitable for structural elements made of reinforced concrete. The results of the leaching test showed that only the washed bottom ash from the mass-burning kiln could be reused following the simplified procedures according to Ministerial Decree 186/2006. For the exhausted sand derived from the fluidized-bed incinerator, the release of some pollutants (especially chromium and arsenic) was higher than the other residues. As concerns the leaching behaviour, concrete mixtures containing the residues derived from fluidized-bed reactor showed a release of pollutants higher than the other mixtures.