Municipal solid waste incinerator (MSWI) concrete

The potential to use municipal waste incineration products in concrete has been examined over many years, both as a source of aggregates and as supplementary cementitious materials (SCM). With an understanding of the chemical evolution of these materials in the cement environment, both applications provide routes to the re-use of these materials in construction. Fly ashes and air pollution control residues must be washed to remove their considerable chloride content before use, after which, the remaining solids (largely aluminosilicates) may replace some fraction of the cementitious binder. Care must be taken when using these materials as SCMs, as volatile heavy metals present in the original waste may be concentrated in the fly ash. The bottom ashes from municipal solid waste (MSW) incineration also show sufficient pozzolanic reactivity when finely ground, to replace some cement in the binder phase. They may also serve directly as aggregate in concrete, although the irregular and angular particle shape may reduce its workability somewhat. Most MSW bottom ashes contain sufficient free aluminium to disrupt the setting reactions of the binder through hydrolysis reactions at high pH. Consequently, this must be removed or reacted by pre- treatment, prior to use in concrete and means of doing so are described here. Slower detrimental reactions are also known, such as alkali silca reaction, especially of container-glass fragments and these are considered here. Lastly, the use of MSW incineration products in manufactured aggregates is described, comparing sintering, melting and recrystallization, and plasma processing, with low temperature methods such as rapid carbonation technology