Effects of a washing pre-treatment of municipal solid waste incineration fly ash on the hydration behaviour and properties of ash–Portland cement mixtures

The effects of a washing pre-treatment of municipal solid waste incineration (MSWI) fly ash with deionised water on both the physico-chemical characteristics of this material and the hydration behaviour and physical properties of ash—Portland cement mixtures rich in MSWI fly ash (55 wt% of total solids) were investigated in view of a possible reuse of such solidified products as concrete aggregates in the building industry. A four-stage washing pre-treatment was found to be able to convert the raw MSWI fly ash into a material with improved chemical characteristics for its incorporation into cementitious matrices (reduced concentrations of alkali chlorides and sulphates, transformation of metallic species in less reactive forms). As a result, the cementitious mixtures incorporating washed fly ash in place of raw fly ash were found to exhibit better performance characteristics in terms of setting, dimensional stability, compressive strength and environmental quality.