Research on potential cementitious reactivity and immobilisation effect by Portland cement on MSW fly ash

Incinerator fly ash is the material collected by the scrubber after incineration of municipal solid wastes (MSW). By composition it belongs to the CaO−SiO₂−Al₂O₃−Fe₂O₃system, and it is similar to the slag and fly ash from electricity generating stations that is usually used. It may contain water-leachable heavy metals and so it is regarded as hazardous and must be immobilised/stabilised. The physical properties of fly ash were studied experimentally and its influence on the mechanical properties of the hardened cement paste, the hydration mechanism when the fly ash was added to the cement system and the pollution from heavy metals within the fly ash were also investigated. The feasibility of using the fly ash derived from the incineration of MSW as supplementary cementitious material was explored. It was shown that the reactivity of fly ash was lower and the addition of fly ash to cement may lead to retardation of cement hydration and, furthermore, that ettringite can be formed during the hydration process, which is beneficial for strength development. It was also shown that the immobilisation effect of cement on this fly ash is good and that heavy metals can be immobilised within the structure of the hydration phases through addition, substitution or sorption mechanisms.