Alkali activation processes for incinerator residues management

• Incinerator bottom ash can substitute in high percentage metakaolin for producing geopolymers.
• Standard alkali activation at room temperature was successfully attained.
• The amount of reactive aluminosilicate phase is important for geopolymers formulation.
• Incinerator bottom ash can be a resource for saving conventional raw materials and energy.

Incinerator bottom ash (BA) is produced in large amount worldwide and in Italy, where 5.1 millions tons of municipal solid residues have been incinerated in 2010, corresponding to 1.2–1.5 millions tons of produced bottom ash. This residue has been used in the present study for producing dense geopolymers containing high percentage (50–70 wt%) of ash. The amount of potentially reactive aluminosilicate fraction in the ash has been determined by means of test in NaOH. The final properties of geopolymers prepared with or without taking into account this reactive fraction have been compared. The results showed that due to the presence of both amorphous and crystalline fractions with a different degree of reactivity, the incinerator BA geopolymers exhibit significant differences in terms of Si/Al ratio and microstructure when reactive fraction is considered.