Feasibility Study of One-Part Alkali Activated Material with MSWI Fly Ash

Abstract

With the growing population, it is also expected that the municipal solid waste (MSW) generation would be increasing in the coming years. Management of MSW is already an identified issue and the incineration process is widely adopted as a disposal solution for non-compostable wastes. Incineration of MSW results in secondary waste residues such as almost 20% of fly ash and 80% of bottom ash. These are rich in silica and alumina content, naturally has the potential to be an aluminosilicate precursor to produce alkali-activated materials. Several issues are pointed out for the application of MSWI residues as cementing materials, either a Supplementary Cement Material (SCM) or an Alkali-Activated Material (AAM). One such issue concerning AAM application is the presence of metallic aluminium. Heavy metals from the MSWI residues are normally extracted before disposal, however metallic aluminium is not effectively removed in most of the cases. Metallic aluminium acts as a pore-forming agent by generating H₂ gas in the alkali environment, thereby reducing the strength properties. In the present study, an attempt is made to understand the influence of the metallic aluminium present in the MSWI fly ash of different size fractions, fine (0–0.5 mm) and coarse (0.5–1.0 mm). MSWI fly ash is activated with solid/liquid alkalis, such as sodium hydroxide (NaOH), sodium silicate (Na₂SiO₃) and combination of both. With the Na₂O content maintained constant across the activators, the sample activated with NaOH is the weakest and the one with sodium silicate is the strongest with small, well-distributed pore structure, irrespective of the size fraction of MSWI fly ash used. Solid activator performed equally well as that of the liquid one.