APC fly ash recycling: development of a granular material from laboratory to a pilot scale

Abstract

The aim of this article is to present the research carried out over a 10 year period to develop an environmentally safe method for recycling Air Pollution Control (APC) residues. The initial studies aimed to formulate a mixture of Weathered Bottom Ash (WBA), APC residues and Portland Cement (PC) to be used as a sub-base in road constructions. Mechanical performance was subsequently enhanced by preparing a mortar prior to mixing it with WBA in order to obtain a granular material. After testing different formulations, the optimum mortar consisted of 50% APC residues and 50% PC. The evaluation was carried out based on the concentration release of the heavy metals and metalloids included in the Catalan legislation for revalorization of residues. After the applicability of the granular material was successfully demonstrated at laboratory scale from an environmental and mechanical point of view, a pilot scale plant was designed in order to assess its performance in a real scenario during four month. Thus, three roads were built: two containing 100% granular material and a third containing 100% WBA. The results showed that the immobilisation of all toxic species from APC residues is accomplished by the pozzolanic effect of the cement. The WBA, APC, and PC proportions show to be the most appropriate for compliance with regard to environmental and mechanics requirements.