Ageing and screening as strategies to increase the quality of manufactured aggregate from fluidized bed incinerator bottom ash for utilization in concrete

Abstract

Since 2023 the mineral fraction from incineration bottom ash (IBA) can be utilized as manufactured aggregate (MAG) to partially substitute natural aggregate in concrete in Austria. The Bundesabfallwirtschaftsplan (BAWP) is the corresponding regulation that states the legal limits in leachate and the total content of a range of heavy metals as well as chloride and sulfate limits in the leachate [1]. Concerning the underlying research, the focus lies on the content of water-leachable chloride and sulfate. The investigation targeted how far the legal limits can be met after a wet IBA treatment process and what measures can be applied to decrease the concentrations. A low concentration of both parameters is feasible to meet regulations and minimize the risk of damage in the concrete due to chemical reactions like corrosion or sulfate attack. The materials for examination, two manufactured aggregates from an IBA treatment plant located in Lower Austria, that operates a wet treatment process, were directly sampled from the conveyor belt drop. The manufactured aggregates originated from two different IBAs, each from a fluidized bed (FB) incinerator for municipal solid waste. Ageing for 12 weeks and screening (wet and dry) of the aged material were conducted. It is observable that the combination of ageing and screening is a successful way to decrease the concentration of water-soluble chloride and sulfate below the legal threshold limit and therefore to generate a manufactured aggregate that can be used in concrete from a legal point of view. Nonetheless, the technical applicability of such manufactured aggregate for its use in concrete must be further investigated in detail before it's utilization can be promoted.