Utilization of fluidized-bed co-combustion bottom ash in replacing natural fine aggregates in concrete production

Abstract

The utilization of ashes from the energy production, incineration of various wastes and from other industries, has been studied for a long time. Bottom ash (BA) is the residue left at the bottom of the combustion chamber and, while it does contain harmful elements, it is generally less hazardous compared to fly ash and air pollution control residues. For this reason, it is already used in many applications such as road construction. The goal of this pilot-based study was to find out whether bottom ash from co-combustion of recovered solid fuel (SRF) and wood would be suitable in replacing raw materials in concrete production and construction. Co-combustion bottom ash (CCBA), derived from wood and SRF, was used as a replacement for fine aggregate in concrete production. Three series of concrete specimens were prepared based on the bottom ash content. The control specimens consisted of 100% natural sand, the second series replaced 50% of the natural sand with CCBA, and the final series used 100% CCBA as a replacement for natural sand. All the specimens were tested in both, laboratory and accredited facilities, to assess key properties influencing the potential utilization of CCBA. Fresh, hardened, and microstructural properties of the concrete samples were analysed, including slump, compressive strength, density, water absorption, porosity, and microstructure through Scanning Electron Microscopy (SEM). Study results suggested that the inclusion of bottom ash slightly reduced consistence, with a 13,9% decrease in slump observed when replacing 100% natural sand with bottom ash. However, a slight increase in compressive strength was noted with bottom ash inclusion, highlighting its potential for structural applications despite the trade-offs in workability.