Preliminary screening of wood biomass ashes for partial resources replacements in cementitious materials

Abstract

Worldwide there is a significant increase in amounts of wood biomass ash (WBA), a waste from wood biomass combustion process. In this case study, 21 different sources of wood biomass ash (WBA), namely fly ash, bottom ash, and mixed ash from 10 different power plants in the Republic of Croatia were characterised based on their physical-chemical properties. Compared to the criteria listed for the use of coal fly ash in the concrete industry (EN 450), most WBAs exhibit higher loss of ignition values, high CaO and MgO contents, and higher total alkali and sulfur content. The results show a higher amount of alkalies and heavy metals in fly ash (WBA-F) as compared to bottom ash (WBA-B), but also their potential stabilisation in glassy phases. Based on WBA characterisation results, collected WBAs were benchmarked and categorised for three different resource replacements in production of cement and concrete: 1) partial replacement of a raw material for clinker production; 2) partial cement replacement as a mineral admixture in cementitious composites, and 3) partial replacement of aggregates used for concrete production. For this a new method for WBAs quality-ranking ordering is proposed, based on a normalisation approach relative to some quality criteria. The proposed preliminary screening methodology enables to address an important technological challenge in high variability in quality parameters of WBAs originating from many different sources. It will help engineers in selecting from the huge number of available WBAs types the most suitable ones, on which further valorisation laboratory tests can be better planned.