As second part of an extensive study on the relation of co-combustion of biomass and fly ash quality, cocombustion fly ashes were investigated from full-scale co-combustion experiments in the Netherlands using agricultural biomass, meat and bone meal, paper sludge and municipal sewage sludge as secondary fuel. The fly ash was investigated in relation to its performance for use in concrete. It was shown that the quality of co-combustion fly ash can be explained from the characteristics of the fuel and the combustion process. Further, it was shown that also fly ash obtained from high co-combustion percentages is able to meet the basic requirements of the European standard for fly ash in concrete (EN 450). Whether an individual co-combustion fly ash does so, depends on the nature of the co-fired fuel and especially on the amount and nature of its inorganic matter. (C) 2014 Elsevier B.V. All rights reserved.