Comparison between the properties of building materials manufactured from bottom ash and fly ash part i. materials and procedures

Bottom ash resulting from combustion of low-quality lignite in Romanian coal-fired power plants contains significant amounts of unburned carbon. This large value is caused by many factors, such as the high humidity value of the raw coal delivered to the plant, advanced wear of the coal mills and large variability of the coal quality. As the unburned carbon reduces significantly the economic efficiency of the power generation, solutions to improve the process were investigated. Within the CHARPHITE project we propose a recycling process of coal ash for obtaining a carbon concentrate that can be used as raw material for graphitization procedure. Various secondary waste materials result from separation and concentration phases of the recycling process. We point out the possibilities to use the by-products with very low carbon content as substitutes for natural aggregates in ceramic bonded construction materials. We tested two kind of coal ash: bottom ash collected from a Romanian power plant and fly ash collected from a Portuguese power plant. In the first part of the paper we present the coal ash characteristics and the methods used to determine them.