In the present work, the feasibility of Greek lignite fly ash recycling in clay bricks production is examined. Large quantities of fly ash are the solid waste of lignite burning in power stations in Northern Greece due to local lignite high ash content. On the other hand, a considerable amount of fired clay bricks is manufactured in the country. Thus, the utilization of this low price and largely available industrial by-product in bricks production constitutes a challenge with apparent technological, environmental and economical importance. For that purpose, a laboratory pilot-plant simulation of the industrial brick fabrication processes was applied. Different clays from Central Greece were selected and characterized, and then various clay-ash mixtures were prepared. Plasticity after mixing with water was measured and extrusion of compact specimens and their drying behaviour were evaluated. The firing temperature was selected taking into account energy saving demands. Apparent density, shrinkage, water absorptivity as well as mechanical strength were determined on fired specimens and studied in relationship with the % fly ash content. The results are encouraging showing that the incorporation of low % amounts of fly ash in bricks is possible without significantly deteriorating the mechanical performance, while porosity progressively increases, which could be of importance in terms of heat insulating behavior. Besides, any possible detrimental effects on the other properties of the bricks appear relatively restricted and tolerable. The role of several intrinsic characteristics of this ash on the bricks elaboration, including its elevated Ca content, its particle size distribution, and a certain degree of inhomogeneity, given a composition variation of lignites, was also investigated.

Keywords:Recycling, fly ash, brick, clay, lignite, physical properties, mechanical properties