Industrial utilization of fly ash from various kinds of fuel plays an important role in the environmentally clean and cost effective power generation. The primary market for fly ash utilization is as a pozzolanic addition in concrete production. The possibility of the utilization of these ashes as an active concrete addition is determined by their chemical and mineralogical composition. The paper concerns the concretes containing fly ash called Fly Ash from Biomass (FAB) from co-combustion of hard coal and wood biomass (wood chips). Characterization of the fly ash was carried on by means of X-ray diffractometry and E-SEM/EDS analysis. The results of laboratory studies undertaken in order to evaluate the influence of FAB on concrete resistan...