Application of fly ash as an admixture into concrete causes some well known unwilling effects as a retardation of strength development, higher rate of water permeability or gas permeability i.e. higher speed of carbonisation. Relatively new technology of treatment of raw fly ash is so called sorting or classification i.e. modification of fly ash particle size distribution. Result of experimental study that compared influence of classified (sorted) or common raw fly ash on properties of tested concrete mixtures will be presented in article. Two types of raw fly ashes and one type of classified fly ash were studied.