INFLUENCE OF SILICEOUS FLY ASH VARIABLE QUALITY ON THE PROPERTIES OF CEMENT-FLY ASH COMPOSITES

22 siliceous fly ash samples from different power stations were investigated and their changeable quality was confirmed. Two of them were collected from the electrostatic precipitator single sections; third and second. These two samples had the highest fineness and the best pozzolanic activity and gave the high diminution of water demand of blended cement paste and good strength of mortars. The quality of the remaining fly ash samples was very differentiated, principally the residue on 0.045 mm sieve and coal content were very changeable. The coarse fly ash had higher loss of ignition = coal content and disadvantageous influence on water demand of blended cement paste, as well as on mortars strength. From the experimental results it can be concluded that the residue on 0.045 mm sieve and loss of ignition are two mane parameters permitting the siliceous fly ash quality evaluation.