Abstract

The possibility to use the various size fractions of fly ashes in cement technology is analysed. Fly ashes are produced in the three hoppers in electrostatic precipitator system. Two size fractions of fly ashes have been analyzed: 0 ÷ 16 µm and 16 ÷ 32 µm and the following properties of cement have been tested: heat released during hydration process, Ca(OH)2 content, hydration degree of alite as well as setting time, compressive strength, microstructure and sulphate resistance. The most beneficial influence was determined for cements with fraction 0 ÷ 16 µm of fly ashes from the 3rd hopper. With these fly ashes high class Portland cement (52.5 according to PN-EN 197-1) and high class pozzolanic cement (42.5 according to PN-EN 197-1) may be obtained. After 2 years of storage in sulphate solution, the linear expansion of mortar containing 40% of these fly ashes was twenty times lower than that found in control cement mortar; the compressive strength reached 88.5 MPa.