PORE STRUCTURES OF FLY ASHES ACTIVATED BY CA(OH)(2) AND CASO4-CENTER-DOT-2H(2)O

The nature of the pore structure which develops when low-lime fly ash reacts with Ca(OH)(2) and CaSO4.2H(2)O under hydrothermal treatment has been investigated. The nitrogen adsorption-desorption isotherms of hydrothermally treated samples of fly ash and activated fly ash were analyzed. X-ray diffractometry was used to characterize the hydration products and SEM was used to analyze microstructure. The shapes and sizes of the hysteresis loops of isotherms and the pore size distribution data indicated that the pore structures of samples were comprised primarily of wedge-shaped pores with open ends. The surface area obtained when fly ash reacted with Ca(OH)(2) under hydrothermal treatment at 100 degrees C was 33.4 m(2)/g, while that of untreated fly ash was only 1.3 m(2)/g. The surface area of fly ash after reaction with CaSO4.2H(2)O was 2.9 m(2)/g. For fly ash reacted with Ca(OH)(2), the volumes of the pores with radii of 19 Angstrom increased with increasing temperature of thermal treatment. Depending on the temperature, calcium silicate hydrate, calcite and anhydrite formed. Because the pozzolanic reaction produces calcium silicate hydrate with a very large surface area, it controls the pore structures in which fly ash is activated by Ca(OH)(2). Therefore, a realistic assessment of the pore structure of activated fly ash is needed to understand those important physical and mechanical properties of concrete.