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 ha s been investigated. The nitrogen adsorption-desorption isotherms of h ydrothermally treated samples of fly ash and activated fly ash were an alyzed. X-ray diffractometry was used to characterize the hydration pr oducts and SEM was used to analyze microstructure. The shapes and size s of the hysteresis loops of isotherms and the pore size distribution data indicated that the pore structures of samples were comprised prim arily of wedge-shaped pores with open ends. The surface area obtained when fly ash reacted with Ca(OH)(2) under hydrothermal treatment at 10 0 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 temperat ure of thermal treatment. Depending on the temperature, calcium silica te hydrate, calcite and anhydrite formed. Because the pozzolanic react ion 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 activ ated fly ash is needed to understand those important physical and mech anical properties of concrete.