Air void system in concrete containing circulating fluidized bed combustion fly ash

The increased use of advanced coal-burning technologies for power generation, such as circulating fluidized bed combustion (CFBC), results in new waste products. The potential for using CFBC fly ash in air-entrained concrete was investigated in order to assess the influence of CFBC fly ash on the microstructure of air voids in hardened concrete. A special specimen surface preparation technique for contrasting the image and enabling measurements of air voids size and distribution using an automated image analysis procedure was used. The microstructure of air voids was evaluated on the basis of the total air content, the spacing factor, and the specific surface of air voids. It was found that a satisfactory air void system in concrete could be produced when using CFBC fly ash for partial replacement of cement. The air-void system was characterized by a decreased specific surface of voids and an increased spacing factor.