Effect of powdered activated carbon on the air void characteristics of concrete containing fly ash

One of the common methods to reduce mercury vapor emissions from coal-fired power plants involves the injection of powdered activated carbon (PAC) into the flue gases to adsorb the mercury vapor. If the PAC then settles along with the fly ash in the electrostatic precipitator, the ability to use the collected fly ash as a supplementary cementitious admixture in concrete must be established. This study examined the influence of PAC in fly ash on the air void networks and consequent properties of concrete produced with an air entraining admixture. Samples included those with PAC added to the fly ash at the laboratory as well as PAC-containing fly ash collected at a generating station. The air void content, specific surface area and spacing factor of hardened concrete were determined using an image analysis technique on epoxy-impregnated and ink-prepared samples. The PAC-containing fly ash had an insignificant effect on the air void content and spacing factor compared to samples with laboratory-added PAC. Image analysis using ink-prepared samples provided improved reliability of the air void network results compared to epoxy-prepared samples.