The substitution of fly ash for cement in concrete is one of America's biggest by-product usage successes. Unfortunately, however, if even a small amount of powdered activated carbon (PAC) is injected into power plant flue gases for mercury emission control, the resulting fly ash has been found to be unusable in concrete. The PAC adsorbs the air entraining admixtures (AEAs) which are added to the concrete mix to create the proper amount of air bubbles which are needed to impart workability and freeze/thaw capabilities. Consequently, upcoming mercury emission standards could threaten the market for fly ash use in concrete. Over the past few years, Sorbent Technologies Corporation researchers have developed a brominated carbon-based mercury sorbent (B-PAC) with superior cost-effectiveness in power plant use. More recently, they discovered a processing method which allows the sorbents to retain high adsorption effectiveness for mercury, yet not interfere with AEAs in concrete slurries. Concretes made with fly ash incorporating representative amounts of the mercury sorbents appear to entrain the same the amount of air and to have the same strength as control samples without any sorbents. This "concrete-friendly" version of B-PAC offers important promise for use by power plants which can sell their fly ash for concrete use.
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