Influence of Powdered Activated Carbon (PAC) in Fly Ash on Alkali-Silica Reactivity and Scaling Resistance of Concrete

Injection of powder activated carbon (PAC) into the flue gases is one of the useful absorption-based techniques to lower the emission of mercury vapor released from coal-fired power plants. This PAC then settles in the electrostatic precipitator along with the fly ash, which has been used as a supplementary cementitious material in the concrete industry for years. Currently, contractors routinely use class C fly ash (CFA) as a partial replacement of ordinary Portland cement that may have an adverse effect on the long-term durability of concrete for containing PAC. The objective of this study is to examine the influence of PAC in CFA on the alkali-silica reactivity (ASR) and scaling resistance of concrete. This study will also propose an optimum amount of PAC to be used in mitigating the effect caused by ASR and scaling of concrete. To this end, test samples were produced with PAC (0%, 0.25%, 0.50%, and 0.75% by weight of CFA) in the laboratory to the CFA obtained from two different sources. The results of the ASR tests had been analyzed based on the expansion rate with time. The concrete mix with a higher amount of PAC (0.75% by weight of CFA) showed more ASR expansion than the mix with no PAC. In addition to that, on the 20th day, all the samples exhibited a 20%-60% reduced expansion than the non-PAC and non-CFA concrete mix. On the other hand, the visual inspection of the scaling resistance tested samples suggested that the PAC-containing fly ash had no impact on the scaling resistance of concrete.