Impacts of low-quantity injected carbon on ash usability in concrete are inconsistent.

Activated carbon injection at low rates did not cause ash to fail the foam index and strength test (that is, the ash could be sold to a ready-mix concrete plant), but one non-carbon sorbent did fail the strength test.

Ash samples were obtained from the baghouse hopper during parametric sorbent injection testing at a plant firing Powder River Basin (PRB) coal and equipped with a baghouse. Ash samples were tested by an ash marketer, Lafarge, for the impact of activated carbon injection on the foam and strength activity indices. The preliminary results show that some of the activated carbon did not appear to affect these two ash use indicators when injected at levels <0.75 lb/Macf. However, a non-carbon sorbent appeared to impact the strength activity index significantly (injected at 5 lb/Macf). This finding was unexpected because the absence of carbon led to the assumption that the sorbent was “concrete friendly.” Data on mercury removal are still being analyzed. The eventual results will be important in understanding the limits of acceptability of sorbents present in fly ash for concrete and other applications, as well as the extent of mercury control feasible within these limits. For more information, contact Ramsay Chang at 650.855.2535 (rchang@epri.com).