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).
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