Fly ash is the finely
divided mineral residue resulting from the combustion of powdered coal
in electric generating plants. It is also called pulverized fuel ash.
Fly ash consists of inorganic, incombustible matter present in the coal
that has been fused during combustion into a glassy, amorphous
The implementation of technologies in order to comply with the Clean
Air Act has led to the deterioration in quality of fly ash
specification provides both chemical and
physical requirements that fly ash must meet before it is allowed to be
used in concrete, the largest market area for Coal Combustion Products
The Loss on Ignition (LOI) of flyash is an important quality when
considering utilization. The LOI is primarily due to the presence of
unburned carbon. The standard specifications for the use of flyash as a
mineral admixture in Portland cement concrete are given in ASTM
C618-89a. which sets an LOI limit of 6%; however, many states have set a
more stringent limit of 3%.
Carbon levels in fly ash impact the
ability to entrain air in concrete.
There are several emerging
technologies that upon implementation will result in a Utilities
compliance with required emission standards but will not require
In order to regain a market for high LOI
flyash, an effective means of removing carbon must be developed. Air
classification is one process that has shown significant potential