Economic consideration
Classified fly ash with high fineness is suitable to use as
a cement replacement in concrete [3–7]. However, the
coarse fly ash residue from the classifying process has to
be disposed mostly to a landfill, which is expensive and is a
major threat to the environment. The grinding of coarse fly
ash to obtain a high fineness can improve the pozzolanic
activity and can be used as a cement replacement.
Silica fume has widely been used to produce highstrength
concrete. However, in Thailand, silica fume is
imported and expensive. Its cost is about 10 times higher
than Portland cement type I and much more expensive than
fly ash. Each year, more than 3.5 million tons of fly ash are
produced in Thailand and the amount is increasing every
year. Moreover, more than 70% of fly ash has been disposed
to landfill. Since the fly ash used in high-strength concrete
must have high fineness, the major cost of the fly ash or
FAG depends on the process of reducing its particle size to
an effective size. The cost of Mae Moh fly ash is very cheap
and is about US$1.6 /ton. In this study, the cost of FAG with
grinding, classifying, and transportation, except for the
grinding machine, is much cheaper than imported condensed
silica fumes. According to the study [15], the use
of FAG in producing high-strength concrete is cheaper than
condensed silica fume by about 13–55% depending on the
amount of FAG replacement to Portland cement type I.