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High Volume Fly Ash Concrete (HVFA)
Fly ash, a by- product of coal fired power
plants can by used to replace Portland cement in the production
of concrete. Fly ash has many added benefits when used as a
replacement for Portland cement. Less energy is used in the
manufacturing process; it has a higher ultimate strength and is
more durable. It uses a waste product therefore less fly ash
ends up in the landfill. Less CO2 is created due to less
embodied energy being used in its manufacture.
6 to 7% of the CO2 generated by humans
comes from the production of Portland cement. The CO2 produced
by this process is equal to 330 million cars traveling 12,500
miles in a year. Concrete is comprised of between 10 to 15%
Portland cement by weight. It is the cement, that causes most of
the environmental impact of concrete. Cement contains lime and
silica, in its production it is kiln fired at 2700 f, using
large amounts of fossil fuel, which release many tons of CO2.
Also the chemical reaction which creates Portland cement
releases additional CO2. The lime and silica in Portland cement
must be mined and trucked to the production facility, using more
fossil fuel and thereby releasing more CO2 into the atmosphere.
The US Navy in studies using 30% HVFA
concrete, found it to be between 5-10% less expensive than
conventional concrete. In some instances less HVFA concrete is
needed to provide structural needs due to its higher ultimate
strength. Because of the ball bearing action of the glass beads
contained in fly ash, less water is needed in HVFA cement to
make it flow during mixing and pouring.
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