Why Use Fly Ash?
Where quality fly ash is available, concrete industry demand for the
product is strong. Here’s why:
- The fly ash difference. Concrete industry fly ash
users know that fly ash in the mix means a more durable, more reliable,
top performance concrete product.
- The fly ash advantage. Fly ash in the mix replaces
more costly materials, producing big savings in concrete materials
costs
- Fly ash is a green solution. Fly ash is an environmentally-friendly
solution that meets or exceeds performance specifications. Fly ash
can contribute to LEED (Leadership in Energy and Environmental Design)
points.
What, Specifically, are the Benefits of Using Fly Ash?
Concrete in its hardened state — with fly ash — shows improved
performance with:
- Greater strength. Fly ash increases in strength
over time, continuing to combine with free lime.
- Decreased permeability. Increased density and
long-term pozzolanic action of fly ash, which ties up free lime, results
in fewer bleed channels and decreases permeability.
- Increased durability. The lower permeability of
concrete with fly ash also helps keep aggressive compounds on the
surface, where destructive action is lessened. Fly ash concrete is
also more resistant to attack by sulfate, mild acid, and soft (lime
hungry) water.
- Reduced alkali silica reactivity. Fly ash combines
with alkalis from cement that might otherwise combine with silica
from aggregates, thereby preventing destructive expansion.
- Reduced heat of hydration. The pozzolanic reaction
between fly ash and lime generates less heat, resulting in reduced
thermal cracking when fly ash is used to replace a percentage of Portland
Cement.
- Reduced efflorescence. Fly ash chemically binds
free lime and salts that can create efflorescence. The lower permeability
of concrete with fly ash can help to hold efflorescence-producing
compounds inside the concrete.
The ball-bearing effect of fly ash in concrete creates a lubricating
action when concrete is in its plastic state. This means enhanced
concrete workability and:
- Increased workability. Concrete is easier to place
with less effort, responding better to vibration to fill forms more
completely.
- Increased ease of pumping. Pumping requires less
energy; longer pumping distances are possible.
- Improved finishing. Sharp, clear architectural
definition is easier to achieve, with less worry about in-place integrity.
- Reduced bleeding. Fewer bleed channels decreases
porosity and chemical attack. Bleed streaking is reduced for architectural
finishes. Improved paste to aggregate contact results in enhanced
bond strengths.
- Reduced segregation. Improved cohesiveness of
fly ash concrete reduces segregation that can lead to rock pockets.
- Reduced slump loss. More dependable concrete allows
for greater working time, especially in hot weather.
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