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The Mix Wizard
Technical Mix Tips
Why is Entrained Air Important?
Air entraining admixtures (AEA) are used to purposely entrain microscopic
air bubbles in concrete. The AEA is added directly to the
concrete materials either before or during mixing. Air
entrained concrete contains millions of minute air bubbles that
are distributed
uniformly throughout the paste fraction of the mix. These
bubbles must have a certain size and distribution to be effective.
Natural, or entrapped air bubbles are too large and spaced irregularly
to be of any benefit. Air entrainment will dramatically
improve the durability of concrete exposed to moisture during
cycles of
freezing and thawing. Entrained air greatly improves concrete's
resistance to surface scaling caused by de-icing chemicals such
as salt. The workability of fresh concrete is also significantly
improved and bleeding and segregation are reduced or eliminated.
CSA Classes of Concrete
The specifications listed are for the minimum strengths and minimum
water to cementing materials (W/CM) ratio. The W/CM ratio is the
total amount of water in the mix, including that in the aggregates,
divided by the by the total weight of cementing materials in the
mix, which include cement, fly ash, and silica fume. The
mixes noted are for 20mm aggregate.
| Class |
Strength
(MPa) |
Water/
Cement Ratio |
Air (%) |
| N |
20 |
No
requirement |
No
requirement |
| F2, C4 |
25 |
.55 |
4-7 |
| F2 |
30 |
.55 |
4-7 |
| F1 |
30 |
.50 |
5-8 |
| C2 |
32 |
.45 |
5-8 |
| C1 |
35 |
.40 |
5-8 |
Higher strength mixes and/or lower W/CM are often supplied, especially
for classes F2, C4 and N.
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