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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.

Higher strength mixes and/or lower W/CM are often supplied, especially for classes F2, C4 and N.