What is Air Entrainment in Concrete
What is Air Entrainment In Concrete
Air Entrainment is the process of intentionally creating small air bubbles in concrete by adding a surfactant during mixing. The purpose of these bubbles is to improve the workability, freeze-thaw resistance, and durability of concrete when hardened.
This process helps concrete retain strength even under adverse conditions such as wet weather and subzero temperatures. An air entrainment agent is generally added during mixing, allowing air bubbles to form throughout the batch, which will remain part of it upon hardening.
What Is The Purpose Of Air Entrainment?
The purpose of air entrainment is to add tiny air pockets to concrete during the mixing process. This helps improve the freeze-thaw durability of the concrete, making it more resistant to scaling or damage from deicing chemicals.
The air entrainment also increases workability and makes handling and finishing easier for contractors and other workers.
Air entrainment is a cost effective way to ensure that concrete can withstand both temperature extremes as well as chemical agents used in deicing applications.
When Should Air Entrainment Be Used In Concrete?
Air entrainment should be used in concrete when a high level of freeze-thaw resistance is required.
The air voids provide pressure relief sites during freeze events, so the water can freeze without inducing large internal stresses.
Additionally, air-entrained concrete may also be used to provide deicer-scaling resistance to maintain its structural integrity in harsh conditions.
What Are the Factors Affecting Air Entrainment?
Air entrainment is affected by multiple factors including the surface area (or fineness) of cement, the cement factor, and the soluble alkali content of cement. In general, an increase in any one of these factors will result in an increase in air content.
A high cement factor concrete will contain less air than a lean mix, while a greater surface area (fineness) of cement will decrease the air content. Type I-P cements are noted to entrain less air than other types. Lastly, as the soluble alkali content of cement increases, so too does the air content.
Should All Concrete Be Air Entrained?
Air entrainment is a significant factor to consider when it comes to concrete construction. All exterior concrete exposed to freeze-thaw conditions should be air-entrained in order to ensure good durability and prevent scaling and cracking due to freeze-thaw damage.
Air entrainment creates tiny air bubbles within the cement paste, leading to greater resistance against temperature changes and freezing that would otherwise cause shrinkage and weakening of the concrete’s structure.
This will help extend the life of the concrete, reducing repair costs over time for the contractor and helping to protect a building’s occupants from weathering damage.
What Is the Difference between Air-Entrained and Non-Air-Entrained Concrete?
The main difference between air-entrained and non-air-entrained concrete is that the former requires less water and sand content than the latter.
Air-entrained concrete usually needs around 3 to 5 gallons of water per cubic yard less than non-air-entrained concrete with the same slump, while its sand content requirement is lower by about 90 to 125 pounds per cubic yard.
Furthermore, air entraining is especially beneficial for southern climates as it provides protection from thermal cracking due to extreme temperatures.
