Figure 1-7. Polished section of air-entrained concrete magnified many times.
Air-entrained materials. Air can be entrained in concrete by using air-entrained cement, by using an air-entrained
admixture at the mixer, or by combining both methods. Use adequate controls to ensure the proper air content at
all times.
Factors Affecting Air Content
Slump and vibration. This affects the air content of air-entrained concrete because the greater the slump,
the larger the percent reduction in air content during vibration. At all slumps, even 15-second vibration
causes reduced air content. However, properly applied vibration mainly eliminates large air bubbles and
little of the intentionally entrained air bubbles.
Concrete temperature. The effects of concrete temperature becomes more pronounced as the slump
increases. Less air is entrained as concrete temperature increases.
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