Mixing action. This is the most important factor in producing air-entrained concrete. The amount of
entrained air varies with the mixer type and condition, the amount of concrete mixed, and the mixing rate.
Stationary and transit mixers may produce concrete having very different amounts of entrained air.
Mixers not loaded to capacity can increase air content, whereas overloading can decrease air content.
Generally, more air is entrained as the mixing speed increases.
Premature finishing operations. This can cause excess water to work to the concrete surface. If this
occurs, the surface zone may not contain enough entrained air and be susceptible to scaling.
Recommended Air Contents
Air contents for frost-resistant concrete are shown in Table 1-5. Such concrete must be used when there is a
danger of concrete freezing while saturated or nearly saturated with water.
Table 1-5. Approximate mixing water and air content requirements for different slumps and maximum
sizes of aggregates.