In the area of concrete construction, where much depends on know-how, patience and careful workmanship, it was only natural that short cuts should be offered in the form of admixtures. Of all the many products put on the market in the last few decades, one has risen head and shoulders above the rest in its effectiveness. It is, of course, the air entraining agent. The introduction of air into concrete mixes has some pronounced effects on the characteristics of both the plastic and the hardened concrete. In fresh concrete, the tiny air bubbles act as a lubricant in the mix which improves its workability and increases its slump. Also, in a sense, the bubbles function as a third aggregate. Because of their small size, the bubbles act as fines, thereby cutting down the amount of sand needed. In hardened concrete, the outstanding attributes of air entrainment are the enhanced weatherability and resistance to scaling afforded. When the mixer truck pulls in with a load of air entrained concrete it is especially important that forms be ready to receive it. Although opinions vary somewhat, it is generally conceded that the amount of intentionally entrained air increases noticeably with mixing during the first 5 minutes. It is apparent, therefore, that a contractor must be ready to receive ready mixed concrete when it is delivered to ensure a constant percentage of air. Since air entrained concrete is more cohesive and workable than non-air entrained, there is not as much danger of segregation and air pockets. Accordingly, vibration need not be prolonged. As to appearance, air entrained concrete has an unusually creamy, fatty look. This, coupled with the virtual absence of bleeding, sometimes results in incorrect handling of the concrete. This is, however, only a problem in slabs requiring finishing.