During the concrete pumping process, the tiny air entrainment bubbles that exist in the concrete can be compromised and the total air content by mass can be reduced from the designed and batched levels. Concrete air entrainment requirements ( which are for exterior concrete to increase freeze/thaw resistance) are usually based on samples taken from the chute of the concrete truck.  Air entrainment loss typically occurs when concrete experiences significant vertical drops, concrete has a high initial slump, and when pumping pressure is increased resulting in a sudden pressure drop as concrete leaves the hose. Below are some ways to reduce such problems:

-Operate boom in an upward or horizontal position as much as possible

-Reduce vertical concrete drops as much as possible (Insert 90 degree elbows)

-Use gate or flow restricting device at end of pump line to provide flow resistance

-Run the last 10-15 ft of pump hose horizontally along ground or formwork to avoid long drops

-Elevate plastic air content of the mix above specified level to compensate for lost air content. Be sure to choose and monitor this carefully as excess air content can have negative impact on compressive strength