Changes in the air content of fresh concrete that is being pumped can occur at a number of places. These locations include the initial loading of the concrete into the pump hopper, as it passes through the pump line, and when it exits the line. This synthesis reviews the findings of recent research studies which deal with air content change in pumped concrete and summarizes methods of reducing air loss caused by handling. Three main mechanisms by which air content is lost in fresh concrete that is being pumped have been noted. These factors include the high-pressure dissolution of air voids, the bursting of air voids by vacuum, and the loss of air content due to impact force. Entrained air content can be retained by proper attention to the pump operation and set-up. Keeping steeply descending sections of pump line to a minimum, using kinks, elbows, or reducers at the end of the line to slow the rate of concrete flow, and pumping the concrete at the lowest pressure possible will keep air content losses to a minimum. Further beneficial actions include not allowing rain water to enter the pump’s hopper, and minimizing the distance that the concrete must fall from the end of the pump line to the placement surface. Testing the air content of concrete at the point of placement will yield the most indicative results of the concrete in the finished structure.

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air content, air-entrained concrete, entrained air, pumping, air voids, SPR-2202

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Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, IN

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