8.4 : Pumped Concrete

Concrete in large quantities can be pumped across long distances for placing in inaccessible sites. This system comprises a hopper that receives concrete from a mixer, a pump to propel the concrete, and pipelines that facilitate its delivery.

For direct-acting pumps, the concrete enters the pump via the inlet valve under the action of gravity and suction created by the movement of the piston. This concrete is then forced into the pipeline and out through the outlet valve by the forward movement of the piston. These pumps can deliver concrete up to a horizontal distance of 1500 feet and a vertical distance of 140 feet. On the other hand, squeeze pumps utilize rotating blades to move concrete from the hopper into a flexible pipe. The concrete is then advanced to the delivery pipe by the squeezing action of revolving rollers. Commonly installed on trucks, squeeze pumps are capable of deploying concrete through an extendable boom to distances in the range of 300 feet horizontally and 100 feet vertically. The diameter of the pipes, crucial for smooth transport, is selected to be three times larger than the maximum aggregate size in the concrete. Furthermore, the consistency of the concrete mix determines the efficiency of pumping. Overly dry mixes can lead to high resistance within the pipes, while overly wet mixes are prone to segregation.