Concrete Mixer with a Pump Boom

About this drawing

A concrete mixer pump truck packs two machines into one: a drum that keeps the concrete mixed and a boom that places it exactly where it is needed. It is handy on smaller jobs and tight streets where there is no room for a separate pump truck.

The drum turns the whole way to the site. Inside are spiral blades, like the threads of a giant screw. Turning one direction, they fold the mix and push it toward the back so the sand, gravel and cement do not separate. When the driver reverses the spin, the same spiral pushes the concrete out the chute.

Timing matters. Once concrete is batched at the plant, crews have a limited window before it starts to set, so the plant and site schedule deliveries carefully. On hot days that window shrinks, and producers sometimes add admixtures that slow setting down.

Before pumping, the truck lowers its outriggers, sturdy legs that brace it against the ground. Then the operator unfolds the boom and steers it with a remote control while another worker guides the end hose, spreading concrete into the trench or forms.

• concrete mixer
• pump truck
• concrete
• construction
• trucks