Types of Cement Mixers
Most of the mixer fleet, especially older batch model trucks, uses a simple tip-and-pour method to get the concrete out of the mixer. A chute attaches to a port and the concrete oozes (or pours, depending on its consistency) out of the mixer to the project. Usually, the driver of the truck operates the machinery and aims the chute. Many transit mixers are coupled to a hydraulic lift bed that can tip up the drum, similar to a dump truck, if needed.
Other trucks, many of them volumetric and the newer transit mixers, use a pump to move the concrete from the truck to the project. The pumps, usually reciprocating piston pumps, can be mounted on the front or the rear of the truck. Having the pump in front allows the driver to maneuver to a section of the work site and direct the concrete from inside the cab. The controls can be mechanical, electro-mechanical, hydraulic or purely electronic. Newer trucks are employing more on-board computers to monitor pumps and other components of the mixers.
Before the concrete is pumped or poured, a number of simpler machines act in concert to keep the concrete from setting, and even mix the concrete at the site. Some of the older portions of the fleet, like early mixers, used paddles to stir the concrete and keep it from "settling out," or separating into its component pieces. This technology has been largely replaced by the use of augers and fins. Inside a traditional batch mixer is a concentric series of fins with a slight corkscrew pattern. The direction of the drum's spin squishes the wet concrete into the back of the mixer. When the mixer arrives at the site, the driver reverses the direction of the machine to push it out of the mixer to the chute. From there, gravity does the rest.
Volumetric mixers use augers to move concrete. These are similar to the blades in the batch mixer but smaller. Inside the mixer, an operator feeds data into the mixer and several augers feed aggregate and cement together. Water is added to the mix and larger augers blend the components.