A hydraulic mixer is a device that is mounted on a heavy truck that is used to mix and transport the materials that go into making concrete. Concrete is a durable building material that starts as a liquid form, while being mixed, is poured into whatever form there is to hold it, finished, and allowed to cure, or dry. The hydraulic mixer has what resembles a large, closed-bucket system that is continuously turning. It keeps the concrete in it's liquefied state as it does this. When the concrete is ready to be dispensed, the containment bucket turns in the opposite direction. Inside, there is a screw type mechanism that is employed to transfer the concrete outside the bucket, to be poured into a chute. The chute is then used to direct the liquefied concrete to the holding form.
Some concrete trucks use a pump to pump the concrete out of them. Concrete is a very heavy building material, so sometimes the truck can not get where the construction site is, due to it's heaviness. This is when the concrete pump comes into play.