A concrete mixer combines cement, aggregate, and water into concrete. It is a machine with a rotating drum or a paddle. The drum turns, and the materials tumble and mix. The result is a uniform, workable concrete. Mixers come in many sizes. A small portable mixer holds a few cubic feet and is used for small jobs. A truck-mounted mixer holds 8 to 10 cubic yards and delivers concrete to the site. A central batch plant mixes large quantities and loads them into trucks.

The mixing process matters. The materials must be proportioned correctly. Too much water makes the concrete weak. Too little makes it unworkable. The mixing time must be sufficient to coat all the aggregate with cement paste. A typical truck mixer rotates at 6 to 18 revolutions per minute. It can also agitate the concrete to keep it workable during transport. If the concrete sits too long, it begins to set and becomes unusable.

Mixers are essential to modern construction. Without them, concrete would have to be mixed by hand, which is slow and inconsistent. With them, concrete can be produced in large quantities and placed quickly. The mixer is not just a machine. It is the reason concrete is the most widely used building material in the world. It turns powder, stone, and water into the foundation of cities.