High-intensity mixers are generally used in plants requiring high mix homogeneity, short mixing times, and minimum amounts of mix water. Most high-intensity mixers are especially suited for producing zero-slump concrete. Due to their speed, these mixers can produce more concrete per hour. Because they produce a highly homogeneous batch, mixes produced by these mixers often require less cement and admixtures to achieve desired characteristics.
The three types of mixers most commonly used are twin-shaft, counter-current and turbine mixers. Twin-shaft mixers consist of two parallel, rapidly rotating shafts mounted inside a rectangular mixing chamber. Counter-current mixers can be subdivided into stationary-pan and rotating-pan types. Stationary-pan mixers have a circular chamber with two to three mixing arms extending down into the chamber. Mixing paddles and blades are mounted in star-like fashion to cross-arms on the ends of the mixing shafts. These assemblies move in a circular motion, mixing the concrete both horizontally and vertically. Rotating pan mixers work on the principle of rotating the entire pan of the mixer, like a record player. Stationary rotating mixing stars agitate and shear the mix. Turbine mixers consist of a stationary drum and a central column. Several arms extend out from the center column with paddles and scrapers of various shapes and sizes mounted on them.