Concrete mixer is the most widely used construction material in the world. No construction site is ever complete without the sight of piles of cement, aggregate and the concrete mixer that puts it all together. Everything from the world's tallest building to the largest dams and some of the longest bridges uses concrete as its primary material. Concrete is a very old construction material. At its simplest, concrete is a mixture of cement, water and aggregates like sand, natural gravel and crushed stone that you place in a concrete mixer for uniform mixing. The general idea is to get the right amount of water and cement for the mix. Too much water and the concrete will suffer from a high degree of slump. Too little and the workability of the concrete suffers. Using aggregates with the wrong gradation could result in a very harsh mix that has a very low slump that cannot be fixed by adding reasonable amounts of water to the mix.
Concrete mixers exist in many forms and sizes. The role of a concrete mixer is to ensure a uniform mix of the concrete in the shortest time possible. On-site mixers allow for working with the material while it is fresh, as this is the time where the concrete's workability is at its best. This is especially true when there is a need for precast or prestressed concrete. Modern mechanical engineering has allowed the design of cement mixers that are small enough to fit through doorways. They still have enough power to produce homogenous mixes in three minutes or less and in large enough volumes.