Mixing concrete is more than simply throwing together some cement, sand, gravel and water. In fact, it is somewhat complicated based on the type of mixer used, the duration of the mixing cycle, the method used to load the materials, and the amount of energy used for the mixing motion.
The two main types of mixers are batch and continuous and each type has its own configuration. The efficiency of the mixer is actually determined by the homogeneity of the product ultimately produced. It is measured either by the composition of the concrete or by the variation of certain properties such as compressive strength and the workability of the concrete.
The loading period is important because the outcome for some of the material properties will depend on the order in which they are loaded, as well as the amount of air induced into the mixer. It is common to use admixtures to reduce the amount of water introduced, which leads to a better dispersion of the cement during the mixing process.
The energy needed to mix a batch of concrete is determined by what type of power is consumed during the mixing cycle, as well as the total duration of the cycle. It is not always easy to anticipate the expected energy just by virtue of the type of mixer being used because a mixer with a powerful motor could be used to mix less workable or higher viscosity concretes.
The final result of mixing concrete will in large part be determined by its micro-structure, which is determined by its composition, curing conditions and the actual mixing method used. Finally, the concrete must be placed and cured both of which are additional crucial aspects for defining the long term durability of the ultimate product.