A Concrete Batching Plant is a machine to manufacture Concrete from its ingredients viz Cement, Crushed Stone, Sand, Water and Admixture Chemicals. Sometimes additives like GGBS (Ground granulated blast Furnace Slag), Fly Ash or Micro-silica are added to change the characteristics of the end product. The word Batching Plant comes from the word "Batch", which essentially means that concrete is manufactured in measured bathes inside a Concrete Batching Plant.
Concrete is manufactured based of various recipes (or Formulas) which essentially is the proportion of various raw materials as described above. We can deal all these raw materials as per the following :
Aggregates : Various sizes of aggregates or crushed stones are separately stored in large steel (sometimes concrete) bins. These bins can have a number of compartments (normally 3-4) to store different sizes of aggregates. For example, the sizes can be 0-5mm (Sand), 5-10 mm, 10-15mm, 15-20mm. Each of these bins has a gate at the bottom that is hydraulically operated. The aggregates flow under gravity through this gate and fall into another bin called Weigh Bin, where these aggregates are weighed. This weigh Bin hangs on load cells that informs the Control System about the measured weight. Control system closes the gate when the required amount of aggregates is available in the weigh bin. Process is repeated for all types of aggregates depending upon the recipe.
Cement : Cement is stored in Cement Silos, which can have capacity from 30 MT of Cement to normal sizes of 70MT, 100Mt or anything unto 200MT depending upon individual requirement of the Concrete Batching Plant. In most countries, Cement Screws are used to convey cement from the bottom of Silos into a Cement Weigh bin, where it is measured using load cells again. Here also, the control system decides how much cement is to be used and switches off the screw accordingly.
Water : Water can either be fed to the plant on flow basis or volumetric basis. Water is fed directly to the mixing area. (Depending upon whether the plant is dry type or wet type).
Admixture : Various chemicals to change the chemical properties of the concrete may be added to the concrete during mixtures. Admixture can hasten or delay the concrete setting and are used according to the specifications of the recipe.
Once all the above are weighed, then there are two options where we can understand the two basic different types of Concrete Batching Plants :
Wet Type Concrete Batching Plant. In this type, All the ingredients above are transferred to a Mixer, and mixed together. Different types of mixers can be used, for example, Twin Shaft Mixer, Pan Type, Planetary Type or Drum type depending upon utilisation and requirements of various customers. You can see this typical example at the page of Concrete Plants.
Dry Type Concrete Batching Plant. In this type, all the ingredients excepting water are added in a transit mixer (also known as Concrete Mixer Truck, Mixer Truck, Agitator Truck etc). Measured water is then added to this in the truck mixer, which is used to mix the ingredients to form concrete for delivery to site.