Types of Batching Plant: Parts, How It Works and How to Choose a Concrete Plant

What is a batching plant?

A batching plant, also called a concrete plant, a concrete batching plant or an RMC plant, is fixed or semi-mobile equipment that measures the ingredients of concrete by weight and mixes them in set batches. “Batching” simply means measuring out one batch. A batch is one load of the mixer, from about a third of a cubic metre on the smallest plants to 3 cubic metres or more on large ones.

The Indian Standard for these machines is IS 4925:2004, Concrete Batching and Mixing Plant: Specification. Its foreword sorts plants into three sizes by output: small plants from as low as 10 m³ an hour, medium plants of 30 to 100 m³ an hour, and large plants above 100 m³ an hour. The standard also says these plants are “usually specially designed to suit the local conditions and the output required”, which is why two plants with the same rating can look very different on site.

A plant makes better concrete than a drum mixer fed by head-pans for one plain reason: it weighs. Cement, sand and stone are measured in kilograms on load cells, and water by weight or through a meter, so the water-cement ratio stays where the mix design put it. That is also why the Indian concrete code leans on plants for large and medium jobs, as the guide to RMC vs site mix concrete explains.

What are the types of batching plant?

There is no single list of types. Makers and buyers sort plants in five different ways, and any one plant has an answer for each. A “60 cubic metre stationary twin-shaft wet-mix plant with inline bins” is one machine described all five ways at once.

Table 1: Types of batching plant and what each choice means on site

Stationary, mobile and compact plants

Stationary plants carry the biggest bins, tall cement silos and the highest output, and they suit a ready-mix business or a long project such as a dam, a metro depot or a precast yard. Mobile plants trade some storage for speed of setting up. As an example of how far that can go, Liebherr says its Mobilmix plant needs no concrete foundation, only compacted soil that can carry 300 kN/m², and can be making concrete about nine days after arriving under the right conditions, against about 15 days for its stationary Betomix series on a base plate or simple foundation strips. Compact plants are the small end. Ajax’s CRB range, for example, starts at 20 m³ an hour, with bins low enough to be filled by a loader from a ramp no higher than 1 m.

Wet-mix and dry-mix plants

In a dry-mix plant the transit mixer is the mixer. IS 4926:2003, the Indian code of practice for ready-mixed concrete, says that when a truck mixer does all of the mixing, the drum must turn at least 60 revolutions at not less than 7 revolutions a minute where no other data is available. At the slowest allowed speed that is about eight and a half minutes of mixing before the concrete is ready. A wet-mix plant mixes each batch in its own mixer, for at least 30 to 40 seconds under IS 4925, and puts every load through the same mixing action, so batch-to-batch variation is lower. Wikipedia’s article on concrete plants notes that dry-mix loading also throws up more dust at the truck loading point.

How the aggregate is stored and fed

IS 4925 lists four arrangements a buyer can ask for: open storage behind retaining walls worked by a boom scraper, ground hoppers for smaller plants, ground hoppers with weighing on the belt conveyor, and overhead hoppers above the weigh batchers. On plants sold today these show up as inline-bin plants, where three to five bins sit in a row over a weighing belt, and cross-bin or compact plants, where the bins sit close together and a skip bucket on a rope hauls the weighed aggregate up to the mixer.

What are the main parts of a batching plant?

IS 4925 clause 4.2 lists the parts every plant must have: storage for aggregates and cement, batching (weighing) equipment, a concrete mixer, a control panel, a feeding and elevating arrangement for materials, and a hopper for the mixed concrete. On a working plant those six become about ten pieces of steel you can point at.

How material moves through a wet-mix batching plant

1. Aggregate bins hold sand and each size of stone in separate compartments, two to six of them (four on many plants, such as Ajax’s CRB range), filled by a wheel loader from the stockpile.
2. The aggregate weigh hopper or weighing belt fills as gates under each bin open and close, until the load cells read the weight the recipe asks for.
3. A belt conveyor or skip hoist carries the weighed aggregate up to the mixer. Inline plants use an inclined belt; compact plants use a skip bucket pulled up rails by a winch.
4. The cement silo is a tall steel tank of bulk cement, often with a dust filter on top. IS 4925 lists available sizes of 20, 30, 45, 60 and 75 tonnes, with bigger ones for central storage.
5. A screw conveyor, a spiral turning inside a tube, pushes cement from the silo to the weigher.
6. The cement weigh hopper weighs cement and fly ash or other cement-like powders on their own scale. IS 4925 asks for a separate cement weigher on plants of 20 m³ an hour and above.
7. Water is measured by a weigher or a meter, and liquid admixtures (chemicals that change setting time or workability) by small dosing units.
8. The mixer is the heart of the plant and has its own section below.
9. A discharge chute or concrete hopper drops finished concrete into the transit mixer, dumper or pump hopper.
10. The control cabin holds the PLC (a small industrial computer) and screen that run the recipe, weigh, mix and print the batch record.

Around the plant you also need site air for the pneumatic gates on many plants, from an air compressor if the maker does not supply one, a power supply, water storage and a level, hard area for trucks to queue and turn.

How does a batching plant work?

A batching plant works in a repeating cycle: weigh every ingredient for one batch, feed them into the mixer in order, mix for a set time, discharge, and start again. On an automatic plant the operator presses one button for the batch and the control system does the rest. In plain steps:

1. The operator picks the recipe, for example M25 with a set cement content and water-cement ratio, and the batch size.
2. Aggregate gates open and the weigher fills, usually with a fast feed first and a slow “dribble” feed near the target weight so it stops close to the mark. IS 4925 asks for this two-stage cut-off.
3. At the same time the screw conveyor fills the cement weigher, and water and admixture are measured.
4. The weighed aggregate travels up by belt or skip. Cement, water and admixture drop into the mixer in the sequence the maker sets.
5. The mixer runs for its mixing time. IS 4925 says all the water must be in before a quarter of that time has passed.
6. The mixer gate opens and the batch drops into the waiting truck. The scales must be empty and back at zero before the next batch can start.

The standard builds safety into that sequence. On an automatic batcher the charging gate cannot open until the scale has returned to zero, within 0.3 per cent of the scale’s capacity, the charging and discharge gates cannot both be open, and the weighed material cannot be discharged until it is within tolerance. A plant that lets the operator skip those locks is not built to IS 4925.

Moisture is the hidden variable. Wet sand carries water into the mix and weighs heavier for the same amount of solid sand. Good control systems read moisture probes in the sand bin and correct the water and sand weights batch by batch; Ajax, for one, lists automatic or manual moisture correction on the control panel of its CRB plants. If your plant has no moisture correction, someone has to test the sand and adjust the recipe by hand, every shift and after every rain.

Which mixer is best for a batching plant: twin-shaft, planetary or drum?

The mixer sets how fast a plant can run and what kind of concrete it mixes well. IS 4925 names drum, pan and shaft mixers and gives each a minimum mixing time, counted after all the materials except the full quantity of water are in.

Table 2: Batching plant mixer types and IS 4925 minimum mixing time

These are minimums for standard mixer speed. The standard adds that mixing time must go up if the batch does not come out uniform.

Of these, twin-shaft and pan or planetary mixers are the two that makers’ current plant pages lead with. Wikipedia’s concrete plant article notes that the twin-shaft mixer is the more common central mixer outside North America and that pan or planetary mixers are more common at precast plants. Liebherr describes its twin-shaft range as the preferred choice for ready-mix work and its ring-pan mixers for high-performance and special concrete. Ajax, an Indian maker that also builds transit mixers and self-loading mixers, fits planetary mixers on its 20 and 30 m³ an hour CRB plants and a twin-shaft mixer on the 120 m³ an hour CRB 120.

Whatever the type, the mixing drum and blades wear. IS 4925 asks for high-manganese or abrasion-resistant steel, or carbon steel with replaceable liners, and asks the supplier to give a price list of recommended spares for two years or 5,000 working hours. Ask for that list before you buy, because it tells you what the plant will eat.

What does batching plant capacity in cubic metres an hour mean?

The capacity in a plant’s name is a best-case figure. IS 4925 clause 3 says the maximum capacity is calculated from the mixer’s minimum cycle time once the materials are fed in, for concrete with an 80 mm slump. (Slump is how far a cone of fresh concrete sags when the mould is lifted.) Real output is lower, and the same standard’s enquiry format tells buyers to work out their need “assuming 75 percent efficiency of the plant”.

Two numbers on a mixer confuse first-time buyers. A plant’s mixer might read “750 / 500 litres”. The first figure is how much loose dry material the mixer takes in; the second is the compacted concrete that comes out per batch. The second one is the number that counts.

Table 3: Three Ajax CRB plants, as listed by the maker (read 3 November 2026), with our arithmetic

*Our arithmetic: rated output divided by concrete per batch, and rated output times the 0.75 factor in IS 4925 Annex A-1. Real batch times also depend on how fast trucks arrive and leave.

Put a truck under each plant and the difference is plain. A 6 m³ transit mixer such as the AJAX AF 6XE takes 12 batches from a CRB 30, about 12 minutes at the rated pace, and 2 batches from a CRB 120, about 3 minutes. So a big plant’s real limit is usually how many trucks you can keep under it, and a small plant’s limit is the mixer. How many mixers and pumps a plant keeps busy is worked through in the guide to transit mixer productivity and output.

Power follows size. The CRB 30’s listed maximum load is 46 kW and the CRB 120’s is 200 kW. At the 0.8 power factor gensets are rated on, that is roughly 58 kVA and 250 kVA of running load before any allowance for motors starting (our arithmetic). Where there is no grid supply yet, size the set as shown in the guide to a diesel generator for a construction site.

How accurate does a batching plant have to be?

Accurate enough that the concrete you ordered is the concrete you get. Two Indian Standards set the limits, and they do different jobs. IS 4925 is the machine specification: it says how accurately each batcher must be able to weigh. IS 4926 is the code for ready-mixed concrete production: it says how close each delivered batch must be to the recipe.

Table 4: Weighing tolerances in the two Indian Standards

There is a catch in the small print of IS 4925. The tolerance only applies above a minimum weight, worked out as 0.3 times the scale capacity divided by the tolerance in per cent. On a cement scale that weighs up to 1,800 kg, the cement weighing capacity Ajax lists for its CRB 120, the ±1% only holds for loads of 540 kg or more (our arithmetic from clause 6.1.3). A big plant making a small part-batch therefore weighs less accurately than its rating suggests.

Scales drift. IS 4926 asks for every weighing system to be tested over its full range at least once every two months for mechanical knife-edge scales and once every three months for load-cell scales, using at least 500 kg of stamped test weights on most plants. IS 4925 also gives a mixing test: samples from the two halves of one batch must not differ by more than 8 per cent for cement, 6 per cent for fine aggregate and 5 per cent for coarse aggregate.

For a ready-mix plant, IS 4925 asks for a computer that stores at least 15 recipes, with a monitor and printer, and a delivery slip that shows the recipe, batch size, number of batches, the moisture of each material at batching and the weighed quantity of each component, along with the transit mixer number and driver. If you buy concrete, ask to see one. If you run the plant, that slip is your defence when a cube fails.

How do you choose a batching plant?

Start from the job, then the plant. IS 4925 is unusually helpful here: its Annex A is a specimen enquiry form that lists what a buyer should tell the maker. Work through these before you ask anyone for a price.

1. Work out peak output. Take the largest continuous pour you expect, in cubic metres per hour, and divide by 0.75. A raft that needs 45 m³ an hour without a break points to a 60 m³ an hour plant.
2. Decide how long the plant stays. A job of a year or two that will move to the next site favours a mobile or compact plant. A ready-mix yard that will sell to a city for ten years favours a stationary plant with bigger bins and silos.
3. Count your materials. Count the sizes of sand and stone in your mixes; that is the number of bin compartments. Count the powders (OPC, PPC, fly ash, slag); that is the number of silos or silo compartments.
4. Pick the mixer. Mixes with bigger stone and high output point to a twin-shaft mixer; precast, special and small-output plants often use a pan or planetary mixer.
5. Set the level of control. IS 4925 recommends manual control up to 20 m³ an hour, semi-automatic below 30, and fully automatic at 30 and above. For a ready-mix plant, insist on recipe storage, moisture correction and printed batch records.
6. Check the discharge height. The chute has to clear the hopper of the trucks you use. Ajax lists 1.7 m for the CRB 20 and about 4 m for the CRB 30 and CRB 120. Check it against your transit mixer, dumper or pump.
7. Settle power, water and ground. Ask the maker for the connected load and the foundation drawing. IS 4925 makes the buyer responsible for telling the maker the site’s electric supply and, if the maker is not supplying the compressor, the pressure of the site air.
8. Think about temperature. For plants of 30 m³ an hour and above, IS 4925 lets the buyer ask for cooling or heating of the concrete, and the plant can be built to take chilled water or ice flakes.
9. Plan the permissions. A plant is a stationary industrial unit, so it needs the state pollution control board’s consents before it runs. The steps are in consent to establish and consent to operate.

If you are weighing the plant as a business, the money side (fleet cost, working capital, haul radius) is covered in the blog on the RMC plant business.

Planning the trucks and pumps that a plant feeds? Compare transit mixers and self-loading mixers with their specifications and listed prices, and send an enquiry to a verified dealer.

When do you not need a batching plant?

When the pours are small, scattered or far from any plant. A plant needs land, power, water, a loader, a fleet of trucks and someone to run it every day, and all of that only pays when it is busy.

For a contractor pouring their own footings, culverts, village roads or a few floors at a time, a self-loading concrete mixer often does the job alone. It loads aggregate with its own bucket, mixes in its drum on the way and pours. The Schwing Stetter SLM 2600 carries a 2.4 m³ drum and the AJAX ARGO 4500 a 4.5 m³ drum, both as listed in their specifications. Both sit in the full range of concrete mixers, listed with specifications and prices.

A volumetric mixer, which carries the dry materials separately and mixes fresh concrete at the pour, is a third route for small and stop-start jobs; see the guide to the volumetric concrete mixer. And in a town with ready-mix suppliers nearby, buying concrete is often simpler than making it.

What machines work with a batching plant?

A plant is only as busy as the machines around it. A wheel loader keeps the bins full from the stockpile; browse wheel loaders for the bucket sizes that suit bin feeding. Transit mixers carry the concrete out, from 6 m³ trucks such as the AJAX AF 6XE to 10 m³ drums such as the AJAX AF 10XP; at a CRB 120 that bigger drum takes three full batches and a part batch.

At the pour, a stationary pump lifts the concrete to the slab. The AJAX ASP 5009, for example, lists a maximum theoretical output of 50 m³ an hour on its rod side. The machines, models and open tenders around ready-mix work are gathered on the RMC plant equipment page.

Ready to price the fleet for your plant? Compare transit mixer models and prices and concrete pumps, and talk to a verified dealer before you fix a plant size.

Sources

The size bands, plant components, mixer types and mixing times, weighing tolerances, interlocks, control recommendations and the specimen enquiry format are from IS 4925:2004, Concrete Batching and Mixing Plant: Specification. Truck-mixer revolutions, ready-mixed concrete batching tolerances and calibration intervals are from IS 4926:2003, Ready-Mixed Concrete: Code of Practice, Annex E. Plant outputs, mixer sizes, discharge heights, weigher sizes and operating loads were read on 3 November 2026 from Ajax Engineering’s CRB batching plant pages. Mobile and stationary set-up times are from Liebherr’s Mobilmix and Betomix page, and the mixer comparison draws on Liebherr’s mixer pages and Wikipedia’s concrete plant article. Transit mixer, self-loading mixer and pump figures are from each machine’s listed specifications.

Prices, specifications and features are indicative, vary by variant, location and date, and should always be confirmed with the official OEM or authorised dealer before any purchase decision. DesiMachines is not liable for decisions taken on the basis of information that may have changed after publication.