The document discusses central mix concrete batching plants. It describes how batching plants measure and combine concrete ingredients according to a mix design. Central mix plants combine ingredients at a central location before transporting the mixed concrete to the job site, allowing for more consistent quality control compared to dry mix plants. The document outlines the production process and components of batching plants, including storage bins, scales, mixers and controls for measuring ingredients.

1. Department of Civil Engineering
Indian Institute of Technology Kanpur
PRESENTATION FOR CE647A – CONSTRUCTION METHODS
Sourabh Vaid
Textbooks or Reference Materials
[1] Concrete Technology - NPTEL
[2] Concrete Plant – (https://en.wikipedia.org/wiki/Concrete_plant)
[3] Technology in practice –
(http://www.nrmca.org/aboutconcrete/downloads/Tip6.pdf)
[4] Foundation, Concrete and Earthquake Engineering –
(https://civil-engg-world.blogspot.in/2014/04/state-moisture-
content-aggregate-Concrete.html)
[5] The Concrete History of Concrete and Cements – History TV Documentry
TOPIC NO. 9
CENTRAL MIX CONCRETE BATCHING PLANT

2. Department of Civil Engineering
Indian Institute of Technology Kanpur
PRESENTATION FOR CE647A – CONSTRUCTION METHODS
Sourabh Vaid
OUTLINE
CONCRETE PRODUCTION
• Production Process
• Batching
• Mixing

3. PRODUCTION PROCESSES
Module 1 - Introduction 3
Batching Mixing Transport Placing
CompactionCuring
Concrete

4. 4
History
• The history of cementing materials goes back to times when prehistoric man abandoned
his cave to build shelters.
• He used mud and clay to fill the gaps between stones to keep out the wind and the cold .
• Later Assyrians and Babylonians used clay mixed with straw.
• The Egyptians used lime and gypsum a mineral rich in calcium sulfate to create a material
that would harden even better.

5. 5
• The Greek made further improvements.
• Then romans perfected a cement that produced structures of
remarkable durability- Pozzolanic cement a volcanic ash.
• Roman concrete Essential in building Pantheon.
• In 1756 English chemist John Smeaton used clay and limestone to
make a material called hydraulic lime.
• In 1824 Joseph Aspin discovered the process of making Portland
cement.
History

6. 6
• Saxons built concrete mixers in the form of shallow bowls cast into
bedrock. A beam fixed with paddles rotated about a central post
hole that was human or animal powered.
• In 1900’s concrete was made at the site manually resulting in poor
quality due to lack if control system
• Drums were soon after invented, and wheels were later added in
order to make it easier for the building of roadways and sidewalks.
HISTORY

7. History
Early mobile concrete mixers driven by Horses

8. Module 1 - Introduction 8
Concrete mixing plant in
Birmingham, Alabama in 1936
Gasoline Powered Mixers used in early
1920’s
History

9.  Batching is the process of measuring and combining the
ingredients of concrete (cement, water, sand,
aggregates)…as per the mix design.
 Batching (measuring and mixing) could be done in two ways:
1. Weight batching
2. Volume batching - This method is very archaic, old and
very inaccurate.
 A concrete plant, also known as a batch plant or batching
plant, is the one that combines various ingredients to form
concrete.
BATCHING

10. a. Dry mix or Transit mix plants: After batching the
ingredients are discharged into a chute which discharges
into a truck. Meanwhile, water is either being weighed or
volumetrically metered and discharged through the same
charging chute into the mixer truck. These ingredients are
then mixed for a minimum of 70 to 100 revolutions during
transportation to the job-site.
b.Central mix or Wet mix Concrete plants. A central mix
plant combines some or all of the above
ingredients (including water) at a central location. The
final product is then transported to the job site.
TYPES OF CONCRETE PLANTS:

11. DIFFERENCES
Module 1 - Introduction 11
a. Central mix plants differ from ready mix plants in that
they offer the end user a much more consistent
product, since all the ingredient mixing is done in a
central location and is computer-assisted to ensure
uniformity of product.
b. Dry mix plants typically see more variation from load to
load because of inconsistencies in mix times, truck blade
and drum conditions, traffic conditions, etc. With a
Central Mix plant, all loads see the same mixing action
and there is an initial quality control point when
discharging from the central mixer.

12. Module 1 - Introduction 12

13. BATCHING PLANT
Module 1 - Introduction 13
Components of a batching plant:
• Aggregate bins for various types of aggregates.
• Feeding mechanisms such as scrappers, conveyors or hoists etc.
to transfer aggregate to scales (balances).
• Cement silos and a conveyor screw or bucket conveyor.
• The storage tank for water and water measuring system.
• Dispenser for chemical admixture.
Plant Type:
• Cyclic or continuous
• Automatic or manual

14. Concrete Batching Plant 14

15. Module 1 - Introduction 15
BATCHING FLOW CHART

16. MEASUREMENTS
• Mechanical level system, load cells etc. for
measurements of mass.
• Controlling the discharge from storage and weigh
hoppers is through gates operated by compressed air
cylinders.
• Presetting of desired batch weights can be done by
devices such as digit switches or rotating dials and
computers.
Module 1 - Introduction 16

17. MEASUREMENTS
• Electrical or microwave moisture gauges can be used
as aggregate moisture meters.
• Water is most commonly measured through flow
meters , although in some plants water is also
weighed.
• With the need of adequate calibration , frequent
regulatory routine and specialist’s checks of weighing
process are required.
Module 1 - Introduction 17

18. Moisture Content
• Moisture States:
• Oven-dry (OD): All moisture is removed from the
aggregate by heating in an oven at 105 °C . All pores are
empty.
• Air-dry (AD): All moisture removed from surface, but
internal pores partially full.
• Saturated-surface-dry (SSD): All pores filled with water,
but no film of water on the surface.
• Wet: All pores completely filled with water with a film
on the surface.
Module 1 - Introduction 18

19. Module 1 - Introduction 19

20. WHY IS MOISTURE MEASURED?
• If the moisture content of wet aggregate is not
compensated for, the slump may be too high and w/cm
will not conform to the mixture requirement.
• The batched water should be less than the mixing water
required by the amount of free moisture on the
aggregate.
• The aggregate in storage prior to batching in concrete
can also be in an air-dry state. In this case, the aggregate
when batched in concrete will absorb water from the
batch water resulting in a lower slump.
• This water that will be absorbed by dry aggregates needs
to be accounted for by adding additional water to the
mixture. 20

21. TOLERANCES (IS 4945)
INGREDIENT BATCHING TOLERANCES (%)
Cement and other cementitious
materials ±1
Water (by volume or by weight) ,%
±1
Aggregates, %
±2
Admixture (by volume or by weight), %
±3
Module 1 - Introduction 21

22. TOLERANCES (individual batch)
• Tolerances apply to:
Minimum weight (kg)= [0.3×scale capacity(kg)]/
Weigh tolerance (%) ] as in table .
WHY ?
• Uniform concrete exhibits less variation.
• Variation depends on variation in proportions.
Eg. Higher errors in cement and water
measurements will result in higher variation in
strength.
Module 1 - Introduction 22

23. MIXING
• Thorough mixing is essential for production of
uniform quality concrete.
• Equipment and method should be capable of
effectively mixing concrete material containing
largest specified aggregate to produce uniform
mixtures of the lowest slump , practical for work.
Mixers:
• Cyclic or batch mixers and continuous mixers .
• Gravity mixers or mixers with forced movements
(tilting or non tilting)
• Counter-flow mixers or open pan mixers.
Module 1 - Introduction 23

24. 24
MIXER
The heart of the concrete batching plant is the mixer, and there are many types
of mixers such as: Tilt Drum, Pan, Planetary, Single Shaft and Twin shaft mixer
1. A. Tilt Drum For large scale projects, this is employed using an Archimedes’
screw that hoists the ingredients, mixing them and then conveying them to
the mixer. At times, the batching machine may be secured onto the truck that
carries the raw materials and when they arrive at the site, the plant
equipment mixes the concrete on-site At times, iron balls are thrown inside
to assist in mixing.

25. Module 1 - Introduction 25
B. Non Tilting Drum

26. Module 1 - Introduction 26
2. Twin shaft mixer.
• The twin shaft mixer can ensure an even mixture of concrete
and large output, while the tilt mixer offers a consistent mix
with much less maintenance labor and cost.
• Known for their high intensity mixing, and short mixing times.
These mixers are typically used for high strength concrete, RCC
and SCC

27. 27
3. Vertical axis mixers :
• Commonly used for precast and pre-stressed concrete. This style of
mixer cleans well between batches, and is favoured for coloured
concrete, smaller batches and multiple discharge points.
• Within this category, the Pan mixers are losing popularity to the
more efficient Planetary (or counter-current) mixers as the
additional mixing action helps in production of more critical
concrete mixes (colour consistency, SCC, etc.).
Pan mixer Planetary Mixer

28. BATCH AND CONTINUOUS MIXERS
• For a mixer which should be operated for an indefinite period
of time for mixing huge quantities then the continuous mixer is
the best option .
• In case if the mixing quantity if less or for a small period of
time then batch mixer will serve the purpose.
28
Non Tilting Drum- Batch Mixer Continuous Mixer

29. BATCH AND CONTINUOUS MIXERS
• In batch operation, all ingredients are loaded and mixed
until a homogenous material is produced and discharged
from the mixer in a single lot.
• The output of a batch mixer is measured in kg/batch
• The continuous mixer on the other hand is generally
dedicated to a single high volume product.
• Ingredients are continuously charged into the mixer in
accordance with the formulation.
• The mixing takes place as the material travels from the
charging port to the discharge nozzle, from where it is
continuously discharged.
• The output of a continuous mixer is measured in kg/hr.
Module 1 - Introduction 29

30. Mixing Time
• This is the duration of time it takes to mix concrete,
once the mixer is fully charged with all the materials.
• Charging is an important step because it gives the
materials an opportunity to pre-blend.
• The type and condition of the mixer, speed of
rotation, size of the charge, and nature of the
materials all determine the correct mixing time.
• The mixing time is not standard for each batch.
For example, a drum mixer with a small diameter
creates a greater velocity than a drum mixer with a
large diameter, therefore, the mixing time would be
decreased. 30

31. MIXING
• Uniformity tests on samples of fresh concrete from
the mixer at different stages of it’s discharge from a
given batch.
• Charging: pre-blending and ribboning effect.
• Mixing time: 1 minute is required for 0.75m³ capacity
mixer and 0.25 minute is required for each additional
0.75 m³ capacity.
Module 1 - Introduction 31

32. Performance of Mixture
• Workability of fresh concrete.
• Density of concrete
• Air content
• Compressive strength
• Coarse aggregate content
• w/powder ratio
• Powder content
Module 1 - Introduction 32

33. SUMMARY
• Concrete production processes
• Batching processes
• Mixing processes for production of uniform
quality concrete
Module 1 - Introduction 33

34. Department of Civil Engineering
Indian Institute of Technology Kanpur
A course on Hydration, porosity and strength of cementitious materials under the Massive Open Online Courses initiative
Dr Sudhir Misra
Dr KV Harish Courtesy: M.S. Shetty