1. Concrete mixing involves coating aggregate particles with cement paste to create a uniform mixture. Different types of mixers are used for manual or machine mixing. 2. Concrete mixers come in various styles including batch mixers, tilting drum mixers, non-tilting drum mixers, pan mixers, dual drum mixers, and continuous mixers. Each has advantages for different applications. 3. Concrete pumps are also used to transfer liquid concrete and come in boom pumps attached to trucks, line pumps mounted on trailers, and specialized pumps for mining and tunneling applications. Proper mixing and pumping ensures uniform, high quality concrete.

1. 1. Mixing of Concrete:
The mixing operation consists of rotation or stirring, the objective being to coat the
surface the all aggregate particles with cement paste, and to blind all the ingredie-
nts of the concrete into a uniform mass; this uniformity must not be disturbed by
the process ofdischarging from the mixer.
Fig.1a (Machine mixing) Fig.1b (Manual mixing)
2. Concrete mixer:
A concrete mixer (often mistakenly called a cement mixer) is a device that homo-
geneously combines cement, aggregate such as sand or gravel, and water to form
concrete.
3. Charging of mixer:
There are no general rules on the order of feeding the ingredients into the mixer as
this depend on the properties of the mixer and mix. Usually a small quantity of
water is fed first, followed by all the solids materials. If possible greater part of the
water should also be fed during the same time, the remainder being added after the
solids. However, when using very dry mixes in drum mixers it is necessary to feed
the coarse aggregate just after the small initial water feed in order to ensure that the
aggregate surface is sufficiently wetted.
4. Uniformity of Mixing:
In any mixer, it is essential that a sufficient interchange of materials occurs
between parts of the chamber, so that a uniform concrete is produced. The
efficiency of the mixer can be measured by the variability of the samples from the
mix. ASTM prescribes samples to be taken from about points 1/6 and 5/6 of the
discharge of the batch and the difference in the properties of the two samples
should not exceed any of the following:

2. 1. Density of concrete 1 lb/ft³
2. Air content 1%
3. Slump 1" when average is less than 4"
4. 1.5" when average is less than 4 to 6"
% of aggregate retained on 4 No. sieve 6%
5. Charging the mixer:
There are no general rules on the order of feeding the ingredients into the mixer as
this depend on the properties of the mixer and mix. Usually a small quantity of
water is fed first, followed by all the solids materials. If possible greater part of the
water should also be fed during the same time, the remainder being added after the
solids. However, when using very dry mixes in drum mixers it is necessary to feed
the coarse aggregate just after the small initial water feed in order to ensure that the
aggregate surface is sufficiently wetted
6. Mixing time:
It is important to know the minimum mixing time necessary to produce a concrete
of uniform composition, and of reliable strength. The mixing time or period should
be measured from time all the cementing materials and aggregates are in mixer
drum till taking out the concrete. Mixing time depends on the type and size of
mixer, on the speed of rotation, and on the quality of blending of ingredients
during charging of the mixer.
Recommendedminimum mixing times:
Table. A
Capacity of mixer
(yd³)
Mixing time
(Minutes)
Up to 1 1
2 1.25
3 1.5
4 1.75
5 2
6 2.25
10 3.25

3. 7. Type of concrete mixer:
7.1 Batch mixer:
Batch mixers enable the mixing of cement slurries and other fluids and feature two
centrifugal pumps for delivering fluid to high-pressure pumps, recirculating
cement slurries for mixing in blending tanks, and transferring fluids from remote
tanks. The batch mixers are cable of handling large volumes of cement slurry and
significantly reduce fluctuations in cement density.
The usual type of mixer is a batch mixer, which means that one batch of concrete is
mixed and discharged before any more materials are put into the mixer. There are
four types of batch mixer.
Fig. 2(Batch Mixer)
7.2 Tilting drum mixer:
A tilting drum mixer is one whose drum in which mixing take place is tilted for
discharging. The drum is conical or bowl shaped with internal vanes, and the
discharge is rapid and unsegregated so that these mixers are suitable for mixes of
low workability and for those containing large size aggregate.
Fig.3 (Tilting drum mixer)

4. 7.3 Non tilting drum mixer:
A non tilting drum is one in which the axis of the mixer is always horizontal, and
discharge take place by inserting a chute into the drum or by reversing the
direction or rotation of drum. Because of slow rate of discharge, some segregation
may occur.
Fig.4(Non tilting drum mixer)
7.4 Pan type mixer:
A pan type mixer is a forced–action mixer, as distinct from drum mixer which
relies on the free fall of the concrete inside the drum. The pan mixer consist of a
circular pan rotating about its axis with one or two stars paddles rotating about
vertical axis of pan.Used to prepare concrete specimens or mixtures,these pan type
mixers ensure an uniform efficient fast mixture action.
The mixers are equipped with a manually controlled discharge opening situated on
the bottom par t of the pan, for direct unloading of the mixture into a wheelbarrow
or suitable container.
Fig. 5(Pan type mixer)

5. 7.5 Dual drum mixer:
A dual drum is sometimes used in highway construction. Here there are two drums
in series, concrete being mixed part of the time in one and then transferred to the
other for the remainder of the mixing time before discharging.
Fig.6(Dual drum mixer)
7.6 Continuous mixers:
These are fed automatically by a continuous weigh-batching system.
The continuous (or 'pug mill') mixer model MAO/C gives a stream of mixed
concrete based on volumetric proportioning. Material is fed into one end from two
or more aggregate conveyors, cement screw feeder and flow-metered water. The
powerful twin-shaft mixing action transforms the raw materials into a continuous
stream of mixed concrete suitable for RCC (Roller Compacted Concrete.
.
Fig.7(Continuous mixers)

6. 8.Concrete pump:
A concrete pump is a machine used for transferring liquid concrete by pumping.
There are two types of concrete pumps. The first type of concrete pump is attached
to a truck or longer units are on semi-trailers
Fig.8(Pumping of concrete)
There are mainly three types of concretepumps:
1. Boom or truck mounted pump
2. Trailer, line, or stationary pump
3. Specialized usage pump
8.1 Boom or Truck Mounted Pump:
This type of pump is attached to a truck and uses a remote controlled articulating
robotic arm, also known as boom, to place the concrete accurately at the
construction site. It is also known as a truck mounted boom pump. Boom pumps
are generally used in large construction projects because of its capability of
pumping high volume of concrete in less time. It also saves substantial labor
because of its multi-purpose robotic arm.

7. Fig.9(Boom or Truck Mounted Pump)
8.2 Trailer, line or stationary pump:
This type of pump is mounted on a trailer and requires steel or rubber hoses to be
attached to the outlet of the machine. The hoses are generally manually attached
and can also be joined to another extension hoses to reach the appropriate site
where the concrete needs to be put. Trailer pumps pump concrete at a rate lower
than that of boom pumps and therefore are used in applications that require smaller
volume pumping such as swimming pools, sidewalks, and small homes concrete
slabs
.
Fig.10( Trailer, line or stationary pump)

8. 8.3 Specialized usage pump:
These pumps are specifically made for specialized job sites suchas mines and
tunnels. They are also skid mounted and rail mounted concretepumps but are not
commonly used due to their high costs and extra specialized mechanism.
Fig.11 (Specialized usage pump)
9. Reference:
 .Hunker, Henry L. (2000). Columbus, Ohio: A Personal Geography. Ohio
State University Press. p. 196. ISBN 978-0-8142-0857-1.
 "ControlTechnology for Ready-mix Truck Drum Cleaning" (PDF). U.S.
Department of Health and Human Services. 31 May 2001. Retrieved 21
October2013.
 Portland Cement Association: History of Ready Mixed Concrete industry
site
 Casey, Jon M. "Parmer Metered Concrete offers precision and quality". Hard
Hat News. Retrieved 24 November 2014.
 "MacGyver" Legend of the Holy Rose: Part 1 (1989) nce :