CEL 774
IIT DELHI

Construction pRACTICES

( Lecture 2-3)
Concrete: Production
B. Bhattacharjee
CIVIL ENGINEERING DEPARTMENT
IIT DELHI

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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General Outline
™Concrete Production.
D Mixing.

B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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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 the
work.

B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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MIXING
– cyclic or batch mixers, and continuous
mixers. .
– gravity mixers or mixers with forced
movements
o They can be tilting or Non-tilting
– Counter-flow mixer or open–pan
mixers

B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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TILTING DRUM MIXER

B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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NON-TILTING DRUM MIXER

B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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PAN MIXER

B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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PAN MIXER

B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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MIXING
– uniformity tests on samples of fresh
concrete collected from the mixer at
different stages of its discharge from a
given batch. .
– Charging: pre-blending and ribboning
effect
– Mixing Time: 1minute is required for
0.75 m3 capacity mixer and 0.25 minute
is required for each additional 0.75 m3
capacity
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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MIXING TIME
– IS guide lines
■IS 4925-1968 “mixing time for each batch
of materials, except the full amount of
water, provided that all the mixing water
shall be introduced before one-fourth the
mixing time elapsed” shall be 1½, 2 and 2½
minutes respectively for mixer capacity up
to 2 m3, 3 m3 and 4 m3 respectively. IS
456 : 2000 guidelines specifies a overall
minimum mixing time of 2 minutes
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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MIXING TIME
–increasing mixing time may result in more
uniform distribution of hydration product
resulting in higher compressive strength
–prolonging the mixing process too long may
not increase the strength proportionally and
may result in a decrease in some cases.
–over grinding of the material and in some
cases may increase the proportion of fines.
Quite often excessive mixing leads to
segregation in case of leaner concretes.

B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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– Strength & Variance

MIXING TIME

Strength

Variance

– Time
B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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SUMMARY
– Concrete production process
–Batching process and its importance in
producing quality concrete
–Mixing process for producing uniform
quality concrete

B. Bhattacharjee
DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI

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THANK YOU
FOR HEARING

DEPARTMENT OF CIVIL ENGINEERING, IIT DELHI
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