1.10 concrete mixing
TRANSCRIPT
8/3/2019 1.10 Concrete Mixing
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ALWAYS SAY “THANKS” TO ANYONE WHO HELPS YOU
ASSALAMUALAIKUM & GOOD MORNING & KALEI VANAKAM
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MIXING OF CONCRETE
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MIXING
• Done in order to ensure each particle of
aggregate in fresh concrete will be coated
with the cement paste
• Also to give a homogenous even coloured
product.
• First stage of mixing is called “BATCHING”.
• Batching is process where it involves
weighing out or measuring out all of the
ingredients for a batch of concrete.
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• The materials that are mixed at any one time
constitute a batch.
• Quality of concrete depends on the accuracy
of the batching operation.
• However, thorough mixing is essential for
complete blending of the materials that are
required for the production of homogeneous,
uniform concrete.
• Inadequate mixing result in lower strength.
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• There are 2 method for concrete mixing that
is:
a) hand mixing
b) machine mixing
• The biggest problem with concrete produced
with construction mixers on site is quality
control.
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HAND MIXING
• Uniformity more difficulty to be achieved
• Aggregate is spread in a uniform layer on a
hard, clean & non porous basic.
• Then cement is spread over the aggregate and
dry material are mixed by turning over from
one end of the heap to another & cutting with
a shovel till the mix appear uniform.
• Water is gradually added to the trough formed
by the uniform dry mix.
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• It involves usage of more labours compared
concrete mixed using machine.• The quality of mix is difficult to be
controlled.
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• Hand Mixing
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MACHINE MIXING
• Ensure the concrete mixer is clean and have
no left over concrete before start mixing new
one.
• There are many types of machine for concrete
mixing such as Tilting Type Mixer, Non-
Tilting Type Mixer and Pan Mixer.
• Machine mixing is efficient & economicalcompared to hand mixing.
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• MIXING TIME
• Optimum length of mixing time depends ona) type of mixer
b) size / condition of mixer
c) Speed of rotation
d) Quality of blending materials
• Uniformity of mix increase together in length of
mixing time.
• Long mixing times may cause some breakdown
of the aggregate.
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• Lean, dry or harsh mixes require longer
mixing times
• Concrete made with angular aggregates need
more mixing than those made with rounded
gravels.
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Tilting Type Pan Mixer
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READY MIX CONCRETE
• Ready mix concrete is concrete that is made
at ready-mixed plant and then transported to
the site in rotating-drum trucks or transitmixers.
• Proportioning, batching, mixing and delivery
are all done by the concrete supplier.• High quality control
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• Advantages of using ready mix concrete:
a) better quality concrete due to usage of
trained personnel and automated
equipment
b) elimination of material storage on
congested building sites
- no need to allocate place at site for
storage of cement, aggregate, sand
c) save the contractor’s time and usage of
labour’s energy to mix the concrete
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• For ready mix concrete supply, the purchaser
should specify the following:
a) Designated max. size of coarse aggregateb) Desired / max. slump at the point of
delivery
c) Air content (for air entrained concrete)d) Mix design requirement – such as cement
content, max. water content & admixtures
or minimum compressive strength at 28days
e) Unit weight required (for structural
lightweight concrete.
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Ready Mix Concrete Truck
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• Ready Mix Batching Plant
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