1.10 Concrete Mixing

8/3/2019 1.10 Concrete Mixing

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MIXING OF CONCRETE



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.



• 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.



• 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.



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.



• It involves usage of more labours compared

concrete mixed using machine.• The quality of mix is difficult to be

controlled.



• Hand Mixing



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.



• 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.



• Lean, dry or harsh mixes require longer

mixing times

• Concrete made with angular aggregates need

more mixing than those made with rounded

gravels.



Tilting Type Pan Mixer



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



• 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



• 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.



Ready Mix Concrete Truck



• Ready Mix Batching Plant



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1.10 Concrete Mixing

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