1 concrete technology concrete construction practices lecture 13 eng: eyad haddad
TRANSCRIPT
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Concrete TechnologyConcrete TechnologyConcrete Construction Practices
Lecture 13
Eng: Eyad HaddadEng: Eyad Haddad
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Chapter 7: Concrete Construction Practices
Batching and mixing.
Transportation.
Placement of concrete.
Finishing concrete.
Special aspects of handling concrete.
The production of high-quality concrete does not rest solely on proper
proportioning.
The concrete placed in a structure must be of :
(1. uniform quality, 2. free of voids and discontinuities, 3. adequately cured)
Lack of sufficient attention to mixing, handling, and placing can result
in poor concrete from a well-designed mix.
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Batching and mixing
A) Batching:
Batching of aggregates and cements is best done by weight, since
dispensing of solids on a volume basis can lead to gross errors.
Only water and liquid admixtures can be measured accurately by
volume. Look at Figure 11.1 of your text book for handling and storing of aggregates, figure
11.2 for methods of batching.
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Cement is preferably batched separately, but aggregates may be
batched separately or cumulatively.
Available materials handling equipment can be divided
into three general categories:
Manual
semi-automatic
and fully automatic.
Manual batching is generally only acceptable for small jobs (up to
400 m3 or 520 yd3) and low output requirements (15 m3fh or
20 yd3/h); otherwise,
semiautomatic should be used in semiautomatic arrangements,
the charging and discharging of the batchers are activated
manually, but are automatically terminated.
In a fully automatic system a single starter switch activates the
batching sequence.
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b) Mixing:
Thorough mixing is essential for the complete blending of the materials
that are required for the production of homogeneous, uniform
concrete. The optimum mixing time depends on:
The type of mixer.
The condition of the mixer.
The speed of rotation.
The size of the charge.
The nature of the components. Lean, dry or harsh mixes require more mixing than those made with rounded
gravels.
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Type of Mixer:
a horizontal shaft with spiral blades may be rotated in the drum.
Tilting drums: which are commonly used for small jobs, are also
available in large sizes. They have the advantage of a quick, clean
discharge even of dry mixes.
Horizontal drums: are discharged by inserting a chute to intercept the
concrete as it is mixing or by reversing the direction of rotation,
which forces the concrete out of the mixer.
C) Transportation
There are many different ways of handling concrete, it depend mostly on :
1. the amount of concrete involved.
2. the size and type of construction.
3. the topography of the job site.
4. the location of the batch plant, and the relative
costs.
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Methods of transportation can be assigned to four general categories:
wheeled transports.
Buckets.
conveyors and chutes.
pumps.
Transport of concrete from the batching plant to the job is generally by
ready mixed trucks equipped with a revolving drum for agitation.
The use of dumpsters should not involve long trip times to avoid
excessive slump loss or segregation.
Buckets, overhead cableways, or trucks can be used to transport
concrete from an adjacent batch plant.
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See table 11.1 in the text book (Methods of transportation concrete)
TRANSPORTATION (pumping)
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Placement of Concrete
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Placement of Concrete
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Placement of Concrete
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Placement of Concrete
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Placement of Concrete
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Placement of Concrete
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Placement of Concrete
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Placement of Concrete