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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)

1111

Placement of Concrete

1212

Placement of Concrete

1313

Placement of Concrete

1414

Placement of Concrete

1515

Placement of Concrete

1616

Placement of Concrete

1717

Placement of Concrete

1818

Placement of Concrete