Concrete Technology: Concrete Production, Properties and Testing Unit 4 Part 2

Que 4.1. Explain the various steps in the manufacturing of



The various stages in the manufacture of concrete are as follows :

1. Batching of Concrete : Batching is the process of measuring concrete

mix ingredients by either mass or volume and introducing them into the

mixer . To produce concrete of uniform quality, the ingredients must be

measured accurately for each batch.

The two methods of batching are as follows :

i. Volume Batching :

a. Volume batching is not a good method because of the inaccuracies it

introduces in the measurement of granular materials.

b. Loose sand in a moist condition occupies more volume than dry compacted

sand due to the phenomenon of bulking. Hence, the effect of bulking

must be considered while measuring sand.

c. Despite drawbacks, for less important non-engineered small works,

this method is adopted because of its ease in application. However, it is

unscientific and hence not recommended for important works.

ii. Weigh Batching :

a. Weigh batching is the correct method of measuring the materials that

are used to make concrete.

b. Use of weigh batching system facilitates accuracy, flexibility, and


c. For large works, a weigh batching plant is used.

2. Mixing : The mixing should ensure that the mass becomes homogeneous,

uniform in colour and consistency.

Methods of Mixing :

i. Hand mixing.

ii. Machine mixing.

3. Transporting : It is the process of transferring of concrete from the

mixing plant to the construction site. It can be done by following

equipments :

i. Mortar Pan : Concrete is carried in small quantities.

ii. Wheelbarrows and Buggies : Short flat hauls on all types of onsite

concrete construction.

iii. Cranes and Buckets : Used for work above ground level , buckets use

with cranes, cableways, and helicopters.

4. Compaction of Concrete :

i. Compaction of concrete is process adopted for expelling the entrapped

air from the concrete.

ii. In the process of mixing, transporting and placing of concrete air is

likely to get entrapped in the concrete.

iii. It has been found from the experimental studies that 1 % air in the

concrete approximately reduces the strength by 6 %.

5. Curing :

i. It is the process in which the concrete is protected from loss of moisture

ii. The result of this process is increased strength and decreased


iii. Curing is also a key player in mitigating cracks in the concrete, which

severely impacts durability.

6. Finishing :

i. The finish can be strictly functional or decorative.

ii. Finishing makes concrete attractive and serviceable.

iii. The final texture, hardness, and joint pattern on slabs, floors, sidewalks,

patios, and driveways depend on the concrete’s end use.

Que 4.2. Explain the mixing and transporting operations of

concrete in a work site.


A. Methods of Mixing : Concrete is mixed either by hand mixing or by

machine mixing, based on the quantity of concrete required.

1. Hand Mixing :

i. Mixing by hand is employed only for specific cases where quality is not of

much importance, either because of the unimportant nature of the

work or because the quantity of concrete required is less.

ii. Hand mixing generally does not produce uniform concrete and hence

should not be normally used, unless it is for very small domestic works.

2. Mechanical Mixing :

i. Mechanical mixers can be divided into two main types : batch mixer and

continuous mixers.

ii. Batch mixers produce concrete batch by batch, one batch at a time. The

operation is intermittent. The raw material is loaded at one end and the

concrete is discharged at the other end. This constitutes a cycle of

operation which is repeated until enough quantity of concrete is


iii. Continuous mixers produce concrete at a specified rate. The raw materials

are continuously entered at one end and mixed concrete exits from the

delivery end.

B. Transportation of Concrete : The following methods are used for

1. Direct Discharge into Forms by Short Chutes :

i. Short chutes in a semi-circular shape stiffened at intervals are simple

and economical to use.

ii. Free fall of concrete from a height of more than 2 m must be avoided.

2. Barrows :

i. Manual wheelbarrows of approximately 80 kg capacity can be used for

long horizontal distances.

ii. For major works, power barrows of 800 kg capacity, up to 300 m hauls

are used.

3. Dumpers and Trucks :

i. These are used for horizontal long hauls.

ii. Because of jolting, especially if the terrain is rough, the concrete during

transit has the risk of segregation.

4. Elevating Towers and Hoist : In multi-storied buildings, elevating

towers are used for lifting concrete buckets. The lifted concrete is then

distributed by either chutes or barrows. This type of transportation can

be used where high lifts are required.

5. Monorail System :

i. In tunnels and in dam sites, a single track is laid to carry a monorail

power wagon which moves at a speed of 80 m/min.

ii. This type of transportation can be used for covering long distances.

6. Cranes and Cableways :

i. When concreting is to be done in a large project covering mountains and

valleys, cranes and cableways are used to provide three-dimensional

transport enabling both horizontal and vertical movement.

ii. Depending on the site condition, the type of crane can be chosen. It may

be a derrick, crawler, or wheel mounted.

7. Belt Conveyor :

i. It can be used when hauling concrete over long distances.

ii. It is not very much recommended because of its vulnerability to


iii. The initial setting-up cost is also high. Discharge can be as high as

115 m3/h.

8. Concrete Bucket and Skip : The capacity of the skip varies from

about 0.2 m3 to 10 m3.

Que 4.3. What are the precautions to be taken while transporting

concrete ? What are the advantages and disadvantages of concrete

pump ?


A. Precautions in Transporting of Concrete : Following precautions

should be used during transporting of concrete :

1. While water is added to cement, the procedure of hydration starts and

with the passage of time, so concrete should be transported as fast as

possible to the formwork within the initial setting time of cement.

2. The procedure of mixing, transporting, placing and compacting concrete

should not take more than 90 minutes in any case.

Concrete Production, Properties & Testing 4–6 D (CE-Sem-5)

3. No water shall be lost from the mix during transportation.

4. The concrete combine should be protected from drying in hot weather

and from rain during transport from the place of mixing to the position

of placing.

5. Segregation of concrete should be avoided under all circumstances.

6. The concrete shall be kept agitated in truck mixer in order to avoid it

from becoming stiff if more time is likely to be spent during transportation.

B. Advantages of Concrete Pump :

1. Concrete pumping is a faster and easier method to complete a project.

2. Concrete pumping reduces labour costs.

3. It reduces site congestion as there are less construction workers.

4. It provides a steady work pace, increasing productivity.

5. It is effective and economical for various sized projects, including

residential and commercial.

6. Several pumps can pour simultaneously for larger projects.

C. Disadvantages of Concrete Pump :

1. Possibility of a concrete pump breaking down.

2. Risk of injury to construction workers and damage to property.

3. During busy periods it is not always easy to find a concrete pump that is


Que 4.4. Define workability. What are the factors affecting the

workability of concrete ?


A. Workability of Concrete :

i. A concrete is said to be workable if it is easily transported, placed,

compacted and finished without any segregation.

ii. Workability is a property of freshly mixed concrete, and a concrete is a

mixture of cement, aggregate, water and admixture.

B. Factors Affecting of Workability of Concrete : Following are the

factors affecting of workability of concrete :

1. Water Content : Workability of concrete increases with increase in

water content.

2. Aggregate/Cement Ratio : The higher the aggregate/cement ratio,

the leaner is the concrete, resulting in lesser workability.

3. Size of Aggregate : For a given quantity of water and paste, bigger size

of aggregates will give higher workability.

4. Shape of Aggregate : Better workability is ensured to rounded

aggregate than angular, elongated or flaky aggregate.

Concrete Technology 4–7 D (CE-Sem-5)

5. Grading of Aggregate : This is one of the factors which will have

maximum influence on workability. A well graded aggregate can lead to

good workability.

6. Surface Texture of Aggregate : Rough textured aggregate will show

poor workability and smooth or glassy textured aggregate will give better


7. Use of Admixture : The right way of improving workability is to use

chemical admixtures such as plasticizers, super plasticizers, air entraining

agents, etc.

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