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
i. Mortar Pan : Concrete is carried in small quantities.
ii. Wheelbarrows and Buggies : Short flat hauls on all types of onsite
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
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
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
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
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
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
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
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
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