precast

1. Precast Concrete
•Precast concrete, sometimes called
“prefabricated” or “pre made” concrete,
is a concrete product that is created offsite,
then delivered to its project destination for
final use.
• The form of construction where concrete
is cast in a reusable mould and then cured
in a controlled environment (precast plant)
is called precast concrete. The casted
structural member is then transported to
the construction site and then erected.
Structural members such as concrete
frames, concrete walls, and concrete floors,
etc. can be constructed using precast
concrete.

2. Precast Concrete
ADVANTAGES
Saves Construction Time:
Precast Concrete construction saves time, and the risk of project
delay is also less. The precast concrete casting can be carried on
simultaneously with other works on site such as earthwork, survey
etc., and thus saves time. It is a major advantage of precast
concrete.
Quality Assurance:
The key factors which regulate the quality of construction such as
curing, temperature, mix design, formwork, etc. can be monitored
for pre cast concrete. So, improved quality construction can be
performed.

3. Precast Concrete
ADVANTAGES
Usage of Prestressed Concrete:
By using pre-stressed precast, structural materials of high strength and
load-bearing capacity can be achieved, which can result in greater clear
span, reduced size of the cross-section of structural members, etc.
Cost-effective:
The simplified construction process reduces time, increases
productivity, quality and safety and thus the cost is reduced.
Durability:
Precast Concrete structure has a longer service time period and
minimal maintenance. The high-density Precast concrete is more
durable against acid attack, corrosion, and impact, reduces surface
voids, and resists the accumulation of dust.

4. Precast Concrete
ADVANTAGES
Aesthetics:
As the structures are made of prefabricated
concrete in a controlled factory environment,
several combinations of colors and textures
can be used. A wide range of shapes and
sizes are available to choose from with
smooth finishing and thus the aesthetical
value of products is increased.
Safe Construction Platform:
No raw materials have to be stocked on the
site for precast concrete construction. It
reduces the requirement of traditional
formworks and props, wastage, workers, etc.,
and thus provides a safe working platform.

5. Precast Concrete
ADVANTAGES
• Expedited construction
•Reduce time on site
•Reduces site defects
•Reduces propping and scaffolding costs
•Lower site labour cost
•Reduce plant, amenities, tools and materials storage on
site.
• Minimize finance cost resulting from reduced build time.
•Earlier revenue receipts because of shorter project times.
•The continued, uninterrupted erection of precast structural
components lends itself perfectly to fast track construction
schedules.

6. Precast Concrete
DISADVANTAGES
High Initial Investment:
For installing a precast concrete plant, heavy and sophisticated
machines are necessary which requires a high initial investment. A
large scale of precast construction projects must be available to
ensure sufficient profit.
Transportation Issue:
The construction site can be at a distant location from the precast
concrete plant. in that case, the precast members must be carried to
the site using trailers. in many cases, the reduced costs of pre cast
concrete are compensated by the transportation cost.

7. Precast Concrete
DISADVANTAGES
Handling Difficulties:
Proper care and precaution have to be taken for handling precast
concrete. Usually, precast members are heavy and large which
makes them difficult to handle without damage. Generally,
portable or tower cranes are used to handle precast members.
Modification:
Limitation in the case of precast structures, it is difficult to modify
the structure. For example, if structural precast concrete walls are
to be dismantled for modification it will impact the overall
stability of the structure.
Sensitive Connection Works:
Assembling the precast members is one of the key points for
ensuring strong structural behavior. Connections between several
structural members must be supervised and done properly to
ensure the intended behavior of the connection such as simple,
semi-rigid, or rigid connections. Besides this, faulty connections
in precast concrete may lead to water leakage and failed sound
insulation.

8. Precast Concrete
DISADVANTAGES
Sensitive Connection Works:
Assembling the precast members is one of the key points for
ensuring strong structural behavior.
Connections between several structural members must be
supervised and done properly to ensure the intended behavior of
the connection such as simple, semi-rigid, or rigid connections.
Besides this, faulty connections in precast concrete may lead to
water leakage and failed sound insulation.

9. Prestressed Concrete
Pre-stressed concrete is a form of concrete where initial compression
is given in the concrete before applying the external load so that
stress from external loads is counteracted in the desired way during
the service period. This initial compression is introduced by high-
strength steel wire or alloys (called ‘tendons’) located in the concrete
section.

10. Prestressed Concrete
The basic principle of prestressing was applied to construction,
perhaps centuries ago, when ropes or metal bands were wound
around the wooden staves to form a barrel (see Figure 1). When the
bands were tightened, they were under tensile prestress, which in
turn created compressive prestress between the staves and enabled
them to resist hoop tension produced by internal liquid pressure. In
other words, the bands and the staves were prestressed before they
were subjected to any service loads.
T.Y. Lin
Like this, in prestressed concrete, initial compression is
given to be balanced by future loading that will create
tension.

11. Prestressed Concrete
In the real case, high tensile
strength steel wires are
inserted into the beam section
and they are stretched and
anchored, then released. Now
the steel tendon wants to gain
its original length and tensile
stresses are transformed into
compressive stress in
the concrete.

12. Prestressed Concrete
• According to AASHTO(The American
Association of State Highway and Transportation
Officials), high-strength seven-wire strands,
high-strength steel wire, or alloys of grade and
type (as specified by the designer) should be
used in pre-stressed concrete. Also, stronger
concrete is required in pre-stressed than normal
RC.
• Generally, minimum 28-day cylinder strength
of 5000 /Sq.inch concrete must be used.
• If the concrete is not strong enough, it can be
cracked or failed when it is stressed by tendons.
As well as high compressive strength offers
higher resistance to tension and shear and so it
is desirable for pre-stressed concrete.
• Moreover, high-strength concrete is less
subjected to shrinkage cracks. It has a higher
modulus of elasticity and smaller creep strain.
As a result, the loss of pre-stressing is small

13. Prestressed Concrete
According to the construction method, there
are three kinds of prestressed concrete:
• Pre-tensioned concrete
• Bonded Post-tensioned concrete.
• Un-bonded Post-tensioned concrete

14. PRE-TENSIONED CONCRETE
In this method, wires or tendons are tensioned at first and concrete is poured
later. It creates good bondage between the tendon and concrete. As a result,
the tendons are protected from corrosion, and tensions are transferred
directly. Tendons are anchored and stretched and the stress is transferred to
the concrete when it is hard. Then the tendon tries to get back to the original
length but is resisted by the bond between the concrete hence it induces
compressive force in it.

15. BONDED POST-TENSIONEDCONCRETE
Concrete is poured first then tendons are tensioned. Tendons are placed
at suitable places in the member and then casting is done. After the
concrete becomes hard, the tendons are tensioned by hydraulic jacks
against the concrete. When the tendons have tensioned sufficiently,
according to design, they are fixed in position. After the jacks are
removed, tension remains and it transfers pressure to the concrete. This
method is widely used in building monolithic slabs for mega house
construction projects where expansive soil sometimes creates problems.
Moreover, post-tensioned concrete is also used in bridges.

16. UN-BONDED POST-TENSIONED CONCRETE
It is a little different from bonded post-tensioned concrete. It allows
freedom to move the cables. For this, each tendon is coated with grease
and covered by plastic. Stress transfer to the concrete is achieved by the
cables through anchors.
There are some advantages to this like-
• The ability to distress tendons before trying to repair work.
• The ability to individually adjust cables
Also, there are some disadvantages like if damaged, one or more cables
can distress themselves and burst out of the slab.

17. •A longer span length increases untroubled floor space and parking
facilities.
•Thinner slabs are important for high-rise buildings as with the same
amount of cost, it can construct more slabs than traditional thicker
slabs.
•As the span length is larger, fewer joints are needed than in
traditional RC structures.
•Because of fewer joints, maintenance cost also becomes reduced
during the design life as joints are the major locus of weakness in a
concrete building.
•Under service loading conditions, the structural member sections
remain untracked. As a result steel corrosion is reduced and long-
term durability is achieved.
ADVANTAGES

18. ADVANTAGES
•As full member section is utilized here, a higher moment of inertia, less
deformations, and high shear capacity is achieved with a lower section
size.
•It requires a smaller amount of construction materials.
•Better finishing of placed concrete
•It resists stresses that are higher than normal RCC structures and is free
from cracks.
•Rapid construction with better quality control is possible.
•Less maintenance is required.
•For repetitive construction, prestressed concrete is more suitable than
regular concrete without prestressing.
•In this type of concrete, multiple uses of formwork are possible. It can
reduce the formwork amount.

19. DISADVANTAGES
•It requires high-strength concrete and high-tensile-strength steel wires.
•The main disadvantage is construction requires additional special
equipment like jacks, anchorage, etc.
•Concrete prestressing requires skilled technology. It needs highly skilled
workers under skilled supervision.
•Construction cost is a little higher than RCC structures as it costs higher
for high-strength materials.

20. APPLICATIONS OF PRESTRESSED CONCRETE
Construction of Bridges:
• The most common use is in the construction of pre-stressed concrete
box girder bridges, where the concrete is pre-stressed in the factory
before being transported to the bridge site. This type of bridge is very
strong and durable and is often used in the construction of long-span
bridges.
• also used in the construction of cable-stayed bridges, the precast
concrete deck slab is supported by a series of cables that are connected to
towers.
Construction of Buildings
• This type of concrete is made by adding steel to the concrete mix, which
gives it added strength and stability. Prestressed concrete is often used
for beams and columns, as well as for floor and roof slabs in prestressed
concrete buildings. It is also commonly used for making precast concrete
products such as wall panels and stairs.

21. APPLICATIONS OF PRESTRESSED CONCRETE
Construction of Parking Structures
• the ability to resist deflection and movement during seismic
events, the ability to resist corrosion, and the ability to resist
wind and water damage
• provide a permanent foundation for the structure, which
eliminates the need for regular maintenance.
Construction of Storage Tanks
•a lighter and thinner wall, which reduces the overall weight of
the tank.
• can be designed to resist external forces, such as wind and
earthquake loading
Rail Tracks:
• Prestressed concrete sleepers or crossbeams or bars are used
in rail tracks
• is also less likely to be damaged by the weight of trains
passing over it, and can be designed to minimize the effects of
vibration.

22. APPLICATIONS OF PRESTRESSED CONCRETE
Telephone and Electricity Transmission Lines:
• the concrete is able to withstand the heavy loads imposed by
the weight of the transmission lines and the forces generated
by the movement of the lines.
Concrete Pavements:
•The pavement is first pre-stressed with high-strength cables or
rods, and then concrete is poured over the top. The prestressed
concrete helps to resist the forces of traffic and weathering and
extends the life of the pavement.
Concrete Piles:
• it can increase the load-bearing capacity of the piles.
• allows for a more efficient transfer of loads from the concrete
to the piles, which results in a higher load-bearing capacity
• Additionally, help to prevent cracking and other types of
damage that can occur in concrete piles
Sewers
• an ideal material for sewers because it is extremely strong and
durable, withstand the high pressures and loads that are
typically exerted on sewer systems. Additionally, is resistant to
corrosion and will not degrade over time.

24. MODULUS OF ELASTICITY
Modulus of elasticity (also known as elastic modulus,
the coefficient of elasticity) of a material is a number that
is defined by the ratio of the applied stress to the
corresponding strain within the ELASTIC LIMIT. Physically it
indicates a material’s resistance to being deformed when
stress is applied to it. Modulus of elasticity also indicates
the stiffness of a material. The value of elastic modulus is
higher for stiffer materials.
Modulus of Elasticity,E= f/s
Here, f= applied stress on a body
s= strain to correspond to the applied stress
Units of Elastic Modulus
Units of elastic modulus are followings:
In SI unit MPa or N/mm2 or KN per square meter

25. What Is M25 Concrete Mix Design?
M25 Concrete Ratio (1:1:2) :
•Uses & Materials Required For 1 Cubic Meter of M25
Concrete.
•M stands for Mix ratio of cement : sand: aggregate & 25
Stands for Compressive Strength @ 28 Days in N/mm².
•M25 grade concrete is 25000Mpa.
• M25 concrete is stiffer than M20

26. Concrete Frame Construction
Concrete frame construction is a
construction method which
comprises a network of columns
and beams to transfer the loads
coming onto the structure to the
foundation successfully.
Holistically, it forms a structural
skeleton for the building which is
used to support other members
such as Floors, Roof, Walls, and
Claddings.

27. Major Parts of Concrete Frame Construction
1. Columns
- Columns are an important structural member of a
frame building. They are the vertical members which
carry the loads from the beam and upper columns and
transfer it to the footings.
- The loads carried may be axial or eccentric.
- Design of columns is more important than the design
of beams and slabs.
- if one beam fails, it'll be a local failure of one floor, but
if one column fails, it can lead to the collapse of the
whole structure.

28. COLUMNS

29. Major Parts of Concrete Frame Construction
1. Beams
- Beams are the horizontal load-bearing members of the framed
structure. They carry the loads from slabs and also the direct
loads of masonry walls and their self-weights.
- The beams may be supported on the other beams or may be
supported by columns forming an integral part of the frame.
These are primarily the flexural members. They are classified
into 2 types :
Main Beams - Transmitting floor and secondary beam loads to
the columns.
Secondary Beams - Transmitting floor loads to the main beams.

30. BEAMS

31. Major Parts of Concrete Frame Construction
Slab
- A slab is a flat horizontal place that is used for covering the
building from the above and provide shelter for the
inhabitants. These are the plate element and carry the loads
primarily by flexure.
- They usually carry vertical loads.
- Under the action of horizontal loads, due to a large moment of
inertia, they can carry large wind and earthquake forces, and
then transfer them to the beam.

32. SLAB

33. Major Parts of Concrete Frame Construction
Foundation
- The sole function of the foundation is to transmit the load
coming from the above columns and beams to the solid
ground

34. Major Parts of Concrete Frame Construction
Shear Walls
- These are important structural elements in high-
rise buildings.
- A shear wall is a structural support element that resists
shear forces
- Shear walls are actually very large columns because of
which they appear like walls rather than columns.
- They take care of the horizontal loads like wind
and earthquake loads.

35. SHEAR WALLS

36. Major Parts of Concrete Frame Construction
Elevator Shafts
- The elevator shaft is a vertical concrete box in which the
elevator is provided to move up and down.
- These shafts help in resisting horizontal loads and also
carry the vertical loads.