Types of Concrete

Contents

1. Plain Cement Concrete (PCC)

 Definition
 Materials Used in Plain Cement Concrete
 Main Purposes of PCC
 Advantages of PCC
 Disadvantages of PCC

2. Reinforced Concrete

 Introduction
 Materials Used in Reinforced Concrete
 Main Purposes of RCC
 Advantages of Reinforced Concrete .
 Disadvantages of Reinforced Concrete.

3. Architectural Concrete

 Definition
 Basic principles
 Formwork systems for walls
 Formwork systems for slabs
 Frameworks Systems for columns
 Formwork systems for 3D free-form surfaces
 Advantages of Architectural Concrete
 Disadvantages of Architectural Concrete
 How to Achieve Architectural Concrete
 Surfing Finishing
 On Site Support

4. Prestressed Concrete

 Introduction

 Types of pre-stressing:
 Advantages of Prestressed Concrete
 Differences between post tensioning and pre tensioning
 Disadvantages of Prestressed Concrete

5. Precast Concrete

 Introduction
 Advantages of Precast Concrete Construction
 Advantages of Precast Wall Systems
 Disadvantages
 Uses of Precast Concrete
 Slabs
 beams
 Walls
 Methods of Attachment of Precast Concrete members
 Joining Precast Concrete member
 Materials of Precast

6. Ready Mixed Concrete

 Introduction
 Equipment Required in RMC
 Materials used in RMC
 Tests carried out on RMC
 Tests on Fine Aggregates
 Tests on water
 Process of RMC
 Applications of RMC
 Types of RMC
 Features of RMC
 Limitations of RMC

Concrete
 Concrete is a mixture of cement, fine and coarse aggregate.
 Concrete mainly consists of a binding material and filler material. If filler
material size is < 5mm it is fine aggregate and > 5mm is coarse aggregate.

Plain Cement Concrete (PCC)

 Mixture of cement, sand and coarse aggregate without any reinforcement
is known as PCC.
 PCC is strong in compression and week in tension. Its tensile strength is
so small that it can be neglected in design.
 The plain cement concrete has considerable strength in compression has
little strength in tension. Therefore the use of plain cement concrete is
restricted to situations where high compressive strength and weight are
the primary requirements.1

Materials Used in Plain Cement Concrete
The general specifications of materials used in PCC are -

1. Coarse Aggregate
 Coarse aggregate used in the PCC must be of hard broken stone of granite
or similar stone, free from dust, dirt and other foreign matter. The stone
ballast shall be 20 mm in size and smaller. All the coarse material should
be retained in a 5mm square mesh and should be well graded so that the
voids do not exceed 42%.

1 . Plain and Reinforced Cement Concrete Construction by Khushbu Sharh

2. Fine Aggregate
 Fine aggregate shall be of coarse sand consisting of hard, sharp and
angular grains and shall pass through a screen of 5 mm square mesh.
Sand shall be of standard specifications, clean and free from dust, dirt
and organic matter. Sea sand shall not be used.

3. Cement
 Portland Pozzolana cement (P.P.C) is normally used for plain cement
concrete. It should conform to the specifications and shall have the
required tensile and compressive stresses and fineness.

4. Water
 Water used shall be clean and reasonably free from injurious quantities
of deleterious materials such as oils, acids, alkalis, salts and vegetable
growth. Generally, potable water shall be used having a pH value not
less than 6. The maximum permissible limits for solids shall be as per IS
456:2000 Clause .2

Main Purposes of PCC
1. t is used as a protective layer for the RCC above so that water from
the RCC is not absorbed by the earth below.
2. Moisture available in soil should not absorbed by R.C.C footings
which causes corrosion of reinforcement.
3. PCC provides a base for the concrete and also helps workers to set out
the structure above in a easier way.

2 Plain Cement Concrete (PCC)- Work Procedure by Fasi Ur Rahman

4. It provides a flat base for upcoming foundation rather than undulated
base.

5. The effective depth of RCC member is achieved as the form-works
can be easily and sturdily fixed.

6. As the Grade of concrete of PCC and Foundation is different it also
provide material difference for ground bacterial effect on foundation.

7. Act as a cover to reinforced cement concrete i.e. resist corrosion of
steel bars in footings.

8. Some time it can decrease the stresses to the soil.3

Dos and Don’ts of PCC Works
Dos
1. PCC shuttering should be of the exact size and thickness

2. Water should be mixed with a bucket, in a measured quantity, as per w/c
(water/ cement) ratio.

3. Use the chute or additional labor to pour the concrete where the depth is
more.

4. Remove any loose material from the sides of the pit, so that no soil or other
material will collapse in the pit during concreting.

5. If the water table is high, then de-watering should be carried out at the same
time during concreting.

3 What is plain cement concrete? by Krishna Chouhan

Don’ts
1. Do not mix the materials on bare land.
2. Do not allow the PCC without formwork.
3. Do not pour concrete without leveling and compacting.
4. Do not pour concrete in the pit from a height of more than 1.5 m.
5. Do not allow extra cement mortar on top of PCC. for smooth finishing.4

4 Plain Cement Concrete (PCC)- Work Procedure by Fasi Ur Rahman

Reinforced Concrete

5Reinforced concrete, or RCC, is concrete that
contains embedded steel bars, plates, or fibers that
strengthen the material. The capability to carry loads
by these materials is magnified, and because of this
RCC is used extensively in all construction. In fact,
it has become the most commonly utilized
construction material.

Reinforced materials are embedded in the concrete
in such a way that the two materials resist the
applied forces together. The compressive strength of
concrete and the tensile strength of steel form a
strong bond to resist these stresses over a long span.
Plain concrete is not suitable for most construction
projects because it cannot easily withstand the
stresses created by vibrations, wind, or other forces.

Materials Used in Reinforced Concrete

Concrete is made from small stones and gravel called aggregate, sharp
sand, cement and water. The small stone and gravel (aggregate) is the
reinforcement and the cement is the matrix that binds it together. Concrete has
good „strength‟ under compression but it is weak in tension. It can be made
stronger under tension by adding metal rods, wires, mesh or cables to the
composite. The concrete is cast around the rods. This is called reinforced
concrete.

Concrete is strong when under a compressive force. This is the case in
most buildings, for example, the foundation of a building. The weight of the
walls press down on the concrete foundations, compressing the concrete.

5 What is reinforced concrete? Alisha Waghmare

Concrete is the ideal material for the foundations because it can withstand this
type of compressive force.

Concrete can be reinforced by adding steel rods to the concrete mixture,
allowing the concrete to set solid. The steel rods ensures that reinforced
concrete can withstand tensile forces. This makes reinforced concrete a
versatile, composite material. It is used widely in the construction industry.6
Reinforced concrete has long steel rods passing through its length, adding
great strength to the final composite material, especially the ability to resist
tensile forces.

The drawing below shows the concrete as being transparent. This is so the grid of steel rods can be seen in position.

Main Purposes of RCC

Among such concrete structural members are beams, girders, joists, structural slabs of all
kinds, some columns, walls that must resist lateral loads, and more complex members
such as folded plates, arches, barrels, and domes. In addition to unintentional omission of
part or all of the reinforcement, improper placement of the reinforcement designed to
resist tension is one of the most common causes of structural concrete failures
(The foloowing fig.)).

6 COMPOSITE MATERIALS - REINFORCED CONCRETE by V.Rayan

If the tensile steel is not properly placed in the tension zone of a structural member, it will
not be effective in resisting tension, and failure may occur.

Other reinforcement applications:-
In addition to its use to resist tension in structural members, reinforcement

is used in concrete construction for other reasons, such as:
• To resist a portion of the compression force in a member. The compressive
strength of steel reinforcement is about 20 times greater than that of normal-
strength concrete. In a column, steel is sometimes used to reduce the size of
the column or to increase the column‟s carrying capacity (The following Fig.).
Compression steel is sometimes used in beams for the same reasons.

• To resist diagonal tension or shear in beams, walls, and columns.
Reinforcement used to resist shear in beams is commonly in the form of
stirrups (The following Fig), but may also consist of longitudinal

reinforcement bent up at an angle near the ends of the beam, or welded wire
fabric. In columns, shear reinforcement is typically in the form of ties, hoops,
or spirals.7

Advantages of Reinforced Concrete :-
1.Reinforced concrete has a high compressive strength compared to other
building materials.
2.Due to the provided reinforcement, reinforced concrete can also withstand a
good amount of tensile stress.
3. Fire and weather resistance of reinforced concrete is fair.
4. The reinforced concrete building system is more durable than any other
building system.
5. Reinforced concrete, as a fluid material, in the beginning, can be
economically molded into a nearly limitless range of shapes.
6. The maintenance cost of reinforced concrete is very low.

7 REINFORCEMENT FOR CONCRETE— MATERIALS AND APPLICATIONS

7. In structures like footings, dams, piers etc. reinforced concrete is the most
economical construction material.
8. It acts like a rigid member with minimum deflection.
9. As reinforced concrete can be molded to any shape required, it is widely
used in precast structural components. It yields rigid members with minimum
apparent deflection.
10. Compared to the use of steel in structure, reinforced concrete requires less
skilled labor for the erection of the structure.
Disadvantages of Reinforced Concrete:-
1. The tensile strength of reinforced concrete is about one-tenth of its
compressive strength.
2. The main steps of using reinforced concrete are mixing, casting, and curing.
All of this affects the final strength.
3. The cost of the forms used for casting RC is relatively higher.
4. For multi-storied building the RCC column section for is larger than steel
section as the compressive strength is lower in the case of RCC.
5. Shrinkage causes crack development and strength loss.8

8 https://civiltoday.com/civil-engineering-materials/concrete/23-advantages-and-disadvantages-of-reinforced-
concrete

Architectural Concrete

Architectural concrete refers to concrete that while providing an
aesthetic finish to the building also serves a structural function.9

Basic principles

The creation of architectural concrete as a design element is influenced by the following:
1. Formlining and formwork system.
2. Concrete mix, including type of cement and aggregates.
3. Added pigments.
4. Selection of a suitable release agent.
5. Subsequent surface treatment, such as washing, sanding, polishing and sand-blasting.
6. Hydrophobising impregnation, colour varnishing and coatings.10

Formwork systems for walls:
1.Panel formwork:-

The panel joints leave a typical impression on the concrete surface. In addition,
the steel or aluminium frames are used for installation of the formwork anchors and also
serve for accommodating the formwork couplers and moving devices.

9 . https://www.cement.org/cement-concrete-applications/products/architectural-and-decorative-concrete
10 Architecture Concrete by Peri group

The grid arrangement of the standard panels and formwork ties varies between 2.7
m and 3.5 m, and the individual panels can be connected with each other either vertically
or horizontally. Panel formwork is robust, long-lasting and easy to use due to its pre-
determined assembly arrangement.

2 Girder formwork:-
Its name is derived from the wooden or metal formwork girders that

are used. Main beams, steel waling and freely-selectable formlining
form prefabricated formwork elements, the so-called formwork sections.
The steel walers connect the system and also serve as support surfaces for the
anchoring system.

3 Circular formwork
Curved walls can be constructed polygonally in the form of a

polygon with panel formwork through inserted trapezoidal cover strips.
Circular wall areas are formed with special girder formwork systems with
which the required radius is achieved by means of adjustable spindles
connecting the single waler sections.

Formwork systems for slabs :-
Likewise as for girder formwork systems for walls, slab formwork is

made out of wooden or metal girders. It stands out through its flexible range
of applications.

Slab tables, which are normally used to form large slab areas, consist
of the same system components. Through the large-sized formlining surfaces,

the number of panel joints is reduced and facilitates a concrete finish which
fully meets higher requirements.

Similar to the panel formwork for the wall area, panel formwork was
developed for constructing slabs. The main advantage of panel slab formwork
is the fast and safe utilisation. According to the design, slab formwork is
divided into:

 Girder slab formwork.
 Panelised slab formwork.
 Girder grid slab formwork.
 Large-sized formwork (e.g. table modules, customised tables).

With slabs, the quality of the concrete surface can vary for different
reasons. This includes panel impressions caused by the panel layout of
the formwork system being used. Likewise the quality, arrangement and size
of the individual sheets of the freely selected formlining influences
the concrete quality.

Frameworks Systems for columns
Column or support formwork is mostly a derivation of panel

or girder formwork. As a result, the special features are very similar. In order
to be able to fulfill the required quality standard for supports and columns, the
correct choice of formwork system also has to be selected here.

Depending on the requirements of the column cross-section,
the finish of the edges or the concrete surface, panel and girder formwork are
used.

Formwork systems for 3D free-form surfaces

Through the use of extraordinary structural forms, owners and architects frequently set
visual accents in the construction of cultural buildings or for prestigious structures which
feature very demanding building requirements. These so-called 3D free-form surfaces
can hardly be realised with conventional formworking methods.

Furthermore, there is the fact that most of the remaining visible surfaces are to
be constructed in the highest quality and with sharp edges. For these extravagant building
structures, an individual customised formwork concept must be realised in each case.

This formwork concept is developed on the basis of a three-
dimensional building model provided by the formwork manufacturer. It consists of
statically supporting basic elements and form-giving 3D formwork units. The
individual elements are easily joined together on the construction site and then positioned
with the help of measuring points, auxiliary axes and erection aids. On-site utilisation
takes place similar to that of systemized formwork.

Advantages of Architectural Concrete :-
 It is durable and low maintenance
 Cost effective in comparison with other systems
 Resists mechanical damage
 Eliminates the need for the application of coatings or paints
 Versatile in design
 Numerous colors are available.11

11 ARCHITECTURAL CONCRETE Sika Group

How to Achieve Architectural Concrete?
UNDERSTANDING THE DESIGNERS VISION IS VITAL
To enable the successful realization of the design to the completed
structure, it needs to be involved at the earliest opportunity. This
collaborative approach ensures good communication and understanding at
all times throughout the project.

PROPER FORMULATION OF THE CONCRETE MIX DESIGN
It is key to achieving architectural concrete of the required quality.

Locally available materials (aggregates and cement) need to be evaluated to
ensure that the selected solutions are optimized providing superior finishes
and durability.

SURFACE FINISHING
There are many different types of surface finish that can be achieved.

Attention should always be given to type of surface finish as this will
always significantly affect the visual appreciation of the structure.

 Formed concrete
 Form lined concrete
 Exposed aggregate finishes

 Toweled finishes
 Brushed finishes
 Blast cleaned or mechanically tooled
 Patented imprinted concrete
 Polished concrete

ON-SITE SUPPORT
It representatives support the owner, designer and contractor on their

projects from the initial design through to completion. Samples of proposed
concrete formulations can also be provided so that the Designer and Owner
can make informed decisions. The technical staff are available on-site during
construction, so that the project is truly supported from conception to
completion.

Prestressed Concrete

Pre-stressed concrete Definition: Concrete in which there have
been introduced internal stresses of such magnitude and distribution that
the stresses resulting from given external loadings are countered to a
desired degree .12

It is the imposition of internal stresses into a structure that are of
opposite character to those that will be caused by the service or working
loads . A common method used to describe prestressing is shown in the
following figure where a row of books has been squeezed together by a
person's hands .13

12 Prestressed Concrete Structures by Mr. P. JAGATEESH
13 A Prestressed Concrete : A fundamental Approach by Ameer Izat

Types of pre-stressing:

Pre-tensioning & Post-tensioning :-

In pre-tensioning the tendons are tensioned before the concrete is placed.
The tendons are temporarily anchored to abutments or stressing beds. Then the
concrete member is cast between and over the wires. After the concrete has
attained the required strength, the wires are cut from the bulkhead and pre-
stress is transferred to the concrete member. In post-tensioning the concrete
member is cast with ducts for the wires. After concrete has attained sufficient
strength, wires are threaded into the ducts, tensioned from both or one end by
means of jack/jacks and at the precise level of pre-stress the wires are
anchored by means of wedges to the anchorage plates at the ends.

RESTRESSED PRE-TENSIONED CONCRETE
 Prestressed Pre-tensioned concrete is when the steel reinforcement is
stressed prior to concrete being placed around the steel.
 Pre-tensioned concrete is cast around already tensioned tendons.

 This method produces a good bond between the tendon and concrete,
which both protects the tendon from corrosion and allows for direct
transfer of tension.

 The cured concrete adheres and bonds to the bars and when the tension
is released it is transferred to the concrete as compression by static
friction.

 However, it requires stout anchoring points between which the tendon is
to be stretched and the tendons are usually in a straight line.

 Thus, most pretensioned concrete elements are prefabricated in a factory
and must be transported to the construction site, which limits their size.

 Pre-tensioned elements may be balcony elements, lintels , floor slabs,
beams or foundation piles. Section for Pre-tensioning.

CONCERNS WITH PRE-TENSION :

 Usually uses a mould which is able to resist the forces within the
tendons. Which are more expensive than regular moulds .

 Concrete sample should be taken for every new mix so that strength
obtained may be determined before cutting the tendons releasing the
stresses onto the concrete.

 Since pre-tension may only be set once calculations for the camber must
be correct. So, pre-stress takes a large amount of preplanning. Must
consider self-weight deflections, pre-stress deflections, dead load
deflections, and live load deflections. .

 Since it may only tightened once and cannot be retightened the designer
must also account for Creep of concrete, elastic shortening of concrete,
shrinkage of concrete, relaxation of steel, slip at the anchorage, and
friction losses due to intended and unintended (wobble) curvature in the
tendons in calculations for the camber of the member in order to have
lasting quality of the structure.14

14 Prestressed concrete design by M.K. Hurst

ADVANTAGES OF PRETENSION :-

Tension caused by the steel is spread throughout the length of the
concrete since it is bonded within the concrete along the length of the
member.

POST – TENSIONING

 It is a method of reinforcing (strengthening) concrete or other materials
with high-strength steel strands called tendons.

 Post-tensioning allows construction that would otherwise be impossible
due to either site constraints or architectural requirements.

 Requires specialized knowledge and expertise to fabricate, assemble and
install.

 After adequate curing of concrete, reinforcing tendons(placed in side the
voids of the structure) are tensioned/stretched by jacks on the sides &
grouts filled with appropriate mix.

APPLICATIONS

Structural members beams, bridge-deck panels, Roof –Slabs, Concrete Silos
Etc.

Benefits :-

 Concrete is very strong in compression but weak in tension.
 This deflection will cause the bottom of the beam to elongate slightly &

cause cracking.
 Steel reinforcing bars (“rebar”) are typically embedded in the concrete as

tensile reinforcement to limit the crack widths.
 Rebar is what is called “passive” reinforcement however; it does not

carry any force until the concrete has already deflected enough to crack.
 Post-tensioning tendons, on the other hand, are considered “active”

reinforcing.
 Because it is prestressed, the steel is effective as reinforcement even

though the concrete may not be cracked .
 Post-tensioned structures can be designed to have minimal deflection

and cracking, even under full load.

Bonded & Un-bonded tendon:-

In post-tensioning systems, the ducts for the tendons are placed along
with the reinforcement before the casting of concrete. The tendons are placed
in the ducts after the casting of concrete. The duct prevents contact between
concrete and the tendons during the tensioning operation.

Unlike pre-tensioning, the tendons are pulled with the reaction acting
against the hardened concrete. If the ducts are filled with grout, then it is
known as bonded post-tensioning. The grouting operation is discussed later.
In unbonded post-tensioning, the ducts are never grouted and the tendon is
held in tension solely by the end anchorages. The following sketch shows a
representation of a grouted post-tensioned member. 15

15 http://www.mocivilengineering.com/2019/03/types-of-prestressing.html

PROCESS:-
o Concrete is casted around a curved duct (usually corrugated), to allow
room for the Tendon to be inserted.
o After the concrete has hardened the tendons are pulled in tension and
then wedged.
o The duct is then injected with grout .

ADVANTAGES:-
o Tendons are less likely to de-stress in accidents .
o Tendons can be easily 'weaved' allowing more efficient designs
o Higher ultimate strength due to bond generated between the strand and
concrete.
o No issues with maintaining the anchor.

UNBONDED POST TENSIONED CONCRETE

 In post-tensioning, the steel in the concrete is stretched after the curing
process.

 Unlike bonded, un-bonded provides tendons freedom of movement by
coating each tendon with grease and covering it with a plastic sheathing.

 Tension on the concrete is achieved by the cables acting against the steel
anchors that are buried in the perimeters of the concrete UN-BONDED.

ADVANTAGES
 Post-stress grouting is eliminated .
 Ability to de-stress the tendons .
 Economical
 Replaceable
 Simple stressing equipment.

DIFFERENCES BETWEEN POST TENSIONING AND PRE TENSIONING :
POST-TENSIONING :

 Can be performed at the project site as well as at precast yards. There is
relatively less loss of prestress due to concrete shrinkage as at the time of
prestressing concerete has already been cured.

 Corrosion of steel is less as compared to pre-tensioning.
 There is more flexibility in design. The prestressing tendons can be

configured to almost any shape. As per requirements the tendons may be
bonded or unbonded.
 They are more prone to anchorage failure as the compressive forces are
transferred at the beam ends. Hence compressive stresses are concentrated.
PRE-TENSIONING :-
 Difficult to perform at site. Only done in precast yards.
 There is greater loss of prestress due to shrinkage of concrete.
 Concrete and steel tendons are in direct contact. So any moisture that
slips through cracks in concrete will cause corrosion in steel.
 Tendons can only be straight or circular.
 Since the compressive forces are transferred over a certain length of
bond, they are less prone to anchorage failure. So to generalize post-

tensioning is usually better than pre-tensioning. However this may not
always be the case. Either method has its applications.16

FORMS :
Wires:- Prestressing wire is a single unit made of steel.
Strands :-Two, three or seven wires are wound to form a prestressing strand.
Tendon:- A group of strands or wires are wound to form a prestressing tendon.
Cable:- A group of tendons form a prestressing cable.
Bars:- A tendon can be made up of a single steel bar. The diameter of a bar is
much larger than that of a wire.
Advantages of Prestressed Concrete :-
Followings are the advantages of prestressed concrete:

 Longer span length increases untroubled floor space and parking
facilities.

 Thinner slabs, that are important for high rise building 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 traditional RC
structures.

16 Prestressed concrete by Udisha Segh

 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.

 Long-term Durability.
 Better finishing of placed concrete.
 It requires a smaller amount of construction materials.
 It resists stresses are higher than normal RCC structures and is free from

cracks.

Disadvantages of Prestressed Concrete :-
Followings are the disadvantages of prestressed concrete:

 It requires high strength concrete and high tensile strength steel wires.
 The main disadvantage is construction requires additional special

equipment like jacks, anchorage, etc.
 It requires highly skilled workers under skilled supervision.
 Construction cost is little higher than RCC structures.17

17 https://civiltoday.com/civil-engineering-materials/concrete/226-advantages-and-disadvantages-of-prestressed-
concrete

Precast Concrete

Precast concrete means a concrete member that is cast and cured at a
location other than its final designated location. The use of reinforced concrete
is a relatively recent invention, usually dated to 1848 when jean- Louis
Lambot became the first to use it. Joseph Monier, a French gardener, patented
a design for reinforced garden tubs in 1868, and later patented reinforced
concrete beams and posts for railway and road guardrails.18

Advantages of Precast Concrete Construction:
 Prestressing is easily done which can reduce the size and number of the
structural members.
 High quality because of the controlled conditions in the factory .
 Rapid construction on site .
 Entire building can be precast-walls, floors , beams , etc.
 Good quality control .
 Very rapid speed of erection.

18 Precast Concrete Construction by Madan Mahan Jana

Advantages of Precast Concrete Wall Systems:
 Economy.
 Low maintenance .
 Security .
 Durability .
 Aesthetic versatility.

Disadvantages of Precast Concrete Construction :
 Cranes are required to lift panels.
 Skilled workmanship is required in the application of the panel on site.
 Joints between panels are often expensive and complicated.
 Need for repetition of forms will affect building design.
 Economics of scale demand regularly shaped buildings.
 Because panel size is limited, precast concrete can not be used for two-
way structural systems.
 Somewhat limited building design flexibility .
 Connections may be difficult .
 Very small margin for error .
 Camber in beams and slabs .
 Very heavy members .

Popular Uses of Precast Concrete
 Ability to precast in three dimensions allows precast panels to form parts

of mechanical systems.
 For structural walls .
 As an exterior cladding (may include exposed aggregate) .
 Concrete curtain walls .

Slabs

a) Flat slab :
 Thickness of 4", 6" and 8"
 Spans up to 25‟-0"
 Standard panel width = 4‟-0"
 Typical designations = FS4 (FS = Flat Slab, 4 = thickness of slab in

inches)
 precast concrete.

b) Hollow Core slab –
 Thicknesses of 4", 6", 8", 10" and 12" .
 Standard panel width = 4‟-0"
 Spans up to 40‟-0" .
 Typical designations = 4HC6 (4 = panel width in feet, HC = Hollow
Core, 6 = slab thickness in inches).

Beams

a) Rectangular Beam (RB) :-
 Typical beam width = 12" or 16"
 Typical designation = 16RB24 (16 = width in inches, 24 = depth in
inches).
 Spans up to 50‟-0"

b) "L" and "IT" (inverted "Tee") beams (LB and IT) :-

 Depths of 20", 28", 36", 44", 52" and 60".
 Typical beam width = 12" .
 Typically used to support slabs, walls, masonry, and beams.

c) Double Tee Beam (DT):
 Designation = 8DT24+2 (8 = width in feet, 24 = depth, +2 = 2"
topping).
 Depths of 12", 18", 24" and 32" .
 Typical width = 8‟-0" .
 Spans up to 100‟-0" .
 Combination beam and slab .

d) Single Tee Beam (ST) -
 Designation = 8ST36+2 (8 = width in feet, 24 = depth, +2 = 2"
topping)
 Typical depths of 36" and 48" .
 Typical width = 8‟-0" .
 Spans up to 120‟-0" .
 Combination beam and slab

Walls:
Wall panels available in standard 8‟-0" widths. Can be flat, or have
architectural features such as window and door openings, ribs,
reveals, textures, sandwich (insulation built-in), sculptured, etc.

Methods of Attachment of Precast Concrete Members:-
Weld Plates

The most common method of attachment of precast members is
by use of steel weld plates. Typically, the precast members have
embedded plates that can be used as welding surfaces for loose
connecting plates or angles.

Rebar and Grout
Used typically with slabs, reinforcing bars are spliced into slabs
and grouted in place (see below):-

JOINING PRECAST CONCRETE ELMENTS

Column-to-Column Connection

Metal bearing plates and embedded anchor bolts are cast into the
ends of the columns.

After the columns are mechanically joined, the connection is
grouted to provide full bearing between elements and protect the metal
components from fire and corrosion.

Beam- to-Column Connection

 Beams are set on bearing pads on the column corbels.
 Steel angles are welded to metal plates cast into the beams and

columns and the joint is grouted solid.

Slab-to- Beam Connection

 Hollow core slabs are set on bearing pads on precast beams.
 Steel reinforcing bars are in inserted into the slab keyways to span

the joint.
 The joint is grouted solid.
 The slab may remain untopped as shown, or topped with several

inches of cast in place concrete.

Sitecast Concrete Toppings over Precast Slabs:-

 Greater floor strength and stiffness
 Greater fire resistance
 Greater acoustic isolation
 Allow easy integration of electrical services into floor system
 Create a smoother, flatter floor.19

PRECAST MATERIALS AND METHODS OF MANUFACTURE
Concrete has been a very versatile and durable material for

replicating natural stone for over a century. The increasing scarcity of
natural stone and the great expense of cutting and transporting it, has
opened up a worldwide market for the production of reconstructed stone
and precast concrete using cement as the binder. Fine dust matched to the
colour and texture of natural stone is combined in a matrix of fine

19 Precast Concrete Structures by Kim S. Elliot

aggregates, cement and pigments and placed in moulds to form stone-like
facing panels, slabs and decorative detailing. In the early years
reconstructed or cast stone was processed by the moist-earth or dry cast
method where the mix was made semi-dry with low water content and
consolidated in timber moulds by ramming or tamping. Modern dry cast
stone has a higher porosity than wet cast methods and lower strength, and
this tends to limit production to relatively small unit sizes. This method is
still used successfully today to replicate both simple and intricate details
including ashlar walling, quoins, cornices, sills, string courses and
columns on buildings.

The more sophisticated wet cast method of production commonly
referred to as precast concrete and the focus of this book, uses very
workable, fluid mixes of aggregates, cement and pigments and water. The
fluid mix is poured into grout-tight moulds or formwork and compacted by
internal and external mechanical vibration and allowed to harden. Precast
concrete has high strength, low porosity, low moisture absorption and
greater durability. Its fluid consistency allows it to be moulded into
complex and intricate shapes. It can be fully reinforced to form large

storey-high panels that can be crane-handled, making site installation fast
and less labour intensive.20

Precast concrete as a structural engineered stone offers new
possibilities in expressing the intrinsic qualities of the raw materials –
cement, aggregates and pigment. Here the material‟s plastic form, the
choice and range of colours, combined with surface texturing and profiling
gives scope and great opportunity to design with freedom and imagination.
The surface can be finished with an acid-etch, grit blast, mechanical
abrasion or diamond polishing to give it a terrazzo like appearance.

For integrating precast with high-tech curtain wall systems, the
dead weight of the panel can be reduced significantly by specifying light-
weight glass fibre reinforced concrete known as GRC. The material is cast
in moulds in exactly the same way as precast concrete except that it is
reinforced with alkali-resistant glass fibre strands – there is no steel
reinforcement – and it can poured in place or spray-applied in layers. GRC
panels are easy to handle, they do not require heavy cranage on site and

20 The Art of Precast Concrete by David Bennett

can be installed using a cradle system, they are resilient and do not
corrode.

The use of recently developed ultra-high performance concrete in the
manufacture of precast concrete offers radically new and dramatically
slender structural possibilities in concrete. Two innovations in the ultra-
high performance materials have shown how these products can be used to
form architectural elements, balcony slabs, staircases and bridge structures
that outperform conventional concrete structures and can compete with
steel for slenderness.

Dry Cast Concrete This technique dates back to Roman times where a
mixture of lime and pozzolanic cement, sandstone fines and aggregates
was made with just enough moisture to hold it together without crumbling.
The semi-dry mix was rammed into wooden moulds and left to harden. It
was used for making simulated sandstone lintels and for repairing
stonework. An example of this can be seen in repair of the Visigoth walls
at Carcassonne in south-west France, built in AD 1135.

With the discovery and commercial development of Portland cement
in the last century, the dry cast method of producing cast stone was used

extensively in the manufacture of artificial stone blocks and facings. It was
employed to imitate with great economy, the natural Portland and Bath
stone façades of classical Georgian buildings for example and later
modelled for Art Deco and Neo-Classical architectural styles. The cast
block can be sometimes carved while still green to decorate and sculpture
the surface, although such detailing would usually be incorporated in the
mould. Cast stone is formed with a semi-dry facing layer comprising a
mixture of crushed stone and cement, backed with an ordinary semi-dry
concrete layer, which can incorporate reinforcement for strengthening
load-bearing elements.

The timber mould for forming the cast stone is filled with a 40mm
layer of the facing mix which is tamped with an air powered hammer to
fully compress the material in the mould. The surface is lightly scratched
to ensure an adequate key for the backing concrete which follows in layers
of 50mm and is similarly consolidated. Small man-handled pieces which
are simple in shape and generally 75mm thick can be de-moulded
immediately after the mix has been rammed. The rammed concrete is firm
enough to be turned out of the mould without damage. This makes the dry
cast method very cost-effective, as one mould can turn out many units per

hour. Where delicate ornamental shapes and deep surface profiles are
required, a more homogenous cement-rich mix is used and the concrete
left to cure in the mould for 24 hours.

Current methods of production are considerably more advanced
than the techniques used in the middle of the last century. There are two
different production techniques – the first of which is suited to high
volume production of small manhandled units. Here the moulds are
immediately turned out once they have been filled. The second method
which results in far higher quality and detail requires the concrete to be left
in the mould overnight before removal. This technique is more commonly
used for casting columns, balustrades and architraves and in ornamental
landscape artefacts.

Both methods require vapour curing to achieve their optimum
strength. The dry cast mix when compressed in the hand will hold together
without crumbling and not leave an excessive residue on the hand. The
mix of cement and pigment will include very fine crushed natural stone
aggregate which has been selected for stone replication, and incorporate a
waterproofing admixture such as aluminium stearate, calcium stearate or

an acrylic emulsion, to reduce porosity. Most mixes contain coarse
aggregates that are generally 3mm in diameter and rarely more than 6mm.
Inorganic pigments are used extensively and blended in with either grey or
white cement at proportions between 2% to 6% by weight of cement.

Dry cast units will usually require no further surface treatment.
Corners and arrises which can be friable should be fully vapour cured. If
they get damaged during handling, they should be repaired at the earliest
opportunity. The hardened surface can be grit blasted, acid-etched, tooled
and traditionally carved. Fixing and detailing of earth-moist units is the
same as for natural masonry construction.

Wet Cast Concrete Increasing mechanisation in construction, the
use of the tower crane, the high cost of labour and the need to build
quickly created the demand for prefabricated building components and of
course large precast façade panels. To form large modern precast panels
economically, the concrete mix must have a liquid consistency that will
allow it to flow into the moulds without segregating and combine with the
reinforcement bars to produce a durable self-supporting structure – hence
the term wet cast production.

When the mix is placed in the mould it has to be consolidated using
internal and external vibration to remove entrapped air voids and draw the
pigment and cement particles to the exposed surface. It is essential that the
moulds are made watertight as any leakage of the cement and pigment will
leave an unsightly discolouration and honeycombing. In relatively small
moulds it may only be necessary to rebate or groove the sides and end of
the moulds before they are clamped tight. Larger moulds may need foam
gaskets at critical joints or neoprene barriers to prevent grout loss.

Some manufacturers of modern precast concrete prefer to use resin
faced plywood or GRP (glass fibre reinforced plastic) lined timber for
constructing the moulds. Others will use metal forms because of the high
re-use factor for the casting of standardised products. For surface profiling
and embossing decorative features, GRP and synthetic rubber liners are
placed in the timber moulds.21

21 The Art of Precast Concrete by David Bennett

Ready Mixed Concrete

Ready Mix Concrete is a ready-to-use material which is a mixture of
Cement, Sand, Aggregate and Water. RMC is a type of Concrete which is
mixed in a batching plant according to the specification of the customer
and delivered to the site by the use of transit mixer as it is away from the
construction site. RMC is a new concreting concept in the Indian
Construction industry introduced before one decade. It was initially not
adopted by the contractors because it is costly due to its large equipments
and machineries and also due to high tax on RMC and easy availability of
manpower at cheaper rate but as time elapsed they understood that in large
or medium scale project it is cheaper as it requires less time, less
manpower and high strength as compared to Site mix concrete. So,
ultimately it is time saving and cheaper. RMC is also eco-friendly as it
reduces the noise and air pollution because mixing is done in closed
chamber as compare to site mix concrete.22

22 Conference: National Conference on: “Trends and Challenges of Civil Engineering in Today’s
Transforming World ”, At 29th March, 2014, Civil Engineering Department S.N.P.I.T. & R.C.,
Umrakh, Volume: ISBN: 978-81-929339-0-0 Dr. Jayeshkumar Pitroda

EQUIPMENTS REQUIRED IN RMC :
1.Inline Bins
Inert raw materials like fine & coarse aggregates are stored in
bins called as “INLINE BINS” where the trucks carrying fine and
coarse aggregate can dump the material easily.

2. Silos :-
Cement & Fly ash are stored in an airtight container called as

“Silos”. The required quantity of cement & fly ash is extracted by the
silos.

3. Screw Conveyer Belt:-
Cement and Fly ash are fed to holding hopper with the help

of a screw conveyer. A heavy duty cement screw conveyor is fixed in
an inclined position to convey the cement from Manual Feeding
Hopper to Cement Hopper.

4. Transit Mixers
Transit mixers are made to transport and mix concrete up to the

construction site. The discharge of concrete is done from front or rear
side of the Transit mixer .23

23 "Introduction of Concrete Mixing Plant" CONCRETE-MIXINGPLANT.COM.

5. Concrete Pumps :-
A concrete pump is a machine used for transferring liquid

concrete by pumping. There are two types of concrete pumps .

6. Vibrator :-
A vibrator is a mechanical device to generate vibrations device to

remove the air voids in concrete and for proper compaction of
concrete.