Slabs producing process

Institute of Technology of Cambodia Technology of Building
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ContentsI. What is slab? ....................................................................................................................1
II. Materials ...........................................................................................................................1
1. Function of concrete in slab:.........................................................................................1
2. Function of bar in slab: .................................................................................................1
3. Function of formwork in slab: ......................................................................................2
III. Concrete Floor Slab Construction Process:...................................................................3
1. Assemble and Erect Formwork:....................................................................................3
2. Prepare and Place Reinforcement:................................................................................4
3. Pour, Compact and Finish Concrete: ............................................................................5
4. Curing Concrete and Remove Formwork:....................................................................6
IV. Different types of concrete slabs in construction ..........................................................8
1. Waffle slab....................................................................................................................9
a) Definition:..............................................................................................................9
b) Characteristics of Waffle Slabs .............................................................................9
c) Waffle Slab Construction Procedure ...................................................................10
d) Formwork tools required in the construction of waffle slab are..........................11
e) Benefits of Waffle Slab Construction..................................................................12
f) Drawbacks of Waffle Slab ......................................................................................13
2. Sunken Slab or Sunk slab: ..........................................................................................14
a) Definition.............................................................................................................14
a) Materials:.............................................................................................................14
b) Construction procedure of Sunken slab:..............................................................15
3. Flat plate......................................................................................................................18
a) Definition.............................................................................................................18
b) Materials ..............................................................................................................18
c) Usage ...................................................................................................................18
d) Flat plate Designing.............................................................................................18
e) How flat plate looks like......................................................................................18
f) Benefits of Flat plate ...............................................................................................19
g) Drawbacks of Flat plate.......................................................................................19
4. Flat Slab ......................................................................................................................20
a) Definition.............................................................................................................20
b) Types of Flat Slab Construction ..........................................................................20
c) Uses of Column Heads ........................................................................................21
d) Uses of Drop Panels ............................................................................................21
e) Application of Flat Slab.......................................................................................21
f) Benefits of Flat Slabs ..............................................................................................21
g) Drawbacks of Flat Slab........................................................................................21
5. Slab with Arches.........................................................................................................22
a) Definition.............................................................................................................22
b) Types of Architectural Arches.............................................................................22
c) Arch construction ................................................................................................23
d) Application of Slab with Arches .........................................................................24
e) Benefits of Arch Slab ..........................................................................................25
f) Drawbacks of Arch Slab..........................................................................................25

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6. Grade slab or Slab foundation.....................................................................................26
a) Definition.............................................................................................................26
b) Material................................................................................................................26
c) The process of making grade slab (From video):................................................27
d) Benefits of Grade slab .........................................................................................31
e) Drawbacks of Grade slab.....................................................................................31
7. Post tension slab..........................................................................................................32
a) Definition.............................................................................................................32
b) Benefits of Post tension slab................................................................................34
c) Disadvantages of Post tension slab......................................................................34
8. Pre tension slab ...........................................................................................................35
a) Definition.............................................................................................................35
b) Benefits of Pre-tensioning ...................................................................................36
c) Drawbacks of Pre-tensioning...............................................................................36
9. Dome slab ...................................................................................................................37
a) Materials used......................................................................................................37
b) Step of construction.............................................................................................37
c) Benefits of Monolithic Dome..............................................................................39
d) Drawbacks of Dome Slab....................................................................................39
10. Pitch roof slab..........................................................................................................40
a) Benefits of Pitched roof type of Slab...................................................................40
b) Drawbacks of Pitched roof type of Slab:.............................................................40
11. Hollow core ribbed Slab or Hollow core slab .........................................................41
a) Hollow core slab installation ...............................................................................42
b) Benefits Hollow core slab....................................................................................42
c) Drawbacks Hollow core slab...............................................................................42
d) Usage of hollow core slab....................................................................................47
V. Reference.........................................................................................................................48

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I. What is slab?
Slab is constructed to provide flat surfaces, usually horizontal, in building floors, roofs,
bridges, and other types of structures. The slab may be supported by walls, by reinforced concrete
beams usually cast monolithically with the slab, by structural steel beams, by columns, or by the
ground. The depth of a slab is usually very small compared to its span.
II. Materials
Slabs are being made by:
• Concrete
• Reinforce bars
• Formworks
1. Function of concrete in slab:
1. Provide a flat surface
2. To support load
3. Sound, heat and fire insulator
4. Act as a divider (privacy) for the occupants
5. Upper slab became the ceiling for the storey below
6. Space between slab and ceiling can be used to place building facilities
2. Function of bar in slab:
1. Primary reinforcement (Main Steel) refers to the steel which is employed to guarantee the
resistance needed by the structure as a whole to support the design loads.
2. Secondary reinforcement (Distribution Steel), also known as distribution or thermal
reinforcement, is employed for durability and aesthetic reasons, by providing enough
SLAB

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localized resistance to limit cracking and resist stresses caused by effects such as
temperature changes and shrinkage.
Sometime, we use crank bar is provided to make RCC slab safe from compressive stresses.
Because crank bars are generally provided:
1. To resist negative bending moment (hogging).
2. To resist shear force which is greater at supports.
3. To reduce the risk of a brittle failure of slab-column connection.
4. To reduce the amount of steel used.
5. For the economization of materials.
3. Function of formwork in slab:
The formwork serves as mold for concrete structural components unless such mold is provided
by the soil, other structural components, etc. Function of formwork such as:
1. To withstand with dead loads and live loads.
2. To retain slab shape
3. Against leakage of cement grout
4. Allow the removal parts of formwork without damage to the concrete

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5. Formwork is cheaper, easy to find and suitable for reuse
6. Light weight
7. To provide flat surface to slab
III. Concrete Floor Slab Construction Process:
1. Assemble and Erect Formwork
2. Prepare and Place Reinforcement
3. Pour, Compact and Finish Concrete
4. Curing Concrete and Remove Formwork
1. Assemble and Erect Formwork:
Formwork must be designed to withstand to construction load such as fresh poured
concrete, weight of workers, operators and their machines.
Furthermore, there are various types of materials available to use such as wood, steel and
aluminum can be used for formworks of concrete slab.
Finally, Site engineer needs to be aware of and prevent to the occurrence of formwork
failure that could occur. The construction deficiencies are provided below:
1. Poor or lack of formwork examination during and after concrete placement to identify
uncommon deflections or other indications of possible failure that could be corrected
2. Inadequate nailing, bolting, welding, or fastening
3. Improper lateral bracing
4. Construct formwork that does not comply with form drawings
5. Lack of proper field inspection to ensure that form design has been properly interpreted by
form builders
6. Use of damaged or inferior lumber having lower strength than needed.

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2. Prepare and Place Reinforcement:
Prior to the placement of reinforcement for concrete floor slab construction, inspect and
check forms to confirm that the dimensions and the location of the concrete members conform to
the structural plans.
Added to that, the forms shall be properly cleaned and oiled but not in such amount as to
run onto bars or concrete construction joints.
Design drawings provides necessary reinforcement details, so it only needs understanding
to use designated bar size, cutting required length, and make necessary hooks and bents.
After preparation is completed, steel bars are placed into their positions with the provision
of specified spacings and concrete cover.
The concrete cover and spacing for floor slabs can be maintained by introducing spacers
and bars supporters. Wires are used to tie main reinforcement and shrinkage and temperature
reinforcement (distribution reinforcement).

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It should be known that incorrect reinforcing steel placement can lead to serious concrete
structural failures. Improper concrete cover exposes reinforcement bars to danger and jeopardize
concrete-steel bond.
Finally, after all requirements of reinforcement placements (positions, concrete cover,
spacing, and correct bars size; length; hooks; and bending) are finalized, then site engineer can
order concreting.
3. Pour, Compact and Finish Concrete:
Mixing, transporting, and handling of concrete shall be properly coordinated with placing
and finishing works. In floor slab, begin concrete placing along the perimeter at one end of the
work with each batch placed against previously dispatched concrete.
Concrete should be deposited at, or as close as possible to, its final position in order to
prevent segregation. So, Concrete placement in large and separate piles, then moving them
horizontally into final position shall be prevented.
Moreover, site engineer shall monitor concreting properly, and look for signs of problems.
For example, loss of grout is the indication of improper sealing and movement of joints. Added to
that, cracking, excessive deflection, level and plumb, and any movement shall be checked and
tackled to prevent further problems.

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Furthermore, fresh concrete should be compacted adequately in order to mold it within the
forms and around embedded items and reinforcement and to eliminate stone pockets, honeycomb,
and entrapped air. Vibration, either internal or external, is the most widely used method for
consolidating concrete.
Lastly, slabs could be finished in many ways based on floor application. Helpful
information about forms before, during, and after concreting can be found in ACI 311.1R.
4. Curing Concrete and Remove Formwork:
After finishing ended, suitable technique shall be used to cure the concrete adequately. Slab
curing methods such as water cure; concrete is flooded; ponded; or mist sprayed.
In addition to water retaining method in which coverings such as sand; canvas; burlap; or
straw used to keep slab surface wet continuously, chemical Membranes, and waterproof paper or
plastic film seal.
Regarding curing, it is recommended to remove formworks after 14 days. For detailed
formwork removal time, Please click here.

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IV. Different types of concrete slabs in construction
There are 16 different types of Slabs in Construction. Some of them are outdated and
many of them are frequently used everywhere. The 16 types of slab are:
• Waffle Slab
• Sunken Slab/Sunk Slab
• Flat Plate
• Flat Slab
• Slab with Arch
• Grade Slab/Foundation Slab
• Post-Tension Slab
• Pre-Tension Slab
• Dome Slab
• Pitch Roof Slab
• Hallow Core Ribbed Slab/Hallow Core Slab

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1. Waffle slab
a) Definition:
Waffle slab is a structural component which is plain on its top and contains grid like system
on its bottom surface. The top slab is normally thin and the bottom grid lines are generally ribbing
which are laid perpendicular to each other with equal depth. Waffle slab has two directional
reinforcement. All the ribs are directed from column heads or beams. The depth of ribs maintained
is as same as depth of column head or beam. Because of the ribs and double reinforcement, it is
more stable and recommended for larger span slabs or foundations.
b) Characteristics of Waffle Slabs
1. Waffle slabs are generally suitable for flat areas.
2. Volume of concrete used is very less compared to others.
3. The reinforcement in the waffle slab is provided in the form of mesh or individual bars.
4. Separate excavation for beams is not required in case of waffle slab.
5. The bottom surface of slab is looks like waffle which is obtained by using cardboard
panels or pods etc.

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6. The thickness of waffle slab recommended is 85 to 100 mm while the overall depth of slab
is limited to 300 to 600 mm.
7. The width of beams or ribs provided in waffle slab are generally 110 to 200 mm.
8. Spacing of ribs recommended is 600 to 1500 mm.
9. Reinforced waffle slabs can be constructed for the span up to 16 meters while beyond that
length pre-fabricated waffle slab is preferable.
10. Waffle slab is good against shrinkage and it is lower than stiffened rafts and footing slabs.
11. Waffle slab requires only 70% of concrete and 80 % of steel from the concrete and steel
used for stiffened raft.
c) Waffle Slab Construction Procedure
The construction of waffle slabs can be done by three ways as follows.
• In-situ
• Precast
• Pre-fabricated
In-situ waffle slabs are constructed by pouring concrete in the site or field with proper
arrangements. In case of precast waffle slab, slab panels are casted somewhere and they are joined
together with proper reinforcement and concrete is filled.
The third case, pre-fabricated waffle slab is costliest than the other two methods. In this case,
reinforcement is provided in the slab panels while casting with some tension. Hence, they do not
need internal reinforcement in the site. To construct a waffle slab in-situ conditions, formwork
should be necessary to support the slab. But some special tools are required for the form work in
case of waffle slab.

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d) Formwork tools required in the construction of waffle slab are
• Waffle pods
• Horizontal supports
• Vertical supports
• Wall connectors
• Cube junctions
• Hole plates
• Clits
• Steel bars

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Horizontal support and vertical supports are arranged first and they are fixed in position by the
connectors. At the edges wall connectors are used to provide connection between wall and slab.
The horizontal beam supports are connected by small beam connectors which form square like
shape in which pods are going to be placed.
The pods are generally made of plastic and they are available in different sizes and different
shapes. Size selection of pod depend upon the requirement and span length. For longer span large
number of pods are required. Same size should be used for one complete slab.
Similarly beam connectors and cube junctions are also available in different sizes based on the
suitability of pod sizes.
Cube junctions are used to fix the corners of pods with the frame work. After fixing the
formwork, reinforcement is placed in the two directions of the slab and then concrete is poured in
the gaps which are called as ribs after hardening.
Thin concrete slab is provided on the top and after its hardening pods and frameworks are
removed from the bottom. Thus, the waffle like shape appears at the bottom surface.
e) Benefits of Waffle Slab Construction
• Waffle slabs are used for larger span slabs or floors and used when there is limited
requirement for number of columns.
• The load carrying capacity of waffle slab is greater than the other types of slabs.
• They provide good structural stability along with aesthetic appearance. Hence, it is
constructed for airports, hospitals, temples, churches etc.
• The waffle slab can be made of concrete or wood or steel among those concrete waffle
slabs is preferred for commercial buildings and other two are preferred for garages,
decorative halls etc.
• It has good vibration control capacity because of two directional reinforcement. So, it is
useful for public buildings to control vibrations created by movements of crowd.
• Waffle slabs are lightweight and requires less amount of concrete, hence it is economical.

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• Construction of waffle slab is easy and quick with good supervision.
• Concrete and steel volume required is small, hence, light framework is enough for waffle
slab.
• Several services like lighting, plumbing pipes, electrical wiring, air conditioning, insulation
materials etc. can be provided within the depth of waffle slab by providing holes in the
waffle bottom surface. This system is called as Holedeck.
f) Drawbacks of Waffle Slab
• Formwork tools required are very costly because of large quantity requirement of pods and
some special tools.
• The floor height should be more hence number of floors are reduced.
• The services provided in the waffle arrangement without proper maintenance may causes
damages to the slab.
• Skilled workers are required during its construction.
• They are not suitable for sloped areas. If there is slope area, the area must be leveled with
filling or by excavating. For soil filling, good soil should be used.
• They are not suitable against high winds or cyclonic areas because of their light weight.

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2. Sunken Slab or Sunk slab:
a) Definition
Sunken slabs are used in the toilets, bathrooms and washing place where we have our
washing machines. The purpose of having a sunken slab is to conceal all the pipes below the floor.
Since the pipes that carry water are concealed below the floor, care has to be taken to avoid leakage
problems. The slab which is provided below the normal floor level at a depth of 200 to 300 mm.
a) Materials:

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b) Construction procedure of Sunken slab:
1. Do leveling, measure and make framework. The height of sunken slab must be 200-
300mm below the floor level. Then we do the preparation and organization as the plan
that are designed.
2. After that we mix concrete and place it. We use vibrator. This helps to ensure that
enough concrete gets into every little nook and cranny and eliminate voids.
3. After pouring concrete, they need to cure the slab. By ACI committee 301, it
recommends a minimum period about 7days.

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4. Now it time to apply waterproof material on it. The surface of slab needs to be cleaned
and wash with clean portable water. The surface should be free from oil, grease, dust,
and algae…etc. The surface should be dried before application of waterproof material.
5. Ultratech sealant dry (seal and dry product) requires 30 to 35% of water by weight of
the powder. A small quantity of water is to be poured into the mixing container
followed by seal and dry. It shall be mixed thoroughly to get uniform thick slurry
preferably. The materials should be consumed within 2 hours.
6. The application can be done using a brush with
soft bristle. This waterproof material is applied in
2 coats with a gap of 2 hours between the 2 coats.
That second coat must be applied perpendicular
to first coat.

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7. The joint of slab and wall is also
coated with waterproof material.

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3. Flat plate
a) Definition
The flat plate is a two-way reinforced concrete framing system utilizing a slab of uniform
thickness, the simplest of structural shapes which doesn’t include either drop panels or column
capitals at columns to resist heavier loads and thus permit longer spans.
b) Materials
In building material and construction, there are various materials required to cast a slab
such as flat plate. Some of them are given such as: water, aggregates (fine & coarse both),
shuttering (wooden or iron), admixtures, sand, dust, water and reinforcement bar of different
diameters. Remember that the proportion of water and concrete (cement + aggregates) must be
important and workability of concrete also.
c) Usage
➢ Commonly used where spans are not large than 6 to 7 meters.
➢ Also loads not particularly heavy than 3000 Pa to 5000 Pa.
➢ When architectural design demands space and style.
d) Flat plate Designing
• Connection & detailing
When installing, ensure that first reinforcement bars should be properly detailed between
the columns and slabs and second, punching shear checks are critical & vertical shear
reinforcement should be detailed accordingly.
• Steps of flat plate slab design
The steps for designing are ranged respectively from determine thickness, dead & live load
calculation, moment calculation by using tables & co-efficient, reinforcement design and shear
check.
e) How flat plate looks like

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f) Benefits of Flat plate
➢ The simplified Formwork.
➢ Reducing the Story Height which makes it economical.
➢ There are no beams to obstruct light & circulation of air.
➢ Less danger of concrete spalling & exposing reinforcement.
g) Drawbacks of Flat plate
➢ Loads due to higher thickness of plate elements as required to control deflection.
➢ Stiffness & weight consideration in earthquake areas

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4. Flat Slab
a) Definition
Flat slab is a reinforced concrete slab supported directly by concrete columns without the
use of beams. Flat slab is defined as one sided or two-sided support system with sheer load of the
slab being concentrated on the supporting columns and a square slab called ‘drop panels.
Drop panels play a significant role here as they are responsible for the overall capacity and
sturdiness of the flooring system beneath the vertical loads thereby boosting cost effectiveness of
the construction. Usually the height of drop panels is about two times the height of slab.
To utilize the slab thickness to optimum
level, the essential aspects that should be kept
in mind are:
• Procedure related to design
• Presence or absence of holes
• Significance of deflections
• Previous layout application
experience
b) Types of Flat Slab Construction
Following are the types of flab
slab construction:
❖ Simple flat slab
❖ Flat slab with drop panels
❖ Flat slab with column heads
❖ Flat slab with both drops
panels and column heads

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c) Uses of Column Heads
❖ It increases shear strength of slab
❖ It reduces the moment in the slab by reducing the clear or effective span
d) Uses of Drop Panels
❖ It increases shear strength of slab
❖ It increases negative moment capacity of slab
❖ It stiffens the slab and hence reduce deflection
e) Application of Flat Slab
❖ To provide plain ceiling surface giving better diffusion of light
❖ Easy constructability with the economy in the formwork
❖ Larger headroom or shorter story height & pleasing appearance.
❖ This kind of slabs are provided in parking
❖ Flat slabs are generally used in parking decks, commercial buildings, hotels or places
where beam projections are not desired.
f) Benefits of Flat Slabs
❖ Flexibility in room layout
❖ Saving in building height
❖ Shorter construction time
❖ Ease of installation of M&E services
❖ Use of prefabricated welded mesh
❖ Buildable score
❖ Auto sprinkler is easier.
g) Drawbacks of Flat Slab
❖ In flat plate system, construction of large span is not possible.
❖ Use of drop panels may interfere with larger mechanical ducting.
❖ Not suitable for masonry partitions (Supporting brittle).
❖ The thickness of flat plate slab is higher compared to the typical RCC two-way slab.
❖ Critical middle strip deflection

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5. Slab with Arches
a) Definition
This is a type of slabs which is generally adopted in the construction of bridges. Bridges
are subjected to two loads moving load from the vehicles and Wind load. These slabs are adopted
at a place where there is a need of redirecting wind load and if there is a long curve in direction of
slab these slabs are adopted. It resists the fall of the bridge due to heavy wind load.
They were originally built by stone or brick but these days these are built by reinforced
concrete or steel. The introduction of these new materials allow arch bridges to be longer with
lower spans. This is a one of the types of concrete slabs.
An arch is a curved structural form that carries loads around an opening,
transferring them around the profile of the arch to abutments, jambs or piers on either side. The
techniques involved in designing and constructing arches have since developed into many other
structural forms, such as vaults, arcades, bridges, and so on.
Arches are compressive structures, that is, there are no tensile stresses. They are self-
supporting which is stabilized by the force of gravity acting on their weight to hold them
in compression. This makes them very stable and efficient, capable of larger spans, and supporting
greater loads than horizontal beams.
The downward load of an arch must be transferred to its foundations. The outward thrust
exerted by an arch at its base must be restrained, either by its own weight or the weight of
supporting walls, by buttressing or foundations, or by an opposing tie between the two sides. The
outward thrust increases as the height, or rise, of the arch decreases.
b) Types of Architectural Arches
❖ Round Arch
❖ Triangular Arch
❖ Parabolic Arch
❖ Segmental Arch
❖ Lancet Arch
❖ Equilateral Arch
❖ Horseshoe Arch
❖ Trefoil Arch
❖ Camber Arch
❖ Ogee Arch
❖ Three-Centered Arch
❖ Four-Centered Arch

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c) Arch construction
Since many building materials, such as masonry and concrete, can
resist compression, arches are commonly constructed using these types of material.

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The construction of traditional masonry arches is dependent on the arrangement of
the bricks, blocks or stone over the opening. Wedge-shaped blocks, called voussoirs, are set flank-
to-flank with the upper edge being wider than the lower edge. Downward pressure on the arch is
the effect of forcing the voussoirs together instead of apart. The voussoir that is positioned in the
center of the arch is known as the keystone.
This arrangement means that the arch is self-supporting, but temporary supports from
below, usually in the form of timber center, must be provided until the keystone has been set
in place.
The interior, lower curve of the arch is known as the intrados. The exterior, upper curve of
the arch is known as the extrados. The spring, or springing line, is the point from which the arch
starts to rise from its vertical supports.
d) Application of Slab with Arches
Arch bridges consist of a load-bearing arch in a state of compression, the strength and
stability of which allows them to carry greater loads than beam bridges. The arch can support the
horizontal deck of the bridge either from above or below.
The construction methods for arch bridges typically include:
❖ Supporting the arch using trestles until construction is complete. This is suitable for
low arch bridges.
❖ Cantilevering the ribs out from the sides of the span. This is suitable for bridges over
high drops which cannot be spanned with trestles.
❖ Where the spans are very large, the arch may be cantilevered in sections using a
creeping crane that is mounted on top of the arch. The crane lifts rib sections from
barges or pontoons below. The bridge deck is then constructed from both ends, meeting
in the middle.

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e) Benefits of Arch Slab
❖ It offers higher levels of resistance compared to other designs.
❖ It offers the option to span a greater distance.
❖ It can be construction from almost any material.
❖ It provides an advantage when carrying loads.
❖ It continues to provide support without distortion over time.
❖ It can become stronger over time.
❖ It adapts to local environmental conditions better.
f) Drawbacks of Arch Slab
❖ It offers a finite span length to use.
❖ It is a time-consuming project to complete.
❖ It is a structure which requires careful maintenance.
❖ It is a bridge option that cannot be built in some locations.
❖ It requires more side support to complete a successful span.
❖ It can sometimes be too flexible.
❖ It cannot have any design flaws for it to work as intended.
❖ It requires expertise to build.

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6. Grade slab or Slab foundation
a) Definition
Slabs which are directly laid on the earth where the ground doesn’t freeze, to support walls and
other structural elements are called as Slab on grade or Grade Slabs or Slab on grade foundation
or Slab foundation. It uses for side walking, floors, support wall, parking lots…etc. Thick of this
slab is about 10 to 15cm. It doesn’t require footing. And it requires less steel for some part. And
for safety, a layer of gravel & bitumen is laid on earth before laying concrete slab to prevent the
entry of moisture content into the slab.
b) Material
• Vapor retarder or Plastic film
• Dowel Baskets

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c) The process of making grade slab (From video):
1. The soil is excavated. Then they made the soil having the same level by using leveling.
2. They put plastic film (Vapor retarder) on the ground. Plastic film is used to reduce moisture
coming up through concrete. That moisture may come from soil or water that flow into this
area. Then they make edge form on plastic film.
3. After put these things, they use drum roller to roll on it. The purpose is to make soil is
compact. (the subgrade is compacted. Subgrade mean the prefabrication).

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4. It’s time to use Dowel baskets. They are placed on the plastic film. They are located at the
future control joint. Dowel baskets allow for load to be transmitted across control joint.
5. Now concrete is placed. That it had been placed from edge of form. Then the laborers use
shovel or other tools to distribute the concrete (Make it homogenous and mixed). Addition,
due to ACI Committee, concrete should place above 40F and not below 20F.
6. After that, they use laser screed machine that is used to level the concrete and get a
uniform the thickness. The laborers also use concrete floats to smooth out concrete
surface prior to final finishing. Hand troweling is required near edge forms.

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7. After placed concrete for 6-8 hours, curing is needed. Water is evaporating from the surface
faster than it is rising out from the concrete. If evaporation happens faster than usual time
than, the only factor that affect is the high temperature. When all the water gets evaporated
from the surface, you need to do some initial curing to minimize the moisture loss.
Following to ACI committee 301, it recommends a minimum period about 7days.
8. A section of slab here is finished. Now
move to next pour section. Once form is
removed and the next section of concrete
is placed, the resulting joint is known as
a construction joint or control joint. Hand
troweling is required where a new meets
and existing slab.
9. When concrete slab dried enough, the
control joint is laid out in a planned grid
using chalk line.

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10. Control joint are cut into the slab
along the chalk lines. These joints
are important since they allow the
concrete which will shrink to
crack. (that it prevents from
cracking when it shrinks.)
11. Final step: They apply sealer and hardener to concrete surface. They use material to spray
on in overlapping pattern to ensure complete coverage. After all of these, they need to
check level of slab with a dipstick and the result are given to contractor for quality control.

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d) Benefits of Grade slab
1. Labor, excavation and forming costs are lower since the concrete slab is built on grade over
undisturbed soil.
2. Projects are completed more quickly since there are no extensive excavations required. The
topsoil is removed and if the soil underneath is stable enough, the slab is poured directly
without having to dig further.
3. Rats and wild vermin are unable to nest under the house since the house sits on a concrete
slab. Crawl spaces are notorious for housing wildlife and feral cats as well as rodents.
4. Leaking plumbing will not affect a slab the same way that a traditional timber structure
will rot. An overflowing toilet will not cause floor joists to become rotted and need
replacing.
5. Slabs are also great insulators and keep heating and cooling bills to a minimum.
6. Homes will have easier access since they are generally built close to the ground. There will
only be one or two steps to the entry doors. People with disabilities find this to be very
convenient.
7. There is less risk of flooding, unless the home is near a floodplain. There will be less mold
and mildew because there is no dank basement or crawl space to grow mold. Gas leaks are
less likely as well since the pipes will be located outside the home.
e) Drawbacks of Grade slab
8. All normal systems and duct work including heating, ventilation and air conditioning will
have limited access. These systems are typically located beneath the floors of a house in
the basement or crawlspace.
9. If the concrete slab is not poured correctly or the finishing on the slab is not correct can
create un-level floors.
10. Tree roots from poorly designed landscaping can grow into the slab and cause it to buckle
or crack. This causes the slab to become weak and not able to hold the weight of the home.
11. Moisture is able to rise through any crack in the slab. This moisture can damage floor
finishes.
12. Since concrete slab foundations are considered to be cheap, this will have a negative impact
on the house’s resale value.
13. Houses with slab foundations will have significantly more damage from earthquakes than
other homes and buildings. They are also prone to insect infestations since the home sits
directly on the ground with only a layer of concrete between.

SLAB P a g e | 32
7. Post tension slab
a) Definition
Post tension is where the tensioning is applied to hardened concrete.in building structures,
an initial post tension is applied within 24 hours (or so), when the concrete reaches a certain
strength. The slab which is tensioned after constructing slab is called Post tension slab.
Reinforcement is provided to resist the compression. In Post tension slab the reinforcement is
replaced with cables/ steel tendons. Post-Tensioning provides a means to overcome the natural
weakness of concrete in tension and to make better use of its strength in compression. The principle
is easily observed when holding together several books by pressing them laterally. In concrete
structures, this is achieved by placing high-tensile steel tendons/cables in the element before
casting. When concrete reaches the desired strength, the tendons are pulled by special hydraulic
jacks and held in tension using specially designed anchorages fixed at each end of the tendon. This
provides compression at the edge of the structural member that increases the strength of the
concrete for resisting tension stresses. If tendons are appropriately curved to a certain profile, they
will exert in addition to compression at the perimeter, a beneficial upward set of forces (load
balancing forces) that will counteract applied loads, relieving the structure from a portion of
gravity effects. This is a one of the types of concrete slabs. In this type of slab, cables are tied
instead of reinforcement. In Steel reinforcement, the spacing between bars is 4inch to 6inch where
as in Post tension slab the spacing is more than 2m. Here some of materials for post tension slab

SLAB P a g e | 33

SLAB P a g e | 34
b) Benefits of Post tension slab
1. It allows slabs and other structural members to be thinner.
2. It allows us to build slabs on expansive or soft soils.
3. Cracks that do form are held tightly together.
4. Post tension slabs are excellent ways to construct stronger structures at an affordable price.
5. It reduces or eliminates shrinkage cracking-therefore no joints, or fewer joints, are needed It
lets us design longer spans in elevated members, like floors or beams.
c) Disadvantages of Post tension slab
1.The post tension slab can be made only by skillful professionals.
2. The main problem with using post tension slab is that if care is not taken while making it, it
can lead to future mishaps. Many a times, ignorant workers do not fill the gaps of the tendons
and wiring completely. These gaps cause corrosion of the wires which may break untimely,
leading to some failures unexpectedly.

SLAB P a g e | 35
8. Pre tension slab
a) Definition
The slab which is tensioned before placing the slab is called Pre tension slab. the slab has
same features of post tensioning. pre-tensioning is preferred when the structural element is small
and easy to transport.
In pre-tensioning system, the high-strength steel tendons are pulled between two end
abutments (also called bulkheads) prior to the casting of concrete. The abutments are fixed at the
ends of a prestressing bed. Once the concrete attains the desired strength for prestressing, the
tendons are cut loose from the abutments.
The prestress is transferred to the concrete from the tendons, due to the bond between them.
During the transfer of prestress, the member undergoes elastic shortening. If the tendons are
located eccentrically, the member is likely to bend and deflect (camber). The various stages of the
pre-tensioning operation are summarized as follows.
1) Anchoring of tendons against the end abutments
2) Placing of jacks
3) Applying tension to the tendons
4) Casting of concrete
5) Cutting of the tendons.
During the cutting of the tendons, the prestress is transferred to the concrete with elastic
shortening and camber of the member.
The stages are shown schematically in the following figures.

SLAB P a g e | 36
The essential devices for pre-tensioning are as follows:
Prestressing bed
End abutments
Shuttering/Mould
Jack
Anchoring device
harping device(optional)
b) Benefits of Pre-tensioning
The relative advantages of pre-tensioning as compared to post-tensioning are as follows:
-Pre-tensioning is suitable for precast members produced in bulk.
-In pre-tensioning large anchorage device is not present.
c) Drawbacks of Pre-tensioning
The relative disadvantages are as follows
-A prestressing bed is required for the pre-tensioning operation.
-There is a waiting period in the prestressing bed, before the concrete attains sufficient strength.
-There should be good bond between concrete and steel over the transmission length.

SLAB P a g e | 37
9. Dome slab
These kinds of slab are generally constructed in temples, Mosques, palaces etc. And Dome
slab is built on the conventional slab. Thickness of Dome slab is 0.15m. Domes are in the semi-
circle in shape and shuttering is done on a conventional slab in a dome shape and concrete is filled
in shuttering forming dome shapes. This is a one of the types of concrete slabs.
a) Materials used
➢ Air form Kits – The air form kit was obtained from monolithic constructors, Italy. The kit
consisted of a 40ft diameter form along with reinforced steel anchors. It is ordered in the
shape of half sphere.
➢ Polyurethane Foam– Sprayed on polyurethane foam insulation was of type using a part
process in which Diaphenylmethane-4, 4-di isocyanate was mixed with blended polyol resin.
➢ Reinforcing steel – Steel in the foundation and slab was 5/8 inch and grade 40 rebar. Dome
shell 13mm and 9.5mm grade 60 rebar was used.
➢ Concrete – Foundation and slab a standard sack concrete foundation mix was used. Concrete
used in the dome shell was 9 sack per cubic yard mix.
b) Step of construction
Step 1
• Ring Beam Foundation
• Monolithic Dome starts as a
concrete ring foundation.
• Continuous reinforcing bars are
embedded in the ring
beam foundation.
• The ring creates a solid base to
construct the dome.

SLAB P a g e | 38
Concrete ring
foundation
Step 2
• Inflate Air form
• Made of tough, weather -impermeable
material.
• The air form is inflated with dual
inflator fans.
• It determines the final shape of the
dome.
Step 3
• Polyurethane foam
• Foam is applied in the interior to stiffen the air form, and provide a secure surface to
which reinforcement bar is affixed.
• It gets hardens and creates a superior insulation layer.
Application of Air form
Application of foam

SLAB P a g e | 39
Application of Shotcrete
Step 4
• Steel Reinforcing
• Steel reinforcing rebar is attached to
the foam using a specially engineered
layout of hoop and vertical steel bar.
• Small domes need small diameter bars
with wide spacing.
• Large domes require larger bars with
closer spacing.
Step 5
• Shotcrete
• It is a special spray mix of concrete, applied
to the interior surface of the dome.
• The steel rebar is embedded in the concrete
and when about three inches of shotcrete is
applied
c) Benefits of Monolithic Dome
• Cost of a dome is less.
• Streamlined construction process and use of only four ingredients contribute to the dome’s
economy.
• Require less maintenance.
d) Drawbacks of Dome Slab
• Only specially trained construction crews.
• Using the modern techniques.
• Wasted space in narrow corners.
• Lack of seams.
Steel reinforcing rebar

SLAB P a g e | 40
10. Pitch roof slab
Pitch roof is an inclined slab, generally constructed on resorts for a natural look. Compared
to traditional roofing materials Tile-sheets used in pitch roof slab are extremely lightweight. This
weight saving reduces the timber or steel structural requirements resulting in significant cost
savings. Tile-sheets are tailor made for each project offering labor cost savings and reduced site
wastage. And the thickness of the slab is depending on the tiles we using it may be 2″-8″. This is
a one of the types of concrete slabs.
a) Benefits of Pitched roof type of Slab
• Pitched roof sheds off rain water better.
• This slab gives you internal storage or room space.
• It is less likely to leak.
• Roof coverings are cheaper.
• If it is a standard pitch, building materials are more cost-effective
b) Drawbacks of Pitched roof type of Slab:
• This type of slabs is not suggested for long spans.
• Repairs in slabs like plumbing repair or electric wiring on slabs is difficult

SLAB P a g e | 41
11. Hollow core ribbed Slab or Hollow core slab
Hollow core ribbed slabs derive their name from the voids or cores which run through the
units. The cores can function as service ducts and significantly reduce the self-weight of the slabs,
maximizing structural efficiency. The cores also have a benefit in sustainability terms in reducing
the volume of concrete used. Units are generally available in standard 1200 mm widths and in
depths from 110mm to 400 mm. There is total freedom in length of units.

SLAB P a g e | 42
a) Hollow core slab installation
By using tower cranes Hollow slabs are inserted between the beams. The gaps between the
slab is filled with screed.
b) Benefits Hollow core slab
1. Hollow core ribbed slab not only reduces building costs it also reduces the overall weight of the
structure.
2. Excellent fire resistance and sound insulation are other attributes of hollow core slab due to its
thickness.
3. It eliminates the need to drill in slabs for electrical and plumbing units.
4. Easy to install and requires less labor.
5. Fast in construction
6. No additional formwork or any special construction machinery is required for reinforcing the
hollow block masonry.
c) Drawbacks Hollow core slab
1. If not properly handled, the hollow core ribbed slab units may be damaged during transport.
2. It becomes difficult to produce satisfactory connections between the precast members.
3. It is necessary to arrange for special equipment for lifting and moving of the precast units.
4. Not economic for small spans.
5. Difficult to repair and strengthen

SLAB P a g e | 43

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d) Usage of hollow core slab
Hollow core is a concrete slab used for roof and floor systems. These types of slabs are Pre
casted and it is used where the construction has to be done fast. A hollow core slab, also known
as a voided slab, hollow core plank or simply a concrete plank is a precast slab of prestressed
concrete typically used in the construction of floors in multi-story apartment buildings. The slab
has been especially popular in countries where the emphasis of home construction has been on
precast concrete, including Northern Europe and former socialist countries of Eastern Europe.
Precast concrete popularity is linked with low-seismic zones andmore economical constructions
because of fast building assembly, lower self-weight (less material), etc. Precast hollow-core
elements are also known as the most sustainable floor/roof system and has far smaller CO2
footprint than even CLT slabs.

SLAB P a g e | 48
V. Reference
• Wikipedia
https://en.wikipedia.org/wiki/Concrete_slab
• Quora
https://www.quora.com/What-is-slab
https://www.quora.com/What-are-the-advantages-of-sunk-roofing-as-my-construction-is-under-
progress
• Civil read
https://civilread.com/16-different-types-slabs-construction/
https://civiltoday.com/structural-engineering/31-advantages-disadvantages-flat-plate-slab
https://civilread.com/slab-on-grade/
• Daily civil
https://www.dailycivil.com/flat-slab-types-uses-advantages-disadvantages/
https://www.dailycivil.com/flat-slab-types-uses-advantages-disadvantages/
• Google
https://www.google.com/search?q=arch+construction+forces&source=lnms&tbm=isch&sa=X&
ved=0ahUKEwivwvXYm9vhAhVPZt4KHYlLDewQ_AUIDigB&biw=1536&bih=754#imgrc=
QQ1FmwCMVoBTmM:
• YouTube
https://www.youtube.com/watch?v=CdNYTjXJPKE
https://www.youtube.com/watch?v=lO9z7xgtf9g
• The constructor
https://theconstructor.org/structural-engg/flat-slab-types-design-advantages/13919/
https://theconstructor.org/structural-engg/waffle-slab-construction-procedure-characteristics-
advantages/20546/
• Others
https://www.designingbuildings.co.uk/wiki/Bridge_construction
https://www.designingbuildings.co.uk/wiki/Arches
https://greengarageblog.org/15-arch-bridges-advantages-and-disadvantages-tied-through-and-
truss
http://www.iitk.ac.in/nicee/wcee/article/13_3028.pdf
https://www.hunker.com/12002961/how-to-build-a-stone-or-brick-arch
https://civilengineeringbasic.com/slab-foundation-advantages-disadvantages/
https://hdfoundationrepair.com/slab-foundation/
https://www.concretenetwork.com/install-concrete.html
https://www.cement.org/learn/concrete-technology/concrete-construction/curing-in-construction

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