TYPES OF SLABS USED IN CONSTRUCTION ⋆ Archi-Monarch

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Introduction

A slab is a flat, horizontal structure used to create floors, ceilings, and roofs in buildings. It is an essential component of building construction as it provides structural support to the building and also serves as a surface for walking, storing, and placing equipment. The thickness of the slab depends on the load it has to bear and the materials used in its construction.

Brief overview of the types of slabs

There are various types of slabs used in construction, each with its unique properties and characteristics. Some of the common types of slabs include:

One-way slab: A one-way slab is a flat, horizontal structure supported on two opposite sides. It is used when the ratio of the longer span to the shorter span is greater than or equal to two.
Two-way slab: A two-way slab is a flat, horizontal structure supported on four sides. It is used when the ratio of the longer span to the shorter span is less than or equal to two.
Flat slab: A flat slab is a flat, horizontal structure without beams or girders. It is used when the floor to floor height is limited and a flat ceiling is required.
Waffle slab: A waffle slab is a flat, horizontal structure with a grid of deep beams forming the underside. It is used when a large span is required, and the floor to floor height is restricted.
Ribbed slab: A ribbed slab is a flat, horizontal structure with ribs running in one or two directions. It is used when a light-weight and economical slab is required.
Beam and slab: A beam and slab system is a flat, horizontal structure supported by a series of beams. It is used when the load capacity of a one-way or two-way slab is insufficient.

By understanding the different types of slabs and their applications, builders and contractors can make informed decisions about which type of slab to use for a particular construction project.

1) Types of Slabs

There are various types of slabs used in construction, each with its unique properties and characteristics. In this article, we will provide an overview of the different types of slabs used in construction, their advantages and disadvantages, applications, and factors to consider when choosing the right slab for a project.

i) Conventional Slabs

A conventional slab is a flat, horizontal structure supported by columns. It is a common type of floor system used in residential and commercial buildings. Conventional slabs consist of a reinforced concrete slab that is cast in situ on top of the ground or on top of a layer of fill material.

The slab which is supported by beams and columns, is called conventional slab. In conventional slab the thickness of the slab is small but depth of the beam is large. The load is transmitted from slab to beam and then from beam to column.

These types of slabs are provided with reinforcement where the horizontal bar is called main reinforcement and vertical bar is called distribution bar. Conventional slabs are two types.

One way slab
Two way slab.

One-way slab: A one-way slab is a slab supported on two opposite sides and spans in one direction. This type of slab is usually used for small spans and is supported on beams or walls. The reinforcement in a one-way slab is provided in only one direction, perpendicular to the span.

One way slab is a conventional horizontal slab rectangular in shape and supported by beams on two of its four sides. The slabs are supported on beams opposite to each other. Therefore, the deflected shape is cylindrical.

In one way slabs the longer span is more than twice of the shorter span. The ratio of longer span to the shorter span is greater than two. As a result, the shorter span is subjected to bending.

The main reinforcements are provided in the shorter directions to resist the bending and the secondary reinforcements are provided in the longer direction.

Two-way slab: A two-way slab is a slab that is supported on all four sides and spans in both directions. This type of slab is used for larger spans and is supported on columns or walls. The reinforcement in a two-way slab is provided in both directions, perpendicular to each other. Two-way slabs can be further classified into two types: flat slab and waffle slab.

Two-way slabs are also conventional slabs mostly rectangular in shape and supported on all four sides of a beam. In two-way slabs, the longer span is less than twice the shorter span. The ratio of longer span to shorter span is lesser than two. The deflected shape of the slab is like a dish or saucer shape.

In this case, both the shorter and longer directions are subjected to bending. Therefore, the main reinforcements would be provided in both directions based on the magnitude of bending. The two-way slabs are economical to a size of 6m x 6m. Also, the quantity of steel used in two-way slab is more than the one-way slab.

Flat slab: A flat slab is a two-way slab without drop panels or beams between columns. It is used for medium to large spans and offers greater flexibility in architectural design.
Waffle slab: A waffle slab is a two-way slab with a ribbed structure. It is used for larger spans and offers greater strength and stiffness compared to a flat slab. The ribbed structure of a waffle slab provides added resistance to bending and deflection.

Advantages and Disadvantages

The advantages of conventional slabs include their simplicity, flexibility in design, and cost-effectiveness. They are easy to construct and require less formwork than other types of slabs, which makes them a popular choice for small to medium-sized buildings.

Additionally, conventional slabs can be designed to meet specific load requirements and can be modified to accommodate future changes to the building.

However, the disadvantages of conventional slabs include their limited span, which makes them unsuitable for large buildings or those with heavy loads.

Additionally, conventional slabs are prone to cracking and shrinkage, which can lead to structural problems over time. Finally, conventional slabs require more excavation and backfilling, which can increase the construction time and costs.

Applications in Construction

Conventional slabs are commonly used in residential and small commercial buildings. They are particularly useful for buildings with simple layouts and light to moderate loads, such as houses, small offices, and retail stores.

Conventional slabs can also be used for foundation slabs, which provide a stable base for the rest of the building. However, for larger buildings, other types of slabs such as two-way slabs or flat slabs may be more appropriate.

In conclusion, conventional slabs are a popular type of floor system used in construction. While they have certain advantages such as simplicity and cost-effectiveness, they also have limitations such as a limited span and a greater risk of cracking and shrinkage.

Builders and contractors should carefully consider the load requirements, span, and other factors when deciding which type of slab to use in a construction project.

ii) Flat Plate slab

A flat plate slab is a type of reinforced concrete slab that does not have any beams, girders, or other structural elements. Instead, the slab is directly supported by columns, which are placed at regular intervals.

The thickness of the slab is determined based on the span between columns and the required load capacity.

Unlike conventional slabs, in flat plates, the loads are not transferred from the slabs to the beams. In flat plates, the loads are transferred directly to the columns. The flat plate system may be one-way or two-way depending on the design plan.

Advantages and Disadvantages

The advantages of flat plate slabs include their simplicity in design, which reduces construction time and costs, and their flexibility in layout, which allows for larger open spaces. Additionally, flat plate slabs can provide a smooth and level surface, which is desirable in certain types of buildings, such as hospitals, laboratories, and clean rooms.

However, flat plate slabs have certain disadvantages as well. They are not suitable for long spans or heavy loads and require more concrete and reinforcement compared to other types of slabs. Flat plate slabs are also more susceptible to vibration and deflection, which can lead to cracking and other structural problems.

Applications in Construction

Flat plate slabs are commonly used in mid-rise buildings such as offices, apartments, and hotels. They are particularly useful in buildings with repetitive floor plans and a need for larger open spaces.

Additionally, flat plate slabs are ideal for buildings with low headroom requirements, such as parking garages or mezzanine floors.

In conclusion, flat plate slabs are a popular type of floor system used in construction. While they have certain advantages such as simplicity and flexibility in layout, they also have limitations such as a limited span and a greater risk of vibration and deflection.

Builders and contractors should carefully consider the load requirements, span, and other factors when deciding which type of slab to use in a construction project.

iii) Flat Slab

A flat slab is a type of reinforced concrete slab that does not have any beams, girders or other supporting structural elements. Instead, the slab is directly supported by columns, which are placed at regular intervals.

The thickness of the slab is determined based on the span between columns and the required load capacity.

Flat slabs are the modified version of flat plates with a column head and/or a drop panel cast monolithically with the slab. There are no beams present in the flat slabs but the drop panels and column heads will transfer the loads smoothly to the columns.

The drop panels are square or rectangular in shape and increase the shear capacity of the slab. The drop panels add deflection to the slab and thus minimize the deflections.

The column heads are provided below the drop panels and they are mostly sloping to meet the column dimensions. A flat slab may have either column head or drop panel or both.

The flat slabs are mostly popular in unconventional structures without column symmetry. The column heads and drop panels act as a special beam confined to that particular space. However, the formworks become complicated due to the need for column heads and drop panels.

The difference between a flat plate slab and a flat slab is that a flat slab has drop panels or column capitals at the columns, which increases the shear capacity of the slab and decreases the deflection.

Advantages and Disadvantages

The advantages of flat slab construction include their simplicity in design, which reduces construction time and costs, and their flexibility in layout, which allows for larger open spaces. Flat slabs can provide a smooth and level surface, which is desirable in certain types of buildings, such as hospitals, laboratories, and clean rooms.

Flat slabs have a higher load carrying capacity compared to flat plate slabs and can span larger distances without the need for additional beams or girders. The use of drop panels or column capitals also increases the shear capacity of the slab, which can improve the performance of the structure under seismic or wind loads.

However, the disadvantages of flat slab construction include their greater weight and thickness, which require more concrete and reinforcement compared to other types of slabs. Additionally, flat slabs can be more susceptible to cracking and other structural problems due to their higher rigidity and lack of ductility.

Applications in Construction

Flat slabs are commonly used in high-rise buildings such as offices, hotels, and hospitals. They are particularly useful in buildings with repetitive floor plans and a need for larger open spaces.

Additionally, flat slabs are ideal for buildings with high headroom requirements, such as parking garages or industrial buildings. The use of drop panels or column capitals can also improve the performance of the structure under seismic or wind loads.

In conclusion, flat slab construction is a popular type of floor system used in construction. While they have certain advantages such as simplicity, flexibility in layout, and high load-carrying capacity, they also have limitations such as greater weight and thickness, which require more concrete and reinforcement.

Builders and contractors should carefully consider the load requirements, span, and other factors when deciding which type of slab to use in a construction project.

iv) Waffle Slab or Grid Slab

Waffle slabs or grid slabs are a type of reinforced concrete slab that has a waffle-like pattern of grid beams and ribs, which creates a series of square or rectangular voids between the beams.

The thickness of the slab is determined based on the required load capacity and the span between the grid beams.

The waffle-like pattern increases the shear capacity and stiffness of the slab, making it more resistant to deflection and vibration compared to other types of slabs.

Additionally, the voids created by the grid beams can be used to conceal electrical and mechanical systems, making waffle slabs a popular choice in commercial and industrial buildings.

Waffle slabs are lightweight slabs with hollow grid-like systems on their soffit. The hollow grid system reduces the self-weight of the slab without compromising its structural stability.

The grids are spaced at equal intervals and they transfer the load from above to the beams. The space between the ribs is sometimes treated as a beam and reinforced to increase the flexural rigidity of the slab.

Due to their lightweight, they can span long distances with ease. The waffle slabs may have a grid system or a girder system where the bands of beam run throughout the slabs. The grids can be or any shape – square, rectangular, triangular etc.,

Advantages and Disadvantages

The advantages of waffle slab construction include their high load-carrying capacity, which allows for longer spans and fewer columns compared to other types of slabs.

The voids created by the grid beams can also be used for utility services, reducing the need for suspended ceilings and increasing the usable space of a building.

Waffle slabs are also more resistant to vibration and deflection compared to other types of slabs due to their high stiffness and shear capacity.

The grid pattern of the slab also provides a unique architectural feature, which can be visually appealing in certain types of buildings.

However, the disadvantages of waffle slab construction include their complexity in design and construction, which can increase the time and cost of construction.

Additionally, the voids created by the grid beams can pose challenges for the installation of lighting fixtures and other architectural features.

Applications in Construction

Waffle slabs are commonly used in commercial and industrial buildings such as shopping malls, warehouses, and office buildings. They are particularly useful in buildings with large spans and high loads, such as airport terminals and sports arenas.

Additionally, waffle slabs can be used in buildings where the aesthetic appeal of the ceiling is important, such as hotels, museums, and theaters.

The grid pattern of the slab can be used to create interesting ceiling designs and lighting effects, adding to the overall architectural appeal of the building.

In conclusion, waffle slab construction is a popular type of floor system used in construction. While they have certain advantages such as high load-carrying capacity, resistance to vibration and deflection, and architectural appeal, they also have limitations such as complexity in design and construction.

Builders and contractors should carefully consider the load requirements, span, and other factors when deciding which type of slab to use in a construction project.

v) Ribbed Slab

Ribbed slab, also known as one-way joist slab or ribbed floor, is a reinforced concrete slab that has a series of parallel ribs running in one direction and spaced at regular intervals. The ribs are typically 75 to 100 mm deep and the width of the rib is usually equal to the width of the beam.

The construction of ribbed slabs involves pouring concrete into a series of pre-fabricated forms that are supported by the beams. Once the concrete is cured, the forms are removed leaving behind the parallel ribs. The flat surface between the ribs is then finished with a thin layer of concrete or a topping slab.

Ribbed slabs are very similar to waffle slabs but often mistaken for being the same. A ribbed slab has wide grids or bands of beams in the soffit of the beam whereas a waffle slab has deeper corresponding parts.

The ribbed slabs like waffle slabs are flexible, light in section, economical and can be constructed for longer spans. They have the same advantages and disadvantages as the waffle or grid slab.

Advantages and Disadvantages

The advantages of ribbed slab construction include their high load-carrying capacity, which allows for longer spans and fewer columns compared to other types of slabs. The ribs also provide a better structural system for resisting the effects of lateral loads such as wind and earthquakes.

Ribbed slabs are also quicker to construct compared to other types of slabs because the pre-fabricated forms can be assembled quickly and easily on-site. Additionally, ribbed slabs are more economical to construct because they use less concrete and reinforcement compared to conventional flat slab construction.

However, the disadvantages of ribbed slab construction include their limited ability to accommodate heavy loads compared to waffle slabs or flat plate slabs. Additionally, the parallel ribs can make it difficult to install mechanical and electrical systems within the slab.

Applications in Construction

Ribbed slabs are commonly used in residential and commercial buildings where the spans are relatively short and the loads are not too heavy.

They are particularly useful in buildings where the floor-to-ceiling height is limited, such as in low-rise apartments and office buildings.

Ribbed slabs are also commonly used in industrial buildings such as warehouses, where the emphasis is on the functionality of the building rather than the aesthetic appeal.

The quick construction time and cost savings associated with ribbed slab construction make them an attractive option for many builders and contractors.

In conclusion, ribbed slab construction is a popular type of floor system used in construction. While they have certain advantages such as high load-carrying capacity, quick construction time, and cost savings, they also have limitations such as limited ability to accommodate heavy loads.

Builders and contractors should carefully consider the load requirements, span, and other factors when deciding which type of slab to use in a construction project.

vi) Hollow Deck Slab

Hollow deck slab is a type of reinforced concrete slab that incorporates hollow voids or cavities within the slab thickness. The voids can be formed using precast concrete blocks, clay pots or other materials that can support the weight of the slab and any loads placed on it.

The hollow deck slab system consists of the precast hollow blocks or pots, which are laid over the beam, and then a layer of reinforced concrete is poured over the top to form the slab. The voids in the deck slab reduce the dead weight of the slab, making it more economical compared to solid slabs.

Hollow deck slabs are special types of prefabricated concrete slabs that use the fundamentals of the stress developed in a section for the design. The concrete takes care of the compression while the steel takes care of the tension. There is no specific use for the concrete in the tension zone other than to provide a solid section.

Taking this principle into account, the hollow deck slab does not provide concrete in the tension zone. It is provided with minimum concrete to hold the steel reinforcements in place. The hollow deck slab can be prestressed or non-prestressed.

Advantages and Disadvantages

The advantages of hollow deck slab construction include its reduced weight and the resulting cost savings in the form of lower concrete and reinforcement requirements. The voids in the deck slab can also be used for the installation of electrical and mechanical systems, making it easier to incorporate these systems into the building design.

Hollow deck slabs also have good fire resistance properties because the voids act as insulation, reducing the spread of fire through the slab. Additionally, the precast blocks or pots used in hollow deck slabs can be reused in other construction projects, reducing waste and helping to create a more sustainable building industry.

However, the disadvantages of hollow deck slab construction include the need for careful placement and reinforcement of the precast blocks or pots to ensure structural stability. The hollow voids also make the slab more prone to cracking and other forms of damage, which can compromise the structural integrity of the slab over time.

Applications in Construction

Hollow deck slab construction is commonly used in residential and commercial buildings where the spans are relatively short and the loads are not too heavy. They are particularly useful in buildings where the floor-to-ceiling height is limited, such as in low-rise apartments and office buildings.

Hollow deck slabs are also commonly used in industrial buildings such as warehouses, where the emphasis is on the functionality of the building rather than the aesthetic appeal. The reduced weight and cost savings associated with hollow deck slab construction make them an attractive option for many builders and contractors.

In conclusion, hollow deck slab construction is a popular type of floor system used in construction. While they have certain advantages such as reduced weight, cost savings, and good fire resistance properties, they also have limitations such as the need for careful placement and reinforcement of the precast blocks or pots.

Builders and contractors should carefully consider the load requirements, span, and other factors when deciding which type of slab to use in a construction project.

vii) Bubble Deck Slab

Bubble deck slab is a type of concrete slab that uses plastic balls or spheres to replace some of the concrete in the slab, reducing its weight while maintaining its strength. The plastic balls or spheres, also known as bubbles, are made of high-density polyethylene (HDPE) and are placed in a predetermined pattern within the concrete slab.

The bubbles are held in place by a specially designed lattice framework or structure, which is placed in the formwork before the concrete is poured. Once the concrete is cured, the bubbles form a void within the slab, reducing its weight by up to 35% compared to conventional solid slabs.

Bubble deck slabs are hollow slabs where the concrete in the tension zone is replaced by recycled high-density polyethylene or HDPE plastic balls. Bubble deck slabs use the same principle as the hollow core slab. The concrete in the tension zone of a section has no structural importance.

The removal of that concrete will not affect the performance of the structure in resisting the loads acting on it. Bubble deck slabs can reduce the amount of concrete in a slab from 40% to 60%. This reduces the dead weight of the structure and also saves on costs.

Advantages and Disadvantages

The primary advantage of bubble deck slab construction is its reduced weight, which leads to cost savings in the form of lower material and transportation costs. The use of plastic bubbles also reduces the carbon footprint of the construction process, as less concrete and steel are needed to construct the slab.

Bubble deck slabs also have good thermal and acoustic insulation properties due to the air-filled voids in the slab, which can improve the energy efficiency and comfort of buildings. Additionally, the reduced weight of the slab allows for longer spans between support columns, providing more design flexibility in building construction.

However, the main disadvantage of bubble deck slab construction is its limited use in high-rise buildings or structures that require high strength and stiffness. The bubbles can also pose a challenge for installation and may require special attention to ensure proper placement and support within the slab.

Applications in Construction

Bubble deck slab construction is commonly used in low-rise residential and commercial buildings where the spans are relatively short and the loads are not too heavy. They are particularly useful in buildings where the floor-to-ceiling height is limited, such as in low-rise apartments and office buildings.

Bubble deck slabs are also suitable for construction in earthquake-prone areas, where the reduced weight and enhanced flexibility of the slab can improve the building’s seismic performance. Additionally, they are suitable for construction in areas with poor soil conditions, as the reduced weight of the slab can reduce the load on the foundation.

In conclusion, bubble deck slab construction is an innovative type of floor system used in construction. While they have certain advantages such as reduced weight, improved insulation properties, and energy efficiency, they also have limitations such as their limited use in high-rise buildings or structures that require high strength and stiffness.

Builders and contractors should carefully consider the load requirements, span, and other factors when deciding which type of slab to use in a construction project.

viii) Hardy Slab

Hardy slabs are special types of slabs consisting of hardy bricks placed in a uniform fashion inside them. The hardy bricks are hollow blocks made of concrete. The depth of the hardy bricks is usually at least 200 mm. Therefore, the depth of the slab is increased.

The formworks are placed over which the hardy bricks are placed in rows with space between them. This space between the hardy blocks is treated as small beams. Reinforcements are placed within these ribs and concrete is poured and the slab is cast monolithically. It is mostly used in regions of high temperature.

Advantages and Disadvantages of Hardy Slab

Advantages:

Hardy slab is more durable and stronger than a conventional slab.
It can span over larger distances between supports compared to a conventional slab.
It can reduce the thickness of the slab, which saves on materials and labor costs.
It has a longer lifespan and requires less maintenance.

Disadvantages:

The cost of materials and labor for constructing a Hardy slab can be higher than for a conventional slab.
The installation of the steel bars and welded wire mesh can be complex, requiring skilled workers.
The design and construction of a Hardy slab may require specialized engineering expertise.

Applications in Construction

Hardy slabs are commonly used in residential and commercial construction projects for floors and roofs. They are particularly suitable for applications where a high degree of strength and durability is required, such as in industrial buildings, warehouses, and parking garages.

They are also commonly used in areas with high seismic activity, as they can provide better resistance to earthquakes.

ix) Dome Slab

Dome slab is a type of structural roofing system that is shaped like a dome. It is constructed using reinforced concrete and steel to form a hemispherical shape. Dome slabs are used in a variety of buildings such as auditoriums, sports facilities, and religious buildings due to their aesthetic appeal.

Dome slabs are hemispherical in shape and are used mostly to enhance the view of a structure. In ancient times, most structures were built in such a way that only compressive forces act on the structure.

Before the invention of steel, there were no tensile materials known to man to resist tension. Therefore, the load was transferred through axial compression as in domes. In the modern era, the discovery of steel has led to thin sections of domes.

Advantages and disadvantages

Advantages of dome slab include:

Aesthetically pleasing: The unique shape of the dome slab provides a visually stunning design element to any building.
Large interior space: The dome shape allows for a large interior space without the need for columns or beams, making it ideal for buildings with large seating capacities or for sports facilities.
Durable and long-lasting: Dome slabs are made using reinforced concrete and steel, which makes them durable and long-lasting.
Good for seismic activity: Dome slabs are naturally resistant to earthquakes and other natural disasters, making them an ideal choice for regions with seismic activity.

Disadvantages of dome slab include:

Costly construction: The construction of a dome slab is more expensive compared to other types of roofing systems.
Difficult to construct: The unique shape of the dome slab requires skilled professionals to construct, which can make it difficult to build.
Limited design options: The shape of the dome slab limits design options and can make it difficult to integrate into existing architecture.

Applications in construction

Dome slabs are used in a variety of applications, including:

Auditoriums: Dome slabs are commonly used in the construction of auditoriums due to their ability to provide a large interior space without the need for columns or beams.
Sports facilities: The large interior space provided by a dome slab makes it an ideal choice for sports facilities such as indoor arenas and stadiums.
Religious buildings: Dome slabs are also used in the construction of religious buildings such as mosques and churches due to their aesthetic appeal and ability to provide a large interior space.
Commercial buildings: Dome slabs can be used in the construction of commercial buildings such as shopping centers and airports to provide a unique design element.

x) Pitched Roof Slab

A pitched roof slab is a type of reinforced concrete slab that is designed to create a sloping roof. It is commonly used in residential and commercial construction to provide a cost-effective and durable roofing solution.

The sloping design of a pitched roof slab allows for rainwater to easily drain off the roof, reducing the risk of water damage and leaks. The pitch or slope of the roof can be customized to suit the specific needs of the building.

The reinforced concrete pitched roofs are sloping slabs mostly preferred in high rainfall regions. The most common shape of a pitched roof is the triangular shape. Proper design must be made beforehand to ensure the smooth construction of the pitched roofs.

Advantages and disadvantages

Advantages of pitched roof slab include:

Drainage: Pitched roof slab provides excellent drainage and helps prevent water damage and leaks.
Versatility: The pitch of the roof can be customized to fit the specific needs of the building, providing greater design flexibility.
Durability: Pitched roof slab is made of reinforced concrete, providing a durable and long-lasting roofing solution.

Disadvantages of pitched roof slab include:

Complexity: Pitched roof slab can be more complex to design and install than other types of roofing systems.
Cost: Pitched roof slab can be more expensive than other types of roofing systems, especially if a high pitch is required.
Maintenance: Pitched roof slab may require regular maintenance to ensure proper drainage and prevent water damage.

Applications in construction

Pitched roof slab is commonly used in residential and commercial construction for roofing applications. It is particularly well-suited for buildings in areas with high levels of rainfall or snowfall.

Pitched roof slabs are also commonly used in the construction of garages, sheds, and other outdoor structures.

xi) Post-tensioned Slabs

Post-tensioned slabs are reinforced concrete slabs that use high-strength steel tendons that are tensioned after the concrete has been poured and has reached its design strength.

The tendons are anchored to the slab on one end and stretched to a specified tension on the other end. Once the tendons are tensioned, they are locked in place by wedges or nuts that are installed at the anchorage points.

The tensioned tendons place the concrete slab in compression, which increases its strength and allows it to span longer distances than conventionally reinforced concrete slabs.

Prestressed slabs are commonly used in the construction of prefabricated buildings. Post-tensioned prestressed slabs have ducts that carry high-strength steel tendons in addition to conventional reinforcement.

The steel tendons are prestressed and anchored at the ends after the concrete slab has hardened. This is called post-tensioning. The post-tensioned slabs are mostly precast and are of various shapes.

Advantages and disadvantages

Advantages of post-tensioned slabs include:

Greater strength: Post-tensioning allows for a greater span-to-depth ratio, which increases the strength of the slab.
Reduced cracking: The compression forces in the slab resulting from post-tensioning helps to reduce the formation and width of cracks, improving the durability of the structure.
Cost savings: The use of post-tensioning can lead to reduced amounts of concrete and steel required in the slab, resulting in cost savings.

Disadvantages of post-tensioned slabs include:

Higher initial cost: The use of post-tensioning requires specialized materials and expertise, which can increase the initial cost of the slab.
Maintenance requirements: Post-tensioned slabs require careful inspection and maintenance to ensure that the tendons remain tensioned and in good condition.

Applications in construction

Post-tensioned slabs are used in a variety of applications, including:

High-rise buildings: Post-tensioned slabs can span longer distances than conventionally reinforced slabs, making them suitable for high-rise buildings.
Parking structures: The increased strength of post-tensioned slabs makes them well-suited for use in parking structures, which are subjected to heavy loads and require a high level of durability.
Bridges: Post-tensioned slabs can be used in bridge construction to span longer distances and provide greater strength compared to conventionally reinforced slabs.

xii) Pretensioned Slabs

Pretensioned slabs are reinforced concrete slabs that use high-strength steel tendons that are tensioned before the concrete is poured. The tendons are stretched between two anchorage points, and then concrete is poured over them.

As the concrete sets and gains strength, the tendons are gradually released, transferring the tension to the concrete slab. Once the tendons are fully released, they remain under tension, providing additional strength to the slab.

Pretensioned prestressed slabs are prestressed before the concrete hardens. The high-strength tendons are pulled and the slab is cast. After the slab has sufficiently hardened, the prestressing strands are cut loose and the stress is transferred to the slab.

Pretensioned slabs are similar to post-tensioned slabs except for the prestressing part. They have the same advantages and disadvantages. However, post-tensioned slabs are widely used because of their ability to be cast in a shorter period of time.

Advantages and disadvantages

Advantages of pretensioned slabs include:

Greater strength: Pretensioning allows for a greater span-to-depth ratio, which increases the strength of the slab.
Reduced cracking: The compression forces in the slab resulting from pretensioning helps to reduce the formation and width of cracks, improving the durability of the structure.
Reduced construction time: Pretensioning can be done off-site, allowing for faster on-site construction.

Disadvantages of pretensioned slabs include:

Higher initial cost: The use of pretensioning requires specialized materials and expertise, which can increase the initial cost of the slab.
Limited flexibility: Once the tendons are tensioned and the concrete is poured, the shape of the slab is fixed, limiting design flexibility.
Transportation issues: Pretensioned slabs are often precast off-site, which can make transportation and installation challenging.

Applications in construction

Pretensioned slabs are used in a variety of applications, including:

Bridges: Pretensioned slabs are commonly used in bridge construction, as they provide a high level of strength and durability.
Parking structures: Pretensioned slabs can be used in parking structures to provide a high level of durability and strength.
Industrial buildings: Pretensioned slabs can be used in industrial buildings, such as factories and warehouses, to support heavy loads and provide a strong, durable floor.

xiii) Prefabricated Slabs

Prefabricated slabs, also known as precast slabs, are reinforced concrete slabs that are cast off-site in a controlled environment before being transported to the construction site for installation.

The precast slabs are typically manufactured in standard sizes and shapes, allowing for efficient and streamlined construction.

Prefabricated slabs are cast in the industry or site and transported to the place of construction. The prefabricated slabs can be of the following types:

Pre-tensioned slabs
Post-tensioned slabs
Hollow core slabs
Ribbed slabs

Advantages and disadvantages

Advantages of prefabricated slabs include:

Faster construction: Prefabricated slabs can be produced off-site while on-site preparation is underway, resulting in faster construction times.
Consistent quality: The controlled environment of the precast plant ensures consistent quality of the slabs, with minimal variations in strength and appearance.
Reduced waste: Precast slabs are manufactured to exact specifications, minimizing waste and reducing the environmental impact of the construction process.

Disadvantages of prefabricated slabs include:

Transportation challenges: Prefabricated slabs are often large and heavy, which can make transportation and installation challenging.
Limited design flexibility: Prefabricated slabs are typically manufactured in standard sizes and shapes, limiting design flexibility.
Higher initial cost: The cost of manufacturing and transporting precast slabs can be higher than traditional on-site casting methods.

Applications in construction

Prefabricated slabs are used in a variety of applications, including:

Flooring systems: Precast slabs can be used as flooring systems in both residential and commercial construction.
Building facades: Precast slabs can be used as building facades, providing a high level of durability and aesthetic appeal.
Bridges and overpasses: Prefabricated slabs are commonly used in the construction of bridges and overpasses, providing a strong and durable foundation for these structures.

xiv) Arched Slab

An arched slab, also known as a barrel vault or a curved slab, is a type of concrete slab that is shaped like an arch or a curved tunnel. The arched shape of the slab provides a strong structural support, allowing it to bear heavy loads without collapsing.

Arched slabs are mostly found in bridges. Arches like domes, transfer the loads through axial compression. The arches are provided in the bridges to resist the wind loads acting on the bridge. In ancient times, arches were built in masonry, but modern developments are giving birth to reinforced curved arch slabs.

Advantages and disadvantages

Advantages of arched slabs include:

Aesthetic appeal: Arched slabs can add a unique and aesthetically pleasing design element to a building or structure.
Structural strength: The arched shape of the slab provides a strong structural support, allowing it to bear heavy loads without collapsing.
Reduced materials: Arched slabs require less material compared to traditional flat slabs, making them more environmentally friendly.

Disadvantages of arched slabs include:

Limited design flexibility: Arched slabs have a fixed curvature, limiting the design flexibility.
More complex construction: The construction process for arched slabs is more complex and time-consuming than traditional flat slabs, requiring skilled workers and specialized equipment.
Higher cost: The cost of constructing arched slabs is generally higher compared to traditional flat slabs.

Applications in construction

Arched slabs are used in a variety of applications, including:

Bridges and tunnels: Arched slabs are commonly used in the construction of bridges and tunnels, providing a strong structural support to bear heavy loads.
Architectural design: Arched slabs can be used to create unique and aesthetically pleasing architectural designs in both residential and commercial construction.
Underground structures: Arched slabs can be used in the construction of underground structures such as basements, providing a strong foundation and structural support.

xv) Cantilever Slab

A cantilever slab is a type of concrete slab that is supported at only one end, with the other end projecting out into space. The unsupported portion of the slab is called the cantilever, which is typically used to create overhangs, balconies, or other architectural features.

Cantilever slabs, as the name suggests, are fixed at one end and free at the other end. The deflection in cantilever slabs is greater than the other slabs due to its support condition. One great example of cantilever slabs is Balconies.

The main reinforcement is provided in the span that is protruding outside. The secondary reinforcements are provided throughout the length of the slab. In RCC work, cantilever slabs should not be extended more than 4 feet.

Advantages and disadvantages

Advantages of cantilever slabs include:

Increased design flexibility: Cantilever slabs can be used to create unique and creative architectural designs.
Reduced need for support columns: Cantilever slabs eliminate the need for support columns, providing more open and usable space.
Enhanced aesthetics: Cantilever slabs can enhance the aesthetics of a building, providing unique features such as overhangs and balconies.

Disadvantages of cantilever slabs include:

Increased complexity: Cantilever slabs are more complex to design and construct compared to traditional concrete slabs.
Greater structural demands: Cantilever slabs require greater structural support at the point of attachment to prevent failure or collapse.
Higher cost: The cost of constructing cantilever slabs is generally higher compared to traditional concrete slabs.

Applications in construction

Cantilever slabs are used in a variety of applications, including:

Residential construction: Cantilever slabs can be used to create balconies or overhangs in residential construction.
Commercial construction: Cantilever slabs can be used in commercial construction to create unique architectural features.
Bridge construction: Cantilever slabs can be used in bridge construction to create extended sections without the need for support columns.

xvi) Low Roof Slab

Low roof slabs are also called lofts and are provided at the sill level of a building. The low roof slab is a cantilever slab that is provided above the doors and windows for storage purposes. The low roof slab is constructed during the construction of the lintel beam.

Advantages and disadvantages

Advantages of low roof slabs include:

Easy to construct: Low roof slabs are simple and easy to construct, making them a cost-effective option for low-rise buildings.
Minimal maintenance: Low roof slabs require minimal maintenance, making them a low-maintenance option for building owners.
Thermal insulation: Low roof slabs can provide thermal insulation, reducing the energy requirements of a building.

Disadvantages of low roof slabs include:

Limited height: Low roof slabs are not suitable for buildings with a height greater than 4 meters.
Limited design options: Low roof slabs may limit the design options available for building owners and architects.
Limited access: Low roof slabs may limit access to the roof, making it difficult to maintain or repair rooftop equipment.

Applications in construction

Low roof slabs are used in a variety of applications, including:

Residential construction: Low roof slabs are commonly used in the construction of low-rise residential buildings.
Commercial construction: Low roof slabs can be used in the construction of small commercial buildings such as retail stores, offices, and warehouses.
Industrial construction: Low roof slabs can be used in the construction of industrial buildings such as factories and workshops.

xvii) Sunken Slab

Sunken slabs, also known as depressed slabs, are a type of concrete slab used in construction where the level of the finished floor is lower than the surrounding ground level. They are typically used in areas where the ground level is sloping or uneven.

Sunken slabs are the slabs that are provided below the bathrooms and washrooms. The level of the slab is reduced below the bathrooms so as to separate the grade between dry areas and wet areas. The sunken slabs shall also be used to provide cover for sewage pipes and fittings.

Sunken slabs are provided in buildings with identical floor plans. The level of the slab can either be increased or decreased based on the need. Special care has to be taken to check water leakage in the pipes.

Advantages and disadvantages

Advantages of sunken slabs include:

Improved drainage: Sunken slabs can improve drainage by allowing water to flow away from the building.
Enhanced aesthetics: Sunken slabs can create an attractive design element in a building by creating a sunken courtyard or patio.
Better insulation: Sunken slabs can provide better thermal insulation by creating a buffer zone between the building and the ground.

Disadvantages of sunken slabs include:

Increased construction cost: Sunken slabs can be more expensive to construct than traditional slabs due to the additional excavation work required.
Increased maintenance: Sunken slabs may require more maintenance than traditional slabs due to the increased risk of water accumulation.
Limited applications: Sunken slabs may not be suitable for all types of buildings or sites.

Applications in construction

Sunken slabs are commonly used in a variety of applications, including:

Residential construction: Sunken slabs can be used to create a sunken living room or patio in a residential building.
Commercial construction: Sunken slabs can be used to create an attractive outdoor seating area or courtyard for restaurants, cafes, or other commercial buildings.
Public buildings: Sunken slabs can be used in the construction of public buildings such as museums, libraries, or community centers to create an attractive and functional outdoor space.

xviii) Slab on Grade or Grade Slab

A slab on grade or grade slab is a type of concrete foundation used in construction. It is a flat, single-layered concrete slab that is poured directly onto the ground, without any basement or crawl space. The slab is typically reinforced with steel bars to provide additional strength.

Slab on grade slab also known as the grade slab is constructed on the ground level and mostly supported by the soil or earth below it. Most of the ground floor slabs are grade slabs.

Before the grade slabs are constructed, the base layer of the earth should be properly compacted to prevent uneven settlements in the future. The base layer consists of well-compacted gravel and moisture barriers.

The depth of the slab should be at least 100 mm and it should be increased towards the edges to increase the structural integrity of the slab. Unlike conventional slabs, grade slabs don’t always require reinforcements but will require expansion joints.

Advantages and disadvantages

Advantages of slab on grade include:

Cost-effective: Slab on grade is often less expensive to construct than traditional foundation types such as crawl spaces or basements.
Easy access: Since the slab is level with the ground, there is easy access to plumbing and electrical systems.
Energy-efficient: Slab on grade provides better thermal mass and can be more energy-efficient than other foundation types.

Disadvantages of slab on grade include:

Limited design options: Slab on grade is limited in design options since it is a single-layered structure.
Vulnerability to moisture: Slab on grade can be vulnerable to moisture issues such as dampness or mold growth.
Difficult repairs: If the slab is damaged, repairs can be difficult and costly since the entire slab may need to be replaced.

Applications in construction

Slab on grade is commonly used in a variety of applications, including:

Residential construction: Slab on grade is often used in the construction of single-family homes and townhouses.
Commercial construction: Slab on grade is also used in the construction of commercial buildings such as warehouses, retail stores, and office buildings.
Industrial construction: Slab on grade is commonly used in the construction of industrial buildings such as factories, manufacturing plants, and distribution centers.

xix) Composite Slab

Composite slab is a type of construction material that is composed of two or more materials, typically concrete and steel. It is a combination of a concrete slab and a steel deck or beam that work together to provide structural support.

An element is said to be composite when it is made up of two or more materials. The composite slab is made up of concrete and steel decking.

The steel decking of trapezoidal, rectangular or re-entrant shape is also used as a formwork over which the reinforcement cages can be placed and concreted. The introduction of the steel decking increases the torsional stability during buckling.

Advantages and disadvantages

Advantages of composite slab include:

High strength: Composite slab provides high strength and stiffness, making it ideal for heavy loads.
Fire resistance: The steel deck in composite slab provides fire resistance, reducing the risk of damage during a fire.
Durability: Composite slab is durable and long-lasting, with minimal maintenance required.

Disadvantages of composite slab include:

Complexity: Composite slab can be more complex to design and install than other types of slabs, requiring specialized expertise.
Cost: Composite slab can be more expensive than other types of slabs due to the cost of the steel deck or beam.
Limited design options: Composite slab may be limited in design options due to the need to coordinate the concrete and steel components.

Applications in construction

Composite slab is commonly used in a variety of applications, including:

Commercial construction: Composite slab is often used in the construction of multi-story buildings such as offices, hotels, and hospitals.
Industrial construction: Composite slab is commonly used in the construction of industrial buildings such as factories and warehouses.
Bridge construction: Composite slab is used in the construction of bridges, providing a lightweight and durable solution.

2) Conclusion

In conclusion, slabs are an essential component in construction that play a crucial role in providing a stable and safe foundation for buildings. There are numerous types of slabs used in construction, each with its unique advantages, disadvantages, and applications. The choice of slab type depends on factors such as the building’s design, intended use, and the structural requirements.

Some of the most common types of slabs include conventional slab, flat plate, flat slab, waffle or grid slab, ribbed slab, hollow deck slab, bubble deck slab, post-tensioned slab, pre-tensioned slab, prefabricated slab, arched slab, cantilever slab, low roof slab, sunken slab, pitched roof slab, and composite slab.

Builders and architects must carefully evaluate the structural and functional requirements of a building to select the most appropriate type of slab for their construction project. With proper planning and construction, a well-designed slab can significantly improve the longevity, durability, and safety of a building.