Introduction of Slab Construction
- The concrete slab is a horizontal surface of a residential building or commercial building, factories, flat, etc.
- The thickness of the steel-reinforced slab is near about 100-500mm. This types of slabs are used for ceiling and floor purpose.
- Less thin slabs are used to construct for exterior paving.
- Sometimes in a domestic or commercial building, a thick concrete slab is constructed directly to the subsoil. These types of the slab are generally classified as the ground bearing slab.
What Is Slab Construction?
Slab construction has some following process. Those are-
- Prepare Formwork
- Preparation of Slab Bedding
- Reinforcement Instalment
- Pour, Compact and Concrete Finish
- Curing of Concrete & Remove the Formwork
#1. Prepare Formwork
- Formwork is the frame for the concrete slab, and it’s necessary to check the measurements according to building plan to set up the formwork correctly.
- Formwork needs correct placement to withstand the considerable load of concrete, leakage and other necessary requirements.
- The height of formwork must be at the top of the concrete slab to finish surface inline with the top of the formwork.
#2. Preparation of Slab Bedding
- It’s very important to set out the slab bedding properly because the whole slab rests upon it in the primary condition.
- The road surface is suitable for the base of the slab bedding.
#3. Reinforcement Instalment
- Reinforcement prevents the slab from cracking, buckling and caving. It totally carries the tensile strength of the structure.
#4. Pour, Compact and Concrete Finish
- This is good to use ready mix concrete, but all the time, we can’t use ready mix concrete.
- After the concrete is being poured, it needs to vibration for compaction.
#5. Curing of Concrete & Remove the Formwork
- Curing of the concrete slab by water is near about seven days. If we use spray curing, then we must spray two times a day.
- After 24 hours of concrete poured the formwork can be removed totally, but we avoid heavy load to seven days.
Types of Slab Design
Types of slab design are available-
- Ground Bearing Slab
- Suspended Slab
- Unreinforced Slab
- Mud Slab
- One Way Slab
- Two Way Slab
#1. Ground Bearing Slab
- Ground bearing slabs are mainly used in a residential or commercial building for floor purpose. This types of slabs are also known as “on-ground” or “slab-on-ground“.
- For this type of slab is necessary to construct according to the condition of the soil because some dynamic grounds create cracking.
- The ground bearing slab needs proper curing to gain adequate strength.
#2. Suspended Slab
- When the corrugated slab is designed, the concrete is poured into a steel tray. This improves the strength of the slab and prevents to bend from its own weight.
- In the case of the ribbed slab, it gains more strength in one direction. This is achieved with concrete beams bearing load between piers or columns, and thinner, integral ribs in the perpendicular direction.
- In waffle slab, it provides adequate strength in both directions using a matrix segment beneath the slab.
#3. Unreinforced Slab
- The unreinforced slab is also known as a plain slab. Here reinforcement is not used; that’s why the entire load of the slab is carried by concrete.
- The load must be within the limit of flexural strength of concrete to prevent cracks.
#4. Mud Slab
- Mud slabs are thinner than suspended slabs or ground bearing slabs; it’s also known as rat slab.
- Mud slab does not contain reinforcement that’s why it is economical and easy to construct.
- Sometimes coarse aggregate is used in the place of mud.
#5. One Way Slab
To construct a one-way slab sone factors are effecting, those are-
- Load Calculation
- Bending moment Calculation
- The effective depth of flexure
- Main Steel
- Effective Steel
- Deflection Checking
- Development length Checking
- Shear Checking
#6. Two Way Slab
- The two-way slab has moment-resisting reinforcement in both directions, i.e. longer & shorter direction.
- This types of slabs can carry a heavy load, vibration, etc.
- To construct a two-way slab, the main thing is to note that lx: ly< 2, where lx is the shorter span, and ly is the longer span.
What Is Floor Slab?
- The floor slab is acting as a floor constructed by concrete, which is one of the most important building components.
- Floor slab formed a floor of a basement of a building, or act as a roof. This is constructed in the site by steel reinforcement or set out readymade prefabricated materials.
- Those floors which are made with timber or other materials is not referred to as floor slab.
- Sometimes floor slabs are supported with beams, and then it’s constructed in the roof of a building then it’s termed as roof slab.
Types of Floor Slab
- The first type is slab is a flat concrete slab which is generally 100mm thickness. It’s supported two sides or more sides of the concrete beam or steel beam.
- The second type of slab is also a flat concrete slab supported with steel ribbed. The steel provides temporary and permanent support of concrete, a steel ceiling is observed from the downside of the slab.
- A waffle slab is the third type of slab. In this type, the concrete is poured over the series of plastic; it results in an egg crate style. The thickness of this type of slab is 500mm or more.
- An in situ concrete slabs over a beam and block with the steel reinforcement is the other type.
- The final type of floor slab is a pre-cast concrete slab.
Concrete Slabs Thickness
- Minimum thickness of the concrete slab totally depends on types of slab-like one way or two way, a span of slab, design load.
- The minimum thickness of concrete slab is near about 4 inches but not less than that according to standard code, but the slab thickness entirely depends on the design load and the span of the slab.
- In the other hand, concrete mix grade is also very important to the thickness of the slab.
- Basically, the actual thickness of the slab is to find out the design of the slab and by the Bar Bending Schedule (BBS).
Prefabricated Concrete Slabs
- Prefabricated concrete slabs are constructed in a factory and transported into the site, and they are ready to use.
- This slab is made through a pre-stressed or post-stressed procedure.
- The precast slab has more advantage because it is constructed with a more controlled environment than a regular slab.
- The slabs are made by pouring concrete into a mould under highly supervised condition.
- Concrete precast slabs are also used in an industrial and institutional building.
Benefits of Precast Slab
- Concrete slabs offer a wide variety of benefits, from initial design to long-standing structure and design.
- Precast concrete slabs are made in a controlled environment that’s why concrete which is used to construct is extremely good; for this reason, cracking is not generally developed.
- Temperature and weather effects don’t impact on this type of slab.
- The precast concrete slab is enough strong and durable, so using this instead of a concrete slab is more stronger and more stable.
- This slab resists both tensile and compressive strength.
- This slab is good in thermal resistance.
Concrete Floor Slab
- The floor slab is a reinforced concrete slab which thickness is near about 5-6cm. Sometimes it can be 7 cm, depends on the cover of reinforcement. This is also called plate slab.
- Sometimes the floor slab is precast, and it’s constructed in a highly controlled environment, so it resists flexural tension.
- The thickness of this precast slab is 12cm or 30cm. It totally depends on the span and loading of the slab.