What is Filler slab?
Filler slabs are those which has a number of empty space at the bottom of the slab. Empty spaces in slabs are made with the help of different materials as shown in the figure.
The slab is a flat structural member of the building or structure like a culvert, bridge, or road. It should be strong and durable enough to carry its load for a long time. The failure of the slab may cause loss of wealth as well as lives.
Whenever a load is applied to the slab, the Slab experience two stress i.e compressive stress and tensile stress. Compressive stress in the slab acted at the bottom of the slab while tensile stress acted at the top of the slab.
So, structural engineers have to design slabs very carefully with full detail. There are different types of slabs according to different purposes like load, structure, capacity, etc. Here we will talk about the filler slab and the materials used in the filler slab.
The empty space is filled by different materials like glass bottles, clay pots, bricks, concrete blocks, glass, etc. It decreases the amount of concrete materials in the required for slab. Now, the question is, Will not the slab be weak?
The answer is no, concrete is weak in tension and strong in compression. As we previously discussed, that the slab experience tensile force at the bottom, we have to design the slab so that it will be strong in tension at the bottom. For that we have to provide steel rebar. The empty space should be place beside the rebar at a minimum distance of 50-70 mm.
The depth of empty space in slab should not be more than 1/3rd of the depth of slab or suggested by the slab designer.
Slab filler material used in construction
- Concrete Block
- Glass Cube
- Plastic pots etc.
Brick is the most common material used as the filler material in the slab. The great disadvantage is that, if we use this material then the formwork should be made stronger to bear the load of bricks. This types of filler provide better looks and geometrical shape to the ceiling of the slab.
Pots filler materials are used mostly in the cities surrounded by villages. Because these types of pots are mostly found in the village area and can be transported easily with cheap cost.
Different types of materials can be used as the filler materials of the slab according to the geometrical shape requirement of the ceiling. In some places, i have seen the use of glass cubes and plastic bottles as filler material in the slab.
Advantages of using Slab filler material
- It reduces the cost of the slab by 20 percent to 30 percent.
- It make an attractive look for the ceiling of the slab.
- It saves the materials like cement, sand, and aggregate to prepare the concrete
- It provides the same efficiency and load-bearing capacity as the normal slab if it is designed properly.
- It acts as a heat resisting device as it contains an air pocket.
- It decreases the total load of the structure.
Advantages of using Slab filler material
- It requires proper design.
- The distance between the empty space and the steel rod should be maintained sufficiently to prevent the failure of the slab.
- Require more experienced and active manpower and supervisor.
- The contact of empty space and steel rod may corrode the rebar and make the slab weak.
Precaution while construction of filler slab
- Filler material should be non-reactive with concrete.
- The proper concrete gap should be maintained between empty space and rebar to prevent rebar from corrosion.
- The rebar used in the concrete slab should be strong enough to carry the tensile stress.
- The materials used to prepare the slab should be lightweight as far as possible.
- The thickness of the slab should not be less than 150 mm above the top portion of the steel bar or as suggested by the designer.
- The capacity to observe water should be checked for filler materials. If the filler material has the capacity to observe water then it will soak water from concrete which decreases the hydration in concrete and cause cracks in the concrete slab.