UGANDA, Kampala | Real Muloodi News | Knowing the right slab to choose for your structure is essential in construction since they provide support and stability. Without them, any building under construction could easily collapse.
For this reason, it is vital to understand the different types of slabs and choose the one that will best suit your project.
According to Herbert Muwonge, a construction engineer, the components needed for the construction of a slab are wire mesh, hardcore, and iron bars.
Polythene is also needed to prevent water from moving from underground to the upper level of the structure.
“One also needs polythene, because it helps to stop water from moving from underground to the upper level of the structure. It is an expensive venture,” he explains.
Abdu-Wahab Nyanzi, an architect with JR Consultants, says there are ground and upper slabs. For example, suspended slabs are used to create upper floors. In such cases, the suspended slab is unavoidable.
Like the foundation, the upper slab, which is supported by beams on a storeyed house, is essential in determining the durability of the structure. If installed carelessly, it can tear the building apart.
When choosing a slab for your house, it is important to consider several factors such as the intended use of the structure, the size and shape of the building, the available budget, and the environmental conditions of the area.
According to Muhammad Nsereko, an architect with 3M Design and Construction, a slab provides the proper support to keep the house strong.
He says, in Uganda, there are two types of slabs mainly used in residential and commercial buildings; solid concrete and hollow (maxi pans) slabs. It is essential to know every bit of both slabs to make the best choice that suits your budget without compromising the strength of the house.
A hollow slab can also be called a voided, hollow core, maxi pan or simply a concrete plank slab. It is also called a semi-solid slab and is commonly used in residential houses since it is cheaper and cost-effective because it requires less material, and provides the necessary strength for the building to stand.
Its components include steel bars, maxi pans or hollow bricks at different intervals, timber, BRC or anti-crack to hold the concrete.
“Steel bars or ribs are laid in between the maxi pans and concrete is cast on top (topping) for extra strength,” Nsereko explains.
He adds that this kind of slab is also supported by beams and bearing walls that help it to stay stable.
“In Uganda, the standard thickness is 5cm which can increase up to 75cm and more depending on the nature of the structure,” he notes.
Nsereko advises that just like solid concrete, a hollow slab should be installed in one go to achieve the best results.
“If you let the bars rust, they will reduce the strength of the concrete. It is safer to gather all materials on time and set the slab at once,” he cautions.
According to Nsereko, the hollow slab can be made to different lengths and widths according to the client’s requirements. This is because it is composed of precast concrete beams that are connected to form a ribbed structure, with the gaps filled by concrete blocks.
Additionally, the hollow slab is known for its excellent sound insulation properties, making it ideal for structures located in noisy environments such as factories, hospitals, and schools.
However, hollow slabs have some disadvantages as well. They are not as strong as solid slabs and can only support a limited amount of weight.
Therefore, they may not be ideal for structures that need to hold heavy machinery or equipment.
Hollow slabs also have poor fire resistance compared to solid slabs.
Solid Concrete Slab
Nsereko says a solid slab is made of solid concrete and steel bars, making it costly but very strong. Due to its strength, it is ideal for commercial structures like skyscrapers and arcades, which hold heavy machinery, vehicles, and many people or a lot of load-bearing capacity.
“For safety, it should have a thickness of 0.15metres, 15cm or 250mm and a level of strength of 25,” he says.
Depending on the structure’s function, civil engineers may increase the depth of the concrete to 200cm and above. A structure with parking lots will have a thicker solid slab compared to one with none.
“The slab once cast is given 28 days to settle and dry, after which, it can serve any purpose it is designed to,” Nsereko elaborates.
Apart from supporting any load, a solid slab is a reliable insulator of sound, heat, and fire. In busy structures, the upper solid slab is a strong ceiling for the storey below.
“The construction of a solid slab doesn’t take long, and it can be designed in customizable shapes depending on the client’s taste and nature of the structure,” he asserts.
There are other types of slabs apart from the ones commonly used in Uganda.
Nyanzi says well-seasoned timber is used to form a structurally sound frame to support live and dead loads.
Expertise and care are necessary when working with this kind of slab since it is prone to pests and vulnerable to fire. The timber should be well-seasoned and treated with an approved preservative.
This is a combination slab made from a steel or timber framework, covered with steel or timber, and finished with a thin reinforced concrete mix not exceeding 75mm. This slab is probably the most economical but least used in Uganda.
Poor mixing of building materials, like cement, sand, and aggregate, can cause cracks in slabs. Normally, poor workmanship results from ignorance, carelessness, negligence, lack of proper supervision, or a combination of these issues.
It is also important to consult an architect or structural engineer when choosing a slab type to ensure that its function is synchronized with the architectural qualities the design is trying to achieve.
They will help you determine the most appropriate slab type for your structure based on several factors, including the soil type, the design of the building, and the intended use of the structure.
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