The construction of a concrete slab is a fundamental stage for any civil construction project is, whether domestic or industrial.
This process has been greatly modernized in recent decades, thereby increasing the quality, safety, and efficiency that can be achieved when building concrete slabs. All this translates into a highly resistant floor with a finish that is as reliable as it is safe.
To achieve these standards, the construction and treatment of concrete slabs must comply with rigorous quality controls, which are carried out with increasingly sophisticated equipment.
Below we will detail what are the construction phases of an industrial concrete slab, as well as some of the technical specifications that must be met for an adequate final result.
1º Subgrade preparation for concrete slab
This stage consists of cleaning the soil on which our floor base will be set on, by removing any vegetation or objects that may hinder and interrupt the correct construction.
In an industrial environment, it is common to resort to demolitions to remove any old building’s remaining structures. All debris and waste must be transported to the respective place of discharge and disposal.
These activities aim to create regularity in the ground and obtain optimum properties for construction. For this reason, improvement processes related to the densification are applied, by compacting the base soil.
2º Placing the welded wire mesh
Wire meshes are made up of steel bars configured in rows and columns. These bars are joined by electro welding or tied with thin bars or wires.
The electro-welded mesh is the most widely used type due to its prefabrication nature, which considerably simplifies the placement of the metal mesh. The mesh must be anchored with metal supports, supported to the sub-base.
In the same way, there are occasions when the mesh can be omitted because the cracks in the concrete are controlled by the joints. However, this is not recommended, since cracks can increase in width, seriously damaging the concrete slab.
3º Pouring and finishing the concrete.
Before pouring the concrete, it is necessary to carry out the formwork process.
These molds determine the dimensions of the concrete slab. They can be metallic, synthetic, or wooden.
Reinforced concrete used for industrial slabs usually has fibers (metallic and synthetic) in its conventional composition, based on a mixture of gravel, sand, water, and cement.
The combination of fibers with the wire mesh significantly improves the concrete’s tensile strength. This effectively allows controlling the cracks that may occur whilst the concrete cures, which are caused by shrinkage and thermal contraction (or expansion).
The concrete must be manipulated as little as possible between its transportation and its placement. This seeks to avoid any segregation of the mixture and its premature setting. Therefore, the use of mixer vehicles with a discharge channel is recommended.
The concrete pour must be distributed homogenously. It needs to be homogenized by vibration to eliminate any possible trapped air.
Likewise, the temperature is an important aspect to consider, since temperatures below 5°C eliminate the hydration reaction between cement and water, damaging the agglomeration of aggregates in the concrete.
And in hot conditions, concrete is susceptible to increased cracking, an issue that occurs as a result of the accelerated water evaporation present in the mix.
Levelling and compaction
Once the fresh concrete has been distributed throughout the section of the slab, filling its entire thickness, it is time to level and smooth the surface.
In the past, an aluminum vibrating screed was used. However, nowadays the trend is laser screeds. This machinery uses a laser emitter, the beam of which is received by a copper receiver in the levelling vehicle.
As the levelling chassis encounters unevenness in the concrete, the copper receiver raises or lowers it for a better alignment.
However, to gain greater smoothness on the concrete surface, levelling correction instruments are used, such as correcting screeds (bump cutter and check rod).
The levelling must be done before the concrete begins to bleed, that is before the water begins to emerge to the surface.
Trowelling is a type of finish for concrete slabs, which produces a hard, dense and, smooth surface.
It is a mechanical process that uses a trowel with blades, which must be inclined to reduce the contact with the concrete surface. The more inclined the blades are, the greater the pressure will be, making the surface smoother and denser.
The trowelling must be carried out systematically and when the excess humidity has disappeared, that is, when the concrete is closer to the hardened state.
After each passing, it is recommended to increase the inclination of the blades, also, the route must be done in the opposite direction to the previous one.
4º Cutting joints in concrete
For this operation, electric or gasoline saws are used, which have abrasive or diamond discs.
There are two types of cut: the conventional wet cut and the dry cut.
Dry cutting is used to create expansion joints in concrete. These joints are made when the polished concrete is not yet fully hardened. With this, we seek to minimize cracking.
For this process, diamond disc cutters are used, obtaining a maximum depth of 32 mm.
The conventional cut is applied between 4 and 12 hours after finishing the slab; 4 hours in warm environments and 12 in cold environments. In this case, the depth of the cut will be one third of the thickness of the slab.
Both types of cuts need to be sealed after. What’s more, they must be carried out before the concrete hardens.
5º Curing the concrete
This is the last stage of the construction of an industrial concrete slab, and it aims to improve the cement’s hydration, preserving the adequate conditions of humidity and temperature in the concrete. Curing can be done by three methods.
- Curing compounds: a superficial sealing of the paving slab is made.
- Polyethylene sheets: by using this type of synthetic waterproof sheet,water loss from the concrete is minimized.
- Wet coatings: The use of materials such as fabrics or materials with high moisture retention help to minimize moisture loss from the concrete.
6º Final concrete finish
Sometimes, depending on the floor you want to obtain and taking into account its use, it is advisable to perform a powerful polishing treatment that will help improve durability, resistance to abrasion, reduce maintenance, eliminate the appearance of dust and many other benefits.
The BECOSAN® treatment helps densify the concrete in newly created or worn floors.
For more information on concrete slabs, you can get more information from this link on the Australian government’s official website.