Pouring of foundations – step 1 Marking out the building.
Before excavation for foundations begins, a surveyor should appear on the building site to mark out axes and other building characteristic points. It is essential to keep both dimensions in the plan and the correct ordinates. It is important to mark the ordinates ±0.00 about which the planned depth excavation will be performed. The surveyor’s measurements should be checked by the site manager, especially if the walls are designed out of alignment.
Pouring of foundations – step 2 Laying the formwork.
The first stage of making foundations is digging trenches and preparing the formwork. In footings, the most commonly used formwork is either earthen (when the soil is compact and cohesive) or wooden (when the ground is of more inferior quality). They are made using excavations of the width and depth of the footings. Then the reinforcement is placed in them and poured over with a concrete mixture.
If it is not possible to make earth formwork, e.g., the ground is filling up, wooden formwork or shuttering boards should be prepared. However, this solution is more expensive than the earth formwork due to the consumption of material to construct the formwork.
The formwork in the foundation slab is usually thermal insulation. For this purpose, the bottom layer of the slab and a rim made of XPS extruded polystyrene elements are laid. Specially shaped elements can also be used, or thermal insulation slabs can be laid with edges reinforced with stays to prevent the concrete mixture from pushing the formwork apart.
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Pouring of foundations – step 3: placing reinforcing bars
Because foundations are reinforced concrete elements, all the rules of making such elements must be followed. It is therefore essential to prepare the reinforcement properly, according to the design. Footings are long elements, so the main reinforcement bars’ appropriate overlap length has to be observed. The bars should be aligned in the footing axis at distances that ensure a good covering.
In the construction of footings, the continuity of the footing reinforcement in corners and joint areas of footings must not be forgotten. Reinforcing bars should be added to the joints. The reinforcing bars have to be correctly dimensioned and positioned.
As the reinforcement is covered, this construction stage should be closely supervised and accepted by the site manager and the investor’s supervisor (if he is appointed).
Pouring of foundations – step 4 Pouring the concrete mix.
During concreting, the mixture must be vented. A bun vibrator is used for this purpose. It is driven into the concrete. The steel must not be touched, leading to the steel not being properly covered with the concrete mixture.
Pouring of foundations – step 5: Concrete treatment
As foundations set and dry, concrete shrinkage occurs, which can cause cracks to form, and moisture build-up can reach the reinforcement. Foundations are cured by pouring plenty of water for seven days. The increased moisture thus maintained protects the foundation from extensive drying out and the formation of shrinkage cracks.
Pouring of foundations – step 6. Protection against dampness
Because foundations are sunk in the ground, they are affected by unfavourable factors such as dampness and low temperature. If the building is founded on footings, damp-proofing is carried out in the form of horizontal waterproofing. In this way, the upper parts of the house are protected against capillary rising. This is done by applying a priming emulsion to the footings’ upper surface and making a waterproofing layer of a special foil or tar paper.
In buildings located on a foundation slab, a wall will be built – water insulation is made of waterproofing emulsion and waterproofing foil or thermal paper.
Puring of foundations – step 7 Masonry work of foundation walls
The following construction stage is the erection of foundation walls (if the building is founded on strip footing) or erection of basement or ground floor walls (if the building has a basement and is founded on a slab).
Although foundations, as reinforced concrete elements, will reach their total load-bearing capacity only after 28 days from pouring, the whole building is not immediately built. Thus the foundations are not loaded with the forces for which they were designed. Therefore, if the concrete has hardened sufficiently, the erection of the foundation walls can begin the next day.