Formwork serves as a mold or structure into which concrete is poured and shaped until it solidifies, making it an essential component of foundation construction. Any construction project needs proper formwork because it guarantees the foundation’s structural integrity, longevity, and alignment. It determines the final form and strength of the foundation in addition to bearing the weight of the concrete.
Selecting the appropriate materials for formwork is crucial. Formwork is typically made of plastic, metal, or wood, each of which has special benefits based on the needs of the project. Wood is widely used because it is inexpensive, readily available, and easy to handle. Larger or more intricate foundation designs benefit greatly from the durability and increased pressure tolerance of metal formwork, such as that made of steel or aluminum. Though less common, plastic formwork is becoming more and more popular because it is lightweight and reusable.
Just as important as careful planning and preparation are before building formwork. This include taking precise measurements, marking out the dimensions of the foundation, and making sure the formwork is level and firmly fastened to avoid any movement when the concrete is being poured. Sufficient bracing and support are essential to endure the pressure that wet concrete applies.
Paying close attention to details is crucial during the pouring process. To prevent weak points or inconsistencies in the foundation, concrete should be poured consistently and evenly. By ensuring that the concrete settles evenly inside the formwork and eliminating air pockets, vibrating the concrete increases its strength and durability.
For foundations to be structurally sound and long-lasting, proper formwork is essential in construction. Concrete is poured into formwork, which acts as a mold to shape the foundation in accordance with design guidelines. It needs to be built carefully to sustain the weight of the wet concrete and offer sufficient support until the concrete hardens. In order to create dependable and durable foundation structures, this article will discuss important factors to take into account when choosing materials, creating formwork layouts, and guaranteeing safe installation techniques. Does this sum up what you’re looking for in its entirety?
Wooden structures for pouring the foundation
Formwork is traditionally constructed from wooden boards or panels. A minimum of 40 mm of board thickness is required if you adhere to SNiP. Strong pressure applied to the formwork walls during the concrete pouring process can cause thin boards to bend in an arc. The sides of the foundation will therefore be convex. But the quantity of wasted concrete matters more than how it looks. As a result, it’s critical to install the formwork in accordance with all dimensions and to choose the material’s thickness for manufacturing precisely.
In practice, for a narrow strip foundation (20 – 30 cm above ground level) a board with a thickness of 25 – 30 mm is often used. But at the same time, the walls of the formwork are reinforced with vertical bars with spacers nailed every m to one and a half meters. Such a structure is made in the form of a right triangle of boards, one leg of which is nailed to the wall of the formwork, the other lies on the ground, resting on a driven wedge, and the third board (hypotenuse), resting on the same wedge, presses the formwork. It is better to install such slopes on the outside of each wall. The walls are pulled together by lintels along the upper edge of the formwork.
The thickness of the boards doesn’t really matter if the formwork is installed entirely in a trench; Chinese plywood with a polymer coating is occasionally used in its place.
The same slopes are used to create the formwork that is placed around the perimeter of the slab. However, there is a need to increase both the width of the strip foundation and the thickness of the wall boards.
Concrete is often poured using a vibrator to prevent air bubbles, which weaken the material. Vibrations on the formwork walls can cause the fastening of simply wedged elements to break, causing concrete to leak and the structure to collapse. Hence, self-tapping screws are used to join all slopes, spacers, and jumpers between the walls. Compared to using nails, this method of fastening is more secure.
To achieve smooth edges on the strip foundation, mark each side by pulling the string level rather than starting from the center of the strip. Pythagorean theorem can also be used to find a right angle with a string.
How to save money during construction
Boards are expensive, so it might not be worth it to spend extra money on wood for formwork that is used frequently.
However, you can use the current boards; just use them sensibly and correctly.
For instance, 50 mm thick boards can be used for formwork and then flooring installation. In order to avoid staining the boards with concrete, it is advisable to apply an antiseptic right away. The walls of the formwork are covered in polyethylene film. Using this same method, you can make multiple uses of a single formwork.
Concrete is not considered when calculating the tension foundation; only reinforcement is, so pouring concrete two or three times won’t negatively impact the structure’s design. Three to four days should be sufficient for the first pour of concrete to partially set. After that, the formwork can be securely moved around to allow for more pouring. It is preferable to create extra notches with a hammer for improved adhesion rather than leveling the concrete’s edges.
The joints of the foundation, where the first fill ends and the next one begins, should be spaced slightly in this situation. One wall is poured longer than the other to avoid gaps in the pouring on adjacent walls from being on the same line.
Although it requires less material, the formwork for the slab is typically installed around the entire perimeter at once. If a ribbed slab is to be poured, the pit area’s interior formwork portion is arranged using foam plastic at the necessary height, creating ribs in the spaces between the sections. The foam serves as insulation beneath the slab.
Occasionally, a slab is cast on top of the individual ribs after they have been poured and the space created between them has been filled with crushed stone and compacted sand. In this instance, slab formwork is employed first, followed by strip formwork technology.
Reinforcement of the assembled structure
Installing reinforcement inside the formwork and remembering to install the ventilation device and lay the water and sewer pipes are essential when assembling the formwork for a strip foundation.
Installing the reinforcement grid comes first. Some would rather put it together immediately there. As a result, longitudinal and transverse reinforcement are frequently tied to vertical rods that are merely driven into the ground. However, it is more practical to construct a basic template ahead of time out of leftover materials, to which the reinforcement bars are affixed at a specific distance. Prior to adding vertical rods or clamps and assembling the lattice along the longitudinal rods’ length, you can tie the horizontal components of each belt.
Following that, you can carry on putting the frame inside the formwork. Working reinforcement bars that are longitudinal must be knitted with a minimum 40 bar diameter overlap; for example, if the rod has a diameter of 12 mm, the overlap must be at least 48 cm. When creating the foundation, the designer determines the working reinforcement’s thickness; its rods need to be ribbed.
In order for the structure to function as a whole and for the concrete at the intersection of the foundation walls to be free of chips and cracks, it is also crucial to properly fasten the corners of the reinforcement frame. It is a major mistake to just tie the cross rods together at the corners. The proper method is to either bend the rods directly or to use additional, identical-diameter rods that are connected to the main ones and bent at an angle.
The reinforcement can also be fastened by welding, although this weakens the reinforcement and necessitates the purchase of additional welding equipment.
Additionally, the completed frame needs to be properly installed inside the formwork. To ensure that the rods are consistently covered by concrete, there needs to be a minimum of 50 mm between the metal and the formwork’s side and base walls. Prefabricated plastic reinforcement clamps are used for this; in severe situations, stones or broken bricks can be positioned beneath the grate.
Pieces of plastic or asbestos-cement pipe installed at the appropriate width and diameter are cut to allow for ventilation and the laying of pipelines inside the formwork. They can be foamed at the intersection with the walls or tied straight to the reinforcement.
Reinforcement of slab foundations
Diagram of a slab foundation with reinforcement.
Slab foundation reinforcement is typically done in two belts. The thickness of the cast slab determines how many belts are needed. Since every rod in this kind of foundation is functional, only ribbed reinforcement with a diameter of 10 to 16 mm is needed. When laying, it is not permitted for adjacent rods to be more than 40 cm apart; typically, there should be a 20 cm step between each rod.
The thickness and rigidity of the reinforcement used determines how far apart the belts are spaced if the slab design calls for multiple belts. Since the reinforcement bars essentially do not experience vertical load, they are used to fasten the belts together with smaller thickness.
As with reinforcing a strip foundation, the reinforcement bars are knitted to each other using soft knitting wire. The main requirement is that the wire not be hardened, and its thickness can range from 0.7 to 1.5 mm. In the rare cases when fiberglass reinforcement is needed, knitting is done with plastic clamps or screeds.
In order to provide the necessary space between the edge of the concrete surface and the metal of the rods, the reinforcement must also be installed on the lining.
In order to ensure the stability and longevity of any construction project, it is imperative to comprehend the significance of appropriate formwork for foundations. Formwork is the mold that forms the foundation of a structure by holding concrete until it hardens. It needs to be strong enough to bear the pressure that wet concrete applies, and it needs to be precisely engineered to keep the correct alignment and shape.
Selecting the appropriate materials is one of the most important factors in formwork construction. Common options include wood, steel, and aluminum, each of which has special benefits based on the needs of the project. Wood is inexpensive and simple to work with, but it might need more upkeep. Steel is strong and able to support large weights, but its fabrication calls for skilled labor. Although it can be pricey, aluminum is corrosion-resistant and lightweight.
Meticulous preparation and close attention to detail are necessary to ensure correct formwork setup. For the formwork to stay in place during the concrete pouring and curing process, it needs to be firmly fastened. Strategic placement of bracing and supports is necessary to distribute loads uniformly and avoid deformations that might jeopardize the structural integrity of the building.
Regular formwork inspections are crucial during the construction process. It’s important to take quick action when you notice any wear, damage, or misalignment to prevent future delays and expensive repairs. In addition to guaranteeing the foundation’s structural integrity, well-maintained formwork enhances the productivity and safety of the building site as a whole.