Void forms are a type of sacrificial formwork that serves the dual purpose of protecting the concrete foundation from the upward movement of expansive soil and providing temporary support for newly poured concrete until it gains enough strength to support its weight. They are also used to reduce the amount of soil excavation required and the volume of concrete used in construction projects.
The depth of void forms installed beneath foundations typically ranges from 5 cm to 60 cm, depending on the underlying soil’s potential for upward movement. Different types of void forms are available for use, including degradable and non-degradable options, as well as collapsible and non-collapsible forms.
Void forms can be made from a variety of materials, including corrugated paper, expanded metal, metal sheet, molded plastic, molded paper, Styrofoam, and wood. The choice of material will depend on the specific needs of the construction project and the type of soil present at the site. By using void forms, construction projects can minimize the risk of foundation damage and reduce costs associated with excavation and concrete usage.
Why are Void Forms Used in Foundation Construction?
Expanding soil volume can be absorbed through certain measures. These measures can be employed to prevent any adverse effects of soil expansion. It is important to consider these measures when constructing a building or laying a foundation. By taking these measures, the risk of structural damage can be minimized.
In order to reduce the amount of concrete required for a construction project, alternative materials can be used. This can help to reduce the overall cost of the project and make it more sustainable. By using materials that are readily available and cost-effective, the amount of concrete required can be reduced without compromising the structural integrity of the project.
Creating a stable slab is essential for any construction project. By using proper construction techniques and materials, a stable slab can be created that will provide a strong foundation for the building. This will help to prevent any damage to the building and ensure its longevity.
Soil excavation can be a time-consuming and costly process. By taking measures to reduce soil excavation, the construction process can be streamlined and the overall cost of the project can be reduced. This can be achieved through the use of alternative construction techniques and materials, which can help to minimize the need for excavation.
Void Form Materials
Corrugated paper is a material that is commonly used for packaging and shipping purposes. It is made by sandwiching a fluted or ridged inner layer between two flat outer layers of paper. This creates a material that is lightweight yet strong, making it ideal for protecting items during transit.
Expanded metal is a type of metal sheet that has been processed in such a way as to create a mesh-like pattern of diamond-shaped openings. This material is often used for fencing, grating, and other applications where a strong, yet open structure is required. Expanded metal is typically made from a variety of metals, including aluminum, stainless steel, and carbon steel.
Metal sheet is a broad term that refers to a wide range of sheet metal products. These products are typically made from thin, flat pieces of metal that have been cut and shaped to a specific size and thickness. Metal sheets are used in a variety of applications, from roofing and siding to automotive and aerospace manufacturing.
Molded plastic is a type of plastic that has been shaped into a specific form through a process called injection molding. In this process, molten plastic is injected into a mold, which is then cooled and hardened to create a solid plastic part. Molded plastic is used in a variety of applications, from toys and household items to automotive and medical devices.
Molded paper is a type of paper product that has been shaped into a specific form using a process called pulp molding. In this process, a mixture of water and recycled paper is poured into a mold, which is then heated and pressed to create a solid, molded paper product. Molded paper is often used for packaging and other disposable items.
Styrofoam is a brand name for a type of expanded polystyrene foam that is commonly used for insulation and packaging. It is a lightweight, yet strong material that is known for its excellent insulation properties. Styrofoam is also used in a variety of other applications, from food containers to surfboards.
Wood is a natural material that is commonly used for construction and furniture manufacturing. It is a renewable resource that is prized for its strength, durability, and versatility. Wood comes in a variety of species and can be used in a wide range of applications, from building structures to decorative finishes.
Types and Applications of Void Forms
1. Degradable Void Forms
Degradable void forms are manufactured using materials that are easily degradable, such as molded paper and corrugated paper. These void forms are designed for use on construction sites where there is an ample water supply in the environment, allowing the material to degrade before soil expansion occurs. The use of these void forms is particularly suitable in areas where water is readily available, allowing for natural degradation of the material without causing any adverse environmental impact. By utilizing degradable materials, such as molded paper and corrugated paper, in the production of void forms, construction sites can implement eco-friendly practices and reduce their environmental footprint.
Figure-1: Degradable Void Forms
Degradable void forms are utilized in construction to create a void or empty space between expansive soil and grade beams (as depicted in Figure-2). These void forms are designed to break down or degrade over time, leaving behind a space that helps prevent soil movement or settlement from affecting the integrity of the structure. They are also commonly employed in the construction of slab-on-grade foundations (as shown in Figure-3), where they create a separation between the foundation and the soil to minimize potential damage from soil heaving or shrinking. Additionally, degradable void forms can be used to isolate foundation piers from the surrounding soil, reducing the risk of soil-related structural issues.
Degradable void forms are a reliable solution for supporting fresh concrete until it gains sufficient strength to bear its own weight. These forms may degrade over time due to moisture exposure, creating a gap between the foundation and expansive soil. They are commonly used in concrete construction projects where removal of formwork is not feasible, or underneath concrete slabs to prevent damage from expansive soil.
To ensure proper performance of degradable void forms, it is important to avoid placing materials such as plastic sheathing or layers of gravel underneath the carton forms. These materials can obstruct capillary water movement and hinder the degradation of the void forms. Therefore, it is crucial to store void forms in a dry place and protect them from moisture until the concrete is poured. Installing plastic sheeting above the degradable void forms can help prevent moisture ingress.
One of the advantages of degradable void forms is their lightweight nature, making them easy to install and cut as needed. They are also available in standard sizes and strengths, making them versatile for various concrete construction applications. Proper handling and storage of degradable void forms are essential to ensure their integrity and effectiveness in supporting fresh concrete until it reaches sufficient strength.
2. Non-Degradable Void Forms
Void forms are structural components used in construction projects to create cavities in the ground where concrete can be poured. These forms can be made from a variety of materials, including metal, wood, Styrofoam, and plastic. However, in some cases, designers may choose to use non-degradable void forms.
As the name suggests, non-degradable void forms are made from materials that do not break down easily over time. While this can make them useful for certain applications, it also means that they will remain in place for a long time once they are installed. This is an important consideration for foundation designers who must ensure that the void forms they use are appropriate for the specific project and will not cause any issues in the future.
Overall, non-degradable void forms can be a useful option in certain construction projects. However, designers must carefully weigh the benefits and potential drawbacks of using them before making a decision. By doing so, they can ensure that their projects are structurally sound and will stand the test of time.
3. Collapsible Void Forms
Collapsible void forms are designed to be used in construction projects where expansive soil is present. These materials are manufactured in a way that allows them to withstand the pressure of fresh concrete, but also be weak enough to collapse when faced with the pressure of expanding soil. It is important that these void forms are not used under reinforced concrete slabs, as the force of expansive soil can be strong enough to lift the structure and its foundation. Therefore, careful consideration should be given to the selection of appropriate materials for construction projects in areas with expansive soil.
4. Non-Collapsible Void Forms
Non-collapsible void forms are recommended in areas where the foundation’s strength is sufficient to withstand the uplift forces caused by soil expansion acting on the forms. These void forms are designed to remain intact and maintain their shape, without collapsing, even under the pressure of expanding soils. They are a suitable choice in locations where the foundation is robust enough to resist the upward forces exerted by the swelling or heaving of the soil, which may occur due to various factors such as moisture changes or frost action. Non-collapsible void forms provide stability and durability, ensuring that the foundation remains stable and intact, and the structure above it is well-supported.
Figure-7: Non-Collapsible Void Form
When constructing a foundation using a grade beam, it is important to use a non-collapsible void form system. This type of form should only be used specifically for grade beams and should not be utilized under a slab area with a long span between stiffening beams and thin unreinforced slab elements. It is essential to avoid using this type of form system in situations where the slab area has a long span between stiffening beams and thin, unreinforced slab elements.
FAQs
What is a void form in concrete foundation construction?
Void form is an element that serves a dual purpose in construction. Firstly, it is sacrificial and is placed underneath a foundation to create a space between the foundation and heave of expansive soil. This helps prevent the foundation from being lifted by the soil, which can cause damage to the building structure. Secondly, it provides temporary support for fresh concrete until it reaches a specified strength. This is important because the weight of the concrete can cause it to deform or collapse if it is not properly supported during the curing process. By using void form, construction workers can ensure that the concrete is held in place and allowed to set properly, which helps to ensure the long-term structural integrity of the building. Overall, void form is an important element in construction that serves multiple purposes and helps to ensure that buildings are constructed safely and securely.
What is a typical space between a foundation and underlying expansive soil to install void forms?
The distance between the concrete foundation and the expansive soil underneath can vary, depending on the potential for upward movement of the soil. This spacing can range from 5 cm to approximately 60 cm. The reason for this variability is due to the fact that expansive soil can cause significant damage to the foundation if it expands too much, which is why engineers take into account the soil’s potential for upward movement when designing a foundation. By providing adequate spacing between the foundation and the soil, the risk of damage to the structure can be reduced. This spacing is a critical factor in ensuring the longevity and stability of the building’s foundation, which is an essential aspect of any construction project.
What are the different types of void forms?
Void forms are structures used in construction to create empty spaces within concrete slabs and walls. These spaces can reduce the weight and volume of the concrete, leading to cost savings and improved performance. Void forms can be categorized into four types based on their properties: degradable, non-degradable, collapsible, and non-collapsible.
Degradable void forms are made of materials that can break down over time, such as cardboard or foam. These materials are chosen specifically because they will deteriorate and disappear on their own, leaving the concrete with the desired void space. This type of void form is typically used for short-term applications, such as in temporary construction.
Non-degradable void forms, on the other hand, are made of materials that will not break down and will remain in place indefinitely. Examples of non-degradable materials include plastic and metal. These void forms are used when a long-term or permanent solution is required.
Collapsible void forms can be compressed and folded to a smaller size, allowing for easier transportation and storage. These forms are typically made of materials such as cardboard or paper, and are often used in areas where access is limited or space is at a premium.
Finally, non-collapsible void forms cannot be compressed or folded and are typically made of more rigid materials such as plastic or metal. These forms are used in situations where the concrete needs to be structurally reinforced and where a strong and permanent void form is required.
What is the type of void form suitable for concrete slab?
When it comes to installing a void form under a concrete slab, it’s important to choose the right type. Specifically, a degradable void form is the only option that’s suitable for this application. This is because the combination of dead and sustained live load, along with the inherent stiffness of the slab, is simply not sufficient to collapse both collapsible and non-collapsible void forms. If you were to use one of these other types of void forms, the heave force would end up being transferred to the slab. This could cause serious problems and compromise the integrity of the entire structure. Therefore, it’s important to make sure you select the appropriate type of void form for your specific needs.
What are the advantages of void forms?
When constructing a building or any kind of structure, it is important to consider the type of soil present at the site. Some soils are known to expand when exposed to moisture, which can lead to structural issues down the line. To counter this problem, it is advisable to use materials that can absorb the expanding soil volume. By doing so, the structure will be more stable and less prone to damage caused by soil expansion.
Another way to enhance the stability of a structure is by reducing the quantity of concrete used during construction. This can be achieved by employing alternative materials that are just as strong and durable. By doing so, the structure will be more resistant to various types of external forces, including soil expansion.
By using materials that can absorb expanding soil volume and reducing the quantity of concrete, it is possible to create a more stable slab. This is especially important for buildings and structures that are intended to last for many years or decades. A stable slab will also help to reduce the amount of maintenance required over time.
Lastly, reducing soil excavation can also help to create a more stable foundation for a building or structure. When excavation is excessive, it can weaken the soil and destabilize the structure. By minimizing excavation and using alternative techniques, it is possible to maintain the structural integrity of the site and ensure that the building or structure is secure and stable.