Concrete is the most commonly used man-made material on earth. Given its particular properties, it is also among the most widely employed options for construction. This mixture of cement, sand, gravel and water begins as a wet substance unable to support its own weight, thereby requiring the use of a mold to achieve the desired shape and structure. In construction applications involving concrete, that mold is referred to as the formwork.
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Because formwork not only controls the concrete's position and alignment, but also bears the weight of materials, equipment and workers, it must be expertly planned and applied. Here, we're breaking down the specific elements of superior concrete formwork to help you develop an approach that meets the needs and specifications of your construction project.
1. Appropriate Material Selection
Concrete formwork, also sometimes referred to as shuttering, is the configuration of forms (or molds) that are utilized to create an overall shape for the concrete. Just as the applications for formwork are varied, so are the types of materials used. Following are some of the different categories of form materials available for concrete projects.
- Timber: Timber, specifically plywood, is perhaps the most commonly used type of formwork material. Derived from trees, it is widely accessible, highly economical and available in a number of different species, sizes and grades. Timber is easy to cut and shape on the job site, and it is a reusable entity if managed and stored properly.
- Steel: This is a stronger and more durable material, and it has the advantage of upholding longer stretches of reusability when appropriately maintained. While the material demands a higher upfront cost, it retains value for a lengthier span of time. Other advantages to steel forms include their ability to deflect moisture, warping and shrinkage, their exposed surface quality and their capacity to be erected and removed quickly.
- Aluminum: This material is both strong and lightweight, making it a valuable source for certain formwork projects. Aluminum formwork is often prefabricated and then assembled on site. This material requires a higher initial expense, but its minimal weight brings down overall handling costs. Because pure aluminum is susceptible to corrosion, alloys are often applied to resist this effect.
- Plastics: Two different types of plastics'glass-reinforced and vacuum-formed'are sometimes employed for formwork applications. Although lighter than metal variations of formwork, plastic formwork is not as durable. Because it is a very flexible material, it's often leveraged to form more nuanced shapes. It also produces a high-quality surface finish. While plastic formwork can be an economical choice that enables reuse, it's important to note its vulnerability to sun and heat exposure.
- Other: Newer (though less commonly employed) iterations of form material include options like fiberglass and fabric. It's important to consider a number of factors pertaining to the needs of your concrete project, such as cost, strength, weight, flexibility, durability, sustainability and reusability, before making an informed decision about which type of material (or combination thereof) is best suited to meet your requirements.
2. Considerations for Strength & Capability
Formwork's fundamental role is to bear all the loads present while casting the concrete, as well as to retain its shape throughout the process. That means superior concrete formwork requires great consideration for:
- Accurate load estimations
- The properties and behaviors of the chosen form materials
- The pros and cons of different forming systems
The design and application of your formwork should be based on its ability to produce the required shape and surface finish, withstand the necessary loads, prevent cement leakage throughout and enable the removal of formwork materials without incurring damage to the concrete. These are critical considerations to be made prior to the installation of concrete formwork.
3. Proper Rate of Pour Based on Height
Conventional concrete, when wet, can weigh from 140 to 150 pounds per cubic foot. That's a lot of weight to account for when calculating the load capacity of concrete formwork. Because of this weight, there's a need to factor pressure into the equation, and pressure can be impacted by both the height and weight of the actual pour.
The greater the height of the poured concrete, the more lateral pressure is exerted on the interior of the formwork. Therefore, it's important to integrate appropriate drying intervals into the rate at which the concrete is poured. This allows a portion of the concrete to cure and strengthen before adding more of it to the mold.
Otherwise, if too much concrete is poured all at once, immense pressure can cause the forms' connecting devices to give way. When that happens, concrete can burst through the connections and out of the formwork'a messy, expensive and potentially hazardous outcome that could be avoided by ensuring a more sustainable pour rate.
4. Focus on Concrete Characteristics
The characteristics of the concrete itself can have an impact on the formwork and overall project. That's why it's important to understand, test and account for the properties of fresh concrete based on attributes such as:
- Type: The choice of concrete mix will depend on factors like required strength and surface finish, performance needs, weather conditions, local codes and cost.
- Weight: The unit weight of fresh concrete is determined by density, air content, water content and cement content.
- Slump: This is the consistency of fresh concrete, or its ability to flow. The project's slump tolerances will determine how the consistency of the concrete must be managed.
- Temperature: Temperature has a vital influence on the properties of fresh and hardened concrete, which is why minimum and maximum limits are specified. Variations in temperature can affect the rate of hydration, thereby impacting slump loss, rate of strength gain and setting and finishing times.
- Vibration: When concrete is poured, it contains air bubbles that can substantially weaken the structure. Concrete vibrators are used to eliminate these bubbles by shaking the freshly poured concrete.
5. Safety Planning & Supervision
Because there are real hazards associated with applying concrete formwork, organizations like the Occupational Safety and Health Administration issue guidelines around it. It's important to heed these guidelines and enforce adequate safety planning.
Without proper safety precautions, there's risk of experiencing the kinds of accidents and liability that stem from improperly designed formwork, hurried removal of forms, bends and breaks during the pouring process and so on.
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The best way to mitigate dangerous risks is to partner with a construction expert with the knowledge and experience to plan ahead, leverage a qualified staff and ensure proper supervision.
Formwork sometimes referred to as shuttering, is a temporary framework or mold used in construction to hold and shape building materials like concrete or other building materials until they harden or become self-supporting. It acts as a template for the concrete, which is poured into it and then allowed to set and acquire an adequate form and structure.
Shuttering is essential in construction because it guarantees that concrete or other materials are poured and cured in the right shape, size, and alignment. It promotes stability during construction and aids in obtaining accurate and reliable outcomes. The choice of material for shuttering is based on the project's scope, budget, and unique building needs. Materials that can be used include plywood, steel, plastic, and wood. The shuttering is removed when the concrete has dried and the finished structure is left in its place.
8 Types of Shuttering
- Plywood Shuttering.
- Steel Shuttering.
- Plastic Shuttering.
- Timber Shuttering.
- Tunnel Formwork.
- Aluminium Shuttering.
- Fabric Shuttering.
- Permanent Insulated Shuttering.
1. Plywood Shuttering
Plywood is frequently used for formwork because of its adaptability, availability, and affordability. Moulds for different concrete structures, including slabs, columns, and beams, are made easily from plywood panels. It is particularly well suited for flat surfaces and is simple to cut and assemble properly.
Plywood Shuttering
Pros
- Versatile and widely available.
- Smooth surface finish for concrete.
- Reusable if maintained properly.
Cons
- Susceptible to moisture damage.
- May require more frequent maintenance.
Criteria for Use
- Budget: Plywood formwork is cost-effective, making it suitable for projects with tight budgets.
- Project Size: Ideal for small to medium sized projects where a smooth concrete finish is required.
- Reusability: Depending on maintenance, plywood can be reused multiple times.
2. Steel Shuttering
Steel formwork has a reputation for being dependable and strong enough to support large concrete loads. It is frequently used in large-scale construction projects when repetitive use is necessary. Steel shuttering may be fabricated into complex forms and designs and is very customizable.
Steel Shuttering
Pros
- Highly durable and can withstand heavy loads.
- Reusable for many construction cycles.
- Provides excellent concrete finish.
Cons
- Expensive upfront cost.
- Heavy and requires machinery for handling.
Criteria for Use
- Load-Bearing Capacity: Suitable for projects requiring heavy loads and high structural stability.
- Durability: Ideal for long-term or repetitive use.
- Concrete Finish: Provides an excellent concrete finish, important for architectural projects.
3. Timber Shuttering:
Traditional timber formwork involves fabricating moulds for concrete with wooden planks and boards. Although it is affordable and adaptable, it requires skilled workers and is frequently used for smaller projects or in circumstances where cost is a major consideration.
Timber Shuttering
Pros
- Versatile and widely available.
- Good insulation properties.
- Cost-effective for smaller projects.
Cons
- Requires skilled carpenters for assembly.
- Susceptible to decay if not maintained.
Criteria For use
- Budget: Cost-effective for smaller projects with budget constraints.
- Skilled Labor: Requires skilled carpenters for proper assembly and maintenance.
- Insulation Needs: Good for projects where thermal insulation is desired.
4. Plastic Shuttering:
Compared to timber, plastic formwork is lighter, easier to handle, and has a longer lifespan. For making curved or unique-shaped concrete components, it is extremely helpful. Additionally resistant to corrosion, plastic formwork is reusable and clean.
Plastic Shuttering
Pros
- Lightweight and easy to handle.
- Resistant to moisture and chemicals.
- Quick assembly and disassembly.
Cons
- Not as durable as steel or aluminum.
- Limited to smaller to medium-sized projects.
Criteria for use
- Project Schedule: Best for projects with tight schedules due to quick assembly and disassembly.
- Moisture Resistance: Resistant to moisture and chemicals, making it suitable for wet environments.
- Size and Complexity: Suitable for smaller to medium-sized projects with less complex shapes.
5. Tunnel Formwork:
Tunnel formwork is used for recurrent constructions, such as apartment complexes. It is made up of a number of linked shapes that combine to make slabs and walls at the same time. Because the formwork is reused for each part, this approach is effective and speeds up construction.
Tunnel Formwork
Pros
- Efficient for repetitive structures.
- Reduces the need for manual formwork assembly.
Cons
- Limited to structures with a similar layout on each floor.
- Not suitable for complex or irregular shapes.
Criteria for use
- Repetitive Layout: Efficient for projects with a repetitive structural layout on each floor.
- Time Efficiency: Reduces construction time by eliminating the need for manual formwork assembly.
- Structural Uniformity: Suitable for structures with consistent design elements.
6. Aluminium Shuttering:
Aluminium formwork is lightweight and simple to use. It is frequently used to develop repetitively laid out commercial and residential constructions. Aluminium formwork has become recognised for its accuracy and efficiency, and it is relatively easy to alter for different dimensions.
Aluminium Shuttering
Pros
- Lightweight and easy to handle.
- Precise and consistent results.
- Reusable for multiple projects.
Cons
- Initial cost is higher compared to some alternatives.
Criteria for use
- Speed and Precision: Ideal for projects where speed and precise construction are priorities.
- Reuse: Can be reused for multiple projects, making it cost-effective over time.
- Complexity: Suitable for a wide range of project complexities.
7. Fabric Shuttering:
Fabric formwork involves using flexible and tension-resistant fabric materials to shape concrete, which often gets supported by a frame or other structural components. It is used in concrete constructions that create unique and distinctive forms. The fabric shutterring allows unusual, free-form patterns.
Fabric ShuttteringFabric Shutttering
Pros
- Flexibility in design and shape.
- Suitable for artistic and architectural applications.
Cons
- Limited to specific decorative or artistic projects.
- May not provide the same structural strength as traditional formwork.
Criteria for use:
- Architectural Aesthetics: Suitable for projects where unique shapes and aesthetics are crucial.
- Artistic Freedom: Provides flexibility for creative and artistic designs.
- Non-structural: Typically used for decorative or non-structural elements.
8. Permanent Insulated Shuttering:
Permanent insulated formwork combines the advantages of formwork with the advantages of insulation. It is frequently used in situations that need for both structural support and insulation, such as constructing insulated concrete walls or building envelopes. It serves as a permanent component of the building's structure after it has been placed.
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Permanent Insulated Shuttering
Pros
- Combines formwork and insulation in one.
- Ideal for energy-efficient buildings.
Cons
- May have higher upfront costs.
- Limited to projects where energy efficiency is a priority.
Criteria for use
- Energy Efficiency: Suitable for projects where energy efficiency and insulation are priorities.
- Long-term Cost Savings: Although it may have higher upfront costs, it can lead to energy savings over time.
- Construction Goals: Appropriate for sustainable and green building projects.