What is Formwork for Concrete? Types of Concrete Formwork

Formwork for concrete is a temporary structure or mold into which concrete is poured and held in place until it gains enough strength to support itself.

It is a framework or mold used to support and shape the concrete until it hardens and gains strength. The formwork must be sturdy and capable of withstanding the pressure of the wet concrete.

It plays a crucial role in shaping the concrete into the desired form, whether that’s a wall, slab, beam, or staircase.

Formwork consists of two main components:

Facing: The material that comes into direct contact with the concrete and shapes it.
Supporting Structure: The system of props, scaffolding, or bracing that holds the facing material in place.

The design and materials used in the concrete formwork can significantly affect the final structure’s surface finish, dimensions, and overall quality.

Different Types of Concrete Formwork

There are several types of formwork systems designed for different construction needs. The choice of concrete formwork depends on factors such as the nature of the project, the type of structure, the desired finish, and budget constraints. Below are the most commonly used types of formwork for concrete construction:

Timber Formwork: This is the traditional method where timber is cut to size and used to build the formwork on-site. Timber formwork is flexible and easy to work with but is labor-intensive and often used in small or one-time projects.
Steel Formwork: Made from prefabricated steel panels, this type of formwork is durable, reusable, and provides a smooth finish to the concrete surface. It’s commonly used in large-scale construction where durability and reusability are essential.
Plastic Formwork for Concrete: Lightweight and modular, plastic formwork is ideal for repetitive tasks. It’s used for low-cost housing projects and allows for quick assembly and disassembly. It’s also popular in plastic formwork for concrete columns due to its ease of use and reusability.
Aluminum Formwork: Known for being lightweight and easy to handle, aluminum formwork systems are gaining popularity in high-rise buildings where speed and precision are critical.
Insulated Concrete Formwork: A modern innovation, insulated concrete formwork (ICF) combines the formwork system with insulation, offering energy efficiency and faster construction times. This is particularly used in colder climates where insulation is vital.

Formwork for Concrete Slab

The formwork for concrete slabs involves creating a horizontal mold that supports the weight of the wet concrete until it hardens. Typically used in floors or roofs, the formwork system for slabs must be able to support not only the weight of the concrete but also the load of workers and construction equipment.

Two common methods for constructing slabs include:

Conventional Formwork: This method uses timber or plywood sheets supported by vertical props to create a flat mold. While labor-intensive, it’s cost-effective for smaller projects.
System Formwork: This involves using prefabricated panels made of materials like steel or aluminum. System formwork for slabs is faster to erect and dismantle, making it ideal for large or repetitive projects.

Formwork for Concrete Walls

Formwork for concrete walls involves creating vertical molds into which concrete is poured to form walls. The process requires strong support systems since the concrete exerts considerable pressure on the formwork, particularly at the base.

Vertical Panels: These are typically made from steel, aluminum, or plywood and are supported by scaffolding or vertical props. The panels must be secured tightly to prevent leakage of wet concrete.
Precast Formwork: For high-rise buildings or large projects, precast wall panels can be constructed off-site and then transported to the construction site for quick assembly.

Formwork for Concrete Beams

Formwork for concrete beams is another specialized area requiring precise planning and execution. Beams, which are horizontal structures designed to carry loads, often require robust formwork to ensure the structure’s integrity during the concrete curing process.

Beam Soffit Formwork: This is the bottom formwork that supports the beam. It is supported by vertical props and must be strong enough to hold the weight of the wet concrete.
Beam Side Formwork: This keeps the concrete in place horizontally and determines the width of the beam. It is connected to the soffit formwork and must be aligned accurately to ensure that the beam’s sides are straight.
Beam Head Formwork: Used to shape the ends of the beams and ensure precise alignment, particularly at junctions where multiple beams intersect.

Formwork for Concrete Stairs/Steps

Constructing concrete stairs requires specialized formwork for concrete steps to ensure that the treads and risers are evenly spaced and aligned.

Prefabricated Formwork for Concrete Stairs: Prefabricated formwork systems are often used to construct stairs, especially in large buildings. These systems can be custom-built off-site and then transported to the construction site for quick assembly. Prefabricated systems save both time and labor.
Traditional Timber Formwork: For smaller or more customized staircases, timber formwork can be built on-site. While more labor-intensive, it offers flexibility in design and allows for unique stair shapes.

Permanent Formwork for Concrete Slabs

Another innovative formwork system is permanent formwork. Unlike conventional formwork, which is removed after the concrete sets, permanent formwork for concrete slabs remains in place and becomes part of the final structure.

Composite Slabs: One common type of permanent formwork is composite slabs, which combine steel or precast concrete elements with poured concrete. This system offers enhanced structural stability and can reduce construction time.
Benefits: Permanent formwork eliminates the need for dismantling, reduces labor costs, and can contribute to the structural integrity of the slab.

Concrete Formwork Design Tables

For engineers, accurate calculations are essential for the safe construction of concrete structures. Concrete formwork design tables provide critical information, such as load-bearing capacities, pressure ratings, and material specifications, to ensure that the formwork system can support the weight and pressure of wet concrete.

These tables typically include:

Formwork Load Data: Information about the vertical and horizontal loads that formwork systems can withstand.
Material Specifications: Details about the type of material used in the formwork, including its strength and durability under different conditions.
Design Pressures: Calculations for the lateral pressure exerted by wet concrete at various depths, ensuring that the formwork can handle the load without deflecting or collapsing.

Concrete Formwork Drawings

Accurate concrete formwork drawings are vital for any construction project. These drawings provide detailed information about the formwork system, including dimensions, material specifications, and the assembly process.

2D and 3D Drawings: Both 2D and 3D drawings are used in formwork design. While 2D drawings show the formwork from a flat, top-down perspective, 3D drawings give a more realistic view, allowing for better planning and visualization of the final structure.
Importance: Formwork drawings ensure that the design is implemented correctly, and they are essential for communicating the construction plan to workers and contractors.

How to Estimate Formwork for Concrete?

Estimating the quantity and cost of formwork for concrete is a critical part of project planning. Proper estimation ensures that the construction is completed within budget and on time.

Area Calculation: The surface area of the structure to be formed, such as walls, slabs, or beams, must be calculated first. This includes all sides of the structure that will require formwork.
Material Costs: The cost of materials, including timber, steel, or plastic panels, must be factored into the estimate. The type of formwork (temporary or permanent) will affect the overall cost.
Labor Costs: Labor is one of the most significant components of formwork costs, particularly for custom or on-site-built systems like timber formwork. Prefabricated formwork systems tend to reduce labor costs due to faster installation times.

Formwork for Structural Reinforced Concrete

In large construction projects that involve structural reinforced concrete, the formwork system must be able to support both the concrete and the steel reinforcements inside it.

Reinforced Beam and Slab Systems: When working with reinforced beams or slabs, the formwork must account for the extra weight and tension caused by the steel reinforcements. This often requires more robust support structures, such as additional props and ties.
Tolerances: The formwork must be designed and constructed with tight tolerances to ensure that the reinforcement is correctly positioned within the concrete, which is crucial for structural integrity.

Formwork Oil for Concrete

To ensure the smooth removal of formwork after the concrete has set, formwork oil is often applied to the surfaces that will come into contact with the concrete.

Mould Oil for Concrete Formwork: Mould oil acts as a release agent, preventing the concrete from sticking to the formwork. This helps in achieving a smooth surface finish and reduces the risk of damage to both the formwork and the concrete.
Types of Formwork Oils: There are various types of release agents, including oil-based, water-based, and chemical-based solutions. The choice of release agent depends on the material of the formwork and the desired finish of the concrete.

Conclusion

Formwork for concrete plays a pivotal role in the successful execution of construction projects, ensuring that structures are built to the desired dimensions and specifications. Whether you’re working on walls, slabs, beams, or stairs, choosing the right formwork system is essential to the structural integrity and finish of the project.

With innovations like permanent formwork for concrete slabs and prefabricated formwork for concrete stairs, modern construction techniques are becoming faster, safer, and more efficient. Understanding the types, materials, and specifications of formwork will help ensure the success of your next concrete project.

What is Formwork for Concrete? Types of Concrete Formwork