Types of Formwork for Concrete Structures
Concrete is one of the most extensively utilized building materials due to its remarkable properties. However, constructing components from concrete requires it to be poured into specifically designed molds, referred to as formwork or shuttering.
Formwork can employ either temporary or permanent molds to hold the poured concrete in shape until it hardens and attains sufficient strength to support itself. It can be classified based on several criteria, including the type of material used, support provided by the concrete element, and whether it is removable or permanent.
Importance of Formwork in Concrete Construction
Formwork is crucial in concrete construction, as it must be robust enough to endure all loads during the pouring process while maintaining its shape as the concrete hardens.
Key Requirements for Quality Formwork
Although there are many types of formwork materials, the general performance characteristics essential for concrete construction are:
Load-bearing capacity: Must withstand both dead and live loads.
Structural integrity: Should maintain its shape with adequate struts and supports.
Leak-proof joints: To prevent leakage of concrete.
Non-damaging removal: If the formwork is removable, it should not damage the hardened concrete.
Reusability: Materials should be reusable to reduce costs.
Lightweight: To facilitate ease of handling and installation.
Dimensional stability: Should not bend or deform under load.
When selecting formwork, it is essential to consider the type of concrete and pouring temperature, as both impact the pressure applied. Additionally, the formwork must withstand the load of both wet and dry concrete. Structures such as poles and stabilizers, known as scaffolding, are used to prevent movement during construction. Ensuring high-quality concrete construction requires skilled labor and adequate supervision.
Common Formwork Materials
Wooden Formwork
Wooden formwork, one of the earliest forms used in construction, is assembled on-site and offers great flexibility. Its advantages include:
Ease of production and removal
Lightweight compared to metal formwork
Flexibility to create various shapes, sizes, and heights
Cost-effectiveness for small projects
Availability of local wood
However, wood must be inspected for termites, and its limitations include a short lifespan and time-consuming assembly for large projects. Wooden formwork is recommended when labor costs are low or when flexible formwork is required for complex concrete sections.
Plywood Formwork
Plywood, often used with wood, is a manufactured wood product available in various sizes and thicknesses. It is mainly used for sheathing, decking, and lining formwork. Plywood formwork shares properties with wood, such as strength, durability, and lightweight.
Metal Formwork: Steel and Aluminum
Steel formwork and hardware are increasingly popular due to their longevity and reusability, despite the higher cost. Key features of steel formwork include:
Strength and durability with a long service life
Smooth finish on concrete surfaces
Water resistance
Reduction in honeycombing in concrete
Ease of installation and removal
Suitability for curved structures
Aluminum formwork, similar to steel, is lighter due to its lower density but also less strong. This difference must be considered in its application.
Plastic Formwork
Plastic formwork consists of interlocking panels or modular systems made from lightweight, strong plastic. It is ideal for small, repetitive projects, such as low-cost housing. Advantages include:
Lightweight and easy to clean
Suitable for large-scale construction and multiple reuse
However, plastic formwork is less flexible than timber, as many components are prefabricated.
Fabric Formwork
Fabric formwork, or flexible formwork, uses lightweight, high-strength fabric panels that accommodate the fluidity of concrete, creating unique architectural forms. This emerging technology is particularly suitable for buildings with irregular and complex shapes, saving costs by using less concrete than rigid systems.
Fixed Formwork
Fixed formwork remains in place after the concrete sets, providing axial and shear reinforcement. Made from prefabricated and fiber-reinforced plastic forms, it is primarily used for piers and columns and is resistant to corrosion and environmental damage. Coffor is another type of fixed formwork suitable for any construction type, consisting of two filter grids reinforced by stiffeners and connected by hinged connectors, facilitating easy transport from the factory to the construction site.
Tunnel Formwork
Tunnel formwork is a construction method used in residential apartments and hotels, producing repeated structural elements for buildings with similar layouts. It employs a steel formwork system constructed on-site to cast concrete walls and slabs in a continuous cycle. This method is particularly effective for projects requiring rapid construction and consistent design, offering advantages such as faster construction, better quality control, and reduced labor costs. Tunnel formwork is widely used in high-rise building projects where speed and efficiency are crucial.
Permanent Insulated Formwork
Permanent insulated formwork is one of the most advanced systems, providing permanent insulation and potentially offering thermal, acoustic, fire, and rodent-resistant properties. Insulated Concrete Formwork (ICF) is the most common type, where the concrete structure is insulated with polystyrene boards that remain in place after curing. This system is energy-efficient and sustainable, helping to reduce the environmental impact of the construction industry.
Classifying Formwork Based on Structural Components
Formwork can also be classified based on the building element it supports:
Wall Formwork
Beam Formwork
Foundation Formwork
Column Formwork
Each type is designed based on the structure it supports, with corresponding construction plans specifying the material and required thickness. It is important to note that formwork construction is time-consuming and can account for 20% to 25% of the structure's cost. To reduce formwork costs, consider the following:
Reuse building elements and geometric shapes: This allows for formwork to be reused.
Large pieces for wood formwork: Ensure it is cut into large enough pieces for reuse.
Concrete structures vary in design and purpose, and no single formwork option is superior for all applications. The best formwork for a project depends on the specific building design and requirements.
