Concrete is one of the most used construction materials, thanks to its exceptional properties. However, to create building elements with concrete, it must be poured into a specially designed mold. This is known as formwork or shuttering.
The formwork can use temporary or permanent molds, which keep the poured concrete in shape until it hardens and reaches sufficient strength to support itself. Formwork can be classified in several ways:
- Type of material used
- By supported concrete element
- Removable or permanent
Formwork plays a fundamental role in concrete construction. It must have sufficient strength to withstand all loads present during casting operations and must then maintain its shape while the concrete hardens.
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What are the requirements for good formwork?
Although there are many formwork materials, the following are general performance characteristics to meet the needs of concrete construction:
- Able to withstand live and dead loads.
- Maintaining its shape with proper supports and supports.
- Joints must be watertight.
- If the formwork is removable, the process should not damage the concrete.
- Reusable material.
- As light as possible.
- The formwork material must not deform or distort.
When choosing the formwork, it is important to consider the type of concrete and the pouring temperature, as both affect the pressure exerted. Furthermore, the formwork must be able to withstand the loads of wet and dry concrete.
Formwork requires structures such as posts and stabilizers to prevent movement during construction procedures, and these are called falseworks. To ensure high quality concrete work, qualified labor and adequate supervision are required.
The following sections provide an overview of some common formwork materials.
Wooden formwork
Wooden formwork was one of the first types used in the construction industry. It is assembled on site and is the most flexible type, bringing the following advantages:
- Easy to produce and remove
- Lightweight, especially when compared to metal molds
- Workable, allowing any shape, size and height
- Economical for small projects
- Allows the use of local wood
However, before using the wood, its condition must be carefully checked, making sure it is free of termites. Wooden formwork also has two limitations that must be considered: it has a short lifespan and is time-consuming for large projects. In general, wood formwork is recommended when labor costs are low or when complex sections of concrete require flexible formwork.
Plywood formwork
Plywood is often used together with wood. It is a material made from wood, available in different sizes and thicknesses. In formwork applications, it is mainly used for cladding, decking and formwork linings.
Plywood formwork has similar properties to wood, including strength, durability and light weight.
Metal Formwork: Steel and Aluminum
Steel formwork and hardware are becoming more popular due to their long service life and multiple reuses. Although it is expensive, metal formwork is useful for multiple projects and is a viable option when many reuse opportunities are expected.
Following are some of the main features of steel formwork:
- Strong and durable, with long service life
- Creates a smooth finish on concrete surfaces
- Waterproof
- Reduces the honeycomb effect in concrete
- Easily installed and dismantled
- Suitable for curved structures
Aluminum formwork is very similar to steel formwork. The main difference is that aluminum has a lower density than steel, which makes the formwork lighter. Aluminum also has lower resistance than steel, and this must be considered before using it.
Plastic Formwork
This type of formwork is assembled from interconnected panels or modular systems, made from lightweight and robust plastic. Plastic formwork works best on small projects that consist of repetitive tasks, such as low-cost housing developments.
The plastic formwork is lightweight and can be cleaned with water, making it suitable for large sections and multiple reuses. Its main disadvantage is that it is less flexible than wood, as many components are prefabricated.
Fabric form
Fabric formwork is also known as flexible formwork. This system uses lightweight, high-strength fabric sheets designed to adjust to the fluidity of concrete and create interesting architectural forms.
This type of formwork uses less concrete than rigid systems, which generates savings. It is an emerging technology in the formwork industry, especially suitable for irregular and complex shaped constructions.
Permanent formwork
This formwork was designed to remain fixed after the concrete has set, acting as axial and shear reinforcement. This formwork is made on site from prefabricated, fiber-reinforced plastic forms. It is mainly used in pillars and columns, in addition to providing resistance to corrosion and other types of environmental damage.
Another type of fixed formwork is coffor, which can be used in any type of construction:
- It consists of two filter grids, reinforced by reinforcements and interconnected by articulated connectors.
- Thanks to its construction, it can be easily transported from the factory to the point of use.
Tunnel Formwork
Tunnel formwork is a common construction method used in residential apartments and hotels that involves producing repetitive structural elements for buildings with the same layout. It uses a system of steel formwork that is built on the construction site to cast concrete walls and slabs in a continuous cycle. This strategy is especially effective for tasks that require fast construction and consistent design.
Tunnel formwork is widely used in high-rise construction projects when speed and efficiency are crucial. The advantages are faster construction, high quality control and lower labor costs. The approach enables the creation of lasting structures quickly and efficiently, making it one of the popular choices in the infrastructure industry.
Permanent Insulated Formwork
This is one of the most advanced formwork systems offering permanent insulation. It may also include thermal, acoustic, fire resistance and rodent resistance properties. Insulating concrete formwork (ICF) is the most common type of permanent insulated formwork, where concrete structures are insulated with polystyrene sheets that remain in place after the concrete has cured.
Permanent insulated formwork offers energy efficiency and sustainability, contributing to a lower environmental impact in the construction sector.
Classification of formwork based on structural components
In addition to being classified by material, formwork can also be classified according to the construction elements supported:
- Wall formwork
- Beam formwork
- Foundation formwork
- Column formwork
All types of formwork are designed according to the structure they support, and the corresponding construction plans specify the materials and thicknesses required. It is important to highlight that the construction of formwork takes time and can represent between 20 and 25% of structural costs. To mitigate the cost of formwork, consider the following recommendations:
- Construction plans should reuse construction elements and geometries as much as possible to allow for reuse of formwork.
- When working with wooden forms, they must be cut into pieces large enough to be reused.
Concrete structures vary in design and purpose. As with most design decisions, no one option is better than the others for all applications; The most suitable formwork for your project varies depending on the building design.
