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Everything you need to know about formwork for curved concrete structures


In the construction world, formwork for curved structures (both walls and slabs) entails a technical and aesthetic challenge that can completely transform the appearance and functionality of a project.

In this article, we will explore the techniques, materials, and key considerations for the successful implementation of formwork for cast-in-place concrete structures.

Execution of a tunnel portal with circular flexible formwork

The importance of curved and flexible formwork

Curved and flexible formwork is essential for creating structures with specific geometric or organic shapes, as it offers unique aesthetic and functional solutions. From landmark buildings to basic infrastructure, it enables the creation of architectural designs that defy traditional straight lines, imbuing spaces with fluidity and movement.

These structures include: curved walls, vaulted ceilings, tunnels, cut-and-cover tunnels, circular tanks, curved sidewalls, water/sewage treatment plants, etc.

Curved sidewalls of a tunnel, executed with one-sided wall brackets and flexible modular formwork

Traditional method, slower and more laborious

In traditional construction, prior to the invention of flexible formwork, curved structures were achieved using more complex methods. A straight formwork system was used as a base, and then support elements such as arched wooden or EPS planks were added to shape the desired curves. These planks are strategically placed along the formwork and adjusted to produce the required curvature.

While this method can be effective, it presents limitations in terms of curve accuracy and uniformity, as it is highly dependent on builders’ skill and experience in manually shaping and adjusting the planks. In addition, the process can be more laborious and time-consuming compared to the use of flexible formwork specifically designed to fit specific curves with greater precision and efficiency.

Differences between curved and flexible formwork

It is crucial to understand the difference between static curved formwork and flexible formwork that adapts to specific curves in construction. Curved formwork has a predetermined shape and cannot be adapted to different radii of curvature. Many formwork companies offer curved metal formwork systems for curved piers up to 2 m in diameter with standard material. It is also possible to order special customized formwork when the situation requires it (oval lintels, truncated conical piers, etc.).

Standard curved metal formwork for a circular 1.5 m diameter pier
Custom metal formwork solution for curved pier with variable cross-section

In contrast, flexible formwork offers versatility since it can be shaped to the exact curves required for a specific structure. In general, these flexible panels can be adapted to achieve a minimum radius of 2.5 m.

This difference is fundamental because it allows for greater precision in the shaping of complex architectural elements, such as curved walls or columns, thereby optimizing the use of materials and reducing production costs.

Circular flexible formwork material adjusted to a given radius. In the background, the same panels can be seen in a straight position

Materials used to construct formwork systems

In curved formwork, mainly robust and resistant materials are used. Common materials include steel, aluminum and high-density plywood. These materials provide the necessary rigidity to support the pressure of the concrete and to ensure the accuracy of the final shape of the circular structure.

On the other hand, flexible formwork uses steel or aluminum frames, and materials such as phenolic plywood as the formwork surface to easily adapt to the required curves without compromising strength. The flexibility of these materials makes it possible to create complex curved shapes with greater ease and precision, reducing the need for additional support structures. In addition, flexible formwork is lighter and easier to handle compared to rigid formwork, which can increase construction efficiency and speed.

Planning and design

Meticulous planning is essential. Designs must consider the radius of curvature, the height and width of the wall, and the pressure of the concrete. Using 2D and 3D modeling software helps visualize the project and identify potential challenges prior to execution.

Plan layout of circular flexible formwork modules for the construction of curved walls in a water treatment plant

Execution and stripping

Precision in execution is crucial to ensuring that the desired wall curvature is achieved. Formwork must be robust enough to withstand the pressure of the concrete without losing its shape. In addition, removal must be done carefully so as to not damage the surface of the wall. As is the case with straight formwork, correct vibration at the time of concreting and the use of a form release agent are fundamental to achieving a good concrete finish.


In conclusion, flexible formwork optimizes on-site production and ensures greater precision in execution. It is widely used in structures such as Wastewater Treatment Plants, Waste Treatment Facilities, Water Tanks, Tunnels, Industrial Tanks, etc.

On the other hand, curved formwork is necessary in cases with a small radius or with repetitive and serial execution (piers, circular columns, etc.).

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