Ten frequently asked questions about wall formwork (part one)

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Industrialized vertical formwork has become a common part of the construction process on on-site concrete structures. They allow fast and well-defined production cycles, guaranteeing greater safety for operators during assembly, concreting and stripping than traditional formwork.

Doubts or questions may arise during its use. Its use is simple, but some technical aspects must be taken into account.

Let’s analyze the 10 most-frequently asked questions about wall formwork!

1.- What is the maximum admissible filling height?

The maximum height for concreting walls with industrialized formwork depends on many factors:

  • Maximum design pressure: Each panel type has been designed for maximum resistance to pressure. Industrialized formwork is usually designed for maximum pressures between 40 and 80 kN/m².
  • Fluidity of the concrete used: More liquid concretes generate higher pressures. Special attention must be paid when using self-compacting concrete “SCC”. (See question #7).
  • Filling time: A faster concrete filling speed generates greater pressure on the formwork. When using more fluid concretes at significant heights, it is essential to maintain a low filling speed, which the formwork supplier must indicate in dedicated tables.
  • External temperature: influences the curing of the concrete: the lower the temperature, the longer the setting time and the greater the formwork’s exposure to the load.
  • Another factor to take into account is the concrete’s vibration, which makes the concrete fluid, maintaining pressures and delaying its setting. Deep vibrations can subject the formwork to very large loads. E.g. Above 6 m in height, it is more difficult to vibrate the concrete with a needle vibrator normally used on site. External wall-mounted vibrators are therefore used, whose positioning must be studied correctly. (See question #9).
What is the maximum admissible filling height

2.- What factor most affects the concrete finish?

Sometimes, once the panel has been stripped, stains with different shades or “small holes” may appear in the concrete finish. There may be several reasons for this. Stains are usually caused by the use of a low quality or inadequate release agent, generating reactions with the concrete in some areas. Small holes or cracks are mainly due to poorly executed vibration or poor choice of concrete. Both effects can also be caused by inadequate formwork cleaning.

In general, for architectural or eye-catching finishes, it is advisable to use phenolic finish panels, since they have a glossy finish due to their very-low-porosity surface.

Coking due to poor vibration
Illustration 1: Coking due to poor vibration
Release agent stains
Illustration 2: Release agent stains
Exposed wall, phenolic finish
Illustration 3: Exposed wall, phenolic finish.

3.- Is it possible to manually handle vertical formwork?

Wall formwork is divided into three main families: manual, lightweight and robust.

  • Lightweight formwork: These are metal-framed panels, with a weight that generally does not exceed 20 kg/m². These panels are manipulable, but have the disadvantage of being less resistant to concrete pressure “around 40kN/m²”, and having a shorter service life. They are mainly used in countries where the crane is still little used or for construction solutions where a crane is not available.
  • Manual formwork: these panels are halfway between the Robust and the Lightweight panels, combining factors that define one and the other, usually weighing between 30 and 60kg/m², providing them with manual portability and usually resisting pressures between 40 and 80kN/m².
  • Robust Formwork: “Robust” panels are designed to be subjected to heavy loads, and can usually only be handled by mechanical lifting equipment. These panels usually weigh in excess of 60 kg/m².

 

4.- What is the standard vertical formwork equipment for a construction site?

Often when planning a new construction project, the well-known question arises: How many square meters of formwork do I need to execute my project?

It is difficult, if not impossible, to define equipment that is standard for every job site. Each project has its own unique aspects. However, it is possible to define the criteria for identifying the optimum equipment for each site:

  • Number of operators: First of all, it is important to define the number of workers and crews that will handle the formwork. On large construction sites, more teams of workers are employed simultaneously, with formwork team needed for each team.
  • Number of cranes: The formwork equipment should not be oversized in relation to the number of cranes on site. Sometimes there is a risk of slowing down production because the formwork equipment is larger than the handling capacity on site.

On-site production times: It is clear that for the execution of walls, times must be respected that, under standard conditions, can be controlled without problems. However, it is true that on some construction sites, the time required by the developer means that these deadlines need to be shortened, so the number of workers and formwork equipment on site has to be increased.

the useful life of metal formwork with phenolic resin as formwork surface

5.- What is the useful life of metal formwork with phenolic resin as formwork surface?

The durability of wall formwork basically on three variables:

  • Formwork material: The service life of the frame is different depending on the material and its quality, the materials chosen to define industrialized formwork is usually aluminum or steel. Aluminum is a less impact-resistant material and therefore has a shorter service life than steel.
  • Quality and protection: The quality and protection of the frame influences the service life of the frame. Galvanized steel frames guarantee a longer service life compared to painted or galvanized frames.

Use on site: On-site use is of course an important factor that has a direct impact on the service life of the material. The construction site is a place where the formwork is exposed to shocks and extreme weather conditions. The treatment, climate and maintenance have a decisive influence on the durability of the formwork.

Civil engineer, has been working with the Alsina Group for almost 17 years. Alejandro is System Manager of Modular Systems, collaborates with the digitalization and improvement department and continues to develop applications for the Alsina group. His professional career includes managing and accompanying projects at the international level.
Alejandro Pardo Medina
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