Formwork Removal

Method and Period of Formwork Removal

In this article, we will discuss the method and period of formwork removal, which are crucial to ensuring the successful completion of concrete construction projects. Proper formwork removal is essential to maintaining the integrity of the structure, achieving the desired finish, and ensuring the safety of workers. Let’s delve into these aspects:

What is Formwork?

Formwork, also known as “shuttering,” is a temporary structure or mold that is used to contain and shape freshly poured concrete until it reaches sufficient strength to support itself and any applied loads. Formwork is a critical component of concrete construction and plays a vital role in ensuring the integrity and quality of the final concrete structure. It provides the necessary support, shape, and surface finish for the concrete during its curing process.

Method and Period of Removing Formwork

The method and period of removing formwork depend on several factors, including the type of concrete being poured, the formwork system used, the ambient conditions, and the desired strength of the concrete. Here’s a general guideline for the method and period of removing formwork:

1. Method of Removing Formwork

The method of removing formwork can vary based on the specific project and formwork system used. Here’s a general sequence:

Vertical Formwork (Walls, Columns, etc.):

Stripping Time: Vertical formwork for walls and columns is often removed once the concrete has gained enough strength to support itself. This is typically within 24 to 48 hours, depending on the concrete mix, ambient conditions, and the specified strength.

Method: Vertical formwork is often removed by using pry bars, hammers, or lifting equipment, as appropriate. Care should be taken to avoid damaging the concrete surface.

Horizontal Formwork (Slabs, Beams, etc.):

Stripping Time: Horizontal formwork for slabs and beams is typically removed after the concrete has reached a specific level of strength to bear its own weight. This can be around 3 to 7 days for normal concrete, but it can vary based on factors such as ambient temperature and concrete mix design.

Method: Horizontal formwork can be removed using mechanical equipment, such as cranes or hoists, to lift and relocate the formwork components. Alternatively, manual methods like pry bars and hammers can be used.

2. Period of Removing Formwork

The period for removing formwork is often defined by certain criteria, such as concrete strength and time, to ensure the structural integrity of the concrete. Here’s a general guideline:

Early Removal: Formwork can be removed earlier if the concrete has reached sufficient strength to support its own weight without deformation or damage. Early removal can speed up the construction process, but caution is necessary to avoid compromising the concrete’s integrity.

Standard Removal: Formwork is typically removed after the concrete has achieved a specified level of compressive strength. This level is often around 70% to 80% of the specified 28-day strength. This usually occurs within the first week to two weeks after pouring, depending on the mix design and ambient conditions.

Delayed Removal: In some cases, formwork may be left in place for a longer period, especially if the concrete is subjected to significant loads or if the structure requires extra curing time. Delayed removal can enhance the concrete’s long-term durability.

Always refer to the project’s specifications, engineering recommendations, and the guidelines provided by the formwork manufacturer when determining the appropriate method and period for removing formwork. Additionally, ensure that proper safety measures are in place for workers involved in the formwork removal process.

Formwork Stripping Time (When Using Ordinary Portland Cement)

Types of Formwork Formwork Removal Time
Wall sides, columns, and beam vertical faces
24 to 48 hours (depending on engineer's decision)
Slab ( props left under)
3 days
Beam soffits (props left under)
7 days
Removal of Slab Props
Slabs spanning up to 4.5m
14 days
Slabs spanning over 4.5m
14 days
Removal of Beam and Arches' Props
Span up to 6m
14 days
Span over 6m
21 days

What Happens If The Formwork Removed Early?

If formwork is removed too early, before the concrete has gained sufficient strength, it can lead to a range of issues that can compromise the structural integrity and appearance of the concrete element. Some of the potential consequences of removing formwork prematurely include:

Surface Defects

Premature formwork removal can cause surface defects such as honeycombing, voids, or rough patches on the concrete surface. This happens because the concrete is still relatively soft and vulnerable to damage when the formwork is removed. Properly cured concrete has a smoother and more durable surface.

Reduced Strength

Concrete gains strength over time through a process called hydration, during which cement particles react with water to form a crystalline structure. If formwork is removed before sufficient strength is attained, the concrete may not be able to bear the intended loads and may develop cracks or even fail.

Cracking

Early formwork removal can lead to cracking due to the lack of support provided by the formwork. Cracks can develop as a result of both external loads and internal stresses caused by shrinkage and temperature changes. Cracks not only compromise structural integrity but can also allow moisture to penetrate the concrete, potentially causing durability issues.

Deformation

The weight of the concrete itself, as well as any additional loads or forces, can cause deformation if the concrete is not adequately cured before the formwork is removed. Deformation can lead to uneven surfaces, misalignment, and structural instability.

Dimensional Changes

Concrete undergoes slight dimensional changes as it cures and dries. Premature formwork removal can interfere with these changes and lead to dimensional inaccuracies or mismatches, especially at connection points or joints.

Incomplete Bonding

Adequate curing and proper hydration of the concrete are essential for achieving a strong bond between concrete layers. If formwork is removed too early, the bond between layers may be compromised, leading to reduced structural performance.

Safety Concerns

Prematurely removing formwork can create hazardous conditions for construction workers as well as anyone who might interact with or use the structure. Weak or damaged concrete can pose a safety risk.

Things to Keep In Mind

Removing formwork requires careful planning and execution to ensure the safety of workers and the quality of the concrete structure. Here are some important points to remember when removing formwork:

  • Comply with the engineer's or contractor's instructions

    The instructions from the engineer or contractor will specify when and how to remove the formwork. To avoid damaging the concrete or putting workers in danger, carefully follow these guidelines.

  • Inspect the formwork

    Inspect the formwork for any signs of wear or damage before removing it. Before the formwork is taken off, any damaged parts should be fixed or replaced.

  • Check the concrete strength

    Before dismantling the formwork, ensure that the concrete has reached the required strength. This will help to prevent concrete damage and ensure the structural integrity of the structure.

  • Use the right tools and equipment

    To remove the formwork safely and effectively, use the correct tools and equipment. This could include lifting equipment, power tools, and hand tools.

  • Prevent concrete damage

    Take extra care when removing the formwork to prevent concrete damage. In order to gently remove the formwork without damaging the concrete surface, it may be necessary to use pry bars or other equipment.

  • Protect workers

    Ensure that formwork removal personnel wear proper personal protective equipment, such as gloves, safety glasses, and hard hats. Workers should also be taught proper lifting procedures and use the right tools and equipment to avoid injuries.

  • Reuse or recycle the formwork

    If possible, try reusing or recycling the formwork to reduce waste and save money. Formwork may last longer and be utilized on more projects if it is handled and maintained properly.

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