8 PRIMARY REQUIREMENTS OF FORMWORK

Formwork Requirements
Formwork Requirements

In the selection of materials for formwork, three general principles of quality, the protection And Economy should be paramount. Material quality can ensure the safety, and contribute significantly to the achievement of economy. Failure of the formwork can result in loss of life and always catastrophic financial loss.

Some general guidelines can be given for form faces and framing materials, and for related components. These can be covered under the headings of


  1. Strength
  2. hardness
  3. impact resistance
  4. Tolerance
  5. weight
  6. Accuracy
  7. compatibility
  8. insulation

1. Strength

The physical strength must be sufficient to oppose the anticipated forces. This is not only a structural design requirement, but also an essential safety aspect.

2. hardness

Structural movement under load should be small and predictable. These distortions and deflections may account for a significant portion of the total deviation in the solid surface formed. When the formwork designer is planning the formwork system, a decision must be made on the total deviation that will be acceptable, and the extent to which workmanship errors and structural deformation will each contribute to it. In order to ensure that the total deviation does not exceed the tolerance, the material hardness and workmanship accuracy must be consistent.

3. impact resistance

Forms must be made to ensure that the damaged form, although unusable, does not generate falling debris. It follows that the way in which the formwork material fails will determine it. To comply with this important safety aspect, materials that exhibit ductile failure are far superior to materials that fail in a precipitate and brittle manner.

4. Tolerance

In the interest of economy, and the achievement of a quality concrete product at each reuse of the formwork, its material must be sustainable. Formwork is almost always made and used in the open. Its contents and components are usually stored in season, between reuses. Ideally, framing, components and formface materials should be resistant to environmental destruction. The rate of their deterioration should slow down under the influence of sun, wind and rain. Their resistance to deterioration can be increased by proper care and maintenance. Material durability is critical not only to the achievement of a good quality concrete surface finish, but also to ensuring that formwork structures are always protected.

5. weight

In the assembly of formwork, most of the individual members and components are moved into position by hand. This also occurs when the completed formwork assembly is so heavy that it can only be moved and deployed by crane. Ideally, for efficiency and economy, framing members, formwork components and formface materials should be sized such that their weight is within the lifting capacity of a form worker. If the load exceeds the load that can be borne by two personnel, the crane is called to handle. The next level of formwork weight restrictions are determined by the on-site crane’s lifting limits.

6. Accuracy

For economy, it should be possible to assemble the formwork with minimal fitting and cutting of material. The size of the material, the consistency of the plywood sheet and framing members are important for this purpose. Wood sizing for accuracy and consistent dimensions of plywood sheets is discussed later in this chapter.

7. compatibility

The material of the formwork should not be incompatible with liquid concrete or hard concrete. The components of the form material on the formface should not react with the hydrating cement of the concrete. For example, some wood contains wood sugar that breaks down cement. After the concrete has hardened, some woods, such as eucalyptus, can seriously stain the concrete. When water flows over this wood and concrete, dark brown spots are usually formed.

8. insulation

Extreme heat and cold cause problems in the selection and preservation of form materials. The rate of concrete setting and subsequent strength gain is slowed by low temperatures, and if water in the mix freezes, ice formation will destroy the chemical bonds within the concrete matrix. In a situation where the concrete is to be kept at a low temperature, the aggregate storage compartment and mixing water can be heated to form a hot concrete that will not cool during the initial setting period while its internal heat builds up.

For all forms, placing fluid concrete especially with crushed rock aggregate may result in some abrasive damage to the formface before use and each reuse. When concrete hardens, the forms are stripped, and this can contribute to surface damage. If the forms are allowed to slide on the solid face there will be friction.

Moisture absorption on the second formface should be minimal. The lack of moisture from the concrete to the formface results in a hydration staining of the concrete, with severely darkened surface patches. For high-quality concrete surfaces, where color control is specified, this is completely unacceptable. For any concrete surface, hydration dampness means poor cement hydration, weak concrete and low surface durability.

Read also: When to remove formwork

Read also: How to achieve economy in formwork



Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.