REQUIREMENTS OF FORMWORK &#; QUALITY, SAFETY & ECONOMY

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In the selection of materials for formwork, the three general principles of quality, safety and economy must be paramount. Material quality can ensure safety, and significantly contributes to the achievement of economy. Formwork failure can result in loss of life and always causes catastrophic financial loss.

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

1. Strength
2. Stiffness
3. Impact Resistance
4. Durability
5. Weight
6. Accuracy
7. Compatibility
8. Insulation

1.

Strength

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

2.

Stiffness

The structural movement under load must be small and predictable. These deformations and deflections can be a significant part of the total deviations in the formed concrete surface. When the formwork designer is planning the formwork system, decisions must be made on the total deviation that will be acceptable, and to what extent workmanship errors and structural deformation will each contribute to this. To ensure that the total deviations do not exceed the tolerances, the material stiffness and the workmanship accuracy must be consistent.

3.

Impact Resistance

The forms must be built to ensure that the damaged form, although unserviceable, does not generate falling debris. It follows, that the way in which the formwork materials fails, will determine this. To comply with this important safety aspect, materials exhibiting ductile failure are far superior to those that fail in a precipitate and brittle manner.

4.

Durability

In the interests of economy, and the achievement of quality concrete product at each reuse of the formwork, its materials must be durable. Formwork is almost always built and used out in the open. Between re-uses, its materials and components are commonly stored out in the weather. Ideally, framing, components and formface materials should be resistant to the ravages of the environment. They should have a slow rate of deterioration under the effects of sun, wind and rain. Their resistance to deterioration can be enhanced by proper care and maintenance. Material durability is not only important for the achievement of good quality concrete surface finishes, but also to ensuring that formwork structures are always safe.

5.

Weight

In the assembly of formwork, most individual members and components are moved into position by hand. This occurs even when the completed formwork assembly is so heavy that it can only be moved and positioned 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 ability of one form worker. If the weight exceeds that which can be carried by two personnel, crane handling is called for. The next level of formwork weight restrictions is set by the lifting limitations of the on-site crane.

6.

Accuracy

For economy, it should be possible to assemble formwork with the minimum of fitting and cutting of materials. Consistency of size of materials, plywood sheets and framing members, is important to this aim. The accuracy of plywood sheets and the sizing of timbers for consistent dimensions are discussed later in this chapter.

7.

Compatibility

The materials of the formwork must not be incompatible with either the fluid concrete or the hardened concrete. At the formface the constituents of the form materials must not react with the hydrating cement of the concrete. For example, some timbers contain wood sugars that break down the cement. After the concrete hardens some timbers, such as eucalypts, can severely stain the concrete. When water runs over this timber and onto the concrete, dark brown stains usually results.

8.

Insulation

Extremes of heat and cold present problems in the choice of form materials and their protection. The rate of setting of concrete and subsequent strength gain is slowed by low temperatures, and if the water in the mix becomes frozen, the formation of ice will destroy the chemical bonding within the concrete matrix. In situation where concrete has to be placed at low temperatures, aggregate storage bins and mixing water can be heated to produce warm concrete that will not cool during the initial setting period, while its own internal heat builds up.

For all forms, the placing of the fluid concrete, particularly with crushed rock aggregate, can cause some abrasive damage to the formface at first use and each reuse. When the concrete has hardened, the forms are stripped, and this can contribute to surface damage. Abrasion will occur if the forms are permitted to slide on the concrete face.

Secondly moisture absorption at the formface must be minimised. Moisture loss from the concrete into the formface causes hydration staining of the concrete, with severely darkened surface patches. For high quality concrete surfaces, where colour control is specified, this is totally unacceptable. For any concrete surface, hydration staining means poor cement hydration, weak concrete and low surface durability.

Also Read: When to Remove formwork

Contact us to discuss your requirements of bespoke formwork systems. Our experienced sales team can help you identify the options that best suit your needs.

Also Read: How to achieve economy in formwork

Watch This Video on Increasing Repetition of Plywood

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Formwork is a concrete construction that is used as either short or permanent molds into which fresh concrete or similar kind of materials are gushed to make it harden. The different types of concrete formwork construction depend on the material and the kind of structural element. They are given various names as per the type of structural member construction like slab framework, beam framework, column framework etc. to use in beams and columns.

The harden process requires time and includes an expenditure up to 20 to 25% of the cost of the structure or more than that; the temporary design structures are made of economic expenditure.

While the removing process of the framework is known as stripping that can also be used later; the unusable are called panel forms and the non-useable are called stationary forms. The most commonly used material for formwork is Timber.

This article is a short knowledge for people about formwork, the different types of formwork and the basic needs to complete a formwork properly. Formwork comes in several types such as:

1. Traditional timber framework

2. Engineering Formwork System

3. Re-usable plastic formwork

4. Permanent Insulated Formwork systems

5. Stay-In-Place structural formwork systems

6. Flexible formwork

Requirements of Formwork: It is stated above that framework varies as per material and material is the main ingredient for every framework, but for any kind of chosen material the three common principles of quality, safety and economy should be the same. While the quality of material ensures safety and also considerably helps to achieve the economy; any kind of failure in framework can cause of the loss of life and tragic financial loss. To avoid the loss the following guidelines should be followed from start to framing materials and for the associated components:

1. Strength: The strength of material must be sufficient to strong the forces expected and this is the important for both the structural design and safety aspect.

2. Stiffness: the structural movement under load should be small and sure; these deformities and separations are the necessary part of the whole deviations in the formed concrete surface. While planning the formwork system, a designer must take decisions upon the total acceptable variations and the extend workmanship errors and structural deformity. The material stiffness and the workmanship accuracy must be stable to ensure the stability of the total deviations to keep the tolerances.

3. Impact Resistance: The forms are made to make sure that the damaged form that is useless does not make falling debris and to make sure this important safety quality, materials displaying ductile failure are far above than those fail in a hasty and brittle manner.

4. Durability: The framework must be durable either it will affect the economy and the achievement quality concrete product at every reuse of the formwork; formwork is always pre made and used out in the open. When the matter of re-uses came the thing is dependable on its reaction of materials and components with weather and the framing, components and formface materials should be strong in any environment. Material durability is important for both the achievement of good quality concrete surface finishes and safe formwork structures.

5. Weight: While the assembling process in formwork, both the members and components are shifted into position by hand that will be applicable after the complete framework which are heavy and need a crane to do the shifting work. So the framing members, formwork components and formface materials must be keep in size so that they must be carried and lifted by the worker or the crane etc.

6. Accuracy: Every construction process is dependable on a lot of money so the work of lifting and cutting of materials must be done within a minimum amount of money and consistency of size of materials, plywood sheets and framing members is very important.

7. Compatibility: The framework materials should be fitted with either the fluid concrete or the strong concrete and at the formface, the elements of the form materials must not react with the wet cement or concrete.

8. Insulation: Some materials react with the environment if it&#;s become extra hot or cold, so the protection for the materials is must; if the mix becomes frozen and the chemical bondage damages then the concrete has to be placed at low temperatures, heat the mixing water etc. The placing of the fluid concrete for all forms can cause some damage with the crushed rock aggregate and the proper steps has to be taken to stop it.

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