What is Formwork (Shuttering)?
Formwork is basically a kind of temporary mould of fresh concrete which is employed in construction for giving or casting desired structural shape & support by pouring concrete within the mold. Once the concrete achieved optimum initial strength, the formwork is practically removed although sometimes it may be left in situ (permanent formwork).
Required Properties of Formwork
It must be strong enough to hold the pressure or the weight of concrete. It is ought to be rigid in order to retain the shape without undergoing deformation.
Additionally, it must affordable in terms of the total cost. They must be watertight to check leakage at the joints.
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Types of Formwork
Types of shuttering in construction (based on materials) are given subsequently:-
- Timber Formwork
- Steel Formwork
- Aluminum Formwork
- Plywood Formwork
- Fabric Formwork
- Plastic Formwork
Classification based on materials:-
1. Timber Formwork
Timber formwork is one of the oldest formwork & is vastly utilized in construction. It’s utilized for bijou works which require fewer repetitions since its initial cost is low.
Timber Formwork should accommodate the subsequent requirements:-
- It needs to be well seasoned It is ought to be light-weight It needs to be effortlessly workable with nails without splitting
- It must be free from loose knots. Timber must have smooth surface on all sides, which comes in direct contact with concrete. Timber formwork is employed in bijou quantity of concrete work.
They are further categorized into:-
1.1 Lumber Formwork
It’s an ordinarily available material & possesses excellent strength, weight & cost factor.
Advantages of Lumber Formwork
Here, the pros of lumber formwork are as follows.
- It is light-weight (it can be effortlessly handled).
- Timber possesses thermal resistance which resists concrete damage in cold areas.
- It can be effortlessly dismantled.
- Timber Shuttering is simple to create any shape, size & height.
- It’s affordable for small projects.
- Timber is more light-weighted than steel or aluminum shuttering.
- Timber can be cut in any size effortlessly.
- The construction method is simple to understand, thus it doesn’t require skilled labor.
Disadvantages of Lumber Formwork
Here, the cons of lumber formwork are as follows.
- If it is dry, it can be soggy & can absorb moisture from the damp concrete which can weaken the resulting concrete member.
- Excessive moisture sogginess (>=20%) of wood, can result in leakage of cement slurry (cup open joints & grout).
- These cannot be utilized for a long time & have restricted reuse (only 5 to 6 times).
1.2 Plywood Formwork
Plywood formwork is a re-molded timber in which resin-bonded plywood sheets are fixed with timber frames to create panels of specific sizes. It is strong, malleable & effortless to handle but its life is too short.
It provides a smooth surface & may even be re-used up to 20 to 25 times if dismantled attentively.. It is actually a BWP (Boiling waterproof) grade plywood. It is preservative-treated & particularly ideal for shuttering.
Advantages of Plywood Formwork
Here, the pros of plywood formwork are as follows.
- It is robust, light-weight & durable under alternate wet & dry conditions.
- It makes formwork rapid & effortless.
- It possesses a rigid surface & possesses sufficient strength to hold a load & vibrations of a concrete structure.
- Plywood can be cut effortlessly within specific sizes & shapes.
Disadvantage of Plywood Formwork
Here, the cons of plywood formwork are as follows.
- Plywood formwork gives more repetition than Timber formwork.
2. Steel Formwork
It’s initial cost is more than that of wood formworks but it can be reused more frequently. It is often utilized for curved structures like tanks, columns, chimneys, sewers, tunnels & retaining walls.
The Steel Panel modules can be fixed altogether by Clamp, Nut, & Bolts. Mostly, this is utilized for Circular & Curved structure. In the long tenure, it is more economical.
Advantages of Steel Formwork
Here, the pros of steel formwork are as follows.
- It is effortless to repair.
- It offers a smooth finish to the surface of the member & doesn’t require further treatment.
- They are fully water-resistant i.e. do not absorb moisture from concrete & minimizes the honeycombing effect.
- It can be reused more than 100 times.
- Steel Panels are installed & dismantled effortlessly & rapidly.
- It doesn’t shrink or warp.
- They can be given any modular shape or size.
- These formworks are extremely strong, durable, possesses long-life span & can hold up more loads than wood formwork.
Disadvantages of Steel Formwork
Here, the cons of steel formwork are as follows.
- As a result of excessive load, handling is strenuous, thus it requires lifting equipment.
- They have limited size & shape.
- They are more costly than wood. It is cost-effective if construction happens in profusion.
3. Plastic Formwork
Plastic formwork is an impenetrable surface which provides concrete a smooth finish. These formworks can be reinforced or un-reinforced. Of late, this is becoming popular for similar shapes & large housing schemes.
Advantages of Plastic Formwork
Here, the pros of plastic formwork are as follows.
- Impairment on the formwork can be simply eliminated.
- They’re extremely helpful for complex-shapes & special features.
- Plastic forms are light -weight interlocking systems & hence requires less handling cost.
- It is often utilized within large concrete section.
- If utilized wisely, multiple reuses are possible making it more economical.
- Can be reused more than 100 times.
- It can be simply cut & nailed.
Disadvantages of Plastic Formwork
Here, the cons of plastic formwork are as follows.
- Their load carrying capacity is low.
- Gets impaired on application of heat.
- It is lighter but less durable than steel formworks.
- It’s costly.
4. Aluminum Formwork
Since, the density of aluminum is less than steel which makes it light-weighted. Shuttering down with aluminum form is more economical if utilized repeatedly.
Advantages of Aluminum Formwork
Here, the pros of aluminum formwork are as follows.
- It gives a smooth finish surface.
- Aluminum formwork may be reused up to 250 times.
- Aluminum Formwork is a rapid process & saves time & labor
Disadvantages of Aluminum Formwork
Here, the cons of aluminum formwork are as follows.
- This is cost-effective if it is employed in a symmetrical type of structure.
- Initially, it consumes time to set up.
- For this sort of formwork, Skilled labors are required for alignment & maintenance.
- Holes caused during formwork by wall tie must be grouted attentively, else there may be a leakage in near future.
- No alteration is possible once the formwork is developed.
- The initial cost is high because of which they’re more costly.
5. Fabric Formwork
Nowadays development of complex-shaped structural members is surged. So the fabric formworkis introduced which makes it possible to produce concrete in any shape. The ductility of fabric formwork aids to generate concrete members of any shape.
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Classification Based on Shape
1. Column formwork
Column formwork is manufactured from timber or metal panels. The box is fixed with steel column clamps or fastening yoke, supported by wooden props.
2. Beam Formwork
Beam formwork has an open-drawn section & it’s not closed at the top to provide more support to the structures.
3. Slab Formwork
Slab formworks requires a vast area of formworks from beam to beam. Timber & metal struts are employed for vertical support. Flexible props are necessary for levelling.
4. Wall construction formwork
Wall construction formwork is extremely low as compared to other concrete since the actual forces are very low against it. The panel on either sides has been put in position, the tie is utilized as a spacer.
Wall support systems are sloped at satisfactory intervals.
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A range of materials may be utilized for formworks.
Plywood is often utilized to form faces. Incredibly smooth finishes are possible with it. The robustness of Steel makes it ideal for formwork that needs to be extensively re-used, e.g. in precast work.
Aluminum may be used for form faces with a condition that it has some sort of coating or protection, to avoid any chemical change between aluminum & wet concrete. Expanded metal is an essential material for construction joint formwork.
Glass reinforced plastics & other plastics can be utilized as a form of face material. They produce a decent finish & can be transformed into complex shapes. Plastic pipes are useful in bijou precast items e.g. garden-ornaments. Cardboard tubes, lined internally with a plastic film, are required for circular columns.
Formwork in Construction
Importance of Formwork in Construction
- It can’t get replaced with other technology.
- A formwork offers appropriate access & working platforms that considerably enhance workers’ scaffold safety.
- Formwork aids in lowering the timeline & costs of the project by lowering the floor-to-floor construction cycle time which is more resourceful.
- Formwork aids construction managers to offer exact on-time shuttering & de-shuttering, which ameliorates project effectiveness & resource usage.
Formwork Construction Steps
In construction of formworks, the subsequent operations are as follows:-
- Propping and Centering: Built to hold up various sorts of dead & live loads.
- Shuttering: Firmly built & effectively hung to maintain ideal shape.
- Provision of Camber: To counteract the effect of deflection, it is recommended to place upward camber in horizontal members of the concrete structure.
- Cleaning and Surface Treatment: The joints within the formworks must be tightened to get rid of the leakage of cement grout.