Formwork intended to form part of the permanent structure will generally be steel or concrete, Temporary formwork designed to be struck and reused may be made from any economic and easily worked material, timber, steel and GRC/GRP being the most common.Formwork to be used underneath water must:

– support the concrete in its designed profile throughout the plastic part
– be simply mounted into position.
– shield the concrete from scour, washout and abrasion till it’s hardened
– tolerate inaccuracies in formation level or alignment of adjacent work
– be able to stand up to static and dynamic loading because of concrete, tides,waves and currents
It may be designed as a part of the permanent works and be left in situ or as temporary works either to be left in situ or smitten and reused.

Permanent form work

Common kinds of permanent formwork square measure masonry, concrete block work, concrete bag work, steel sheet pile and formed concrete panels. Unless such formwork is thus large on be independent it’ll need some system of support till the in place concrete has been placed and gained strength. Concrete block work and masonry square measure sometimes keyed to the concrete heating by parturition different stretcher and header courses; concrete panels and steel sheet piles ought to be anchored to the in place concrete by means that of hook bolts or ties.

Reusable formwork

Reusable underwater formwork should be strong, tolerant of uneven foundations and, above all, easy to erect and strike. It ought to be prefab on the surface into panels as massive as is handled by different assisted by accessible plant. The method of tying/propping to resist horizontal loading can rely on the actual circumstances however can in theory be identical as might need been adopted had the works been toward land, bearing in mind the tough operating conditions beneath water and also the chance of loading from either or each side.

Flexible Formwork

techniques supported tailored baggage and mattresses, however currently victimization high-strength artificial materials able to retain cement-sized particles while permitting water to bleed off, are developed. Mattresses or forms square measure placed, deflated, in position on the ocean bed or at intervals the void to be stuffed and grout or concrete is wired directly into place, thus inflating the bag to its style profile.The concrete is separated from the surrounding water by the fabric so that no special precautions are necessary to prevent washout. The flexibility of the fabric allows it to mould itself to the sea bed, existing structure or pipe as required. 

Formwork are temporary structures (moulds) used at site usually to maintain the shape of the structural members like slab, beam, column and to help placing the concrete in desired form.

Formwork can be made of plywood, steel or timber based on the need and site conditions. It is usually removed after the primary hardening of concrete poured. But the removal of formwork should be done with extreme caution, not to damage the structural members.

Factors Affecting Removal Time of Formwork

The removal time of formworks is affected by various factors like

• Type of concrete used: There are many concrete types available and the based on the materials (e.g. cement, mineral admixtures) used their hardening time can vary, for example the formworks can be removed soon if rapid hardening cement is used in the concrete.

• Quality of materials used: If high quality materials are used especially if cement and mineral admixtures like silica fume are of good quality then the concrete attains early strength quickly, thus formworks can be removed soon.

• The temperature at site: This plays an important role influencing the setting time of concrete and also the strength development. The formwork removal time is more in cold weather and it is less in hot weather concreting.

• Curing: The type of curing and the rate at which it is done influences the development of strength in concrete, for instance if steam curing is used the strength development rate in concrete is rapid thus formwork removal time required will be less.

• Exposure condition: severe exposure conditions can result in slow development of strength in concrete thus delaying the formwork removal time.

In addition to the above factors there is another important criteria which is based on the stresses and load applied on the concrete while removal, thus the formwork removal can be done only after the concrete attains considerable strength approximately twice the load implied during removal.

The type of structural members is also taken into account during the formwork removal. For slabs and beams which carry its own self weight and also the live load in the building, more time is required to remove the formwork and also the formwork should be removed carefully so as to not cause any damage to the member.

Time for Removal of Formwork

In normal circumstances (generally where temperature is above 20⁰C), and where ordinary cement is used, forms may be struck after expiry of following periods depending upon the type of structural member

As already mentioned you can see the formwork removal time for beams and slabs is more comparatively. The above mentioned time varies based on the type of cement used.

How to Properly Remove the Formwork

The formwork removal is one of the most hazardous jobs in the site. If not properly done it not only affects the structure but also can result in high risk for the labours working at site. Thus the following points must be kept in mind during formwork removal

• Proper tests are conducted (mostly NDT) to determine the strength of concrete developed.
• The formwork of vertical members are removed first.
• The props of soffits are not removed until it is ensured to bear its own self weight and external stresses effectively.
• The crowbars are not to be inserted in the sides to remove the formwork as it can damage the edges of concrete.
• Any loose material of concrete found in the edges and corners are to be removed.
• The quality engineers should inspect the site before removal of formwork to ensure suitable conditions.
• To ensure safety of workmen, it is to be inspected weather sufficient bracings and work platforms are provides to remove the formwork at higher elevations.

Thus from the above data we can understand the importance of removal of formwork in time with necessary precautions to be taken care at the site.

Formwork is a mold or open box, like a container in which fresh concrete is poured and compacted. When the concrete is set, the formwork is removed and a solid mass is produced in the form of the interior face of the formwork. The top of the formwork is normally left open.Falsework is the necessary support system that holds the formwork in the correct positionFormwork for concrete structural should be

1- Strong enough to resist the pressure or the weight of the fresh concrete plus any constructional live loads.

2- Rigid enough to retain the shape without undue deformation.

3- Economical in terms of the total cost of the forms and the concrete surface finishing when required.

4- Sufficiently watertight to avoid leakage at the joints.Formwork materials

Formwork intended to form part of the permanent structure will generally be steel or concrete, Temporary formwork designed to be struck and reused may be made from any economic and easily worked material, timber, steel and GRC/GRP being the most common.

Formwork materials can be classified as:

1- Timber Formwork

2- Metal Formwork

3- Plastic Formwork

4- Insulating concrete form or insulated concrete form (ICF)