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Selection of Type of Formwork



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 blockwork,concrete bagwork, 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 blockwork and masonry square measure sometimes keyed to the concrete hearting 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.