Noun
formwork (usually uncountable, plural formworks)
(construction) A temporary mold, made from planks, into which concrete is poured
Synonym: shuttering (chiefly British)
The formwork for using in-situ concrete would have been prohibitively expensive, and, because there was no repetition in any of the roof forms, the construction of precast concrete for each individual section would possibly have been even more expensive. Source: Internet
The achievement of this solution avoided the need for expensive formwork construction by allowing the use of precast units (it also allowed the roof tiles to be prefabricated in sheets on the ground, instead of being stuck on individually at height). Source: Internet