Formwork-free construction

Formwork-free construction is the production of concrete geometry without moulds or shuttering, with the fresh material holding its own shape as it is placed. In 3D concrete printing this is achieved through rheology: the mix must flow through the pump and nozzle, then rebuild enough yield stress to carry the layers above it. The concept also covers related methods such as shotcrete 3D printing and slip-forming, where a mould is either absent or reduced to a moving edge.

In practice

Removing formwork removes a large part of the labour, timber and steel on a conventional concrete job, and it makes curved or varying geometry no more expensive than straight geometry, since the cost sits in print time rather than in a new mould. The constraints move elsewhere. Vertical accuracy and surface tolerance now depend on the mix and the machine rather than on a panel, overhangs are limited by what the fresh material can cantilever, and reinforcement has to be introduced by other means, since there is no cage to cast around. In practice many printed elements still use local formwork for slabs, lintels and infill zones.

Related terms

• Additive construction — building by depositing material layer by layer.
• Buildability — how many layers fresh material can carry without deforming.
• In-situ printing — printing directly on the building site rather than in a workshop.