Structure of Concrete Formwork
Concrete formwork is a temporary or permanent mold used to shape and support freshly poured concrete until it hardens and gains sufficient strength. Its structure typically consists of the following key components:
1. Form Panels (Facing Material)
Primary Function: Direct contact with concrete, defining the shape, surface finish, and dimensions of the structure.
Materials:
Plywood: Phenolic-coated or film-faced plywood (most common for reusable formwork due to smoothness and durability).
Steel: Metal sheets or aluminum panels (used for high-reuse projects like bridges or tunnels).
Plastic/Composite: Lightweight panels for curved or complex shapes.
2. Supporting Framework
Horizontal Members (Walers/Joists):
Wooden or metal beams (e.g., H20 timber, steel channels) placed horizontally behind the form panels to distribute concrete pressure.
Vertical Members (Studs/Stiffeners):
Vertical supports (wood studs or metal frames) that transfer loads to the ground or lower structures.
3. Ties and Fasteners
Tie Rods:
Steel rods or threaded bars that connect opposite form panels, resisting bursting pressure from wet concrete.
Equipped with cone bolts or snap ties for easy removal after curing.
Clamps and Wedges:
Adjustable fasteners (e.g., wedge clamps, pins) to secure panels and framework tightly.
4. Bracing and Props
Diagonal Braces:
Steel or timber braces to stabilize the formwork against lateral forces (wind, concrete vibration).
Adjustable Props (Shores):
Telescopic metal props or wooden posts to support vertical loads, especially for slabs and beams.
5. Sealing and Release Agents
Sealants:
Foam tapes or rubber gaskets applied to panel joints to prevent concrete leakage.
Release Agents:
Oil or chemical coatings sprayed on form surfaces to ease demolding and preserve panel finish.
6. Additional Components (Optional)
Kickers: Short braces at the base of wall forms to prevent shifting.
Spreaders: Temporary spacers to maintain consistent wall thickness during pouring.
Inserts: Embeds for bolts, pipes, or electrical conduits cast into the concrete.
Key Structural Considerations
Load-Bearing Capacity: Must withstand hydrostatic pressure from wet concrete, worker loads, and equipment.
Alignment and Tolerance: Precision in assembly ensures dimensional accuracy of the final structure.
Reusability: Modular design and durable materials (e.g., phenolic plywood) maximize reuse cycles.
Safety: Locking mechanisms and redundant supports prevent collapse during pouring.
Workflow of Formwork Assembly
Erect Framework: Install vertical studs and horizontal walers.
Mount Panels: Attach form panels to the framework.
Secure Ties: Insert tie rods and fasten with clamps.
Stabilize: Add diagonal braces and props.
Seal Joints: Apply sealants to prevent leaks.
Coat Surfaces: Spray release agent before pouring.
