A composite cast floor is a concrete floor in which the structural topping layer is cast in one operation on site, usually on top of precast elements. Casting in situ creates a monolithic bond between the elements, so the floor acts as a single stiff slab.
How it works
Composite cast floors combine the benefits of precast with those of in-situ concrete:
- Place precast elements — hollow-core, wide-slab or rib floors are laid on the beams
- Install reinforcement — top steel over joints and in the compression zone
- Pre-wet — the precast underside is dampened so it does not draw moisture from the topping
- Pour topping — concrete is cast over the whole floor and bonds with the precast
- Cure — the young topping is covered and kept moist
The topping is usually 50 to 100 mm thick.
Applications
Composite cast floors are widely used in housing and utility buildings:
- Wide-slab floors — the precast shell is topped up to the full structural depth
- Hollow-core floors — a topping stiffens the whole floor and distributes loads
- Combination floors — precast ribs with an in-situ slab
- Strengthening existing floors — a new topping is poured over an old floor
Advantages
- Stiffness — the cast slab provides horizontal bracing
- Sound insulation — extra mass improves resistance to sound
- Fire performance — more concrete cover over reinforcement
- Easy services — pipes and ducts can be embedded before pouring
Points to consider
- Bond — a clean, rough precast surface is essential
- Shrinkage cracks — adequate shrinkage reinforcement is required
- Propping — precast elements must be supported during casting
- Adequate thickness — for proper concrete cover
Related terms
- Wide-slab floor
- Hollow-core floor
- Structural topping
- Precast
- Shrinkage
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