Jointless Bay

Summary

Jointless Bay - A jointless bay is a large pour with no induced joints.

Technical Information

The aspect ratio of a jointless bay has to be less than 1:1.5, though ideally no greater than 1:1.2, to allow uniform shrinkage as it is one single large slab. Typically fibre-reinforced, although steel or a combined reinforcement can be used, jointless bays can be ground or pile supported.

The term “jointless” can be misleading as formed free-movement joints are installed between each pour. The maximum size of a jointless bay should not exceed 35x35m. Bays larger than this will have increased shrinkage and cause unacceptably wide openings at the formed free-movement joints. Isolation joints are provided to keep the slab detached from restraining features; such as walls or columns.

The positioning of the joints should take into account the racking and pile head layout.

Shrinkage and restraint are minimised in the construction of a jointless bay by:

Ensuring excellent isolation around any immovable features, e.g. columns.
Providing a well-laid slip membrane beneath the slab.
Using a concrete mix less prone to shrinkage.
Delaying the loading of the slab until the concrete has undergone most of its early shrinkage.

For jointless pile supported floors, there will be:

Free-Movement Joints – to minimise the restraint from when adjacent bays undergo shrinkage.
Isolation Joints – to minimise restraint from fixed elements in the floor when the slab is undergoing shrinkage.
An additional layer of slip membrane placed over each pile head, extending past the edge by 300mm in each direction.