Sawn Joints

Summary

Sawn Joints - Joints designed to allow limited movement to relieve shrinkage-induced stresses in a slab at predetermined positions.

Technical Information

Sawn joints are usually 3 to 4mm wide and are cut as soon as practicable after placing the concrete when the concrete is strong enough to avoid damage to the arrises, normally 24 hours after placing. They are cut to a depth of typically 25-30% of the slab depth, creating a line of weakness in the slab that induces a crack below.

It should be noted that deeper saw cuts will reduce aggregate interlock and the associated load-transfer capacity of the joint.

The concrete at the arrises of a sawn joint is representative of the slab as a whole, being fully packed with aggregate and without excess cement paste. Sawn joint edges are relatively resistant to damage where the joint opening is limited, but can be damaged by intensive traffic with small hard wheels, such as from pallet trucks.

Surface levels across a sawn joint are consistent with the profile of the floor to either side of the joint. Generally, there will be minimal interruption to wheeled traffic across sawn restrained-movement joints. However, sawn free-movement joints can be expected to have wider openings.