Sawn Restrained Movement Joints

Summary

Sawn Restrained Movement Joints - These are the most common form of restrained movement joints. They are formed by cutting the slab at predetermined points to to induce cracks which divide the slab into panels relieving the shrinkage stresses in the slab. These cuts should be made within 24 hours of casting to ensure that the shrinkage stresses have not already exceeded the tensile capacity of the concrete.

Technical Information

In a fabric reinforced slab where the quantity of reinforcement is between 0.1 and 0.125% of the cross sectional area the steel bars crossing the cracks are able to yield which allows for limited shrinkage movement. The depth of the cut needs between 1/3 and 1/4 the depth of the slab to ensure that the slab is weakened sufficiently to induce a crack.

Load transfer is provided by doweling action of the reinforcement and aggregate interlock.

This type of joint is not recommended in a fibre reinforced slab as the fibres are not of sufficient strength to restrain the slab movement and also do not provide any load transfer.