Joints are an important part of all concrete floors and their design and construction require careful attention. The improper use of a right joint will lead to floor failure with continual deterioration. Joints can be a potential source of problems because the edges of slab panels are vulnerable to damage.

1. Types of floor joints and their
advantages

2. Floor Joints
• Joints are an important part of all concrete floors and
their design and construction require careful attention.
Joint selection will be based on the following
characteristics:
• Resistance: Tied or reinforced, dowelled, non
dowelled, plain
• Configuration: Butt, lap, tongue, and groove.
• Formation: Sawed, hand-formed, tooled, grooved,
insert form.
• Location: Transverse, longitudinal, vertical, horizontal.

3. Floor Joint Types
• Free-movement joint
• sawn
• formed
• Restrained-movement joint
• sawn
• Formed
• Tied joints
• Isolation joints

4. FREE-MOVEMENT JOINTS
• There is no reinforcement across the joint.
• Free movement and load transfer are both achieved
by the installation of dowels.
• Free-movement joints which are going to be heavily
trafficked should be of an armoured type to minimise
damage to the joint.
• These joints are usually provided between pours.

5. Sawn free-movement joints
• Debonded dowels set in position in dowel
cages before the concrete is placed provide
load transfer.
• The dowels must be horizontal and
perpendicular to the line of the joint and that
their positions are not disturbed during the
placing of the concrete.

6. Formed free-movement joints
• Dowels can be round, square or plate types.
• Round bars allow longitudinal movement only.
• The sleeves of square dowels have compressible side
inserts to allow lateral as well as longitudinal movement.
• Sleeves should be of a shape compatible with the dowel
and with a good fit and sufficient stiffness to prevent
vertical movement.

7. Sawn restrained-movement joints
• They are made by cutting the slab at predetermined
points 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.
• Load transfer is provided by the doweling action of
the reinforcement and aggregate interlock.

8. Formed restrained-movement joints
• The joint is designed for some limited horizontal
movement
• The bar dimensions and spacing give
approximately equivalent cross-section per metre
length of joint to that of the fabric in the slab.
• Deformed bars are set in the concrete across the
joint to provide load transfer between the two
slab sections, as the fabric reinforcement does
not continue through the joint.

9. ISOLATION JOINTS
• Isolation joints are created by placing the preformed
joint material in the desired location before the
concrete slab is poured.
• The slab is then cast with the isolation joint material
acting as formwork between the slabs, though unlike
formwork, the joint material remains permanently
within the slab.
• When the concrete has cured enough so that it will
retain its shape, the top cap of the preformed joint
material can be removed and the gap filled with
sealant.

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