Expansion joints are created by casting two concrete slab
panels with a pre-formed opening in between (usually in the order of 10mm). After
the slab has undergone drying shrinkage and early thermal contraction, an
expansion joint allows the panels space to expand into than a normal joint if
the ambient temperature rises.
One drawback of using an expansion joint is that when the
ambient temperature isn’t as high as the designer anticipated, the joint may
have an excessively wide opening. This leaves the joint arris much more prone
to damage. It is therefore important to avoid installing an expansion joint
unless completely necessary.
They usually contain a soft, compressible filler to allow
for the extra anticipated change in joint width. Load transfer is achieved
across the joint by debonded dowels.
These joints are required:
- For external slabs in countries with large daily
temperature fluctuations such as South Africa.
- For external slabs which have been laid in
winter. The increase in temperature between seasons may be enough to cause
expansion to exceed shrinkage.
- Slabs which have been laid using low heat
cements. These will exhibit a smaller early thermal contraction; therefore,
thermal expansion due to a change in ambient temperature could exceed total
- For internal slabs where a very
heat-intensive industrial process will be performed e.g. in a building
containing a blast furnace.
slabs do experience a degree of thermal expansion, this type of joint is rarely
installed due to the rate of expansion being less than the contraction from