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Expansion Joint

Summary

Expansion joints are typically installed in external concrete slabs to accommodate the thermal expansion of the slab to prevent damage to surrounding elements or the floor itself.

Technical Information

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 shrinkage.
  • For internal slabs where a very heat-intensive industrial process will be performed e.g. in a building containing a blast furnace.

Although internal 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 drying shrinkage.

Resources

  1. The Concrete Society: Technical Report 34; 11.2.

  2. The Concrete Society: Technical Report 66; 5.2.2

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