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An expansion joint is an assembly designed to safely absorb the heat-induced expansion and contraction of various construction materials, to absorb vibration, or to allow movement due to ground settlement or earthquakes. They are commonly found between sections of sidewalks, bridges, railway tracks, piping systems, and other structures.
Throughout the year, building faces, concrete slabs, and pipelines will expand and contract due to the warming and cooling through seasonal variation, or due to other heat sources. Before expansion joint gaps were built into these structures, they would crack under the stress induced.
The expansion joint can be as simple as a caulked separation between two sections of the same materials. More recently, expansion joints have been included in the design of, or added to existing, brick exterior veneer walls for similar purposes. In concrete and concrete block ("CMU") construction, the term applied is control joint, but serves a similar purpose.
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Road / bridge expansion joints
Expansion joints are cut into the concrete or asphalt to help with expansion and contraction of the material through the change in temperature, or due to movement of the road or bridge. The joints are cut into the structure at regular intervals to prevent it cracking or splitting. Road expansion joints can be sealed with hot tar, cold sealant (such as silicone), or compression sealant (such as rubber), or constructed in more elaborate ways, such as interlocking metal edges or 'spikes'.
Pipe expansion joints
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Pipe expansion joints are necessary in systems that convey high temperature commodities such as steam or exhaust gases, or to absorb movement and vibration. A typical type of expansion joint for pipe systems is a bellows which can be manufactured from metal (most commonly stainless steel), plastic (such as PTFE), or an elastomer such as rubber. A bellows is made up of a series of one or more convolutions, with the shape of the convolution designed to withstand the internal pressures of the pipe, but flexible enough to accept the axial, lateral, and/or angular deflections. Expansion joints are also designed for other criteria, such as noise absorption, anti-vibration, earthquake movement, and building settlement.
Pipe expansion joints are also known as compensators, as they 'compensate' for the thermal movement.
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