Expansion joint of a bridge; image taken in winter

An expansion joint is an assembly designed to safely absorb the heat-induced expansion and contraction of various construction materials. They are commonly found between sections of sidewalks, bridges, railway tracks, piping systems, and other structures.

The "assembly" 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 similar purposes.

Throughout the year, building faces, concrete slabs, and pipelines will expand and contract due to the warming and cooling through seasonal variation. Before expansion joint gaps were built into these structures, they would crack under the thermal stress induced (thermal expansion and contraction). Expansion joints are often neglected during the design process,^{[citation needed]} and simple caulking is used to fill the gaps to complete a project. This simple caulking cannot handle the thermal expansion due to the change in temperatures, ultimately creating a leak point in the structure.^{[citation needed]} Applying material into the gaps helps to keep the structure from cracking and leaking.

Pipe expansion joints

Pipe expansion joints are necessary in systems that convey high temperature commodities such as steam or exhaust gases. 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. The bellows are designed to withstand the internal pressures of the pipe, but are flexible enough to accept the axial, lateral, and angular deflections. They 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.

Roadway 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. The joints are cut at regular intervals to prevent random cracking of the roadway. The first cut is done with a saw using a green saw blade which is usually ¼ inch thick. After the concrete has completely cured the joint is then widened to a thickness of ¾ inch. Roadway expansion joints can be sealed with hot pour (tar), cold sealant (silicone), or compression sealant (rubber).

See also

• Slip joint

Source: adapted by the editor from Wikipedia, the free encyclopedia; from the article "Expansion joint". Image Credit.

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