What is the difference between a control joint and a contraction joint in concrete?

A control joint is a deliberate break in a long/large concrete installation, especially when the concrete expands, eg. concrete will buckle if the expansion cannot be absorbed or controlled. The size or width and number of control joints will be dependent on how much the concrete will lengthen for a given temperature.

Concrete will expand or contract depending on the external temperature being subjected. Cold concrete will shrink in length, and hot concrete will expand in length.

A contraction joint ( I think you mean expansion joint), is where there is a calculated construction separation between the two materials. The Structural engineer will calculate the concrete expansion and then this dimension is used in the contraction joint construction.

For example, you will see a contraction joint (expansion joint) located at the end of a bridge… this contraction joint is covered with a sliding steel plate to cover the separation and make the road level… no riding bump.

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