Expansion joints are small spaces or grooves in an otherwise solid expanse of concrete, installed to allow for the concrete's expansion and contraction caused by temperature and moisture changes. Expansion joints prevent these changes from cracking the concrete.
Expansion and Contraction
As the temperature increases, a substance affected by the change will expand slightly, and as the temperature decreases, the substance will contract. The presence of moisture can accelerate these processes.
Though temperature-caused changes are often very slight, in a large expanse of concrete even a small change will add up, and could be very damaging.
Accepting the Problem
Because it is useless to resist the expansion and contraction of concrete, it is far better install expansion joints than allow the concrete to crack on its own.
By cutting expansion joints, you are essentially ensuring that you have an active role in the way the concrete cracks, and that the line is straight. This keeps the concrete expanse aesthetically pleasing.
Expansion joints should be spaced, as measured in feet, two to three times the concrete's thickness in inches. The cuts should be about 25 percent of the concrete's thickness in depth.
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