Concrete Joint Use and Spacing

[James DeRoussel]

Extensive research on the subject has confused me with regards to the use and spacing of different joint types in concrete. I learned over the course of my career at multiple firms to place control (contraction) joints 6-12 feet apart depending on slab thickness and dimensions. On top of that, expansion joints were placed every ~20-25 feet max.

Now I am reading multiple sources (including the Portland Cement Association) that suggest the use of expansion joints is generally unnecessary:

“Pavement expansion joints are only needed when:
1. the pavement is divided into long panels (60 ft or more) without contraction joints in between to control transverse cracking.
2. the pavement is constructed while ambient temperatures are below 40°F (4°C).
3. the contraction joints are allowed to be infiltrated by large incompressible materials.
4. the pavement is constructed of materials that in the past have shown high expansion characteristics.

Under most normal concrete paving situations, these criteria do not apply. Therefore, expansion joints should not normally be used.”

This implies that we have been using expansion joints in concrete walks and other applications unnecessarily. Further reading implies that the over-use of expansion joints may actual be detrimental to the long term performance of concrete.

To further confuse matters, the literature identifies four types of joints: control (contraction), expansion, isolation, and construction. In most cases, the difference between expansion and isolation joints is poorly defined.

So, a short informal poll:
-What are the standard practices in your office with respect to the use and spacing of control joints and expansion joints?
-Do you distinguish between “isolation joints” and “expansion joints”? Or do you use these terms interchangeably?
-Do you use expansion joints at regular intervals in paved areas, or do you use expansion joints only at the interface of two independent elements (paving/building, new paving/existing paving)?

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