Typically, joints are placed 24 to 30 times the thickness of the slab apart. When joints are more than 15 feet apart, weight transfer devices (dowels or diamond plates) must be used.
Why are there gaps between sidewalks?
Because of the concrete sidewalk construction in portions, the size may vary depending on the weather. If it were attached, the entire structure would sag and fall. When designing everything from bridges to skyscrapers, engineers must consider this fundamental feature of matter.