eli5: Why are sidewalks, driveways, curbs and other surfaces made of concrete and/or cement always made with a line dividing it into sections, when it’s all just one big pour?
In: Engineering
Concrete is going to crack. You can give it places to crack that don’t cause problems, or you can let it crack where it wants to. The dividing lines give the concrete preferred places to crack. That why they also sometimes put some fiberboard between sections of concrete so that there is a place for relative movement without cracking.
Concrete has thermal expansion… it gets bigger when it gets hot, and smaller when it is cold. The lines allow the concrete to move without cracking or buckling
These are called stress joints. Because of the weight and how brittle concrete is it is expected to crack, these joints are usually cut into the concrete to give the concrete a weak point so that when I’d does crack it cracks in an expected place. Sometimes these spaces can also be what is called an expansion joint to sometimes when a piece of new conrect is poured up against an old piece of concrete an expansion joint will be installed this is usually just a small piece of material set between the two slabs. These are the thicker black lines you see.
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