Roads are broken up into sections as well, they are just larger. This is done for a few reasons:
1. Thermal expansion. Without some empty space between sections every so often the stress from temperature changes would cause cracks to form. Small gaps give room for the concrete to expand into, releasing the stress.
2. Larger sections are harder to poor. Pretty self explanatory, you want the entire section to cure at the same time.
These also apply on the smaller scale of sidewalks but there is also the threat of tree roots breaking sections. It is better for a smaller section to be broken than a larger one.
Sidewalks are laid in sections for several good reasons:
1) If a section is damaged, it can be pulled out and replaced without affecting the rest of the walkway.
2) Services like water pipes, gas and communications often run under sidewalks. In order to service these it is easier if workers can pull up sections of the sidewalk instead of having to cut into and later repair a larger strip.
3) Sidewalks sometimes need to be changed and sectioning allows this without having to replace large strips.
Roads also have similar issues regarding services and damage, however, it is the material that makes them different. Roads made of concrete are usually sectioned just like sidewalks for the same reasons. Concrete is very durable, and repairing long strip is not easy and the repair itself can leave cut lines that degrade over time. Most roads are made with asphalt for this very reason. Asphalt is soft compared to concrete, it can be cut out much more easily and a patch can be put down easily. Asphalt cut lines also degrade over time, but because it is so easy to patch it doesn’t matter much, it just gets patched again and again. Eventually asphalt must be fully removed and the whole surface gets repaved, but this is way easier and cheaper than concrete and that’s why it gets used.
This is also not universal. In the UK for example, it’s common to see sidewalks made of concrete tiles ( 20-45cm a side and usually rectangular – that’s 8-18” on a side for the Americans among us), but it’s also common to see them as poured and rolled tarmac like the surface of a road, with a heavy stone/concrete piece as the outer edge to keep it in.
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