|MadSci Network: Other|
I guess it is to stop water getting down into the cracks and causing more damage. If you live in a cold part of country, you may have seen cracked pipes, where the water has frozen and expanded. The same things will happen in the cracks in the sidewalk. Rainwater will naturally accumulate in the cracks, and if it gets cold enough it will freeze and force the crack to get bigger. So it is better to fix the cracks before winter comes, so that the sidewalk doesn't worse and worse.
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