Why do sidewalks have blocks, instead of being solid?
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Most of these ‘blocks’ are not separate blocks. What you’re seeing is a solid concrete sidewalk with grooves on the surface.
I believe these are to allow thermal expansion/contraction with the outside temperature. The temperature at the surface of the concrete can get much hotter than points deeper underneath. So it’s only the surface that needs these grooves. It doesn’t need to go all the way down to create separate ‘blocks’
Concrete cracks. You know how when dirt dries up in the summer and gets hard, it often gets big cracks in it? When concrete gets hard, it gets cracks in it too. When the concrete is still wet, the workers will use a tool that makes a groove across the concrete. That groove makes the concrete a little weaker there, so as the concrete gets hard and starts to crack, it’ll usually crack along that groove. That means you can control where the crack goes and kind of hide it. That makes it look better, and it helps keep chunks of concrete from breaking off the edges where the cracks meets it.
It is to either reduce or control cracking. Concrete over time will crack for various reasons (freezing and/or heating, rain, ground settling, etc). Large slabs of concrete are more likely to crack. Also some of what you see are joints on the surface. A crack here is more likely, but it won’t show because it is on the part you don’t see.
There are also logistical reasons. Manpower limitations and how concrete dries / cures means only a certain amount can be poured, smoothed, etc at a time. It isn’t always possible to do one big pour, so the sectioned concrete hides the fact that they were done on different days.
Another add is exterior concrete is poured with air ( carbon dioxide) interior concrete is not … the air bubbles are added to add an insulating factor and you cannot hard trowel concrete with air ( slick finish )
These are control points. When concrete cures it shrinks because of the moisture is evaporating. Those lines are there to help guide the cracks and after so many control points there are also expansion points, were rods are inserted between the lines to help it when the earth moves.
They are solid, at least they are where I am in southern Ontario, Canada. The sidewalk slabs are poured in one go, then control joints are added with a hand tool. The slabs are generally 4-6 inches thick while the joint is only around an inch or so deep. The joints are there so that when the concrete cracks due to shifting or thermal expansion/contraction, it cracks at the joint rather than in a random location.
There have already been a lot of answers about the advantages of individual concrete squares being better than solid paving at conforming to shifting ground.
But then the relevant question becomes “If that’s so much better, why is that ONLY done on the sidewalks and not the street?”
Answering that that’s the second half of the answer.
And the answer is that while it may be a cheaper way to keep the paving from breaking up as the ground settles and shifts, but it does it by making the paving squares mismatch a little as they settle on the shifting ground. If the main road was paved this way, it would mean the cars are driving on a very uneven surface that makes the wheels vibrate “BudaBudaBudaBudaBudaBuda” as the car goes over the tiles quickly. That reduces the top safe speed, and damages suspensions. To avoid that, it’s worth the extra ground preparation work it takes to make smooth surface paving. But on the surface that cars never go on, and only pedestrians do, the expense of doing that is harder to justify, since a person on foot isn’t going to be going that fast, and is going to be stepping rather than rolling, making the gaps between uneven tiles less of a problem.
Concrete (and everything else) grows and shrinks with daily/seasonal temperature changes.
When concrete shrinks, the ground it’s sitting on pulls back against it, causing it to stretch. This causes it to crack.
When the concrete grows, it presses against the concrete next to it, and it gets crushed.
When you build a sidewalk out of concrete, you put contraction joints (pre-built “cracks”) every few feet so that the concrete cracks in a neat, predictable manner. You put expansion joints further apart (every [20?] feet or so) filled with softer material that allow the concrete to expand without crushing at the edges.
If you ever see a sidewalk that someone tried to pour without these joints, it will likely have ugly cracks spaced every few feet and will be all busted up at the ends.
Also, modestly sized sections are more manageable to pour than giant expanses of concrete.
The section near my house has had bits removed 4 different times this year for utility work. If it was all one thing, it would be full of ugly patches. The panels are provide flexibility in expansion, movement and ease of replacement.
My town the only block sidewalks are the main street on the river. All other sidewalks are paved
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