Why are there lines in the sidewalk?

Answer 1

They are there to prevent fractures from traveling the lenght of the sidewalk. Ever notice how a fracture travels in the trough of those lines?

Answer 2

The lines in the sidewalk are an aesthetic feature to control the cracking. All concrete cracks under tension. If the lines were not there, the cracking would occur at random, resulting in undesirable effects. The cracking occurs at the least resistance, which is the thinnest part of the sidewalk, which is straight (and at set intervals, barely noticable) thanks to the line. Next time you walk on a sidewalk, look at the lines and you will see a crack in almost every one.

Answer 3

They form a kind of stress relief

Thermal expansion and contraction would cause more cracks and failures if the lines were not there.

I am sure also there must be some more practical answer, like the average sidewalk area is equal to the amount of cement in a standard construction wheelbarrow. Therefore the forms were made to contain that amount of cement.

Answer 4

Due to temperature changes, the concrete expands and contracts. Since the material around the concrete expands and contracts at a different rate, this would cause undue stress on the concrete. Therefore lines are put in the concrete to give it room to contract. The stress then goes to the line, not in the main material of the concrete slab.

Understand?

Answer 5

They are expansion joints. They allow the concrete somewhere to expand when it gets hot so they won't crack.