Concrete Sidewalks: Why are there spaces between slabs?

Why are spaces placed between slabs of concrete in city sidewalks?

1) Allow for expansion and contraction of the concrete
2) Improve the aesthetics of the sidewalk
3) Reduce the weight of the concrete slabs
4) Prevent cracking of the concrete

Answer:

Spaces between concrete sidewalk slabs are primarily designed to allow for thermal expansion and contraction, thereby preventing thermal stress and cracking of the concrete.

Spaces are placed between slabs of concrete in city sidewalks primarily to allow for expansion and contraction of the concrete due to changes in temperature. This consideration in design helps to prevent thermal stress from developing in the concrete. Additionally, these gaps also help to prevent cracking of the concrete. When the temperature rises, the concrete expands and the provided gaps accommodate this expansion. Conversely, the slabs contract when it gets colder and the gaps prevent the creation of internal stress that relates to contraction.

While it may also improve the aesthetics of the sidewalk or seem to reduce the weight of the concrete slabs in perception, these aren't the primary reasons. The choice of materials also contributes in managing thermal stresses where, for instance, reinforcing rods in concrete structures are often made of steel as its coefficient of linear expansion is nearly equal to that of concrete.