Let’s go over some basic physics…
What is Tension?
Consider the rope in the image above. The two forces are both pulling on the rope in opposite directions. This action is putting the rope in tension.
What is Compression?
Now consider the spring in the above image. The two forces are both pushing the spring together. This action is putting the spring in compression.
Tension and Compression in Concrete
How do these two concepts tie together in concrete construction? By itself, concrete is strong in compression yet weak in tension.
Steel on the other hand is just the opposite: weak in compression yet strong in tension. By combining the two materials (think concrete + rebar) concrete ultimately becomes much stronger with the added ability to resist tensile forces.
The most common advantage that rebar provides is the reduction of crack propagation. The reinforcing steel acts as a sort of skeleton that supports the concrete despite the formation of cracks and other undesirable forces that may appear within the slab (such as curling).
The end result is a stronger, longer lasting, and more durable concrete product.