Concrete’s greatest weakness is its tensile strength, which can be less than 10% of its compressive strength. So, we often reinforce it to create a composite material strong against all types of stress. This video briefly touches on conventional rebar and prestressed/post-tensioned reinforcement.
source/image: Practical Engineering
When the concrete sets and hardens around the bars, we get a new composite material, reinforced concrete (also called reinforced cement concrete or RCC),That works well in either tension or compression: the concrete resists squeezing (provides the compressive strength), while the steel resists bending and stretching (provides the tensile strength).
In effect, reinforced concrete is using one composite material inside another: concrete becomes the matrix while steel bars or wires provide the reinforcement.The steel bars (known as rebar, short for reinforcing bar) are typically made from twisted strands with nobbles or ridges on them that anchor them firmly inside the concrete without any risk of slipping around inside it.
Theoretically, we could use all kinds of materials to reinforce concrete. Generally, we use steel because it expands and contracts in the heat and cold roughly as much as concrete itself, which means it won’t crack the concrete that surrounds it as another material might if it expanded more or less.