Concrete is an aggregate made up of a number of materials like stones and sand that are mixed with a binder like cement and water. The mixture is then left to dry and harden. It's a flexible material that can be formed on the spot or poured into molds, hardened and then transported.
Even though it had been around for hundreds of years, it wasn't until 1860, when someone realized that concrete could be reinforced to increase its tensile strength (the amount of force or stress it could withstand), that concrete started gaining wide acceptance.
Reinforced concrete can be formed into many shapes with a supporting structure of narrow steel rods embedded right in the concrete when it's poured. Rebar reinforcement makes concrete an ideal material for walls, beams, slabs, foundations, frames and many other applications. The use of metal rods and mesh, together with a relatively inexpensive concrete medium, make reinforced concrete a flexible, reliable and economical building choice.
Twentieth century refinements have made reinforced concrete an even bigger player in modern building design and construction. Pre-cast concrete is made under controlled manufacturing conditions that increase its water repelling characteristics and limit its capacity to expand and contract. Pre-stressed concrete, made by placing stretched steel strands in the hardening concrete, increase reinforced concrete's tensile strength and resistance to downward pressure.
Let's proceed to the next section, where we'll take a look at how steel is being used to do more than just reinforce concrete in building construction.