The marriage between
concrete and steel has lasted long. The
first structures we know of in which stone and iron were used together were
built by the ancient Greeks. Over the
years, the stone was replaced by concrete and iron by steel. The reasons for
the union between steel and concrete are simple. Concrete is strong in compression but weak in
tension. In contrast, steel bars are
strong in tension. If we put steel bars into
concrete, we get a composite that can handle both compression and
tension. And we can use this composite
to make elements of almost any shape we can imagine without the need for melting
and handling molten material at high temperature. We shape concrete by casting it into molds
soon after we mix its ingredients –stone, sand, water and cement– while the mix
is still a fluid. The operation is
relatively simple. In addition, the
composite is lighter and, in many instances, cheaper than steel. Putting concrete and steel together, we gain
the best of both materials.