Reinforced Concrete

Reinforced concrete is a composite building material in which steel reinforcing bars are embedded within concrete before it hardens, so that the steel's tensile strength compensates for concrete's own weakness in tension while the concrete continues to carry compression. The French builder Francois Coignet constructed the first iron-reinforced concrete building, a four-story house near Paris, between 1853 and 1855; the English builder William B. Wilkinson demonstrated an understanding of where to place tensile reinforcement in 1854; and the French gardener Joseph Monier later developed reinforcing techniques using grids of iron rods, beginning with reinforced concrete flowerpots. The material owes its effectiveness to three properties: concrete and steel expand and contract by nearly the same amount as temperature changes, so the two do not pull apart; the hardening cement paste bonds tightly to the steel's surface, letting stress transfer between the two materials; and concrete's alkaline chemistry forms a protective film on the embedded steel that resists corrosion; the material was in widespread use by the early twentieth century, including the sixteen-story Ingalls Building completed in Cincinnati in 1904.