Reinforced concrete

Reinforced concrete, also known as ferroconcrete, is a composite material. It combines concrete, which is weak in tension and lacks ductility, with a reinforcement material that has higher tensile strength or ductility to compensate for these shortcomings. While steel reinforcing bars (rebar) are the most common reinforcement, they are not the only option. Typically, the reinforcement is placed into the concrete before it hardens, though post-tensioning is another method used to add reinforcement. By volume, reinforced concrete is one of the most widely used engineering materials in the world. When properly designed, the concrete’s alkalinity protects the steel rebar from corrosion.

Reinforcing schemes are usually intended to handle tensile stresses in specific areas of the concrete, preventing unacceptable cracking or structural failure. Modern reinforced concrete can incorporate various reinforcing materials, including steel, polymers, or other composites, sometimes alongside rebar and sometimes not. The material can also be permanently stressed—with the concrete kept in compression and the reinforcement in tension—to improve how the final structure behaves under normal loads. In the United States, the two most common methods for this are pre-tensioning and post-tensioning. For a construction to be strong, ductile, and durable, the reinforcement must meet several requirements: it needs high relative strength, a high tolerance for tensile strain, a good bond with the concrete regardless of pH or moisture, thermal compatibility to avoid stress from temperature changes, and durability within the concrete environment despite corrosion or sustained stress.

The early development of reinforced concrete happened simultaneously in England and France during the mid-19th century. French builder François Coignet was the first to use iron-reinforced concrete as a building technique. Between 1853 and 1855, he built the first iron-reinforced concrete structure for himself—a four-story house at 72 rue Charles Michels in the Paris suburbs, now known as the François Coignet House. His descriptions suggest he reinforced the concrete not to add strength but to keep monolithic walls from overturning. The Pippen Building in Brooklyn, built in 1872–73, stands as a testament to his technique, though Coignet did not design it. In 1854, English builder William B. Wilkinson reinforced the concrete roof and floors of a two-story house he was constructing. The placement of his reinforcement shows he understood tensile stresses, unlike earlier builders. Between 1869 and 1870, Henry Eton designed, and Messrs W & T Phillips of London built, the wrought-iron reinforced Homersfield Bridge over the River Waveney in England, with a 50-foot (15.25-meter) span. Joseph Monier, a 19th-century French gardener, was a pioneer in structural, prefabricated, and reinforced concrete, having been dissatisfied with the materials available for durable flowerpots. He received a patent in 1867 for reinforcing concrete flowerpots with a wire mesh and mortar shell. In 1877, he obtained another patent for a more advanced technique using iron rods arranged in a grid pattern to reinforce columns and girders. While Monier knew reinforcing improved concrete’s inner cohesion, it is unclear if he understood how much it increased tensile strength. In 1877, Thaddeus Hyatt published a report titled *An Account of Some Experiments with Portland-Cement-Concrete Combined with Iron as a Building Material, with Reference to Economy of Metal in Construction and for Security against Fire in the Making of Roofs, Floors, and Walking Surfaces*, detailing his experiments on reinforced concrete’s behavior. His work was crucial in turning concrete construction into a proven, studied science; without it, progress might have relied on more dangerous trial and error. Before the 1870s, concrete construction was not yet scientifically proven, even though it dated back to the Roman Empire and was reintroduced in the early 19th century. Ernest L. Ransome, an English-born engineer, was an early innovator in reinforced concrete techniques at the end of the 19th century. Building on knowledge from the previous 50 years, he improved nearly all the styles and techniques of earlier inventors. His key innovation was twisting the reinforcing steel bar to improve its bond with the concrete. As his concrete buildings gained fame, Ransome constructed two of the first reinforced concrete bridges in North America between 1886 and 1889; one still stands on Shelter Island in New York’s East End. One of the first concrete buildings in the United States was a private home designed by William Ward and completed in 1876, specifically built to be fireproof. G. A. Wayss, a German civil engineer and pioneer of iron and steel concrete construction, bought the German rights to Monier’s patents in 1879. In 1884, his firm Wayss & Freytag made the first commercial use of reinforced concrete. Until the 1890s, Wayss and his company greatly advanced Monier’s reinforcing system, establishing it as a well-developed scientific technology. The Lamington Bridge, designed by Alfred Barton Brady, was Australia’s first large reinforced concrete road bridge.