Reinforced concrete

In 1867 Joseph Monier, a Parisian gardener, patented flower tubs and basins made of cement mortar strengthened with an iron wire mesh. Concrete is strong when squeezed but weak when stretched or bent, and steel has the opposite strength, so embedding steel bars in concrete makes a material that resists both. Monier soon extended the idea to pipes, tanks and bridges, and he patented reinforced beams and railway sleepers in the 1870s.¹

The idea had several parents. Portland cement had given builders a reliable, strong binder, and the Bessemer process, from 1856, made iron and steel cheap and standardized. In England, William Wilkinson patented iron-reinforced concrete floors in 1854, and in the United States Thaddeus Hyatt ran load tests in the 1870s that showed the two materials expand with heat at nearly the same rate, which is why steel does not tear free of the concrete. The French contractor Francois Hennebique turned experiments into an engineering system in 1892, with stirrups and a continuous frame, and licensed it across Europe through a network of agents. Ernest Ransome's twisted bars and the Ingalls Building in Cincinnati, a sixteen-story concrete skyscraper finished in 1903, showed it could rise high.²¹

Reinforced concrete is shaped while wet, fire-resistant and cheap, and it can be cast by relatively unskilled labor. It became the standard material of twentieth-century construction: dams, bridges, factories, apartment blocks, airport runways and the stunning thin shells of modernist architects such as Pier Luigi Nervi and Le Corbusier. Later prestressed concrete, from Eugene Freyssinet in the 1920s and 30s, allowed longer spans. Its weakness is that water can corrode steel inside, so the lifespan of many mid-century concrete buildings is now a major maintenance problem.