by Vaclav Smil
Rolled in a single piece directly from an ingot, H beams had a substantially higher tensile strength (Cotter 1916; Hogan 1971). An undisputed paragon of structures using this new material is New York’s Woolworth Building at 233 Broadway, designed by Cass Gilbert (1859-1934) and finished in 1913. The building used for the first time all of the key techniques that still characterize the construction of skyscrapers. Its 57 stories (241 m high) are founded on concrete piers that reach Manhattan’s bedrock; sophisticated wind bracing minimizes its swaying, and high-speed elevators provide local and express service. A new, elite group of fearless construction ironworkers emerged to assemble these massive and tall steel skeletons—and a hundred years later they still form a special professional caste (figure 4.7).
The Woolworth building remained the city’s tallest structure until 1930, when it was surpassed by the Bank of Manhattan and Chrysler buildings and, a year later, by the Empire State Building (Landau and Condit 1996). All of these structures, and most of their post-1970 companions—in the United States peaking with 443 m of Sears Tower in Chicago, and globally, as of the year 2000, with 452 m of Petronas Towers in Kuala Lumpur (figure 4.8)—share the same fundamental structural property, as all of the world’s tallest skyscrapers hide variably shaped steel skeletons adorned with ornamental cladding of stone, metal, plastic materials, or glass.
FIGURE 4.7. The beginnings of the skyscraper era. The Home Insurance Building in Chicago, completed in 1885 (and demolished in 1931), was the first structure supported by steel beams and columns. The engraving of New York’s ironworkers building an early skyscraper and taking “coolly the most hazardous chances” is reproduced from The Illustrated London News of December 26, 1903. A century later, safety harnesses are compulsory, but the basic assembly procedure and the need for casual tolerance of great heights and uncommon sense of balance and physical dexterity have not changed.
The other major use of steel in construction, burying it inside concrete, also emerged during the pre-WWI period. This technique, whereby concrete gets its tensile strength from embedded steel bars or steel lattices, created much of the built environment of the 20th century. Concrete—a mixture of cement, sand, gravel, and water—is of course an ancient material, the greatest structural invention of the Roman civilization. The Pantheon, the pinnacle of its concrete architecture, built between 126 and 118 B.C.E., still stands in the heart of Rome’s old city: its bold dome, spanning 43.2 m, consists of five rows of square coffers of diminishing size converging on the stunning unglazed central oculus (Lucchini 1966).
FIGURE 4.8. Height comparison of five notable steel-skeleton skyscrapers built between 1885 and 1998.
Better cement to produce better concrete has been available only since 1824, when Joseph Aspdin began firing limestone and clay at temperatures high enough to vitrify the alumina and silica materials and to produce a glassy clinker (Shaeffer 1992). Its grinding produced a stronger Portland cement (named after limestone whose appearance it resembled when set) that was then increasingly used in many compressive applications, mainly in foundations and walls. Hydration, a reaction between cement and water, produces tight bonds and material that is very strong in compression but has hardly any tensile strength, and hence it can be used in beams only when reinforced: such a composite material has monolithic qualities, and it can be fashioned into countless shapes.
Three things had to happen in order to have a widespread use of reinforced concrete: a good understanding of tension and compression forces in the material, the realization that hydraulic cement actually protects iron from rust, and understanding that concrete and iron form a solid bond (Peters 1996). But even before this knowledge was fully in place, there were isolated trials and projects that embedded cast or wrought iron into concrete beginning during the 1830s, and the first proprietary system of reinforcement was introduced in England and France during the 1850s (Newby 2001). In 1854 William Wilkinson patented wire rope reinforcement in coffered ceilings, and a year later François Coignet introduced a system that was used in 1868 to build a concrete lighthouse at Port Said. Fireproofing rather than the monolithic structure was seen as the material’s most important early advantage.
During the 1860s, a Parisian gardener, Joseph Monier (1823-1906), patented a reinforced concrete beam (an outgrowth of his production of garden tubs and planters that he strengthened with simple metal netting in order to make it lighter and thinner), and in 1878 he got a general patent for reinforced structures. Many similar patents were granted during the two following decades, but there was no commensurate surge in using the material in construction. The pace picked up only after 1880, particularly after Adolf Gustav Wayss (1851-1917) bought the patent rights to Monier’s system for Germany an Austria (in 1885) and after a Parisian contractor, Francois Hennebique (1842-1921), began franchising his patented system of reinforced construction, particularly for industrial buildings (Straub 1996; Delhumeau 1999). Inventors designed a variety of shaped reinforcing steel bars in order to increase the surfaces at which metal and concrete adhere (figure 4.9).
FIGURE 4.9. Shaped steel bars for reinforcing of concrete: spiral twist by E. L. Ran-some, a square design with projections by A. L. Johnson, alternating flat and round sections by Edwin Thacher, and a bar with bent protrusions by Julius Kahn and the Hennebique Co. Reproduced from Iles (1906).
During the 1890s came the modern technique of cement production in rotary kilns that process the charge at temperatures of up to 1,500°C, and engineers developed standard tests of scores of various cement formulas and concrete aging. Thomas Edison got into the act with his cast-in-place concrete houses that he built in New Jersey (they still stand), but such utilitarian structures did not make concrete a material of choice for residential construction. Much more creatively, two architects, Auguste Perret and Robert Maillart (1872-1940), made the reinforced concrete esthetically acceptable. Perret did so with his elegant apartments, including the delicately facaded 25 Rue Franklin in Paris, and with public buildings, most notably the Theatre des Champs-Elysées. Maillart designed and built (in Switzerland between 1901 and 1940) more than 40 elegant concrete bridges (Billington 1989). By the 1960s, new high-strength reinforced concrete began to compete with the steel frame in skyscraper construction (Shaeffer 1992).
By 1990 the world’s tallest reinforced concrete structure, the 65-story 311 South Wacker Drive building in Chicago, reached 292 m, and even taller structures, with concrete able to withstand pressures of more than 100 MPa, were planned. After 1950 came widespread commercial applications of pre-stressing, another fundamental pre-WWI invention involving concrete and steel. Its origin can be dated exactly to 1886 when Carl Dochring came up with an ingenious idea to stretch the reinforcing bars while the concrete is wet and release the tension after the material had set (Abeles 1949). This puts the individual structural members, which are usually precast offsite, into compression and makes it possible to use much less steel and concrete (about 70% and 40% less) for the same load-bearing capacity and hence to build some amazingly slender structures. During the first decades of the 20th century, Eugene Freyssinet (1879–1962) developed much of the underlying technical understanding, and he also came up with the idea of poststressing by tensioning wires that are threaded through ducts formed in precast concrete (Grotte and Marrey 2000; Ordóñez 1979).
Reinforced concrete is simply everywhere—in buildings, bridges, highways, runways, and dams. The material assumes countless mundane and often plainly ugly shapes (massive gravity dams, blocky buildings) as well as daring and visually pleasing forms (thin shells). Its unmatched accretion is the world’s largest dam—China’s Sanxia on the Yangzi, 185 m tall and 2.3 km long—which contains nearly 28 million cubic meters of concrete reinforced with nearly half a million tons of steel bars. In terms of both global annual production and cumulatively emplaced mass, reinforced concrete is now the leading man-made material, seen as flat expanses and stunning arches, unimaginative boxes and elegant projections.
The material has been used for the shoddily built apartment blocks of Beijing’s Maoist period (they looked dilapidated even before they were completed) and for the elegant sails of Sydney Opera House, which look permanently inspirational. Unadorned reinforced concrete forms the world’s tallest free-standing structure, Toronto’s oversize CN tower, as well as Frank Lloyd Wright’s perfectly proportioned cantilevered slabs that carry Falling Water over a cascading Pennsylvanian stream. As Peters (1996:58) noted, “[R]einforced concrete has been variously attacked as the destroyer of our environment and praised as its savior,” but whatever the reaction may be, his conclusion is indisputable: “Our world is unthinkable without it.” Yet only a few history-minded civil engineers and metallurgists know its origins, and so reinforced concrete may be perhaps the least appreciated of all fundamental pre-WWI innovations, an even more obscure foundation of modern civilization than the electrical transformer described in chapter 2.
Aluminum
This light metal is much more common in nature than is iron: this most common of all metallic elements is, after oxygen and silicon, the third largest constituent of Earth’s crust, amounting to about 8% by mass (Press and Siever 1986). But because of its strong affinity for oxygen, the metal occurs naturally only in compounds (oxides, hydroxides, fluorides, sulfates, and silicates) and never in a pure state. And unlike iron, which has been known and worked for more than 3,000 years, aluminum was identified only in 1808 by Humphry Davy (of the first electric arc fame), isolated in a slightly impure form as a new element only in 1825 by Hans Christian 0rsted (of the magnetic effect of electric currents fame), and two years later produced in powder form by Friedrich Wohler (of the first ever urea synthesis fame). Despite many subsequent attempts to produce it in commercial quantities, aluminum remained a rare commodity until the late 1880s: Napoleon III’s infant son got a rattle made of it, and 2.85 kg of pure aluminum were shaped into the cap set on the top of the Washington Monument in 1884 (Binczewski 1995).
The quest for producing the metal in quantity was spurred by its many desirable qualities. The most notable attribute is its low density: with merely 2.7 g/cm3, compared to 8.9 g/cm3 for copper and 7.9 g/cm3 for iron, it is the lightest of all commonly used metals. Only silver, copper, and gold are better conductors of electricity and only a few metals are more malleable. Its tensile strength is exceeded only by best steels, and its alloys with magnesium, copper, and silicon further enhance its strength. Moreover, it can be combined with ceramic compounds to form composite materials that are stiffer than steel or titanium. Its high malleability and ductility mean that could be easily rolled, stamped, and extruded, and it offers attractive surface finishes that are highly resistant to corrosion. The metal is also generally regarded as safe for use with food products and for beverage packaging. Finally, it is easily recyclable, and its secondary production saves 95% of the energy needed for its production form bauxite.
Bauxite, named after the district of Les Baux in southern France where Pierre Berthier first discovered the hard reddish mineral in 1821, is the element’s principal ore, and it contains between 35% and 65% of alumina (aluminum oxide, Al2O3). But the first attempts to recover the metal did not use this abundant ore. Henri Saint-Claire Deville (1818-1881) changed Wohler’s method by substituting sodium and potassium and began producing small amounts of aluminum by a cumbersome and costly process of reacting metallic sodium with the pure double chloride of aluminum and sodium at high temperature. This expensive procedure was used on a small scale for about 30 years in France. In 1854 Robert Bunsen separated aluminum electrolytically from its fused compounds, and shortly afterward Deville revealed his apparatus for reducing aluminum from a fused aluminum-sodium chloride in a glazed porcelain crucible that was equipped with platinum cathode and with carbon anode.
Although this process did not lead to commercial production, Borchers (1904:113) summed up Deville’s contribution by noting that he introduced the two key principles that were then “repeatedly re-discovered and patented, viz: 1. The use of soluble anodes in fused electrolytes; and 2. The addition of aluminium to fused compounds of the metal during electrolysis, by the agency if alumina.” This created a situation similar to pre-Edisonian experiments with incandescing carbon filaments: the key ingredients of a desirable technique (filament and vacuum for the light bulbs, soluble anodes, and addition of alumina for the electrolysis of aluminum) did not have to be discovered, but the techniques had to be made practical and rewarding. And, as with the history of incandescent lights, many impractical solutions were put forward between 1872 and 1885 to solve the challenge of large-scale smelting of aluminum. Worldwide production of the metal was just 15 t in 1885, and even after Hamilton Y. Castner’s new production method cut the cost of sodium by 75%, aluminum still cost nearly US$20/kg in 1886 (Carr 1952).
A Duplicate Discovery
When the commercially viable solution finally came—during that extraordinarily eventful decade of the 1880s—it involved one of the most remarkable instances of independent concurrent discovery. In 1886 Charles Martin Hall and Paul Louis Toussaint Héroult (figure 4.10) were two young chemists of the same age (both born in 1863, and both died in 1914), working independently on two continents (the first one in a small town in Ohio, the second one near Paris) to come up with a practically identical solution of the problem during the late winter and early spring months of 1886. Just two years later, their discoveries were translated into first commercial enterprises producing electrolytic aluminum.
FIGURE 4.10. Portraits of Charles Hall (left) and Paul Héroult from the late 1880s when the two young inventors independently patented a nearly identical aluminum reduction process. Photographs courtesy of Alcoa.
Hall’s success was the result of an early determination and a critical chance encounter: his aspiration to produce aluminum dated to his high school years, but after he enrolled at the Oberlin College in Ohio in 1880, he had the great luck of meeting and working with Frank F. Jewett, an accomplished scientist who came to the college as a professor of chemistry and mineralogy after four years at the Imperial University in Tokyo and after studies and research at Yale, Sheffield, Gottingen, and Harvard (Edwards 1955; Craig 1986). Jewett provided Hall with laboratory space, materials, and expert guidance, and Hall began intensive research effort soon after his graduation in 1885.
Hall first excluded the electrolysis of aluminum fluoride in water because it produced only aluminum hydroxide. His next choice was to use water-free fused salts as solvents for Al2O3, and his first challenge was to build a furnace that would sustain temperatures high enough to melt the reactants, but he was not able to do so with his first externally heated gasoline-fired furnace. He then began to experiment with cryolite, the double fluoride of sodium and aluminum (Na3AlF6), and on February 9, 1866, he found that this compound with melting point of 1,000°C was a good solvent of Al2O3. As with so many early electrochemical experiments, Hall had to energize his first electrolysis of cryolite, which he did on February 16, 1886, with inefficient batteries. Graphite electrodes were dipped into a solution of aluminum oxide and molten cryolite in a clay crucible, but after several days of experiments he could not confirm any aluminum on his cathode.
Because he suspected that the cathode deposits originated in the crucible’s silicon lining, he replaced it by graphite. On February 23, 1886, after several hours of electrolysis in a woodshed behind Hall’s family house at 64 East College Street in Oberlin, he and his older sister Julia found deposits of aluminum on the cathode. Hall’s quest is a near-perfect example of a fundamental technical advance that was achieved during the most remarkable decade of the Age of Synergy by the means so emblematic of the period: the combination of good scientific background, readiness to experiment, to persevere, and to make necessary adjustments (Hall built most of his experimental apparatus and also prepared many of his reactants), and all of this followed by prompt patenting, fighting off the usual interference claims, and no less persistent attention to scaling-up the pr
ocess to industrial level and securing financial backing.
Hall’s first American specification was received in the Patent Office on July 9, 1886—but it ran immediately into a problem as the office notified him of a previous application making a very similar claim: Héroult filed his first French patent (Patent 175,711) on April 23, 1886, and by July 1887 he formally contested Hall’s priority. But as Hall could prove the date of his successful experiment on February 23, 1886, he was eventually granted his U.S. rights, divided among two patents issued on April 2, 1889. U.S. Patents 400,664 and 400,766 specified two immersed electrodes, while U.S. Patents 400,667 specified the use of cryolite (figure 4.11).
While his patents were pending, Hall looked for financial backing, and after some setbacks and disappointments he finally found a committed support of a Pittsburgh metallurgist Alfred E. Hunt, and a new Pittsburgh Reduction Co. was formed in July 1888 and began reducing alumina before the end of the year (Carr 1952). This was a fairly small establishment powered by two steam-driven dynamos and producing initially just more than 20 kg of aluminum per day, and 215 kg/day after its enlargement in 1891 (Beck 2001). Its electrolytic cells (60 cm long, 40 cm wide, and 50 cm deep) were made of cast iron, held up to about 180 kg of cryolite, and had 6-10 carbon anodes (less than 40 cm long) suspended from a copper bus bar, with the tank itself acting as the cathode.