It is difficult if not impossible to imagine the 20th century without concrete. Surely the landscape of modernity and modernization would be unrecognizable without it. By 1900 concrete may indeed have been considered modern, but as pointed out by technical manuals throughout the century, it was by no means a new material. Ancient builders put it to use, most notably the Romans, who built walls (faced with brick) and arcuated spans (the 145-foot span of the Pantheon’s dome the most famous and well-preserved example). This classical pedigree appealed to many architects of the early 20th century, although modern concrete practice had more recent origins.
Europeans experimented with it in the 18th century, when the English engineer John Smeaton used a form of hydraulic cement (a cement that hardens underwater) to rebuild the wall and lighthouse at Eddy-stone off the Cornwall coast in 1756. The French began their own experiments some 30 years later, using a combination of clay and cement from limestone. Louis Vicat perfected hydraulic cement around 1800, and by 1850 Joseph Monier was producing concrete flowerpots and sewer pipes using wire mesh and timber molds. In 1824 the English bricklayer John Aspdin invented a type of cement dubbed “Portland,” after the stone it resembled. This high-strength variety proved crucial, for it became, and remains, the standard binding agent in the concrete used today. Portland cement was exported to the United States at the end of the American Civil War, and as in much of Europe, concrete frame structures were constructed for a variety of industrial uses. Particularly valuable for fireproof attributes, concrete effectively insulated the iron or steel embedded within. In some places, such as the American northeast, they were a relatively common sight by the start of the 20th century. By 1887 the French engineer and building entrepreneur François Hennebique patented a host of techniques for embedding steel bars in concrete.
How best to utilize concrete and how to appreciate and interpret its cultural meaning remained one of the more interesting and politically volatile architectural debates of the century. This ongoing state of flux involved more than technical development. By the end of World War II engineers, architects, builders, and others helped develop concrete as a common building material across the globe. From great hope to corporate or state-induced eyesore, perhaps no other material would be perceived in so many contrasting ways during the 20th century. One of several materials embraced by avant-garde architects for its revolutionary prospects, critics would come to vilify the material, associating it with the oppressive characteristics of modern power structures. Through it all the material maintained a pragmatic usefulness.
Concrete is a composite material produced by mixing a paste of cement and water with inert materials called aggregates. Because concrete is mixed and poured, it is well suited for molds and can be molded around reinforcing steel, a practice so common that by 1900 nearly all concrete structures were reinforced in some way by steel hidden from view. The first ingredient, cement paste, is the binding agent, and a number of different types were developed throughout the century. Consisting of Portland cement and water, this paste hardens via a curing process called hydration. The second ingredient, aggregates, varies considerably in size from sand particles to 3-inch rocks mixed with the paste. Lightweight varieties of concrete substitute these aggregates for expanded shale, slate, or slag to reduce the finished product’s weight.
Because concrete’s usefulness is complicated by its own dead load, a variety of engineers and builders have sought inventive alternatives. One of the more unusual experiments was conducted by the American architect Bernard May-beck (1923), who sought a low-cost remedy for the housing shortage after a fire devastated a portion of Berkeley, California. In a clotheswashing drum he combined cement paste, water, and sand; added some chemicals; and after mixing the concoction he dipped burlap sacks into the tank and pasted them onto wooden wall studs to form a concrete cladding. Calling this technique Bubble Stone for its unique appearance, Maybeck boasted that home owners could use it themselves because an average man could lift a hay-bale-sized chunk of this “stone” above his head.
Well-made concrete enjoys significant resistance to compression, but unlike steel it has little strength against tensile stress. The compressive strength of concrete is primarily based on the ratio of water to cement. Experiments both in the field and in laboratories led engineers in an ongoing effort to increase the material’s strength and decrease curing time. Generally speaking, the smaller the ratio of water to cement paste (i.e., the less water compared to cement paste), the stronger the concrete.
Once mixed, concrete is poured into molds called formwork, which may vary from a hole dug out of the earth for a foundation, to wood boards bolted together, to fiberglass panels. In some cases an entire substructure of forms must be constructed, itself a selfsupporting structure requiring careful design and inspection by engineers and contractors. In order to ensure a more controlled mixing process, concrete elements are often poured in a factory or in a semiremote location on the building site set aside for the purpose. The pour is crucial because laborers must work the paste and aggregates evenly throughout the formwork so that they do not shift prelaid rebar out of its intended positions. Pipes and conduits that must pass through the finished concrete must be set into position prior to the pour as well and remain undisturbed by laborers’ efforts to fill the forms. As the mix is spread within the formwork, laborers must ensure that all voids are filled and that the aggregate is evenly distributed. The more fluid the mix, that is, the greater the ratio of water to cement paste, the more workable the pour. Increasing the water makes for easier construction, but weakens compressive strength. In colder climates air-entraining agents are often added to increase workability and resistance to the heaving resulting from water turning to ice. Concrete must be mixed for a sustained period of time, so that the finished product exhibits the properties of strength and durability designed by engineers.
The development and widespread marketing of gasoline-powered automobiles and trucks have had an influence in the mixing process, especially in the United States. The truck was both a prerequisite and a consequence of the parallel development of concrete construction. Improvements in road construction, a development that was facilitated by the concrete industry, in turn facilitated the widespread acceptance of the automobile. Likewise, the cement-mixing gasoline-powered truck is ideally suited to concrete construction because while en route from the factory the truck mixes the cement paste, water, and aggregates in a revolving drum.
Once poured and left to remain still, concrete sets in up to three days, then cures for usually one month, depending on the type of ingredients in the mixture and the climatic conditions at the site or factory. After engineers determine the concrete is strong enough to support its own weight, laborers remove the formwork for reuse at the next pour. In cold conditions curing concrete must be covered to ensure the temperature necessary for developing a designed compressive strength. Curing is a chemical process (not a process of desiccation) in which water reacts with the cement paste and generates heat. Although hydration can occur even when concrete is underwater, even well-made concrete is not completely watertight. Over time exposed surfaces tend to absorb water that can pass into interior space.
Other liabilities were discovered throughout the century, such as the material’s poor insulating properties and the particularly dangerous problem called creep. Horizontal concrete structural members (slabs and beams) develop the tendency to gradually deflect over long periods of time, and this can become so severe as to make buildings uninhabitable. Structural engineers devised prestressing strategies to counter this creeping deflection.
Properties of strength and workability have not monopolized experimentation. Designers and builders have devised myriad ways of altering the construction process to obtain specific aesthetic effects. Various admixtures, especially those added at the end of a pour, have been used to alter the color of the finished material. Paolo Soleri experimented with using mounds of sand as a formwork in building concrete shells and half domes in the Arizona desert, even using the red and yellow color of the local sand and clay as part of the cement paste and aggregate mixture (Arcosanti, c.1970). These colors were transferred to the finished product. The subtractive volume of the formwork, and even the texture of its interior surfaces, has absorbed the attention of architects interested in manipulating the texture and the quality of concrete’s finished surface. Ornamental aggregates have been left exposed to give concrete a more rustic appearance, and a variety of surface treatments have been developed to alter the appearance of the finished concrete.
The 1960s and 1970s in particular was a period in which concrete surfaces were used as a finish on a massive and widespread basis. Paul Rudolph’s Art and Architecture Building at Yale University (1964) was a grand experiment in finish treatment, where the architect and contractor devised a method of using grooved forms that left corresponding vertical fins that ran the full sevenstory height of the building’s towers. Workmen removed the forms and then with hammer and chisel knocked away a portion of the fins to create a rusticated and jagged finish. The resulting grooves channeled rainwater down the facade in a controlled manner, which in turn limited the effect of stains on the finished surface, and at a distance the rough texture of the towers blended into the neo-Gothic architectural context of the neighborhood.
By 1920 concrete helped inspire architects to visualize massively scaled cities, and for the next 40 years they sought to refashion the urban landscape in a wholly new and modern reconfiguration of the 19th-century city. With the turning over of the colonial order following World War II, much of the world embraced concrete and its promise, but by the last quarter of the century, the material’s own success wrought a searing critique against its aesthetic properties and monolithic application. Finally, in the hands of a few architects across the globe, concrete once again continued as a material with striking aesthetic possibilities at the close of the century.
The fact that steel-reinforced concrete structures were already fairly common by the start of the 20th century, at least in parts of Western Europe and North America, is attested to by the number of notable works designed and constructed between 1900 and 1910. Thomas Edison was already promoting his “monolithic houses” by that time, Frank Lloyd Wright had designed Unity Temple (Oak Park, 1906), Antoni Gaudí had begun construction on his Casa Milá apartment block (Barcelona, 1905), and Auguste Perret had completed the apartment house at 25 bis, rue Franklin (Paris, 1903), followed by a concrete-frame garage (Paris, 1905).
Although concrete had already been employed for some 30 years as an industrial building material, by the turn of the century it was still too new to be associated with industrialism. That distinction belonged to iron and steel, the constituent elements of a landscape troubled by smokestacks and locomotives. Many architects and engineers also looked to concrete as an alternative to stone, perhaps because of the many similarities between the two materials. The weight of stone tended to be a prime factor as a building material, requiring extensive formwork during construction. Concrete was perceived as the thinking man’s building material, requiring a scientific mind to fully exploit its properties, which helped rehabilitate its status as a rough and crude version of stone. Mixtures and ratios, after all, required experimentation and theorizing by engineers who took out patents on their ideas.
The possibility of creating a monolithic structure excited architects who understood that with concrete each element (walls, columns, floor, and roof) would resist loads as one integrated structure. This was an important and tantalizing potential, because for many architects in the early 20th century, the key problem of the day was finding a way to bring pragmatic considerations of the engineer together with the architect’s taste for beauty and formal unity. The French architect Perret is generally looked to as the first 20th-century architect to fuse the new medium of concrete with existing attempts to find a modern and modernized expression of architecture.
Greatly influenced by the ideas of Viollet-le-Duc, Abbé Laugier, and especially his mentor Julien Guadet, he sought to extend and embrace classical ideas about proportions and order to the technology of the 20th century. He saw concrete as an ideal medium for creating frame structures, articulating columns in a clear and rational expression of their structural use, rather than clothing and thus obscuring them in cladding. To emphasize the trabeated character of the structural frame at the apartment building at 25 bis, rue Franklin, Perret designed the street-facing fenestration as large as local ordinances allowed. The structure was not clearly articulated; however, Perret used a subtle technique of varying color and texture to distinguish what was load bearing from what was not. By varying the color and texture of the facade panels and by recessing windows and cantilevering the second floor beyond the ground floor ever so slightly, Perret deemphasized the mass-wall characteristics of the concrete. The effort to read the facade like a frame-and-panel assemblage, a more truthful reading of the structure, was Perret’s way of maintaining continuity with the neorational ideas of the past.
The engineer, builder, and pioneer in concrete construction, François Hennebique, acted as consultant on Perret’s project. Hennebique had several patents for concrete members already, and unlike the architect who strove for a homogeneous and uniform structural expression, Hennebique articulated the joints between column and beam by thickening the columns and extending the beams in a cantilevered bracket (Hennebique House, Paris, 1904).
Engineers such as Robert Maillart and Eugene Freyssinet, however, were the first to appreciate concrete’s nonrectilinear potential. Maillart designed arcuated bridges whereas Freyssinet built factories with curvilinear concrete-shell roofs, and perhaps their lack of concern over spatial enclosure allowed them the freedom to experiment more easily with form and thus more fully capitalize on the unique prospects of the material.
Late 19th-century experiments with concrete reinforced by wire mesh produced curvilinear ship hulls that prefigured this later engineering development. Perret by necessity had to think in terms of both space and structure, and influenced by the architectural concerns of his day, he was less willing to depart from the rectilinear norm that marked architectural design at the turn of the century.
Although concrete may have seemed an alternative to the industrial steel aesthetic, ironically architects increasingly saw in the material an opportunity to use it as a medium for expressing the machine age. For many repetition of the rectilinear module was the key. Le Corbusier’s influential post-World War I solution to the housing shortage in Flanders was the Domino housing project. Six concrete columns, three horizontal slabs, foundation blocks, and switchback stairs comprised the fundamental elements of this kit of parts, and the articulation between column and slab was without beams, the trabeation fully embedded and embodied in the clean and ornament-free lines of the steel-reinforced concrete. Le Corbusier asserted this system was an economical solution that could be mass-produced, with wall elements added to complete this housing scheme. Although this model had little practical application during and immediately after the war, it was nonetheless a powerful inspiration among architectural thinkers who sought a fit between modern materials and modern architectural aesthetics. As an idealized shelter, stripped of non-load-bearing elements and reduced to the purity of column and horizontal planar members, it was hailed as a bold gesture toward a new symbolic architectural representation free of historical iconography.
Thirty years later Le Corbusier was busy designing an entire city (Chandigarh, India) out of concrete and masonry, but in 1946 he remarked on an important transformation of thought that had taken place. From a “machine infatuation” to a more “spiritual” pursuit of the material’s potential, he claimed that architects now sought to tease out less sterile formal aspects of concrete. The small music pavilion for the Phillips Company at the 1958 World Exposition in Brussels reveals how concrete could be thought of as more than a respite from historical reference. As a technologically sophisticated building material ripe with technical problems, it was deemed ideal for creating a space that celebrated a marriage between multiple and technologically sophisticated art forms. The project architect, Iannis Xenakis, designed the general layout, leaving Le Corbusier to concentrate on finding formal expression to match the “electronic poem” composed by Edgard Varèse, the multimedia piece that combined visual projection with electronic sound. The architects devised a hyperbolic paraboloid shell to enclose the exhibition space, believing that using concrete here would be economical because this complex form could be created with straight lines and repetitive rectilinear sections. The shells of the paraboloid needed to be thin—too thin, in fact, to cast in place—so the architects sought the expertise of engineers in devising a system of prestressed panels formed on sand in a nearby warehouse, then bolted together and stiffened by longitudinal precast ribs. The Phillips Pavilion, however, was an exception. For the most part, concrete had supplanted stone as the building material of weight and dignity. Although engineers occasionally utilized its fluid-form properties to advantage (see especially the most famous case, the Chapel Notre-Dame-du-Haut by Le Corbusier), architects typically bowed to the thrift of rectilinearity.
Concrete remained a conservative but increasingly popular building material. Louis Kahn’s Salk Institute (1959–65) is perhaps the best example illustrating how an architect could use the modernist idiom to create dignified space. The blank gray laboratory facades alternating with fenestration and the mass of concrete stair towers created a serene yet monumental outdoor court. Kahn christened this space “sublime,” a term repeated by critics at a loss to surpass the analysis of the designer. The spiritual quality of this central but little-used space was the result of the architect’s effort to bring together in an artistic treatment two disciplines that seemed to be yawning further apart in the 20th century.
Again, architecture was to marry the rationalism of science to the romanticism of art, a marriage many architectural thinkers believed was more important than ever after World War II and the advent of what many thought was the ultimate work of science, the atomic bomb. It was, in fact, the technical demands of materials like concrete that led architects like Pier Luigi Nervi, a pioneer in the use of concrete himself, to insist that “architecture is and must be a synthesis of technology and art,” rather than “separate aspects” of a building process. The architect’s role was changing—no longer an agent of technological change, but a mediator of technology. Nervi gave a series of lectures at Harvard University in the early 1960s urging students and practitioners to embrace a disciplinary unity, a sentiment that belied anxieties over the architect’s weakening influence. The technical demands of concrete forced engineers to specialize in its design and maintenance, a task few architects were capable of handling competently. Although a naïve booster of a synthesized design process, Nervi was at least prescient about one aspect of concrete’s future. In those same lectures he predicted that concrete would be utilized as the principal building material in ever-larger public and commercial projects.
Across the globe governments and government agencies, as well as wealthy groups of profit-interested private companies, had already been forcing dramatic interventions in the landscape. Urban renewal and new towns, often composed of largescale multiblock buildings, housing blocks, hotels, convention centers, and government administration centers, came to dominate wherever they were built. Modernist vocabulary did not change by this embrace of the large and the hard as much as it grew in scale. The Brutalism movement grew out of this application of concrete and masonry, and the multilane freeway elevated on giant-sized piers designed entirely by civil and structural engineers came to mark the American urban landscape in particular.
Even before Nervi finished his lectures, a skepticism of this progressive gigantism gained momentum, particularly with such books as Jane Jacobs’s The Death and Life of the Great American City (1964). She fronted a chorus questioning the inhumane character that resulted in part from gross-scaled concrete construction. Although but one of many building materials put to use in this boom, concrete had finally supplanted steel as the epitome of modernity’s failings. Archi tects who achieved fame via an expertise in the design of the monolithic concrete environment watched as their careers withered into obscurity (see especially Paul Rudolph).
The rise of critical regionalism as a critique of modernism, and especially the development of Postmodern architecture, has meant a shift away from the monolithic at many scales. The large-scale concrete block has given way in architectural importance to smaller works that have been built in a whole range of locales across the world. Even large-scale building complexes have been commissioned in smaller pieces to a handful of architects. By the end of the 20th century, however, concrete continued to offer a small number of architects the possibilities of abstract design in a medium affording a range of formal possibilities limited not so much by physics as by budgets. Although concrete remained a vital structural material, as an aesthetic medium it was perceived as a stylistically austere means of creating minimalist space but only at great expense. Architects such as Enrique Norton of Mexico City and Tadao Ando of Osaka relied on many techniques from the modernist boom, using concrete as a decorative as well as spatial and structural medium. They went to the trouble of designing the formwork themselves to create a grid of indentations punctuated by bolt holes left over from the forms during curing. In House Le by Norton (Mexico City, 1995), the three-story concrete facade was articulated with this pattern in a way that softened the otherwise massive plane while maintaining an expression of urban privacy that embodies the heart of this compact courtyard house. Ando’s austere but elegant Church of the Light (Osaka, 1989) used a similar texture derived from impressions left by the formwork. In this case the partitioning of the concrete walls by the grid of form lines gave the finished surface a taut effect, one that makes the mass wall seem more like a tensile surface. The small size of the church, coupled with the application of simple but stark openings articulating one space from the next, meant that as the principal finish material, the concrete was not overwhelming or oppressive.
Political and Economic Influences
Concrete persistently teased architects with the allure of its fluid form and sculptural potential. Steel-reinforced concrete has indeed been designed and constructed as curvilinear elements, but such practice proved expensive because forms typically had to be customized and could not be used repetitively. Using concrete as a finish material meant ensuring a smooth and visually clean and stainless appearance. This required increased care, skill, and on-site inspection, which translated into higher budgets. It is perhaps ironic that at the end of the century, when curvilinear forms had become an obsession for many architects in a wide variety of materials, concrete had become associated with a rectilinearity that Perret would have appreciated 100 years earlier.
The Stone Cloud House by Kyu Sung Woo (Seoul, 1996) reveals the pragmatic uses concrete was often put to at the end of the century. The villa encloses a courtyard that spatially unites the extended family, each unit of the family dwelling in spaces enclosed by castin-place concrete bearing walls, but finished with stone from a local quarry. The stone is arranged in a pattern of square-panel courses that echo the stone flooring as well as the rectilinearity of the various spatial units that enclose the court-yard. The pattern is also vaguely reflective of the concrete it hides and adorns.
The success of concrete as a building material early in the century stemmed in large part from the argument by builders, engineers, and architects that concrete was cheaper than timber and stone. This was true only because the majority of labor required in creating concrete structures demanded less skill and training than stonemasonry. Concrete construction demanded a shift in thinking, a shift that had profound consequences in the construction industry at large. At the turn of the century those few architects, engineers, and contractors who insisted on the application of steel-reinforced concrete strove to bring science into a practice dominated by a craft tradition. In their view the demands of concrete construction meant that technical innovation would prevail over what was perceived as the monopoly of an artisan class. Unlike stone construction, a monumental material that concrete ultimately came to supplant in many respects, concrete requires a small group of highly skilled technicians to ensure a proper and safe construction process. This stratification of labor between the skilled engineers and foremen, and the unskilled and in some cases untrained laborers, proved to be an important and distinctive aspect of the modernization of the building industry as a whole and became typical of virtually every modernizing industry.
Demanding empirical testing both in the laboratory and in the field, as well as inspections that only well-educated and trained engineers were capable of, this new organization effectively diminished the power of older family and regionalbased trade networks. These older craft unions, as historian Amy Slaton has argued, the bricklayers and the stonecutters in particular, “had little influence in the concrete industry, and technological advance helped render their diminished role both possible and permanent” (2000). The success of this managerial transformation has been amply demonstrated by the widespread synthesis of the concrete construction industry across the globe, particularly in the post-World War II period, and its effect on other construction trades. Steelreinforced concrete structures, many resembling in skeletal form Le Corbusier’s Domino house, have appeared in regions where unskilled labor is plentiful. The limiting factor in such construction tended to be set by the cost of reinforcing steel rather than the technical expertise of the engineering profession in the newly liberated nations, many of which realized an acute need for large-scale buildings to house new political, financial, and domestic populations. Many governments, particularly in the Soviet Union, as well as myriad newly independent nations after the war, built large-scale projects in concrete to house the populace. Urban renewal in the United States and postwar reconstruction largely funded by the Marshall Plan vaulted concrete into a position as the preeminent building material during the 1950s and 1960s and even later.
In some regard the modernist effort to make architecture relevant to social and economic problems, an effort epitomized by massively scaled visions of new cities such as Le Corbusier’s plans to remake Paris, came as near realization during this period as it ever would. Although concrete was by no means the only material put to use in these grand visions, by the 1970s it was a material that not only seemed to epitomize modernity and modernization both materially and politically, it had become inextricably associated with the problems of excess and scale in both socialist and capitalist planning.
Sennott R.S. Encyclopedia of twentieth century architecture, Vol.1 (A-F). Fitzroy Dearborn., 2004.