After a gap in engineering research and development during the Dark Ages, the West moved slowly towards an investigation of concrete’s potential.
Held back by poor access to pozzolanic materials, stone and mortar remained the civil and architectural engineering material of choice in the majority of European centers. In some regions, work progressed towards eventual rediscovery of hydraulic cement and sophisticated admixtures. Concrete development continues into the present, with the application of biomimetic admixtures and continuing refinements in production, composition, and tensile reinforcement of concrete materials.
(Part of a series on the history and future of concrete technology. Part One is available here.)
“A Hidden Fire in Heated Lime”
After the fall of the Roman Empire, significant chemical and structural engineering knowledge was lost – including the proper composition and use of sophisticated Roman cements. The quality of mortar declined sharply, halting massive concrete construction for almost a thousand years.
It wasn’t until the 1300s that development began again, in earnest, with a rediscovery of pozzolanic reactions. Given the analytical tools available at the time, of course, engineers were restricted to learning through trials and experiments rooted in Classical engineering texts. These efforts were accelerated with the recovery of Pollio Virtruvius’s writings in 1414, but the core reactions remained mysterious. Even in 1678, Joseph Moxon – mathematician, cartographer, Royal Society Fellow, and author of the classic Mechanick Exercises – could only offer that there was “a hidden fire in heated lime” exposed to water.
The Eddystone Lighthouse
One-hundred and six years later, Rudyard’s lighthouse burned down.
This was the second lighthouse to guard the Eddystone Rocks, a formation just outside the Plymouth Sound. They were a hazard to Channel shipping until the beginning of the Eighteenth century, when Henry Winstanley erected the fist lighthouse. It was an unenviable task; the rocks were a nightmarishly difficult site and Henry was abducted by privateers. (The direct order of His Majesty Louis XIV freed him.) Five years into service, the Great Storm of 1703 smashed his lighthouse to splinters.
An entrepreneurial sea captain commissioned John Rudyard to erect a combination of lighthouse and toll booth on the rocks in 1709. His design called for a central column of masonry within a larger, wooden structure, and burned to the ground forty-six years later.
Work began on Smeaton’s Eddystone Lighthouse within the year.
Civil engineers should recognize the name; John Smeaton is the father of their trade. He was the first in modern history to identify himself as a civil engineer, contributed foundational mechanical and scientific insights to the Industrial Revolution, and uncovered some of the mathematical relationships between pressure and velocity underlying early aerospace engineering.
Smeaton saw the lighthouse as a perfect application for his work redeveloping hydraulic lime. After exhaustively testing lime, soil, and admixtures, Smeaton produced the closest match yet for Roman hydraulic lime concrete. Combining his new concrete with innovative stone joinery techniques, Smeaton’s Eddystone Lighthouse was a civil engineering marvel. It stood for a century, until erosive undermining exposed the structure to excessive tensile stress during high seas. The lighthouse began to sway at high tide and was quickly abandoned.
The Origins of Portland Cement
In 1824, an English bricklayer named Joseph Aspdin made the first key contribution to modern Portland cement by calcinating ground lime and clay. He named the design mix due to a resemblance between the cured concrete and stone quarried from the Portland area. While he is credited with inventing modern Portland cement, a number of his contemporaries contributed important work to its development.
Aspdin’s process was relatively low and slow. This, and proprietary control of the design mix, kept prices high. Commercial competition lead Isaac Charles Joseph, a chemist and plant manager for the JB White cement company, to reverse engineer Aspdin’s product with considerable process improvements in 1845.
Key to Joseph’s process was clinkering. When ground clay and limestone are heated to between 1430 and 1650 C, the two form grayish, spherical pellets of nearly uniform composition known as “clinker”. Adding gypsum to control set time and grinding the mixture to between 5 and 45 um yields Portland cement.
Josephy’s cheaper, more uniform design mix was a tremendous commercial and engineering success, making widespread experimentation with reinforcement of large structures practical.
The Reinforced Concrete Revolution
Tensile stresses doomed the Eddystone Lighthouse. While concrete has impressive compression strength, it cracks under tensile stress unless reinforced. Active development of reinforcement solutions was necessary before concrete use could approach modern levels
The first reinforced concrete building was erected in 1854, by a plasterer named William B. Wilkinson. It was a two-story servant’s dwelling with concrete walls, floors, and roof. His French contemporary, Jean-Louis Lambot, experimented earlier with concrete boats and secured a patent covering the use of reinforced concrete as an architectural and Naval building material in 1856.
Iron-reinforced concrete was accepted practice within the decade. Large-scale builders and developers made use of it in the latter half of the nineteenth century, most notably in the concrete homes of Francois Coignet and the sprawling concrete empires of Ransome, Wayss, and Hennebique. Ransome specialized in the construction of massive industrial and public buildings, such as the Leland Stanford, Jr Museum, at the University.
Ransome’s work would be adapted to design the Ingalls Building, the world’s first concrete skyscraper.
Hennebique, more of a builder, created a thriving franchise network of construction offices throughout France and Belgium. Employing a proprietary reinforcement system, his company took on 1,500 contracts per year around the turn of the twentieth century. Perhaps more than an other, single individual, he is most responsible for the popularization of Portland cement concrete construction in Western Europe.
Shell forms for reinforced concrete were soon to follow, restoring the material to its Classical versatility. Hennebique’s contemporary, Auguste Perret, cast buildings such as the Theatre Champs Elysee (1913) and Notre Dame du Raincy (1922, an acknowledged masterpiece). In Mexico, the soaring arches and parabolic structures of Felix Candela proved that modern design mixes, reinforcement techniques, and methods of application enabled new levels of architectural and engineering freedom. Massive infrastructure projects followed, such as the Hoover, Three Gorge, and Grand Coulee dams.Image Source: “Eddystone Lighthouse” (The Smeaton lighthouse) engraved by W.B.Cooke, 1836
The Modern Cement Industry
According to the US Geological Survey, domestic cement production in 2010 came to 61 million tons of Portland cement and 1.8 million tons of masonry cement. These numbers are part of a Western trend in decreased cement production since 1975; four years earlier, in 2006, combined production totals were close to 98 million tons, and the 2010 numbers are the lowest in twenty-seven years. Reduced demand lead to a wave of plant closures, idling, and capacity reduction in active plants (eliminating excess kilns or increasing maintenance downtime on active processing equipment).
This trend echoes in Europe, as well, with mature markets lowering their concrete consumption figures by anywhere from twenty to forty percent.
In China and India, on the other hand, capacity and consumption are very much on the rise. Over forty-four percent of global concrete production takes place in China, 1.8 of 3.3 million tons. Clinker production is very energy intensive (requiring 200kg of coal per ton of cement), so the massive growth in Chinese and Indian concrete consumption may complicate efforts to control atmospheric carbon dioxide levels.
Reducing carbon pollution, increasing tensile strengths, and improving field performance of concrete design mixes are ongoing targets for materials and civil engineers. In the last article of our concrete series, we’ll pull together some of their most interesting lines of research.
Why not share your favorite concrete facts and megaprojects, modern or historical? Leave a note in the comments or tweet @EngineerJobs.Featured Image by Matthias Rhomberg