Popular Mechanics recently published an article on the history of concrete. The extended history article begins 12,000 years ago … The invention of concrete is a story of ancient discovery, experimentation, and mystery. Emperors and kings became legends for erecting great concrete structures, some of which are still standing, yet still a mystery to engineers today. Many of history’s skilled architects found inspiration in slabs of the gray building material, common bricklayers advanced the technology, and a con man played a crucial role in the development of concrete recipes.
The First Cement—and Maybe Concrete?
Cement and concrete are not the same. Cement is an ingredient—a mixture of powdered limestone and clay—added to water, sand, and gravel to make concrete. Concrete was made possible by the development of cement, and to trace the history of cement, we must trace the use of its components.
10,000 BCE to 8,200 BCE
The earliest known use of limestone in a structure was found in the Göbekli Tepe temple in modern-day Turkey, from about 10,000 BCE—7,000 years before the Great Pyramid of Giza. Göbekli Tepe is the oldest known example of monumental architecture—the first structure human beings put together that was bigger and more complicated than a hut. The cleanly carved, T-shaped pillars of the Göbekli Tepe were made of limestone—splashed with bas-reliefs of animals … a cavalcade of gazelles, snakes, foxes, scorpions, and wild boars. When these pillars were erected, so far as we know, nothing of comparable scale existed in the world.
Over the next several millennia, cultures around the world developed better building materials, some of which might be seen as a kind of proto-concrete.
2325 BCE
Archaeologists have questioned whether an early form of concrete can be found in the Egyptian pyramids. One of the Seven Wonders of the Ancient World, the pyramid of Giza is the oldest, largest of the three pyramids bordering what is now El Giza, Egypt, and only one to remain largely intact. The hypothesis holds that the immense blocks toward the top of the Great Pyramids of Egypt might have been cast in molds to give them their shape—the world’s first concrete—instead of just carved whole from quarries, and hoisted into place. Most archaeologists believe that they are made of limestone, and possibly naturally contained clay. Linn Hobbs, Professor, Materials Science-Massachusetts Institute of Technology (MIT) said, “It could be they used less sweat and more smarts. Maybe the ancient Egyptians didn’t just leave us mysterious monuments and mummies, but invented concrete 2,000 years before the Romans started using it in their structures.” That is a notion that would dramatically change engineering history.
GREEKS
According to Robert Courland’s book Concrete Planet: The Strange and Fascinating Story of the World’s Most Common Man-Made Material, the Minoans of Crete used an artificial building material for floors, foundations, and sewers. Maybe it was a mixture similar to the concrete known today—clay with volcanic ash: Today’s pozzolana derived from Pozzuoli, Italy.
200 BCE
ROME
Volcanic ash also helped the Romans create the first known concrete in the world—and the strongest concrete humanity has ever seen. The Latin term “concrete” is derived from concretus, meaning “to grow together,” just the way the components of concrete mix to form a solid building block. But the Romans called their concrete caementis, meaning “rocky stuff”, and caementis is the word that gave us “cement”. Roman concrete is impressive because of its ability to endure substantial weathering, survive earthquakes, and crashing sea waves.
Ancient Romans built ramps, terraces, and roads with concrete made in much the same way we do today—mixing kilned limestone with water. They added volcanic pozzolana to thicken the mixture, ground rocks, and sand. In a semi-liquefied state, the mixture was then poured into carved wooden molds to create smooth, sturdy pieces of concrete, which allowed the Romans to build vaults, domes, and the arches of the empire’s great aqueducts. By 200 BCE, the Romans began making walls out of concrete and coating it with brick masonry, as they preferred the aesthetics of brick. After the Great Fire of Rome in 64 CE that destroyed 10 of the city’s 14 districts, concrete was revealed to be fire-resistant—though not fireproof—so the outer brick helped in that regard.
23 BCE
ISRAEL—SEBASTOS HARBOR
During a time when concrete was still a largely unproven material, concrete’s rise to prominence within the Empire began with the daring engineering feat of Sebastos Harbor in Caesarea, Israel. King Herod of Judea, whose land was a territory of the Roman Empire, wanted to improve his kingdom’s economy, and to build a better port on the shores of the Mediterranean Sea. It was the perfect test of concrete’s resilience.
Construction of the harbor took eight years, and was the second largest harbor in the world (first was Alexandria in Egypt). The jetties and seawalls were made of pure concrete, likely lowered into the water with a crane. Divers—holding their breath—went into the Mediterranean to position each heavy piece of concrete, aligned them, then tamped them down. Five years after the harbor was completed, the city of Caesarea finished construction, and the thriving port earned King Herod the title “Herod the Great.”
More than 2,000 years later, the concrete harbor is still intact, submerged under the Mediterranean. Sebastos Harbor was only the beginning: The Romans would go on to erect some of the most famous concrete structures in the world.
70 CE
Peak of Roman Concrete—ROMAN COLOSSEUM
In 70 CE, General Flavius Vespasianus “Vespasian” became Emperor and set out to build the largest theater in the world, and the world’s first stadium. He called it The Flavian Amphitheater, known today as the Roman Colosseum, which held more than 50,000 spectators, and provided a full elliptical view of the events from every seat. Completed 1,937 years ago, it stands today as one of the enduring symbols of the Roman Empire. According to Concrete Planet, the Colosseum is made of concrete and brick, with concrete found throughout the arena and 80% of the foundations. After the course of two millennia of bumps, bruises, earthquakes and lightning strikes, about one third of the original construction is left today, and literally a testament to the endurance of Roman concrete.
117 CE
THE PANTHENON
The most pristine ancient concrete structure in Rome was not built for the people. “The Pantheon” was Emperor Hadrian’s brainchild and his grandest structure as a testament to the gods, with the largest dome the world had ever seen. The engineers who constructed the great temple of Rome were far ahead of their time. How did Hadrian and his engineers create the Pantheon to be sturdy and last through today … more than 1800 years? They tinkered with the concrete recipes. The dome—poured into a curved wooden mold, a perfect half sphere, propped up on scaffolding—contained a bit more volcanic ash than rock to make it slightly lighter, while the walls contained much more rock aggregate, and bricks interiorly and exteriorly, to make them heavy and strong. But to this day we still don’t know all the secrets of the Pantheon. When the Western Roman Empire officially fell in 476 AD, the recipe for the Pantheon’s concrete was lost to history.
1500 CE
THE RENAISSANCE
It took over a millennia for concrete to make a comeback. Europe went through the Dark Ages, and ancient Roman texts were not rediscovered until the Renaissance. Renaissance engineers studied Vitruvius’s On Architecture, but with no knowledge of the mysterious gray building material, scholars could not decipher the terminology.
In the early 1500s, Giovanni Gioconda, an Italian friar trained in archaeology and architecture, was able to crack the code. Giocondo noticed something impressive about caementis. Its resistance to weathering suggested it must be hydraulic, meaning it hardens under water, so Giocondo replicated concrete by building structures that mixed lime and pozzolana, as Vitruvius’s On Architecture, instructed. The original Pont Notre-Dame Bridge was his first attempt. Giocondo’s efforts would go down in history as the only attempt to create concrete during the Renaissance. But bigger breakthroughs were on the horizon. In 1786, the structure was demolished because houses had been built atop the bridge, putting too much stress on this primitive version of concrete. For a detailed history of the original bridge, download the PDF titled “The Planning and Building Process of Two Paris Bridges in the Sixteenth and Seventeenth Century”: https://www.arct.cam.ac.uk/Downloads/ichs/vol-2-2223-2240-mislin.pdf
1700’s
GERMANY—TRASS
In Andernach, Germany, trass was discovered—a volcanic ash similar to pozzolana. A bricklayer tried using it in lime mortar, a mixture quite similar to concrete, and learned that the resulting material was stronger and water resistant. The result was a chain reaction that led to the creation of modern cement. The Dutch began selling trass to France and Britain for buildings that required hydraulic properties. Through constant conflict and competition, France and Britain began efforts to create their own hydraulic building materials.
1750s
BRITAIN
John Smeaton from Britain, known as “The Father of Civil Engineering”, created a formula for air pressure’s effect on an object’s velocity, which contains the “Smeaton Coefficient”. And more than a thousand years after the fall of Rome and the loss of concrete’s secrets, Smeaton rediscovered how to make cement and was commissioned to build a lighthouse on a troublesome perch on the Eddystone Rocks, England’s southern coast. After three lighthouses on the site had all been destroyed—First by winter; second in a hurricane; and third wooden-interior one by fire from the light. Smeaton, up to the challenge, was determined to build the strongest lighthouse in the world.
He discovered that lime by itself dissolved, but the lime combined with trass endured. He experimented with known hydraulic materials, rolled up balls of lime (the cooked version of limestone) and trass, then dropped them into boiling water. He then tested limestone from the town of Aberthaw, dropping it into water and a nitric acid solution used to separate minerals, revealing that about 1/10th of the limestone from Aberthaw contained clay. Smeaton took note of the high strength of this limestone-clay conglomerate, and using his hydraulic cement-filled mortar, constructed the Seaton lighthouse between 1756 and 1759. Today we call the same material natural cement. Over 100 years later, the rocks beneath the lighthouse had eroded, so the lighthouse was disassembled and rebuilt in Plymouth, England in 1882.
Every businessman in Britain wanted to capitalize on the new building material. For marketing purposes, manufacturers started referring to their natural cement as “Roman cement”. Deception in the concrete business would follow, and in a stroke of luck, lead to even sturdier materials.
1820s to 1850s
PORTLAND CEMENT and The Con Man
Joseph Aspdin, a bricklayer from Leeds, England stole bricks of limestone from the paved roads of town. He was fined twice, but the limestone thief continued off with the bricks for his materials science tests. Aspdin managed to invent his own cement mixture, named “Portland cement” after Isle of Portland. Like the term “Roman cement”, the name “Portland cement” became a marketing scheme.
But, Joseph Aspdin’s son William was the con man. Young William left Leeds to find his own way in London. During this time, there was a common engineering practice called slurry mixing in which powdered un-kilned limestone was mixed with clay and water. The concoction turned into a paste, then the paste was then kilned into a solid and crushed, turning it into cement powder. If the paste was kilned too long, the resulting material called “clinker” was generally thrown out.
William decided to test the unwanted scraps of clinker, and began taking the clinker “off cement makers’ hands”. He used a hammer to break it down, mixed it with the other cement materials, creating a new cement that years later would confirm to be twice as strong as strong as “Roman cement”.
With no employees and no kiln, William Aspdin had created a cement that was better than the rest. He found investors who knew nothing about the cement industry, egregiously lied about his product to the public, swindled his partners, and started all over again. For his first cement firm, William wrote that his cement had been around for years in Northern England, fraudulently claiming his own “Portland cement” was the same recipe his father had developed. The first firm went bankrupt.
William began a second firm with new inexperienced investors, using one of his previous factories. He published more lies, claiming that his father’s Portland cement had been around since 1821, and that it was used in one of England’s most grueling construction projects where several men died due to flooding during construction—the Thames Tunnel. William lied, claiming that workers used Portland cement to patch up holes, but in reality was that holes were patched with only clay. William’s second firm failed.
During his third business enterprise, the board of directors granted him 300 GBP to invest in the factory and to buy a steam engine. He did, but for only 80 GBP, forged the receipt and kept the rest of the money. Learning of the forgery, the board of directors investigated and learned that he had swindled them from the beginning—created records of fake employees, took home the salaries, and embezzled funds. He was out.
But, by the 1850’s he quickly found another investor and started a fourth cement business. Competitive firms tried to figure out the recipe for his Portland cement, so to hide his secret of over-kilning the cement mixture, he displayed different chemicals on the open floor of his factory for everyone to see. Eventually, he stopped paying rent on the factory and was arrested for longstanding debts. William went to Germany and bounced from cement business to cement business, ultimately dying in 1864 at age 48 from a head injury obtained during a fall. A century and a half later, we still use his Portland cement.
1850s to 1880s
The Birth of Modern Concrete and Rebar
In the mid-1800s, most industrialized countries were making Portland cement on their own. Around this time, the United States, Britain, and France each had the same idea to increase concrete’s tensile strength, or its ability to resist an exerted force. Concrete was poured over iron bars to form reinforced concrete.
In the 1880s, Ernest Ransome, a California Engineer, began his construction firm. Ransome noticed that reinforced concrete tended to crack, subsequently weakening significantly. He successfully experimented, using 2-inch iron rods to see if they’d bond with the concrete. Ransome then successfully twisted the iron bars in accordance with the concrete’s desired shape. He called his idea the “Ransome system”. Today it is called the reinforcing bar, or rebar, and modern engineers typically use steel.
Ransome’s first rebar concrete building was the Arctic Oil Company Works warehouse in San Francisco, completed in 1884. In 1889, he built the Alvord Lake Bridge in San Francisco—the world’s oldest surviving reinforced concrete structure.
1865
WORLD’S FIRST CONCRETE PAVEMENT built in in Inverness, Scotland
1872
CONCRETE PAVEMENT in Edinburgh, Scotland—is still in use today!
1891
FIRST CONCRETE PAVEMENT in North America!
In 1891, George Bartholomew built the first concrete street in Bellefontaine, Ohio.
1899 the Vienne River Bridge, Chatellerault, France, is one of the most famous reinforced concrete bridges in the world. Canals, like the Panama Canal, are also made of concrete. Factories, offices, and bunkers built during the World Wars all used concrete.
1903 to 1935
World’s First Skyscraper and Frank Lloyd Wright
In 1903, construction was completed on the world’s first concrete skyscraper—the 16-story Ingalls Building in Cincinnati. Ransom was not personally involved in the skyscraper’s construction, but it would not have been possible without his reinforcing bar method.
Famed architect Frank Lloyd Wright paved the way for reinforced concrete’s use in modern architecture. Concrete poured into a mold can be formed into shapes that even the most skilled masons could never achieve. Wright’s first concrete building (from 1905 to 1908) was Unity Temple in Oak Park, Illinois, is considered to be the world’s first modern building. A Mayan-inspired decoration along the top of the building is carved into concrete. The concrete was poured into the mold and over the rebar very slowly and meticulously to ensure it would set smoothly.
Wright would become the United States’ preeminent architect. He incorporated concrete into many of his designs. In 1935, the material was used liberally in perhaps his most famous work: Fallingwater in Mill Run, Pennsylvania. Fallingwater would not have been possible without Ransome’s reinforced concrete. Wright’s idea of Fallingwater was to seamlessly integrate humanity and nature. The building is a U.S. National Historic Landmark and considered one of the greatest works of American architecture in history. Ever since Ransome developed the perfect rebar, concrete has been used to build all types of monumental buildings and infrastructure works.
1936 The Hoover Dam was built to hold back the mighty Colorado River, contains 3.25 million cubic yards of concrete, with an additional 1.11 million used for the powerplant and surrounding structures.
1956 and 1992 The American Interstate Highway System is also made of reinforced concrete.
The Future of Concrete
In general, modern concrete can last about a century without major repairs or replacement, according to Concrete Planet. Some of the toughest buildings in the world rely on a concrete foundation. Others, like the Sydney Opera House, are considered symbols of their country. And yet even now, in this 21st-century concrete jungle, there may be ways to improve the famed gray building material. Rebar made the modern world possible. But in terms of longevity, reinforced concrete is no match for what the Romans used, because rebar oxidizes and rusts over decades. Seawater is particularly harmful to rebar, as the salt will corrode the steel within just five decades. Freeze-and-thaw cycles leave cracks in concrete roads as well, and while spreading salt will deter ice formation, it harms the rebar just as seawater does. Roman concrete is not just waterproof—it actually strengthens when in contact with seawater. A recent report suggests it’s possible to replicate the Roman concrete of Sebastos Harbor and the Pantheon. Volcanic ash pozzolana was fundamental to the strength of ancient Roman concrete, though we still have not pieced together the full recipe. In July, researchers announced they would use similar volcanic ash off the coast of California in an attempt to solve the ancient mystery. The goal is to reverse-engineer the process that created the most durable concrete in history. A combination of Rome’s secret concrete recipe and modern rebar engineering techniques could allow concrete to revolutionize infrastructure and architecture yet again.
Today, the world is filled with concrete. The word itself has become a synonym for something that is real and tangible. Press your handprints into the sidewalk and sign your name to history!
For the ISCP article on this ancient concrete in the sea titled: “Scientists Research as to Why Roman Concrete Lasts Millennia, While Modern-Day Concrete Lasts a Half Century”, please go to: https://www.concretepavements.org/2017/07/11/scientists-research-as-to-why-roman-concrete-lasts-millennia-while-modern-day-concrete-lasts-a-half-century/
For links, please go to:
Entire Popular Mechanics article: http://www.popularmechanics.com/technology/infrastructure/a28502/rock-solid-history-of-concrete/
“Göbekli Tepe” in National Geographic: http://ngm.nationalgeographic.com/2011/06/gobekli-tepe/mann-text
“Did the Great Pyramids’ builders use concrete?”: http://www.nytimes.com/2008/04/23/world/africa/23iht-pyramid.1.12259608.html
“The Great Pyramids of Egypt”: https://en.wikipedia.org/wiki/Great_Pyramid_of_Giza
“Colosseum” in National Geographic: http://www.history.com/topics/ancient-history/colosseum