Concrete is such a given in our daily lives that it’s entered our vocabulary: When we say something is “concrete,” we mean it’s substantial, solid, permanent, to be counted on. Plus, most of us spend our lives on and around concrete, on sidewalks and roads, inside buildings and structures that are all constructed with the miraculous material. Without concrete, the developed world would look radically different.
Did you ever wonder, though, where concrete originated and how it came to be everywhere in modern life? There’s a long and impressive history behind this important building material, beginning thousands of years ago, even before the Egyptian pyramids, spanning through the time of the Romans’ unprecedented structures, and reaching forward into modern construction.
We’ll take a look at what concrete is (and isn’t), how it came into being, how it played a part in creating the great cities and monumental buildings of the world, and how it shapes our lives every day.
An Important Distinction: Cement vs. Concrete
Before delving into the history of concrete, there’s one important misconception that needs to be cleared up first: Concrete is not the same thing as cement. Although the two words are often confused for each other, there’s one main distinction: Cement is an ingredient in concrete.
Cement is made from varying combinations of limestone, clay, shells, chalk, shale, slate, silica sand, and sometimes even blast furnace slag or iron ore. These ingredients are crushed then heated at high temperatures to result in a material called clinker. Gypsum is added to the clinker, then the whole mixture is finely ground to produce cement powder.
Just add water, and the process gets interesting. Hydration is the process that happens when the minerals contained in cement powder — calcium, silicon, aluminum, iron, and others — form chemical bonds with water molecules. As this process finishes, the water evaporates and the paste dries, leaving behind these bonds organized in a rock-like substance.
So, concrete is a mixture of this cement-and-water paste and a sand-and-rock aggregate. The paste coats the surface of the sand and rocks, binding them together into the concoction we know as concrete. In its soupy liquid form, concrete can be formed into just about any shape the builder wants — sheet, column, block, slab, arch, bowl, etc. Once the water in the paste dries, the concrete becomes hard as a rock and retains that shape.
Cement generally makes up about 10-15 percent of the concrete mix. Nearly all types of concrete use Portland cement. It’s not a brand name, but instead a recognized type of cement that’s used widely across the industry (think “stainless steel” or “sterling silver”). Its originator named his concoction for the high-quality building stones found at a nearby quarry in Portland, England.
Hard Facts About Concrete
Concrete became so popular (and has remained that way) because of its three prominent qualities: plasticity, durability, and economy. When it’s wet, concrete can pour into virtually any shape, fit into any space, fill practically any void, coat nearly any surface. But once it dries and cures, it holds its shape, becoming stronger, harder, and more settled over time.
Concrete that’s made with the right concentration and under the right conditions can be waterproof, stormproof, and fireproof. And owing to that durability, it lasts essentially forever. A million years from now, when all the steel we used to build our world has rusted through and the wood has rotted into dust, it’s concrete that will remain.
But concrete is not only strong; it’s also economical enough to support a global industry that produces more than 2 billion tons of concrete each year — which averages out to about 5 tons per person per year, an already shocking rate which is expected to double by 2050! China alone poured more concrete for construction between 2011 and 2014 than the U.S. did during the last hundred years.
If you find those facts surprising, follow us down “the concrete road” through a timeline of other fascinating advancements. You’ll see how concrete became the material that literally paved the way for life as we know it today.
Concrete History Through the Ages
So how did we arrive at the current state of concrete? Through a process of evolution, like so many other means of construction and development. First, ancient people made discoveries about naturally occurring materials they could use it to improve fundamental parts of their infrastructure — homes, fences, wells, etc. The generations who followed them built upon that knowledge, making improvements here and there until the industrial age descended and sped up building developments to their current level.
Origins and Precursors
On land that is now Israel, spontaneous combustion produced reactions between limestone and oil shale, resulting in natural deposits of “naturally occurring cement” that would make possible the future formation of concrete.
Limestone — also often called “lime” — plays the earliest role in the story of concrete, as the base ingredient in cement, and it’s been used for millennia. Predating another massive stone temple, Stonehenge, by 6,000 years, the Göbekli Tepe in modern-day Turkey was the earliest known limestone structure. Limestone made up the T-shaped pillars of this temple, which were built and carved by prehistoric people who had not yet developed metal tools or even pottery.
The first concrete-like structures, secret underground cisterns for storing scarce water, were built by Nabataea or Bedouin traders who developed a small empire in the desert oases of southern Syria and northern Jordan. Some of these cisterns still exist in those areas today.
In the former country of Yugoslavia, in the area of Lepenski Vir along the Danube River, huts were found in the mid-1960s with a semblance of concrete floors. The lime cement that was used probably came from a deposit upriver and was mixed with sand, gravel, and water to resemble concrete mixtures of our time.
Monuments of Antiquity
Limestone rocks or concrete blocks? Despite some hotly debated speculation about blocks in the Egyptian pyramids being formed with an early type of concrete more than 5,000 years ago, it’s more widely believed across the field of archaeology that the limestone blocks were hauled from quarries nearby. To make the mortar for holding the blocks together, the builders mixed straw with mud that contained crushed limestone, gypsum, and clay.
The Minoan society on the island of Crete, forerunners to the Greeks and credited as the first European civilization, used a building material that mixed clay and a type of volcanic ash called pozzolana for building for floors, foundations, and sewers.
Middle Eastern builders burned limestone and mixed it with water, then used the mixture to coat the outsides of their pounded-clay walls. When the mixture reacted with the air, it formed a hard, protective surface — and laid the foundations, so to speak, for modern versions of cement.
The Mycenaeans used their early form of cement to build tombs. You can see some of them today in the Peloponnese in Greece.
The northern Chinese used a form of cement for building boats and their section of the Great Wall. Over the centuries of the wall’s construction, materials used for its entire span included reeds, willow branches, wood, compacted sand, mud, and 100 million tons of stone and brick. Where these weren’t cemented by limestone mortar, they were held together by a mortar made of glutinous, sticky rice.
The same Bedouins who pioneered underground cisterns later built kilns to produce a rudimentary kind of hydraulic lime — cement that hardens underwater — for waterproof mortar that advanced the construction of houses, floors, and newly waterproof cisterns underground.
From Roman Empire to Renaissance
The Romans started with the same raw materials as the Minoans — volcanic ash found near Pompeii and Mount Vesuvius, which they used to thicken a mixture of kilned limestone, ground-up rocks, sand, and water — allowing them to build ramps, terraces, and the roads that eventually connected the whole empire. Pouring the mixture into molds soon allowed builders to create vaults and domes, as well as the arches of the empire’s iconic aqueducts and bathhouses. Roman concrete has endured earthquakes, lightning strikes, crashing sea waves, and thousands of years of weathering.
After Rome’s civil war, the emperor known as Vespasian set out to build the largest theater in the world, with more than 50,000 seats. Today we know the world’s first stadium, completed 1,937 years ago, as “The Colosseum.” About a third of the structure still stands nearly two millennia later, an iconic symbol of the Roman Empire.
Rome’s Pantheon, soon to celebrate its 1,900th birthday, is as sturdy as ever. The temple’s unreinforced concrete dome was twice as wide and high as any dome ever created at the time, spanning 143 feet with its famed “oculus” in the center. Its mammoth weight is buttressed by incredibly thick concrete walls and eight barrel vaults, all reinforced with brick — but no internal support.
Today’s engineers wouldn’t dare build an unreinforced dome of that size, and they may never know the secret to the Pantheon’s enduring stability. We do know that Emperor Hadrian’s engineers adjusted the concrete recipes, using more volcanic ash than rock to make the dome lighter, and more rock aggregate in the walls for heavier reinforcement. But when the Roman Empire fell in 476 AD, the unprecedented Roman recipe for concrete was lost to the world.
Just after the Dark Ages, an Italian friar named Giovanni Giocondo built the Pont Notre-Dame Bridge in Paris using remnant information from the ancient Roman cement recipe. About 250 years afterward, the structure was demolished because houses built atop the bridge added too much weight. Giocondo would go down in history as the only person to attempt building with concrete during the Renaissance.
Advancements in Concrete
A bricklayer in Andernach, Germany, tried mixing volcanic ash called trass with lime mortar. The resulting material was water-resistant and strong — and the chain reaction started by the discovery would lead to the creation of modern cement.
In the 17th century, the Dutch (who were already adept at building in water) sold trass to France and Britain for use on buildings that required waterproof properties. The two rival countries immediately began competing to create their own hydraulic building materials.
When British civil engineer John Smeaton was commissioned to build a new lighthouse on the Eddystone Rocks in Cornwall, England, he set about searching for the most durable and waterproof building material he could find. After finding limestone nearby with a high concentration of clay, he fired it in a kiln and turned it into clinker. He ground it into powder and mixed it with water to create a paste, with which he built the lighthouse.
In the process — and more than 1,000 years after the secrets of concrete were lost — Smeaton rediscovered how to make cement. Before long, manufacturers started marketing his discovery as “Roman cement.” And the Eddystone Lighthouse stood for nearly 130 years, outlasting the rocks that eroded out from under it.
Englishman Joseph Aspdin refined the process by carefully proportioning limestone chalk with clay and burning the mixture in a kiln until the carbon dioxide was removed. He also heated alumina and silica until the materials became glass-like, then pulverized them and added them into the limestone mixture along with gypsum.
The resulting chemical combination of calcium, silicon, aluminum, iron, gypsum, and other mineral ingredients makes up the distinct formula for Portland cement, the basic ingredient of concrete. Aspdin named the result “Portland” cement because it resembled the high-quality building stones quarried in nearby Portland, England.
The first testing of concrete’s tensile and compressive strength took place in Germany. Tensile strength is the ability to resist tension or pulling apart; compressive strength is the ability to resist compression, or pushing together.
A French gardener, Joseph Monier, experimented successfully with pouring concrete over a steel mesh. (Concrete and steel expand at a similar rate when they heat up, making them a perfect pairing). Monier patented several variants of his invention for use with railway sleeper cars, building slabs, and pipes. Reinforced concrete is much stronger and more practical than the unreinforced stuff. It can span larger gaps, allowing concrete to soar in the form of bridges and skyscrapers.
California engineer Ernest Ransome began testing concrete and 2-inch iron rods to see if the materials would bond. When they did, Ransome went a step further by twisting the iron bars to create an armature around which he could “build” concrete into any desired shape — an experiment which also worked. Today we call this system reinforcing bar, or rebar, although modern engineers typically use steel instead of iron.
Ransome’s system soon would be used in commercial buildings, roads, bridges, and even the first skyscrapers. Famed architect Frank Lloyd Wright began to implement rebar concrete technology in modern architecture. Some of Wright’s most famous buildings — including Unity Temple in Oak Park, Illinois, considered the world’s first modern building; and Fallingwater in Mill Run, Pennsylvania, his most celebrated work — were made of reinforced concrete.
The process of prestressing steel was patented to make concrete stronger and allow engineers to use less steel and concrete.
Modern Concrete Structures
Ever since Ransome developed the use of rebar, concrete has built all types of monumental buildings and infrastructure works. The Panama Canal, World War II bunkers, and the famed Sydney Opera House share a building material with some of the toughest — and most visionary — buildings in the world.
Alvord Lake Bridge was built in 1889 in San Francisco, CA. The first reinforced concrete bridge, it survived the 1906 San Francisco earthquake and others with no damage. It still exists today, more than 100 years after it was built.
In 1891, a man named George Bartholomew built the first concrete street in America in Bellefontaine, Ohio. Today, pervious concrete is being advocated as the best, and most environmentally friendly, surface for streets.
In Cincinnati in 1903, Ransome’s system made possible the first concrete high-rise, the 16-story Ingalls Building. That neck-breaking height made the skyscraper one of the great engineering feats of its time.
The Vienne River Bridge in Chatellerault, France, built in 1899, is one of the most famous reinforced concrete bridges in the world.
The nation’s first concrete homes were designed and built in Union, New Jersey, by none other than Thomas Edison. These homes still exist today.
The first load of “ready-mix” was delivered in Baltimore. Having concrete mixed in one place (a central plant) and then delivered by truck for use at a job site was a revolution for the concrete industry.
Lynn Mason Scofield founded L.M. Scofield, the first company to produce color for concrete. Their products included color hardeners, color wax, integral color, sealers, and chemical stains.
In 1930, air-entraining agents were used for the first time in concrete to resist damage from freezing and thawing — a decided boon to cold-weather building practices across the United States and the world.
The Hoover Dam is located on the border of Arizona and Nevada. Completed in 1936 to hold back the mighty Colorado River, the dam is made of 3.25 million cubic yards of concrete, with an additional 1.11 million used for its power plant and surrounding structures.
All of America’s roads in the interstate highway system are made of reinforced concrete.
The first sports arena with a concrete dome was built on the campus of the University of Illinois at Urbana-Champaign in 1963. Known as Assembly Hall, the arena looks like a flying saucer and seats more than 16,000 in a perfect concrete circle.
Fiber reinforcement, in which glass, carbon, steel, nylon, or other synthetic fibers are mixed into wet concrete before pouring, was introduced as a way to strengthen concrete. Fiber reinforcement can be used to strengthen buildings as well as outdoor features from driveways, slabs, and sidewalks to swimming pools, patios, and decks.
At 65 stories, the skyscraper at 311 South Wacker Drive in Chicago was the world’s tallest reinforced concrete building at the time it was built. The postmodern structure is known only by its street address.
The Future of Concrete?
Concrete was once thought to be the answer to the world’s building problems; it’s malleable when wet, strong and durable when dry, and cheap enough to build almost whatever you want.
The problem is, it’s not permanent. At least, it doesn’t stay intact and viable permanently (even though it doesn’t break down easily, either). Despite all its impressive tensile strength, modern concrete can only keep its integrity without major repairs or replacement for about a century, at best. Today’s reinforced concrete is no match for “Roman concrete.”
Especially if reinforced concrete is cheaply made — say, with an unbalanced mix, inferior ingredients, or a careless pour — it can begin to disintegrate from the inside. As it weathers, water gradually seeps in through tiny cracks and makes its way toward the steel in the middle. As the concrete surrounding it cures, the rebar oxidizes and can expand enough to crack the concrete it’s supposed to be supporting.
Saltwater is particularly harmful to rebar, as salt will corrode the steel within five decades. Repeated cycles of freeze and thaw also can create and expand cracks — especially on concrete roads. Spreading salt does indeed deter the formation of ice, but it works in tandem with moisture to harms the rebar just as much as if seawater were constantly washing across it.
There are many emerging methods for improving concrete, including special treatments to prevent water from getting through to the steel. Other advancements respond to the increasing global attention being paid to sustainability: “Self-healing” concrete contains bacteria that secrete limestone, resealing any cracks that occur. The mix for “self-cleaning” concrete is infused with titanium dioxide, which breaks down smog, keeping the concrete sparkling white. Improved versions of this technology may even give us street surfaces that clean out the exhaust from cars.
Also, a recent report suggests that it’s possible for us to replicate the recipe for Roman concrete, (which, despite its lower tensile strength, exhibits unparalleled durability). Roman concrete is not just waterproof; it’s been found to actually become stronger when in contact with seawater. Scientists surmise that microscopic crystals grow in the ancient concrete when it’s submerged in water, making it even less vulnerable to weathering.
Though they still haven’t fully pieced together the lost recipe, researchers know that volcanic ash pozzolana was fundamental to the strength of ancient Roman concrete. A recently announced project will experiment with similar volcanic ash off the coast of California to try reverse-engineer the process that created the most durable concrete in history.
If this happens, the combination of Rome’s secret concrete recipe and modern rebar engineering techniques just might revolutionize the use of concrete — and the world’s infrastructure and architecture — all over again.