Welcome to what we can thoughtfully called the history of concrete (or perhaps the more interesting title: Concrete: The Origin Story). In the paragraphs that follow we want to cover the most important aspects in the history and timeline of the amazing substance called concrete.
Let’s get to the basics: first of all what is concrete—in the most literal sense of the word? Most people think it is just a slab of hard material that we walk on, but what is it really comprised of?
Concrete is made up of three basic components: water, aggregate (rock, sand, or gravel) and Portland cement. Cement, usually in powder form, acts as a binding agent when mixed with water and aggregates.The combination of these simple ingredients produces an exothermic reaction that creates one of the most important building materials in human history.
Though concrete has taken off in the last one hundred years it might surprise you to learn that the history of concrete stretches back almost to the beginning of human history
Perhaps the earliest known occurrence of cement was before recorded history. A deposit of cement was formed after an deposit of oil shale, located adjacent to a bed of limestone, burned due to natural causes. These ancient deposits were investigated in the 1960s and 1970s.
Nabataean Concrete Use
The first known users of concrete were the Nabataean traders in 6500BC, long before the Romans and the Greeks built their famous structures. Their small empire was located in and around Syria and Jordan, and some of the remains of their concrete structures still stand. With the discovery of hydraulic cement (the ability to harden concrete underwater enabled them to create structures much more quickly. Later, they had modernized to build kilns, and even underground cisterns. They realized the product needed to be dry (as wet, it would allow for weakness), and bonded them together with the gel created from a tamping process.
They were the first to utilize local products that were available to them. They used pozzolan (ash) to mix with lime and heat in their kilns. The Nabataea were known to have homes with concrete floors in the Yugoslavia area by 5600 BC. Their basic formula is still what we use today.
Around 3000 BC, the ancient Egyptians used mud mixed with straw to form bricks. Mud with straw is closer to adobe than concrete; however, they also used gypsum and lime mortars in building the pyramids, although most of us think of mortar and concrete as two different materials. The Great Pyramid at Giza required about 500,000 tons of mortar, which was used as a bedding material for the casing stones that formed the visible surface of the finished pyramid. This allowed stone masons to carve and set casing stones with joints open no wider than 1/50-inch.
Concrete In China
About this same time, the northern Chinese used a form of cement in Pagodas, docks and in building the Great Wall. Spectrometer testing has confirmed that a key ingredient in the mortar used in the Great Wall and other ancient Chinese structures was glutenous, sticky rice. Some of these structures have withstood the test of time and have resisted even modern efforts at demolition.
Classical Era Concrete History
In the Roman era, it was re-discovered that adding volcanic ash to the mix allowed it to set underwater. Similarly, the Romans knew that adding horse hair made concrete less liable to crack while it hardened, and adding blood made it more frost-resistant. Crystallization of strätlingite and the introduction of pyroclastic clays created further fracture resistance.
German archaeologist Heinrich Schliemann found concrete floors, which were made of lime and pebbles, in the royal palace of Tiryns, Greece, which dates roughly to 1400–1200 BC. Lime mortars were used in Greece, Crete, and Cyprus in 800 BC. The Assyrian Jerwan Aqueduct (688 BC) made use of waterproof concrete. Concrete was used for construction in many ancient structures.
The Romans used concrete extensively from 300 BC to 476 AD, a span of more than seven hundred years. During the Roman Empire, Roman concrete (or opus caementicium) was made from quicklime, pozzolana (volcanic ash), and an aggregate of pumice. Its widespread use in many Roman structures was a key event in the history of architecture, termed the Roman Architectural Revolution. This freed Roman construction from the restrictions of stone and brick material, and allowed for revolutionary new designs in terms of both structural complexity and dimension.
Concrete, as the Romans knew it, was a new and revolutionary material. Laid in the shape of arches, vaults and domes, it quickly hardened into a rigid mass, free from many of the internal thrusts and strains that troubled the builders of similar structures in stone or brick.
Modern tests show that opus caementicium had as much compressive strength as modern Portland-cement concrete. However, due to the absence of reinforcement, its tensile strength was far lower than modern reinforced concrete, and its mode of application was also different:
Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of rubble. Second, integral reinforcing steel gives modern concrete structures greater tensile strength, whereas Roman concrete could depend only upon the strength of the concrete bonding to resist tension.
The Pantheon was one of the wonders of the ancient world: it has exterior foundation walls that are 26 feet wide and 15 feet deep and made of pozzolana cement (lime, reactive volcanic sand and water) tamped down over a layer of dense stone aggregate. That the dome still exists is something of a miracle. Settling and movement over almost 2,000 years, along with occasional earthquakes, have created cracks that would normally have weakened the structure enough that, by now, it should have fallen. The exterior walls that support the dome contain seven evenly spaced niches with chambers between them that extend to the outside. These niches and chambers, originally designed only to minimize the weight of the structure, are thinner than the main portions of the walls and act as control joints that control crack locations. Stresses caused by movement are relieved by cracking in the niches and chambers. This means that the dome is essentially supported by 16 thick, structurally sound concrete pillars formed by the portions of the exterior walls between the niches and chambers. Another method to save weight was the use of very heavy aggregates low in the structure, and the use of lighter, less dense aggregates, such as pumice, high in the walls and in the dome. The walls also taper in thickness to reduce the weight higher up.
Roman Concrete Guilds
Another secret to the success of the Romans was their use of trade guilds. Each trade had a guild whose members were responsible for passing their knowledge of materials, techniques and tools to apprentices and to the Roman Legions. In addition to fighting, the legions were trained to be self-sufficient, so they were also trained in construction methods and engineering.
The Concrete Dark Age
After the Roman Empire, the use of burned lime and pozzolana was greatly reduced until the technique was all but forgotten between 500 and the 14th century. From the 14th century to the mid-18th century, the use of cement gradually returned. The Canal du Midi was built using concrete in 1670.
Industrial Era Concrete Use
Perhaps the greatest driver behind the modern use of concrete was Smeaton’s Tower, the third Eddystone Lighthouse in Devon, England. To create this structure, between 1756 and 1759, British engineer John Smeaton pioneered the use of hydraulic lime in concrete, using reef stones and powdered brick as aggregate.
A method for producing Portland cement was patented by Joseph Aspdin in 1824.
Reinforced concrete was invented in 1849 by Joseph Monier. In 1889, the first concrete reinforced bridge was built, and in 1891, George Bartholomew poured the first concrete street in the Bellefontaine, Ohio, and it still exists today. The concrete used for this street tested at about 8,000 psi, which is about twice the strength of modern concrete used in residential construction.
The 1930’s was an exciting time for concrete technology. In 1930, air-entraining agents were developed that greatly increased concrete’s resistance to freezing and improved its workability. The use of fly ash as a pozzolanic ingredient was recognized as early as 1914, although the earliest noteworthy study of its use was in 1937. The first concrete mixed off site and delivered to a construction site was effectively done in Baltimore, United States in 1913, just before the First World War. The first concept of transit mixer was also born in 1926 in the United States. The first ready-mix factor, however, was built in the 1930s.
In 1935, the Hoover Dam was completed after pouring approximately 3,250,000 yards of concrete, with an additional 1,110,000 yards used in the power plant and other dam-related structures. Bear in mind that this was less than 20 years after a standard formula for cement was established.
Renewed Interest in Concrete buildings
In the years following the construction of the Ingalls Building in 1904, most high-rise buildings were made of steel. Construction in 1962 of Bertrand Goldberg’s 60-story Twin Towers in Chicago sparked renewed interest in using reinforced concrete for high-rises. The world’s tallest structure (as of 2011) was built using reinforced concrete. The Burj Khalifa in Dubai in the United Arab Emirates (UAE) stands 2,717 feet tall.
Decorative Concrete History
Once it became an accepted fact that metallic oxide shades do not fade due to ultraviolet exposure from sunlight, early in the 20th century, craftsmen started using pigments to apply color into concrete. What began as the innovative use of colors and stains ultimately created new artistic techniques, which appeared in publications during the 1800s. The evolution of technique has taken the industry to where it is today. Techniques included adding color to concrete, stamping patterns, chemical stains, overlay cement, paper stencil patterning, and polishing concrete.
In 1915 in Chicago, Lynn Mason Scofield became the first company to manufacture color for concrete. Other products became available: chemical stains, color hardeners, integral color, and sealers. After moving his company to Los Angeles in the 1920s in pursuit of a better market, Charlie Chaplin, Groucho Marx, and Mary Pickford were among his celebrity clients.
The next significant invention to generate interest in decorative concrete was a series of tools and a process for stamping patterns in the early 1950s. Brad Bowman developed aluminum platforms and platform stamps that made several pattern units at a time in concrete flatwork.
In 1970, the Bomanite Corp. used Brad Bowman’s patents to encourage contractors to install decorative concrete using his process. The late 1970s saw the development of a urethane stamp by Jon Nasvik, which was useful for stamping pattern and texture on fresh concrete. Modern decorative techniques use polymer modified cement, urethanes, epoxies, and polyaspartics to make concrete look like wood, tile, granite, marble and more. Decorative concrete has exploded in the last two decades by 2013 it had grown to a $745.8 Million industry and is projected to grow to 1.2 billion by 2020. $1.2 Billion: That’s 7% compound annual growth rate.
Polished Concrete History
The polished concrete trend began in Europe in 1991, about eight years before appearing in the United States. Originally, warehouse floors were polished in order to fix concrete moisture issues and high maintenance costs. The first Polished Concrete floor in the US was a 40,000 sq. ft. floor in Las Vegas at the Bellagio.
In 2000, Home Depot signed up as the first large-scale company to convert to polished concrete floors. The initial locations were all existing stores, but as the benefits of polished concrete became clear, Home Depot mandated the floors in all store locations, both new and existing. It was not long before Lowes, Wal-Mart, Bed Bath and Beyond, and other large retailers signed on to use polished concrete as their primary flooring system. Today, many large-scale big-box stores as well as smaller retail outlets polish their floors.
Modern Concrete Production
Since 1950, the cement industry has seen massive growth as our world has urbanized. From 133 billion metric tons in 1950, production has increased more than sevenfold to one billion metric tons in the 33 years to 1983; then hitting 2 billion metric tons in 2004, 3 billion metric tons in 2010, and 4 billion metric tons in 2013. In 2014, around 4.2 billion metric tons of cement were produced.
China used more cement between 2011 and 2013 than the U.S. used in the entire 20th Century. All of America’s cement consumption during the century adds up to around 4.4 gigatons (1 gigaton is roughly 1 billion metric tons).
In comparison, China used around 6.4 gigatons of cement in the three years of 2011, 2012 and 2013, as data from the International Cement Review, an industry publication based in London, shows. U.S. Geological Survey estimates on China’s cement consumption are similar: According to Hendrik van Oss, a mineral commodity specialist at the USGS, China’s cement consumption between 2010–12 was about 140 percent of U.S. consumption for 1900–99.
Concrete is an amazing product that has become the single most widely used building material in the world. The future for concrete is bright as new technologies improve sustainability, strength, and potential new uses for concrete.