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How Concrete Started Part 1: A History of Concrete by Luke Snell

This is part one of a six - part series on the origins of concrete, originally published World of Concrete 360. Republished with permission from the Author. Full six part pdf can be viewed here.

How Concrete Started—Part 1: Sun Dried Brick

I set out on a quest to learn when and how concrete got its start. After reading several books and reviewing research reports and internet blogs, it became apparent that the starting point of concrete hinges on how you define concrete. Thus we must first define two terms we use today, sometimes (incorrectly) interchangeably. Merriam-Webster defines:

• Concrete as “a mass formed by concretion or coalescence of separate particles of matter in one body.”
• Cement as “a substance to make objects adhere to each other.”

Although these definitions are rather vague, they give us a starting point. One of the earliest methods of creating a concrete would be construction using sun dried bricks. To make the construction stable they used mud as a cement and plastered the entire wall with mud to give it a smooth finish.
Today we would call this construction style masonry, however it does meet the above definitions of concrete and cement and may be the genesis of today’s concrete.

Sun-Dried Brick

Archeologist have found evidence of sun-dried brick structures in Jericho dating to 9000 BC. These bricks are made from clay and reinforced with straw. The technique of making these bricks was quite simple. Clay, water, and straw was mixed to form a slurry. This slurry was then cast into forms or hand-shaped into bricks and left in the sun to dry. The straw was a reinforcement that kept the bricks from cracking while they were drying.

During the drying time, the bricks needed to be turned to achieve uniform drying. Typically, the drying process takes 2 to 3 weeks. The mortar used to hold the bricks
together was also clay mud as shown below.
 

Building a wall with sun dried brick and mud mortar.

Sun dried bricks have played key roles in the history of several religions. The biblical story of Exodus starts with the Jews in Egypt being forced to make sun-dried bricks. As punishment for asking for time off to celebrate a religious holiday, the Pharaoh demanded they also gather the straw needed to make the bricks. Previously other people had gathered the straw and provided it to the brick makers. Now the Jews had to also gather the straw plus maintain the same production quota. This extra work set the stage for intense negotiations between Moses and Pharaoh ultimately resulting in the exodus from Egypt. For more detail, see Exodus, Chapter 5.

As Islam developed in northern Africa, mosques were built. These were in the desert and needed to use local building materials—mostly sun-dried bricks.The great Mosque at Djenné, built in Mali in 1120 was rebuilt in 1907. This mosque hold over 3,000 worshipers and is believed to be the largest building ever constructed with sun-dried brick and mud mortar. Since Mali has a rainy season, the mosque requires routine maintenance to replace any clay that washes away. Thousands of Djenne residents participate each year in the plastering ceremony of the Grand Mosque, which will now be powered by solar electricity.

The Great Mosque of Djenne.

In North America, Casa Grande was built in the Arizona desert around 1300. It was an elaborate settlement with a main building, irrigation canals, housing, and a sports field. Although it was not built with sun dried bricks, it was built using mud (called caliche or hard pan). The caliche was mixed with water and placed by baskets. The sun-dried caliche mixture resulted in a type of concrete structure. This method of mixing the caliche, placing it into the structure, and letting it harden is much like modern day concrete construction.

Casa Grande with its protective cover in place.

No one is sure of the purpose of this structure. It appears to have been built to celebrate the summer and winter solstices so was likely part of religious ceremonies. Casa Grande was abandoned around 1450 so little is known about the builders or it purpose. It is now a national monument with a roof installed overhead to protect it from the weather.

But the main use of sun-dried bricks, historically and still today, is for housing. Homes made with sun dried brick help moderate the interior temperature. During the day the heat slowly increases. During the cool nights, the heat will slowly be released thus providing a relatively comfortable living space in hot, dry areas.

Ruins of mud-dried brick homes in Saudi Arabia.

Sun dried bricks worked well in very dry areas however they were problematic in areas that received much rain. Our ancestors saw the need to improve the sun-dried brick and the mortar that holds them together.

The next steps required toughing the bricks so they were more durable and stronger plus developing better bonding materials to hold the bricks together in any type of weather. We’ll cover that in Part Two

Full six part pdf can be viewed here.

How Concrete Started Part 2 - Fired Brick: A History of Concrete by Luke Snell

This is part two of a six - part series on the origins of concrete, originally published World of Concrete 360. Republished with permission from the Author. Full six part pdf can be viewed here.

How Concrete Started—Part 2: Fired Brick

The Tower of Babel by Pieter Bruegel the Elder, built with fired brick.

In my quest to learn the origins of concrete, I choose as a starting point the sun-dried brick with mud as its cement or binder. But sun-dried bricks were not very strong or durable, thus our ancestors began a search to improve the brick. The improvement appears to have been inspired by the development of pottery, which also eventually led to the discovery of new cements.

Archeologist tell us that Homo Sapiens figured out how to make and control fire about 125,000 years ago. This was a major milestone in man’s development. With fire they had the means to cook food, keep warm in cool weather, security from wild animals and insects, and a place for social interaction. We are still drawn to campfires where we sit staring into the flames, share food, sing songs, tell stories, and pass onto younger generations traditions from our past.

Campfires are not extremely hot with temperatures around 1000 F. Someone got the idea that they could harden clay by using the heat of the campfire and begin experimenting with this new technology. As a result, around 29,000 years ago people in Central Europe made a clay figurine and put it in a campfire. Archeologist have determined that the Venus of Dolce Věstonice it was fired at about 800 F (well within the temperature of a campfire).
 

The Venus of Dolce Věstonice 

This figurine is the oldest artifact in which clay had been fired. Thus we can conclude that the process of using heat to improve an object made of clay was understood or was in development by 29,000 years ago.

Pottery artifacts using this same technique were found in China, dating to 20,000 years ago. This fired clay pottery provided better containers for storage of food and liquids and represented a major step in finding new applications for this advancing technology. The technology of making fired clay pottery appears to have spread slowly. Archeologist have found fired clay pottery in Japan and Russia from 16,000 years ago and in the Middle East from 11,000 years ago.

Oldest fired clay pottery - found in China

Applying this technology to make a better brick first appears in China around 6400 years ago. These bricks were fired at about 600 F (easily achieved by a campfire). These bricks were used as a flooring material for houses.

The Bible (Genesis, Chapter 11) mentions using fired brick in the construction of the Tower of Babel. Biblical scholars estimate that this event occurred about 2200 B.C. ago in the Middle East. Various dates are attributed to when this account was written varying from 1300 B.C. to 500 B.C. The builders that attempted to build this tower must have understood that mud bricks were not strong enough for the planned tower so they decided to make and use fired bricks. Thus we know that the technology of making fired bricks was understood at least by the time of the event was recorded. The tower was never completed but it did become a popular topic of religious painters.
 

The Tower of Babel as envisioned by a late German Medieval painter around 1370 A.D..

The Biblical account also introduces the use of tar as a mortar. Since there were several tar pits mentioned in the Bible in this general area (Genesis chapter 14, verse 10), tar appears to be a logical material for them to have used.

Tar would have been relatively abundant and easy to collect. Tar was superior to mud as a mortar, however its use was limited to areas that had tar pits. It would also have been rather unsightly and so thankfully this technique never caught on.

In the next two articles in this series, we will discuss theories of how new and improved cements were discovered and how this discovery resulted from the campfire and attempts to make improved pottery.

Full six part pdf can be viewed here.