Before the use of cement and concrete in the Ancient World, the traditional building materials in the Middle East were mud blocks and clay, which were dried in the sun or in a kiln and placed one on top of the other to build a wall.
Thousands of years ago the Ancients discovered that if chalk rock was burned in ovens and water was added to it, a white paste would be formed. This paste could then be used as plaster (which insulates) and cement. It could then be attached to the mud building blocks in order to act as an adhesive.
When exposed to the open air, the white paste dried and formed a tough artificial stone, which gave might and stability to the block wall.
The chalk-based cement strengthened the wall very much, but the weight which the wall could hold was limited. The structures could be built of two or three floors, but not much more than that.
A significant breakthrough in Roman construction technology occurred around the Third Century BC. Roman builders discovered that adding volcanic ashes to the chalk cement formed an artificial stone much stronger than anything they had seen before. They mixed this new light and airy form of cement with sand and volcanic tuff rock.
The outcome was concrete.
The invention of concrete brought about a dramatic revolution in Roman architecture. The great strength of the walls and concrete columns allowed Roman engineers and architects to dare to dream of bigger structures and monuments than ever before.
They could now build thinner concrete walls, which allowed engineers to design structures with larger and more impressive spaces.
For hundreds of years, Roman builders improved upon the technique of concrete construction, until around the year 27BC, during the early years of the reign of Caesar Augustus, when it reached perfection.
The Romans discovered that a specific type of volcanic ash, called Pozzolana (named after a Roman town called Puteoli, close to which large deposits were found), could be used to form the strongest and most durable cement made from any type of volcanic ash known to them until then.
In addition, the concrete formed from this particular type of volcanic ash had another very important quality: it was capable of drying and hardening even when exposed to water. This discovery allowed Roman engineers to build bigger and more sophisticated harbors than ever before.
Port scene. Roman Fresco from Stabiae. Perhaps the harbour of Puteoli (ancient Pozzuoli)
Soon after, the use of Pozzolana became a uniform standard in all the major projects of Roman Architecture.
With the fall of the Roman Empire, concrete technology was also lost. As long as the Roman Empire existed, the engineering knowledge was preserved, and the recipe for making concrete was passed down between builders from one generation to another.
When the Roman Empire crumbled around the late 5th Century AC, its economy crumbled as well, and no-one had enough money to fund the construction of huge, magnificent structures like those of the Colosseum and the Pantheon.
Smaller structures could be built from bricks and simple chalk cement, leading to a decrease in the use of concrete. Additionally, the transportation of thousands of tons of volcanic ash was very expensive to fund.
The builders stopped using concrete, and within a generation or two, the secret of how to form Roman concrete was forgotten.
The architects of the Medieval Period stood astonished in front of the architectural masterpieces built by their ancient predecessors. Unfortunately, they didn’t have a clue how to recreate them.
Only towards the end of the 18th Century was the technology of concrete rediscovered in the United States, almost 1500 years after the Roman period.
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