Solving The Mystery Of The "Pantheon" Building's Steadfastness For Nearly Two Thousand Years In Rome
The famous Pantheon building in Rome has stood for two thousand years and remained intact, while many modern concrete buildings collapse after only a few decades, which has baffled engineers for a long time.
The reason for the durability of the Roman concrete structures of the Pantheon has remained a mystery, and researchers may finally have discovered the secret of ancient construction methods - and it's all to do with small pieces of lime that have "self-healing" abilities.
The Pantheon (Temple of All Gods) was founded in 27 BC by Marcus Vipsanius Agrippa. It was rebuilt by Emperor Hadrian between 120 and 124 AD, after the fires of 80 and 110 AD that damaged the pre-Augustus building.
Careful analysis of Roman concrete revealed small, shiny white mineral chunks called “limestone.”
Initially, it was thought that these were the result of sloppy mixing practices, or the use of poor quality raw materials.
Admir Masik, an environmental engineer from MIT, said that although Roman author and philosopher Pliny the Elder pointed out that concrete can become stronger with age, it is unlikely that the Romans would have known about the chemistry used - or how long the material would last.
"They knew this was a wonderful material, but they probably didn't know it would last for thousands of years," Masek said.
Roman concrete was produced using blocks of lava rock and other aggregates held together with a mortar made from ingredients including pozzolan (as volcanic ash), lime source (calcium oxide) and water.
The team, which also included researchers from Harvard University and labs in Italy and Switzerland, used high-resolution imagery and chemical mapping to closely examine the lime layers.
They discovered that lime may actually help concrete "heal" itself when it cracks or breaks.
During the hot mixing process required to make concrete, the lime slits become brittle, creating an easily accessible source of calcium for the rest of the concrete.
This means that when small cracks form in the concrete, the lime blocks react with water and produce a calcium-saturated solution, which can quickly recrystallize and fill the crack.
To prove that this was indeed the mechanism responsible for the durability of Roman concrete, the team produced samples of hot-mixed concrete incorporating ancient formwork and intentionally cracked them, then passed water through the cracks.
Within two weeks, the cracks had completely healed and the water could no longer flow. While the identical piece of concrete made without lime never cured, water kept flowing through the sample.
As a result of these successful tests, the team is working on marketing the modified cement.
Their findings have been published in the journal Science Advances.
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