How the Pantheon has stayed intact for almost 2,000 years

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How the Pantheon has stayed intact for almost 2,000 years: Study reveals how small chunks of lime gave Roman concrete ‘self-healing’ capabilities

  • Scientists have finally discovered secret behind ancient construction methods
  • Analysis of Roman concrete revealed white mineral chunks called ‘lime clasts’
  • Experts believe lime clasts help the concrete ‘heal’ itself when it cracks or breaks

By Xantha Leatham Deputy Science Editor For The Daily Mail

Published: 19:00 GMT, 6 January 2023 | Updated: 19:00 GMT, 6 January 2023

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It’s a riddle that has left engineers scratching their heads for a very long time.

How is it that Rome’s famed Pantheon has stayed intact for almost 2,000 years while many modern concrete structures crumble after just a few decades?

Now, researchers may have finally discovered the secret behind ancient construction methods – and it’s all to do with tiny pieces of lime that come with ‘self-healing’ capabilities.

Close analysis of Roman concrete has revealed tiny, bright white mineral chunks called ‘lime clasts’.

It's a riddle that has left engineers scratching their heads for a very long time. How is it that Rome's famed Pantheon has stayed intact for almost 2,000 years while many modern concrete structures crumble after just a few decades?

It’s a riddle that has left engineers scratching their heads for a very long time. How is it that Rome’s famed Pantheon has stayed intact for almost 2,000 years while many modern concrete structures crumble after just a few decades?

Roman concrete is ‘self-healing’ 

The team, which also included researchers from Harvard and laboratories in Italy and Switzerland, used high-res imaging and chemical mapping to look at the lime clasts more closely.

And they discovered the lime may actually help the concrete ‘heal’ itself when it cracks or breaks.

During the hot mixing process needed to make concrete, the lime clasts become brittle – creating an easily accessible source of calcium for the rest of the concrete.

This means that when tiny cracks form in the concrete, the lime clasts react with water and create a calcium-saturated solution, which can recrystallize and quickly fill the crack.

Initially, it was thought these were present as a result of sloppy mixing practices, or using poor-quality raw materials.

Admir Masic, an environmental engineer from the Massachusetts Institute of Technology, said: ‘Ever since I first began working with ancient Roman concrete, I’ve always been fascinated by these features.

‘These are not found in modern concrete formulations, so why are they present in these ancient materials?

‘The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me.

‘If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimised over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product?

‘There has to be more to this story.’

The team, which also included researchers from Harvard and laboratories in Italy and Switzerland, used high-res imaging and chemical mapping to look at the lime clasts more closely.

And they discovered the lime may actually help the concrete ‘heal’ itself when it cracks or breaks.

During the hot mixing process needed to make concrete, the lime clasts become brittle – creating an easily accessible source of calcium for the rest of the concrete.

The team, which also included researchers from Harvard and laboratories in Italy and Switzerland, used high-res imaging and chemical mapping to look at the lime clasts more closely

The team, which also included researchers from Harvard and laboratories in Italy and Switzerland, used high-res imaging and chemical mapping to look at the lime clasts more closely

The team, which also included researchers from Harvard and laboratories in Italy and Switzerland, used high-res imaging and chemical mapping to look at the lime clasts more closely

The researchers discovered the lime may actually help the concrete 'heal' itself when it cracks or breaks

The researchers discovered the lime may actually help the concrete 'heal' itself when it cracks or breaks

The researchers discovered the lime may actually help the concrete ‘heal’ itself when it cracks or breaks

This means that when tiny cracks form in the concrete, the lime clasts react with water and create a calcium-saturated solution, which can recrystallize and quickly fill the crack.

To prove that this was indeed the mechanism responsible for the durability of the Roman concrete, the team produced samples of hot-mixed concrete that incorporated ancient formulations, deliberately cracked them, and then ran water through the cracks.

Within two weeks the cracks had completely healed and the water could no longer flow.

An identical chunk of concrete made without the lime never healed, and the water just kept flowing through the sample.

As a result of these successful tests, the team is working to commercialize the modified cement material.

Their findings were published in the journal Science Advances.

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How England spent almost half a millennium under Roman rule

55BC – Julius Caesar crossed the channel with around 10,000 soldiers. They landed at a Pegwell Bay on the Isle of Thanet and were met by a force of Britons. Caesar was forced to withdraw.

54BC – Caesar crossed the channel again in his second attempt to conquer Britain. He came with with 27,000 infantry and cavalry and landed at Deal but were unopposed. They marched inland and after hard battles they defeated the Britons and key tribal leaders surrendered.

However, later that year, Caesar was forced to return to Gaul to deal with problems there and the Romans left.

54BC – 43BC – Although there were no Romans present in Britain during these years, their influence increased due to trade links.

43AD – A Roman force of 40,000 led by Aulus Plautius landed in Kent and took the south east. The emperor Claudius appointed Plautius as Governor of Britain and returned to Rome.

47AD – Londinium (London) was founded and Britain was declared part of the Roman empire. Networks of roads were built across the country.

50AD – Romans arrived in the southwest and made their mark in the form of a wooden fort on a hill near the river Exe.  A town was created at the site of the fort decades later and names Isca. 

When Romans let and Saxons ruled, all ex-Roman towns were called a ‘ceaster’. this was called ‘Exe ceaster’ and a merger of this eventually gave rise to Exeter.   

75 – 77AD – Romans defeated the last resistant tribes, making all Britain Roman. Many Britons started adopting Roman customs and law.

122AD – Emperor Hadrian ordered that a wall be built between England and Scotland to keep Scottish tribes out.

312AD – Emperor Constantine made Christianity legal throughout the Roman empire.

228AD – The Romans were being attacked by barbarian tribes and soldiers stationed in the country started to be recalled to Rome.

410AD – All Romans were recalled to Rome and Emperor Honorious told Britons they no longer had a connection to Rome.

Source: History on the net

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