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

Daily Mail UK ^ | January 6, 2023 | Xantha Leatham, Deputy Science Editor

[SunkenCiv]

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'...

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...

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.

[blam]

I read an article about a very durable Roman concrete that was 'special' because it contained ash only from a certain volcano.

Roman Concrete: Volcanic Material Created An Empire

[SunkenCiv]

My pleasure.

[SunkenCiv]

That's the stuff.

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KEYWORDS: pozzolana; pozzolano;

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[Paal Gulli]

As brilliant a piece of engineering as it is, it still bears proof to the old axiom, "The best laid plans of mice and men, oft go astray." Something you might never have noticed if you've only seen it from ground level.

See the "chevron" on the wall above the roof of the portico (indicated by arrows)? That's where the designer intended the portico's roof to have come to.

So why doesn't it? Nobody knows. But the columns are mismatched, too, different diameters, different styles, and made from stone from different quarries. Which gives rise to speculation that the original columns never arrived so the builders had to make do with whatever they could scrounge. They were supposed to have been quarried in Egypt, and the majority of the shipping route to Rome would have been over water, and shipwrecks were a common occurrence. Maybe pirates. Maybe Egyptian bureaucracy, who knows?

[Paal Gulli]

And in case you were wondering, the answer is, “Yes.”

When it rains, the floor inside the Pantheon gets wet. The “oculus” is just like any other hole in a roof, only bigger.

[GOPJ]

ping

[GOPJ]

I'd like to see supercharged lime clasts that can eliminate driveway cracking caused by poor base preparation before laying down the concrete slab.

Good idea. Better for the short sighted would be coatings on existing 'cracked' driveways...

[colorado tanker]

At its like time travel back to the Roman world. Amazing.

[SunkenCiv]

I’ve often wondered if the portico was either changed, or as it was the last thing constructed, there was a budget problem, maybe that whole part was available from another project, so they used that. Perhaps the portico survived from the original version, which was largely wood construction.

[SunkenCiv]

The Roman world is not so far away from us. The last gasp of the Roman Empire was the fall of Constantinople to the Turks, in 1453 -- 39 years before Columbus sailed off with his famous three ships.

[Red Badger]

They didn’t use Union Labor.....................