Saw an article or documentary and it said something to the effect of Roman buildings heal themselves after being damaged or weather damage.
How can that be
In: Engineering
So basically all concrete is self-healing. Recently the Roman concrete has been in the press because of papers by researchers at MIT and another at the University of Utah a few years ago.
None of the authors really know that much about modern concrete and talk about stuff that is discussed in the paper that has been known for decades as if they are new. The head of the lab at MIT had a particularly bad press release and talked about self-healing in a way that made it clear that the field was new to him – and makes a big deal out of the self-healing of hot-mixed lime concrete. The media made it out that this ‘magical’ and makes it more durable than modern concrete, but it isn’t.
Modern Portland cement concrete is already self-healing, though we refer to it as ‘autogenous healing’. And it works in a similar way as described here in the paper – cracks expose the unhydrated cement grains, which then hydrate sealing the crack, or the Portlandite carbonates and expands in volume. Self-healing in OPC concrete has been known and studied since at least 1913.
Hot mixed lime has been known to be self healing for decades. But even the Roman use of hot-mixed lime wasn’t a new discovery – they actually discuss in the paper the translation of the Latin words for slaking from Vitruvius works 2000 years ago and how it indicates that two different methods of slaking were used (basically one methods is slaked and used immediately, and one is slaked and used cool). They also discuss in their literature review other authors who have discussed the use of hot-mixes lime concrete dating back to the 1960s (iirc).
It also is unlikely to ever be implemented in any modern construction. The reactions involved in making this type of concrete deplete Portlandite, which removes all the alkalinity from the concrete and means you can’t use any reinforcing. So there’s very few practical applications for it. This paper is fine, but the media circus around it is a joke. They’ve over sold it in their press release, and uninformed journalists have blown it waaaay out of proportion.
Long story short, modern concrete cracks and self-heals already. Roman concrete lasts better than some modern concrete (survivorship bias) because they made their walls 8+ feet thick and loaded them in compression and without steel reinforcement. Most Roman architecture is also sat in a really hospitable climate for concrete and doesn’t undergo the massive wear and tear that modern infrastructure does.
The Romans also didn’t use disposable formwork (except for vaulting) – they mixed and cast their concrete inside two masonry walls. So all their concrete also had additional protection from a layer of masonry.
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