Go to southern France today and you might come across a structure that is nothing but
amazing.
There you’ll find the three-tier aqueduct known as the Pont du Gard.
It’s one of the best preserved Roman aqueducts anywhere in the world and also the highest,
but what’s hard to get your head around is that this magnificent structure was built
roughly two thousand years ago in the first century AD.
UNESCO has called it a testament to human genius, while no one disagrees that this ancient
structure shows us that those Romans, or at least some of them, were exceptionally talented
engineers.
There are myriad buildings that tell us this, such as the Roman baths in the English town
of Bath, or the mighty Pantheon, both still in good condition.
The question is, how did they do it?
And can we recreate their incredible formula today?
Let’s first have a look at when the Romans got their hands on concrete.
The Romans were masters at making concrete, but they didn’t start using some form of
concrete until around until the 3rd century BC.
There is even a period known as the Roman “Concrete Revolution”, which is when engineers
experienced and explosion in their use of very creative building processes and architectural
elements thanks to the incredible concrete formula that they could exploit to build much
more impressive structures.
Without this concrete we wouldn’t have all those amazing structures still standing today.
The ancient Romans of course didn’t call it concrete, but the latin words “opus caementicium.”
It would be an understatement to say concrete wasn’t important to the Romans, because
it helped build a lot of things they were famous for, such as the large Roman edifices,
houses, those great bridges, and those tough Roman roads we’ve all heard about.
Butis how did they make this amazing concrete of theirs?
Historians tell us that their magic formula for opus caementicium was to add a volcanic
dust called pozzolana to a mortar that was made from lime or gypsum with bits of rock,
brick, tile and some water, added.
As many of you know, to mix concrete you have to add each part carefully, making sure not
to have too much or too little of any one thing.
The Romans did just that, perfecting the exact ratio to that yielded the strongest concrete.
They would mix the mortar and then add to it the pozzolana, and for every one part volcanic
dust there would be three parts lime or gypsum.
Historians tell us that the magic was in the volcanic ash, because it contained silica
and alumina, which together in the mix created a chemical reaction that strengthened the
mortar.
Voila, perfect Roman concrete and structures all over the place which would stand up straight
for centuries, long after the empire itself had fallen.
But as we said, there was a Concrete Revolution and during this phase the Romans would advance
their concrete, make it even stronger, and learn how to make it waterproof.
The genius who came up with waterproof concrete found that by adding crushed terracotta that
would do the job.
In the first century AD they even figured out that by mixing a certain amount of volcanic
ash and lime and letting it sit in seawater, that would harden the concrete over time.
That’s why you have Roman structures that have stood in water for 2000 years that are
still standing, whereas modern concrete would deteriorate in the saltwater.
That concrete is reinforced with steel, too, and steel doesn’t like saltwater.
In fact, Roman marine concrete has been called, “the most durable building material in human
history.”
So, you might now be wondering, if Roman concrete was that good, and it obviously was, why don’t
we use it now?
Well, you can find research out there that indeed tells us that Roman concrete was superior
to the stuff we use today.
In fact, recent research conducted by the U.S. Department of Energy and scientists at
the University of California tell us that the best Roman concrete was not just more
durable than modern concrete but it is less environmentally damaging to make it.
One of those researchers said in an interview, “It’s not that modern concrete isn’t
good – it’s so good we use 19 billion tons of it a year.
The problem is that manufacturing Portland cement accounts for seven percent of the carbon
dioxide that industry puts into the air.”
Portland cement is the glue that holds everything together, but the process of making it releases
carbon from burning fuel.
To make it you mix silica sand, limestone, clay, chalk and more, and then melt it together
at super-high temperatures.
Some of those researchers believe if we go back to using Roman concrete not only will
there be less carbon emissions but we’ll also have longer-lasting structures, which
is also good for the environment.
Surely we should be going back to the stuff made with volcanic ash.
Some environmentally friendly concretes these days do take the Roman route, and the results
have been good.
Another good thing, according to scientists, is that the world does not have a shortage
of pozzolan.
One of the reasons we haven’t been using marine Roman concrete is pretty simple, and
that’s because scientists just didn’t know for a while just what the magic was.
For instance, a study published in the American Mineralogist in 2017 explained to us how when
seawater gets into the Roman concrete the minerals actually toughen the concrete over
time, not weaken it.
We should add, though, that this toughening process can take a century or two, so modern
scientists are working on something that won’t take so long.
Surely then, we can just make it?
Well, it’s not that easy, because the Romans didn’t leave behind the exact recipe and
it seems us moderns have not been able to perfect the process just yet.
One scientist said that the recipe for Roman marine concrete was “completely lost.”
Another scientist in an interview with The Guardian in 2017 said more work needs to be
done in creating those mixtures.
A bit of fine-tuning needs to happen he said, adding that, “The challenge is to develop
methods that use common volcanic products – and that is actually what we are doing
right now.”
Nonetheless, as we said, that volcanic ash is used in some concretes today.
As one researcher put it, engineers are by no means ignorant regarding how good this
stuff is.
But the one thing we want to have is the concrete that strengthens in seawater as that’s where
our modern concrete has a lot of problems.
Those scientists are trying hard to reverse engineer marine Roman concrete, but as we
speak we still can’t make it like the Romans did.
Another researcher said that the Romans got lucky in what rocks they had available to
throw into the mix, and in much of the world today you won’t find those rocks, so substitutes
would have to be found.
And at this point it’s worth saying that the new school way of making concrete with
Portland cement is relatively cheap, so while it might be worse for the environment, businesses
will always think about the bottom line – and concrete is big business.
So big in fact, that it’s said Portland cement accounts for around 5 percent of human
greenhouse gas emissions.
That’s what an article in Natrure.com tells us, and that’s why researchers right now
are still trying to master how to make what is sometimes called “one of the most complex
substances known in materials science.”
That same article said some progressive companies in the USA are working on the Roman concrete
model to help reduce carbon emissions, but it also said those companies are merely bit-players
in the concrete business.
What we need according to that piece is everyone in the construction industry to embrace next-generation
cement.
With that in mind, don’t be surprised if we soon start doing it like the Romans did
it.
As one professor told The Washington Post, “The Romans formulated a material that still
wows us today.”
Perhaps we will have to go back to the past to create a better, more sustainable future.
What do you think?
Do you know enough about concrete to add something more to this story?
Tell us in the comments.
Also, be sure to check out our other video The Horrible Life of an Average Roman Empire
Slave.
Thanks for watching, and as always, don’t forget to like, share and subscribe.
See you next time.