It’s been a mystery why Roman concrete often lasted thousands of years, but ours decays in mere decades. Turns out they incorporated chemicals in a process that induces self-healing; scientists at MIT just figured this all out – in 2022.
Scientists in a MIT, Harvard University study found that Romans actually relied on a process called “hot mixing” to whip up their hyper durable concrete.
“The benefits of hot mixing are twofold,” MIT professor of civil and environmental engineering Admir Masic told MIT News. “First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form.
“Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction,” he added.
Masic was first alerted to the concept after noticing millimeter-small bright white minerals in the ancient concrete.
The outlet said these deposits, described as “lime clasts” and not found in concrete today, were once chalked up to poor mixing practices.
But the MIT professor took issue with this line of thought.
“The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me,” Masic told the publication. “If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product?”
Masic and his team discovered that the white specs were actually calcium carbonate that had been formed after the mixture, which include quicklime, reached an “extreme temperature.”
His team then ran a series of tests using modern and ancient techniques with and without quicklime.
The team are now working to commercialize the ancient practices for modern use.
Carla Jasper says
That’s fabulous. Thanks for sharing.
It appears the Romans knew about concrete and a quick set (calcium carbonate Acetylene gas ?) who would of thought
Paul Plante says
“We Finally Know Why Ancient Roman Concrete Outlasts Our Own”
By: Laurie L. Dove
Updated: Dec 2, 2021
Why are millennia-old ancient Roman piers still standing strong as veritable concrete islands, while modern concrete structures built only decades ago crumble from an onslaught of wind and waves?
The answer lies in an until-now undocumented Roman recipe.
Researchers at the University of Utah discovered that as seawater filters through piers and breakwaters made of age-old Roman concrete, the structures actually become increasingly stronger because of the growth of interlocking minerals — including some minerals that are rare or expensive to cultivate in lab settings.
The study, published in the journal American Mineralogist, found that as seawater percolates through the concrete in the piers and breakwaters, it dissolves parts of the volcanic ash that was used in construction.
This allows new minerals like Al-tobermorite and phillipsite to grow from the leached fluids.
These minerals, similar in shape to the crystals in volcanic rocks, then formed interlocking plates in gaps within the ancient concrete, making the concrete stronger over time.
This is pretty much the opposite of what happens to modern concrete structures, which are worn down by the elements and become increasingly cracked and brittle as pores and gaps are compromised by infiltrating seawater.
So why aren’t we using Roman-style concrete?
For one, we don’t know the recipe.
We may think we’re at the height of human knowledge, but the ancients did possess precious knowledge that has been lost to time.
Although University of Utah geologist and lead study author Marie Jackson has pored through ancient Roman texts, she hasn’t yet discovered a precise method for mixing the marine mortar.
“The recipe was completely lost,” said Jackson, who is working with geological engineers to recreate the right mix, in a press release.
Ancient Romans made concrete by mixing volcanic ash with lime and seawater to make a mortar, and then incorporating into that mortar chunks of volcanic rock.
The concrete was used inland as well, as in structures like the Pantheon in Rome.
There’s also a load-bearing issue.
“Ancient” is the key word in these Roman structures, which took a long, long time to develop their strength from seawater.
Young cement built using a Roman recipe would probably not have the compressive strength to handle modern use — at least not initially.
But that doesn’t mean concocting a concrete mix using Roman engineering savvy wouldn’t be useful.
The concrete could potentially be used to replace other corrodible building materials — like steel and modern concrete — in newly constructed tidal lagoons, for instance, and other sea or sea-adjacent structures.
Stuart Bell says
It was better because they had someone else to mix it to their desired perfection. With motivation driven by the small end of a whip.
Paul Plante says
Ancient concrete works
Amelia Carolina Sparavigna
Dipartimento di Fisica
Politecnico di Torino
On April 12, 2011, in concurrence with an exhibition in the Oxford’s Ashmolean Museum of some ancient treasures of Greece, the BBC announced that Macedonians created cement three centuries before the Romans.
Unearthing some tombs of a royal complex belonging to Alexander the Great and his father Philip, at Vergina, archaeologists determined that Macedonians were “not only great warriors but revolutionary builders as well“, since they used concrete before the Romans.
This information is quite interesting because shows the location of an early use of concrete.
Unfortunately, if we want to shed light on the origin of the material, this simple comparison between Macedonian and Roman concretes is a little bit misleading.
Moreover, it is raising another question: were Macedonians the first people using concrete?
The answer is negative.
Concrete was older even than Alexander the Great.
Let me show you how we can deduce this fact from some Latin essays and their English translations and from the reports of Schliemann’s excavations of Mycenaean archaeological sites.
The Roman cement
First, let us remember what concrete is.
It is prepared by the hardening of cement and aggregate.
The cement is a binder or mortar, which is a substance that sets when mixed with water and then hardens binding together the particles of aggregate.
The aggregate could be made of pebbles, ceramic tiles and brick rubbles obtained from the demolition of buildings.
It is commonly believed that the ancient Romans were the first to create and use concrete.
This is not true, as we can easily learn from the Latin literature itself.
For sure, Romans were able to prepare high-quality hydraulic cements, because they used lime and pozzolana, the volcanic dust of Puteoli.
The mixture of pozzolana and lime produces a hydraulic binder.
The Romans called this binder “caementum”.
“Opus caementicium” was the Roman concrete.
The Roman caementum has much in common with its modern counterpart, the Portland cement: that is, the composition of Roman pozzolana cements is very close to that of modern cement.
Probably, it was during the third century BC that hydraulic cement was first prepared by mixing pozzolana with the lime produced by heating limestone.
The resulting concrete was used for building the harbour at Puteoli (c.199 BC).
Let me remember that Puteoli (Pozzuoli), such as Cumae and Naples, before being Roman towns, were Greek colonies of Magna Graecia.
Maybe, the use of concrete could had come from Greece in Italy through these colonies, and, due to the local presence of pozzolana, the hydraulic cement developed and used there, and then, in all the Roman Empire.
To the author’s knowledge, caementum was the only ancient material similar to the modern Portland cement.
It would be interesting to analyse the compositions of Macedonian and Roman concretes to compare their features.
Early information on the properties of caementum appeared in the books written by Vitruvius and Pliny the Elder.
Vitruvius devoted a chapter of his book, De Architectura, to pozzolana.
Pliny in his Natural History described pozzolana too, but also other concretes had been known in Rome.
One was the opus signinum, which is obtained from broken pottery, “beaten to powder, and tempered with lime, it becomes more solid and durable than other substances of a similar nature; forming the cement known as the ‘signine’ composition, so extensively employed for even making the pavements of houses”.
Pliny considered also the “formaceos walls” that can be found in Africa and Spain.
He is telling: “they are moulded, rather than built, by enclosing earth within a frame of boards, constructed on either side”.
For Pliny, “these walls are superior in solidity to any cement.”
“Even at this day, Spain still beholds watch-towers that were erected by Hannibal, and turrets of earth placed on the very summits of her mountains”.
Even if Pliny is telling that formaceos walls are of “earth”, he is probably referring to the tapias, created with a mixture of lime, sand and gravel, that is, with a mixture for concrete.
There is another reference to formaceos walls in a book on the “Rerum Rusticarum” written by Varro, reinforcing the hypothesis of concrete.
When Varro is discussing the fences used to mark the farm boundaries, he tells that fences can be masonry works too.
“There are usually four varieties: those of cut stone, as in the country around Tusculum; those of burned brick, as in Gaul; those of unburned brick as in the Sabine country; those of gravel concrete, as in Spain and about Tarentum”.
Varro does not describe the components of the mortar.
Paul Plante says
To this engineer, something about this “heating concrete mixtures to high temperatures” does not ring true.
First of all, as to why our concrete doesn’t hold up, I would say because it wasn’t made to, because we are used to doing things on the cheap here on government jobs.
I have poured plenty of concrete for myself made with my recipe and it has held up over the years just fine, because I intended it to, and those made sure of my mix when I poured it.
There are many blends of concrete, including the use of additives such as pozzolans, and they are not at all the same in terms of durability, or price.
As to Portland Pozzolana Cement (PPC), it is a type of blended cement consisting of 15-35% pozzolanic material, 4% gypsum and the rest is clinker.
And here is the important part, which is no different today than it was in Roman times, to wit: since the pozzolanic material reacts with calcium hydroxide liberated by the hydrating Portland cement and forms cementatious compounds, PPC makes the concrete more impermeable and denser.
Thus, it can be confidently employed in construction of hydraulic structures, marine works, mass concreting etc., because it protects concrete against alkali-aggregate reaction.
Pozzolana is extensively used as an addition to Portland cement in countries such as Italy, Germany, Kenya, Uganda, Turkey, China and Greece.
So why not here?
Because we don’t want longevity?
Because we want to go back next year with a new contract to repair what we poured this year?
Makes one wonder.