Having visited Italy many times, I'm always impressed how long many ancient Roman works have survived, concrete being the 'glue' to much of it. The self-healing aspects I did not know about, pretty crazy.
An unexpected ancient manufacturing strategy may hold the key to designing concrete that lasts for millennia. David L. Chandler | MIT News Office Publication Date: January 6, 2023
The ancient Romans were masters of engineering, constructing vast networks of roads, aqueducts, ports, and massive buildings, whose remains have survived for two millennia. Many of these structures were built with concrete: Rome’s famed Pantheon, which has the world’s largest unreinforced concrete dome and was dedicated in A.D. 128, is still intact, and some ancient Roman aqueducts still deliver water to Rome today. Meanwhile, many modern concrete structures have crumbled after a few decades.
Researchers have spent decades trying to figure out the secret of this ultradurable ancient construction material, particularly in structures that endured especially harsh conditions, such as docks, sewers, and seawalls, or those constructed in seismically active locations.
Now, a team of investigators from MIT, Harvard University, and laboratories in Italy and Switzerland, has made progress in this field, discovering ancient concrete-manufacturing strategies that incorporated several key self-healing functionalities. The findings are published today in the journal Science Advances, in a paper by MIT professor of civil and environmental engineering Admir Masic, former doctoral student Linda Seymour ’14, PhD ’21, and four others.
For many years, researchers have assumed that the key to the ancient concrete’s durability was based on one ingredient: pozzolanic material such as volcanic ash from the area of Pozzuoli, on the Bay of Naples. This specific kind of ash was even shipped all across the vast Roman empire to be used in construction, and was described as a key ingredient for concrete in accounts by architects and historians at the time.
Under closer examination, these ancient samples also contain small, distinctive, millimeter-scale bright white mineral features, which have been long recognized as a ubiquitous component of Roman concretes. These white chunks, often referred to as “lime clasts,” originate from lime, another key component of the ancient concrete mix. “Ever since I first began working with ancient Roman concrete, I’ve always been fascinated by these features,” says Masic. “These are not found in modern concrete formulations, so why are they present in these ancient materials?”
Previously disregarded as merely evidence of sloppy mixing practices, or poor-quality raw materials, the new study suggests that these tiny lime clasts gave the concrete a previously unrecognized self-healing capability. “The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me,” says Masic. “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? There has to be more to this story.”
Upon further characterization of these lime clasts, using high-resolution multiscale imaging and chemical mapping techniques pioneered in Masic’s research lab, the researchers gained new insights into the potential functionality of these lime clasts.
Historically, it had been assumed that when lime was incorporated into Roman concrete, it was first combined with water to form a highly reactive paste-like material, in a process known as slaking. But this process alone could not account for the presence of the lime clasts. Masic wondered: “Was it possible that the Romans might have actually directly used lime in its more reactive form, known as quicklime?”
Studying samples of this ancient concrete, he and his team determined that the white inclusions were, indeed, made out of various forms of calcium carbonate. And spectroscopic examination provided clues that these had been formed at extreme temperatures, as would be expected from the exothermic reaction produced by using quicklime instead of, or in addition to, the slaked lime in the mixture. Hot mixing, the team has now concluded, was actually the key to the super-durable nature.
“The benefits of hot mixing are twofold,” Masic says. “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.”
During the hot mixing process, the lime clasts develop a characteristically brittle nanoparticulate architecture, creating an easily fractured and reactive calcium source, which, as the team proposed, could provide a critical self-healing functionality. As soon as tiny cracks start to form within the concrete, they can preferentially travel through the high-surface-area lime clasts. This material can then react with water, creating a calcium-saturated solution, which can recrystallize as calcium carbonate and quickly fill the crack, or react with pozzolanic materials to further strengthen the composite material. These reactions take place spontaneously and therefore automatically heal the cracks before they spread. Previous support for this hypothesis was found through the examination of other Roman concrete samples that exhibited calcite-filled cracks.
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 both ancient and modern formulations, deliberately cracked them, and then ran water through the cracks. Sure enough: Within two weeks the cracks had completely healed and the water could no longer flow. An identical chunk of concrete made without quicklime never healed, and the water just kept flowing through the sample. As a result of these successful tests, the team is working to commercialize this modified cement material.
“It’s exciting to think about how these more durable concrete formulations could expand not only the service life of these materials, but also how it could improve the durability of 3D-printed concrete formulations,” says Masic.
Through the extended functional lifespan and the development of lighter-weight concrete forms, he hopes that these efforts could help reduce the environmental impact of cement production, which currently accounts for about 8 percent of global greenhouse gas emissions. Along with other new formulations, such as concrete that can actually absorb carbon dioxide from the air, another current research focus of the Masic lab, these improvements could help to reduce concrete’s global climate impact.
The research team included Janille Maragh at MIT, Paolo Sabatini at DMAT in Italy, Michel Di Tommaso at the Instituto Meccanica dei Materiali in Switzerland, and James Weaver at the Wyss Institute for Biologically Inspired Engineering at Harvard University. The work was carried out with the assistance of the Archeological Museum of Priverno in Italy.
Posts: 15255 | Location: Wine Country | Registered: September 20, 2000
I saw this the other day on Fox, I believe. Interesting story, will wait to see what modern applications they'll have for our newly (re)discovered better concrete.
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Posts: 6393 | Location: Mogadishu on the Mississippi | Registered: February 26, 2009
Actually the one Roman archway I examined a few years back and was right at 2,000 years old and still standing like the day it was built... there was no cement... it was just rocks... with a key stone right at the top middle.
But as for the article... it has been known a lot longer than recently that high lime mortar is self healing... I was taught that in chimney sweep school about 35 years ago.
Originally posted by old dino: Interesting ... been historically curious about this, and know I know. Just might try a small experiment. Heck, am retired and why not.
Just make sure her feet are firmly planted on the bottom of the washtub before you pour in the hot mix.
Posts: 6978 | Location: NoVA | Registered: July 22, 2009
I also have been fascinated with the ancient building methods. Perhaps the ancients knew more than what evolutionists think. They seem to think that knowledge is constantly increasing. Perhaps the Renaissance period was only a small event compared to what happened long ago.
Regardless of speculation, I'd still think that if penndot used this knowledge to make better roads and bridges, they'd still find a way to continuously close down portions of roads.
--Tom The right of self preservation, in turn, was understood as the right to defend oneself against attacks by lawless individuals, or, if absolutely necessary, to resist and throw off a tyrannical government.
Interesting story to follow. Some years ago (2017?) the theory being floated around in the press was that the Romans used volcanic ash (apparently from a specific source in Italy, but I can't find the citation) along with seawater and lime to form those crystals described in the original post's linked article.
I used to haul loads of coal fly ash from Milliken Station back in Lansing, NY to be blended into concrete. At its youth Milliken Station could take in over 10,000 train car loads of coal in a year. The fly ash is used around the globe in concrete and dry wall. Much of it is land filled or stored in lined ponds as it seeps off some awsome polutants.
Posts: 18044 | Location: The Bluegrass State! | Registered: December 23, 2008
Originally posted by TRIO: I also have been fascinated with the ancient building methods. Perhaps the ancients knew more than what evolutionists think. They seem to think that knowledge is constantly increasing. Perhaps the Renaissance period was only a small event compared to what happened long ago.
Regardless of speculation, I'd still think that if penndot used this knowledge to make better roads and bridges, they'd still find a way to continuously close down portions of roads.
I wouldn't lay it so much at the feet of evolutionists but, the general population who are largely ignorant to history and HOW things evolved.
When people travel, they gain perspective; traveling throughout Europe (and if you're paying attention), you see why after the fall of Rome, that period from the Fall to the Renaissance, was known as the Dark Ages or, Middle Ages. Lots of technology was 'lost', dispersed and not concentrated or, forgotten due to the collapse of the Roman civilization. Pius adherence to religion during these times, (along with petty squabbles) was paramount to daily life and many religious-based decisions eschewed some of the advances and developments in engineering and material usage. Methods and techniques had be 're-discovered'
There's been other points in human history where civilization collapse led to the loss of technology and methods, the Fall of Rome being the most recent. For all our own advances in modern society, there's always things to learn from the past; may not be revolutionary but, helps explain Why's and How's.
Posts: 15255 | Location: Wine Country | Registered: September 20, 2000
Well, I was taught in grade school that the Romans used puzzalan cement that was based on volcanic ash, but never any expansion of the idea. That was an interesting article. Several types of concrete of different densities were used in building the Pantheon.
Originally posted by David Lee: I used to haul loads of coal fly ash from Milliken Station back in Lansing, NY to be blended into concrete. At its youth Milliken Station could take in over 10,000 train car loads of coal in a year. The fly ash is used around the globe in concrete and dry wall. Much of it is land filled or stored in lined ponds as it seeps off some awsome polutants.
I had an electrician from my work who does side jobs install a subpanel this past summer and as he’s drilling my basement wall to mount it he says “whoa, you have REAL cinder block here!”
I asked him what he meant and he pointed to the dark gray dust coming out of the bore holes and told me that the original cinder block had actual coal cinders in them.
Posts: 35257 | Location: Pennsylvania | Registered: November 12, 2007
Originally posted by old dino: Interesting ... been historically curious about this, and know I know. Just might try a small experiment. Heck, am retired and why not.
Just make sure her feet are firmly planted on the bottom of the washtub before you pour in the hot mix.
After giving your comment a little thought, maybe I should be making wine instead.
Posts: 3190 | Location: PNW | Registered: November 16, 2012
A few years back I looked at the Pantheon in Rome with a sense of ever-growing awe, as I took in the sheer beauty and elegance of the structure, getting on for two thousand years old.
Then when I got back to UK, my local streets were disfigured with pot-holes in the recently-repaired potholes.
Posts: 11524 | Location: UK, OR, ONT | Registered: July 10, 2003
there was a different time in this world.... a number of years ago I was in Prague looking at the Cathedral up on the hill. Seems it took over 600 years to build... my thought was who on the 'church building committee " approved that? Can you imagine someone actually proposing to build something today and then estimating that it would take 6 centuries to build?
They didn't know, or care, that it took six centuries to build. They started to build, and carried on until it was finished.
Our local church dates from the late 900's. The 'new' spire was built in the 1460's. If I drive about thirty miles I can visit one of the most wonderful ecclesiastical building on earth, Ely Cathedral - the original of the Ken Follett historical novel 'The pillars of the Earth'. That took over 700 years to build, but it wasn't built to any kind of work schedule. Nearer to me is Peterborough Cathedral, home of the largest painted ceiling of any medieval church on earth. It was built on foundations that predate the Norman invasion by over 250 years...
Posts: 11524 | Location: UK, OR, ONT | Registered: July 10, 2003
Originally posted by tacfoley: They didn't know, or care, that it took six centuries to build. They started to build, and carried on until it was finished.
Our local church dates from the late 900's. The 'new' spire was built in the 1460's. If I drive about thirty miles I can visit one of the most wonderful ecclesiastical building on earth, Ely Cathedral - the original of the Ken Follett historical novel 'The pillars of the Earth'. That took over 700 years to build, but it wasn't built to any kind of work schedule. Nearer to me is Peterborough Cathedral, home of the largest painted ceiling of any medieval church on earth. It was built on foundations that predate the Norman invasion by over 250 years...
This is such a dramatically different perspective than we have in the states. The oldest church on the mainland is from the 1600s and anything build before 1800 is considered very old. The oldest building here in Florida is the fort at St. Augustine which was begun in 1695, and that's ancient by US standards.
Posts: 1017 | Location: Tampa | Registered: July 27, 2010
