How to Make Roman Concrete, One of Human Civilization’s Longest-Lasting Building Materials




More than a millennium and a half after its fall, we still look back with wonder on the accomplishments of the ancient Roman Empire. Few elements of its legacy impress us as much as its built environment — or in any case, what’s left of its built environment. Still, the fact that anything remains at all of the structures built by the Romans tells us that they were doing something right: specifically, they were doing concrete right. Just how they made that astonishingly durable building material has been a subject of research even in recent years, and we even featured it here on Open Culture back in 2017. But could we make Roman concrete today?

Such is the task of Shawn Kelly, host of the Youtube channel Corporal’s Corner, in the video above. Using materials like volcanic ash, pumice and limestone, he makes a brick that looks more than solid enough to go up against any modern concrete.

TASCHEN

As of this writing, this simple video has racked up more than three million views, a number that reflects our enduring fascination with the question of how the ancient Romans created their world — as well as the question addressed in the higher-tech Practical Engineering video below, “Was Roman Concrete Better?”

The fact of the matter is that, despite possessing technologies the Romans could hardly have imagined, their concrete lasts longer than ours. Why that should be the case comes down, in large part, to water: we put a great deal more of it into our concrete than the Romans did, in order to pour it more cheaply and easily. But this makes it more fragile and subject to deterioration over time (as seen in the early dilapidation of certain Brutalist buildings), even despite our use of chemical additives and steel reinforcement. Roman concrete was also mixed with seawater, which caused the formation of crystals within the material that actually strengthened it as it aged — thus cementing, as one wag in the comments puts it, the Romans’ place in history.

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Related content:

How Did the Romans Make Concrete That Lasts Longer Than Modern Concrete? The Mystery Finally Solved

The Roman Roads and Bridges You Can Still Travel Today

How Did Roman Aqueducts Work?: The Most Impressive Achievement of Ancient Rome’s Infrastructure, Explained

The Beauty & Ingenuity of the Pantheon, Ancient Rome’s Best-Preserved Monument: An Introduction

Roman Architecture: A Free Course from Yale

Based in Seoul, Colin Marshall writes and broadcasts on cities, language, and culture. His projects include the Substack newsletter Books on Cities, the book The Stateless City: a Walk through 21st-Century Los Angeles and the video series The City in Cinema. Follow him on Twitter at @colinmarshall or on Facebook.


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Comments (74)
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  • Joan says:

    In case we should ever want to do things in the best way possible. Political interference notwithstanding.

  • John holland says:

    Fact is we dont know how to make concrete
    I patented a method and displayed same at a local trade fair.
    I showed how all equipment was based on an erknekus assumption.
    That all aggregates srexdiddesrnr and concrete tgusxreqires an adjustable frequency and intensity of vibration.

    A German company tried to stale my patent hence I have rejected the west in my deliberations.

  • Big o says:

    The fuck you say? Spell check that garbage.

  • Christ Jones says:

    Hahaha… that’s right

  • tanetovic says:

    Another thing that happens nowadays with concrete is carbonation… And all of the steel reinforcement when in contact with air will rust to the point of total deterioration and damage the structure

  • robert j. walters says:

    Yes indeed , SEAWATER was the secret however , the salinity of seawater during Roman times is different from the salinity in modern seawater …

  • Ignacio Granados says:

    The problem with this is that Romans didn’t use “iron bars”in as we do now with reinforced concrete. So from this point of view, we’re even, about all because it’s hard to think they just want make eternal buildings, as we’re not looking for that either.

  • Ralph says:

    If the block soaks in water, what happens if it freezes?

  • Lee S says:

    Lol… Not many sensible comments here .. but I find this fascinating, I’m sure the use of rebar has not much to do with the difference between current and Roman concrete, just theirs was better.
    Brains 2000 ago were just the same as ours.. just with less screen time… Big up the Romans…

  • Robert West says:

    It was saltwater so I doubt having it freeze will be a problem.

  • Lee S says:

    Not that much different mate, you wouldn’t taste the difference… Salt water might have a difference in the process… I don’t know, but the difference in salinity of seawater between now and then next to zero.. at least when it comes to mixing concrete!

  • Lee S says:

    Not that much different mate, you wouldn’t taste the difference… Salt water might have a difference in the process of making concrete. I don’t know, but the difference id salinity of seawater between now and then next to zero.. at least when it comes to mixing concrete!im sure its just the romans had a better recipe than us.

  • Brooke Radding says:

    “Roman” concrete is a type known as pozzolan concrete.

  • Brooke Radding says:

    That is not true. Theirs was not “better.” It’s well known what it is. It’s Pozzolan concrete. If it were better it would be in industrial use today. Modern concrete mixes are engineered and specified in construction for different applications. I did have one professor say, however, that it is still not understood well. “We only know two things for certain about concrete,” he announced.
    “It’s gray and it cracks.”

  • Dave says:

    I read recently that the Romans used volcanic ash in the mix with lime . The ash was creating a crystal grow that made it harder and more resilient as it aged. The exact method of mixing or ratios is yet to be found .

  • Euwe says:

    Took the words right out of my mouth

  • Kraig Richard says:

    If theory valid, resisting acids of weather might likely be a combination of different reasons. Right balance of various particle sizes, some kind of impurity creating a reaction. Maybe they added aged camel piss. It’s hard to believe whst we can’t say about their cement… if we can send a Tesla (without Musk in it) into infinity and watch it forever with our starry eyed space scope.

  • Tony says:

    No shit. LITERALLY LMAO!!!

  • John boy says:

    U’s say tomato we say to-mar-o

  • Hugo Gallipoli says:

    exactamente, es así, la tendencia esperada es hacia la meteorización o la desintegración y no solo por los cambios de temperatura en el día, el mes, el año, sino que el aumento de la entropía es siempre algo espontáneo, pero este concreto cristaliza cada vez más, ¿los alumini-silicatos se entrecruzan?, seguramente pero ¿quien sabe?, hay que continuar estudiando su estructura interior.

  • Brian says:

    Fun fact, the longevity of the concrete used as the base of the statue of Liberty and the Brooklyn bridge is because they were made of Rosendale cement, which is stronger than Portland cement but takes longer to set up. You can find the old kilns used to process limestone in the Hudson Valley, near and in towns like Rosendale for which the cement is named.

  • Joe Sickler says:

    I would like to learn more of this different types of cement n how its all mixed n how each bond

  • Roger says:

    In Chicago, they build inferior roads purposely so they can rebuild again next year to keep those budgets in use, or they don’t get the money next year.

  • Sean Laughlin says:

    I live in Chicago and confirm your statement. Really is ridiculous how poorly our roads are made here. 294 N at the Bensenville bridge being resurfaced 2 yrs after construction?

  • Ibuyminefromtheman says:

    It really comes down to water if you want highstrenth concrete don’t put it in a mixer a truck or a pump. Just barely wet it. So it looks like wet sand at the beach. Then scoop it and pack it into the footing. It will finish the same as the poured concrete but instead of being 5 to 9000psi its 20,000psi. Roman’s hand mixed used very little water and packed it in. You will get the same quality out of a sack of quikcrete if you use the bare minimum of water. Had mix and pack don’t pour the concrete. More water equals much lower strength. Whicm means cracked driveways.

  • Anonymous says:

    Seriously? Do u have anger issues?
    Or just a better speller than you syndrome?

  • Dennis The Menace says:

    Very interesting…some of U guys (gals?) are really funny!! And talkin’ bout syndromes, some of U may have been previously diagnosed with “my pee pee is bigger than yours syndrome” lol 😆
    That said, I do believe that using water sparingly is critical in getting the most outa ur concrete!

  • James Bone says:

    Bad concrete is why that condominium collapsed in Florida last year or whenever it was. I personally live in a 3-story building that was literally “poured” and the outer walls & floor are made of concrete reinforced with steel. The building was poured in the 1970s so should still be good for a few more decades I would guess. But I don’t really know…

  • OC says:

    Out of curiosity, does anyone know what site is sending folks to our site/post today?

    Thanks for any insights,
    Open Culture

  • James Bone says:

    Job security for road builders…

  • James Bone says:

    I found your article in my Google News feed…

  • Heywood Jabloeme says:

    I’m new here.
    I opened Google on my phone and it was listed as an “interesting story I might like”. I have zero idea how articles like this are chosen. Most often it’s for garbage I do not care about. This was cool though.

  • Ron says:

    To say our concrete is inferior is false. The big secret, i believe, is carbon… easily acquired from a fire pit. The right amount of carbon makes concrete incredibly strong. For reference watch the documentary on the construction of the Petronas (Twin) towers in Kuala Lumpur.

  • Daniel Miller says:

    Science X digest

  • Doug says:

    I like to know what engineering background goes into testing the hardness of concrete by scratching it with a fingernail and tapping it with your knuckle.
    I’ve had stale bread that would pass those tests.

  • David Unvert says:

    I did a science fair project in 7th grade using tap water, deionized water and seawater to make concrete and the sea water was the strongest which was opposite of my hypothesis

  • Clelie says:

    Where did you get the Volcanic Ash and Pumice (Ingredients). I’d like to make some.

  • Mike Sanchez says:

    Either that or the fact that 50GB of hacked info on ruling elites was stored as protection by software founder.

  • BillyBaroo says:

    “More than a millennium and a half after its fall, we still look back with wonder on the accomplishments of the ancient Roman Empire.”

    I realize that the appeal to ancientness is the hook for this article and that 1500 years is allot of time; however the Roman Empire didn’t come to an end until the fall of Constantinople in the 15th century.

    Those who lived in the city called themselves Romans and so did the Muslim invaders who finally conquered it.

  • Withnail says:

    modern cement does the same thing, fly ash from power stations is used.

  • Lord Piddlepuck says:

    The Romans made an almost eternal kingdom work but in the end, they had lunatics like Nero and Caligula rule their demise, the once infallible Empire now crumbled to the ground, though hoisted upon their own petard, the wealthy seem to always cream to the top like sour milk, then the rich refuse to help anyone but themselves, the same racket has been going on since Cain.

  • Damiel says:

    My Google feed recommended this article.

  • Leo says:

    The use of flyash /carbon has also negative impact on placing concrete and durability. Carbon or flyash floats on water it weakening to top layer of concrete when poured. Water is needed For workability and making the concrete level.
    In my experience flyash or cabon will come to the surface and will cause scaling and Spalding in freezing conditions.
    As far as I know or read in roman times in concrete there was use of blood for use of airentrainment.
    Also intresting is the statement that salt water is used,new concrete has tobe free of sodium or calcium for making the new concrete.
    Great discussion thank you.

  • David says:

    Republicans make it, so it’s designed to fail. The Romans never considered making such a thing.

  • Kaden says:

    Republicans made it, because Democrats never work and they hate progress.

    Now, what the HELL did you put a political statement on a non-political article? Was it about politics? No, it was about cement.

    This teenager thought the article was interesting.

  • Thomas Edward Shultz says:

    What if the steel were completely cleaned of rust, (or immediately at the end of its production process, before any rust could form), then coated with some anti-rust compound?
    I worked in a warehouse, selling steel repair for use in construction. I know, and can certify, almost all steel reinforcement rebar is rusty as hell, when bought for construction use. They don’t give a f___.

  • Thomas Shultz says:

    I wrote REBAR, not “repair”! Sh!t.

  • Bryan says:

    They do, or did, market an epoxy coated rebar that solved the rust issues, but the price was prohibitive and I don’t think it Caught on.

  • Mike says:

    This showed up in my standard Google “news/stories” feed.
    Was under your openculture link.

  • Brian k says:

    @Thomas Edward Shultz

    My understanding is that surface rust on the steel at the time of pouring is of no consequence because the acids absorb the surface oxidation which actually helps the steel to bond to the cement during the curing process. Once the concrete has cured however, if the steel begins to rust – that is a problem because it results in the de-bonding of the steel from the concrete and eventual spalling. How does the steel start to rust once it’s embedded in concrete? Moisture migrates into the concrete due to its porosity. If this moisture is exposed to freeze/thaw cycles it can cause cracking. Then the spiral of disintegration begins: the cracks formed by freeze-thaw cycles introduce more moisture, more freezing induced expansion and cracking, and eventual disintegration of the structural integrity of the concrete. Throw road salts into this process and you have a recipe for the US infrastructure spending bill.

  • Maria Hicks says:

    Me too, Google news!

  • Will says:

    From Google News aggregator on Samsung fold home screen.

  • Kurt says:

    Google news feed for me

  • Zafiel says:

    Umm, I think you are all forgetting that these buildings we currently see are their critical infrastructures. We have even fewer remains of normal infrastructure from their time. So to say that Roman concrete in general is better than our modern concrete is to say that high grade concrete of the past is being compared to our normal concrete.

    The best comparison for our concrete that would be used is probably the concretes used in highly sensitive military infrastructure and governmental buildings.

  • pimalu says:

    Business are business…you know..

  • pimalu says:

    Better use stainless steel bars

  • Some guy says:

    I found this page from my newsfeed

  • John deforest says:

    Did u notice most spelling Nazis usually have little or no substance to contribute !

  • Aldarindi says:

    Thanks for an interesting and thought provoking segment.
    One of my engineering teachers told me that the construction of many of the ancient world’s concrete structures employed the deliberate use of voids, empty amphora and such, to give the structural advantages of massive thickness, with minimum expenditure of materials, and a structure of least weight, for its dimensions.
    Thanks again this was fun.

  • J Moore says:

    Nice summary of the basic concepts of roman concrete and the issues which surround it. These are discussed in more detail on my father’s web site, romanconcrete.com and in his book “The Roman Pantheon, The Triumph of Concrete”. Its great that Mr. Kelly actually made test samples and showed the importance of water ratio on concrete strength and how modern additives can allow less water to be used while maintaining workability.
    My father, David Moore P. E., actually attempted to recreate roman concrete itself using natural materials such as pozzolan from Italy and lime and to simulate the process of compacting to minimize water usage. But he passed on in 2012 before he could finish the research. He loved to study this marvelous material and the creative Romans who made it!

  • Tamerin says:

    Lol what it seems like we could make concrete on that level it’s just cheaper and more convenient not to.

    Saying there’s is better because commonly we use one that’s pretty cheap even though we have the ability to make many different qualities and kinds of concrete is so silly.

  • carlar says:

    found it on a flipboard email, someone flipped it into Archetypes

  • Eric griffin says:

    Bout time someone finally said it .there are some other minor additions you can add or subtract .but less water and packing it .calcium And other things add to more cracking .never set fence posts in wet mixed concrete.just pour in dry bags.they will harden when they do.tgere won’t be that moisture collecting void that holds water between hard ened concrete and post.from wind or fence movement it also depends on it’s use a less brittle concrete mix that is much softer than a harder stronger on3 may last longer life it it was used in something needing to Alex more

  • Eric griffinits not from anywhere with much knowledge.especially Craftsman's first hand type.m says:

    Bout time someone finally said it .there are some other minor additions you can add or subtract .but less water and packing it .calcium And other things add to more cracking .never set fence posts in wet mixed concrete.just pour in dry bags.they will harden when they do.tgere won’t be that moisture collecting void that holds water between hard ened concrete and post.from wind or fence movement it also depends on it’s use a less brittle concrete mix that is much softer than a harder stronger on3 may last longer life it it was used in something needing to Alex more

  • Leni says:

    Learn from the best. In the case of Romans…they learned pretty much everything from Greeks and to a lesser extent the Etruscans.

  • Me says:

    Nothing worse than the grammar Nazi

  • Phat Khat says:

    Google feed for me, too.

  • Tim says:

    Google feed. Love articles like this.

  • Tim Kluxdal says:

    Google feed. Love articles like this.

  • Jpm says:

    I hate to be the guy trying to chip a hole or work with such a hard concrete..but for structure purposes I’ve worked on so many different jobs..some concrete amazes me how strong it. Is cureing the answer.maybe

  • Alex says:

    Working on bridges the last couple years I noticed all the rebar is epoxy coated a light green…
    I’d guess this is to eliminate the oxidation factor and degradation of the concrete…
    Alex

  • Steven says:

    A retired IRS executive told me in the 90’s that over nearly 20% of the federal tax dollar is graft from road construction.
    It’sTexas as well. Highway 45 going thru Houston, except for 1day, has been under constant reconstruction.
    Sir, you are correct. Criminal behavior is too often rerwarded in these United States

  • Mike says:

    Roman concrete uses Pozzolanic cement – not as we use, Portland cement. Hence this volcanic derivative produces for more coherent structures.
    PS I haven’t a clue what you said in your message – too much gobbledegook – maybe you need to learn to use a spell checker?

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