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Was Roman Concrete Better?

Was Roman Concrete Better?


The largest unreinforced concrete dome in
world is on the Pantheon. It’s not a modern marvel, but rather an
ancient Roman temple built almost two thousand years ago. So, if concrete structures from the western
Roman Empire can last for thousands of years, why does modern infrastructure look like this
after only a couple of decades? Hey I’m Grady and this is Practical Engineering. In today’s episode, we’re taking a look
at the factors that affect the design life of concrete. This video is sponsored by Brilliant. More on that later. If you haven’t seen the previous videos
in this series about concrete, here’s a quick synopsis. We’ve talked about how concrete’s made,
why it often needs reinforcement, and how that reinforcement can sometimes lead to deterioration. Concrete reinforced with steel bars is the
foundation of our modern society. The reinforcement is required to give the
concrete strength against tensile stress. We use steel as reinforcement because of its
strength, its similar thermal behavior, its availability, and low cost. But steel has an important weakness: it rusts. Not only does this corrosion reduce the strength
of the reinforcement itself, but its by-product, iron oxide, expands. This expansion creates stresses in the concrete
that lead to cracking, spalling, and eventually the complete loss of serviceability – i.e.
failure. In fact, corrosion of embedded steel reinforcement
is the most common form of concrete deterioration. But it hasn’t always been that way. The Romans got around this problem in a very
clever way: they didn’t put steel in their concrete. Simple enough, right? They harnessed the power of a few clever structural
engineering tricks like the arch and the dome to make sure sure that their concrete was
always resisting compression and never tension, minimizing the need for reinforcement. One of those clever tricks was just making
their structures massive, and I mean that literally, because the simplest way to keep
concrete in compression is to put heavy stuff on top of it, for example, more concrete. We use this trick in the modern age as well. Most large concrete dams are gravity or arch
structures that rely on their own weight and geometry for stability. In both gravity and arch dams, the shape of
the structures are carefully designed to withstand the water pressure using their own weight. You can see how they get larger, the deeper
you go. So, even with the tremendous pressure of the
water behind the structure, there are no tensile stresses in the concrete, and thus no need
for reinforcement. But lack of steel reinforcement isn’t the
potential only reason Roman concrete structures have lasted for so long. One of the other commonly-cited suggestions
for the supremacy of Roman concrete is its chemistry. Maybe they just had a better recipe for their
concrete that somehow got lost over time, and now those of us in the modern era are
fated to live with substandard infrastructure. In fact, in 2017, scientists found that indeed
the combination of seawater and volcanic ash used in ancient roman concrete structures
can create extremely durable minerals that aren’t normally found in modern concrete. But that’s not to say that we can’t make
resilient concrete in this modern age. In fact, the science of concrete recipes,
also known as mix design, has advanced to levels a Roman engineer could only dream of. One of most basic, but also most important
factors in concrete’s chemistry is the ratio of water to cement. I did an experiment in a previous video that
showed how concrete’s strength goes down as you add more water. Extra water dilutes the cement paste in the
mix and weakens the concrete as it cures. The Romans knew about the importance of this
water to cement ratio. In historical manuscripts, Roman architects
described their process of mixing concrete to have as little water as possible, then
pounding it into place using special tamping tools. Interestingly enough, we have a modern process
that closely mimics that of the ancient Romans. Roller Compacted Concrete uses similar ingredients
to conventional concrete, but with much less water, creating a very dry mix. Rather than flowing into place like a liquid,
RCC is handled using earth moving equipment, then compacted into place using vibratory
rollers like pavement. RCC mixes also usually include ash, another
similarity to Roman concrete. It’s a very common construction material
for large gravity and arch dams because of its high strength and low cost. Again, these are usually unreinforced structures
that rely on their weight and geometry for strength. But, not everything can be so massive that
it doesn’t experience any tensile stress. Modern structures like highway overpasses
and skyscrapers would be impossible without reinforced concrete. So, generally we like our concrete to be more
viscous or soupy. It’s easier to work with. It flows through pumps and into the complex
formwork and around the reinforcement so much more easily. So, one way we get around this water content
problem in the modern age is through chemical admixtures, special substances that can be
added to a concrete mix to affect its properties. Water reducing admixtures, sometimes called
superplasticizers, decrease the viscosity of the concrete mix. This allows concrete to remain workable with
much lower water content, avoiding dilution of the cement so that the concrete can cure
much stronger. I mixed up three batches of concrete to demonstrate
how this works. In this first one, I’m using the recommended
amount of water for a standard mix. Notice how the concrete flows nicely into
the mold without the need for much agitation or compaction. After a week of curing, I put the sample under
the hydraulic press to see how much pressure it can withstand before breaking. This is a fairly standard test for concrete
strength, but I’m not running a testing lab in my garage so take these numbers with
a grain of salt. The sample breaks at around 2000 psi or 14
MPa, a relatively average compressive strength for 7-day-old concrete. For the next batch, I added a lot less water. You can see that this mix is much less workable. It doesn’t flow at all. It takes a lot of work to compact it into
the mold. However, after a week of curing, the sample
is much stronger than the first mix. It didn’t break until I had almost maxed
out my press at 3000 psi or 21 MPa. For this final batch, I used the exact same
amount of water as the previous mix. You can see that it doesn’t flow at all. It would be impossible to use this in any
complicated formwork or around reinforcement. But watch what happens when I add the superplasticizer. Just a tiny amount of this powder is all it
takes, and all of a sudden, the concrete flows easily in my hand. In many cases, you can get a workable concrete
mix with 25% less water using chemical admixtures. But most importantly, under the press, this
sample held just as much force as batch 2 despite being just as viscous as batch 1. The miracle of modern chemistry has given
us a wide variety of admixtures like superplasticizers to improve the characteristics of concrete
beyond a Roman engineer’s wildest dreams. So why does it seem that our concrete doesn’t
last nearly as long as it should. It’s a complicated question, but one answer
is economics. There’s a famous quote that says “Anyone
can design a bridge that stands. It takes an engineer to build one that barely
stands.” Just like the sculptors job is to chip away
all the parts of the marble that don’t look like the subject, a structural engineer’s
job is to take away all the extraneous parts of a structure that aren’t necessary to
meet the design requirements. And, lifespan is just one of the many criteria
engineers must consider when designing concrete structures. Most infrastructure is paid for by taxes,
and the cost of building to Roman standards is rarely impossible, but often beyond what
the public would consider reasonable. But, as we discussed, the technology of concrete
continues to advance. Maybe today’s concrete will outlast that
of the Romans. We’ll have to wait 2000 years before we
know for sure. Thank you for watching, and let me know what
you think! Thanks to Brilliant for sponsoring this video. In my career as an civil engineer, I’m constantly
on the lookout for new ways to do my job better, and often that means learning new skills. Recently, I’ve been using Brilliant to brush
up on my understanding of probability. Civil engineers work on projects that can
last many years, so for me, being able to anticipate risks and estimate their probability
has helped me get ahead at work. Brilliant starts you with the fundamentals
and provides interesting exercises and puzzles to help you master each concept at your own
pace. I find that I learn best when I can apply
the skills immediately, so I love the interactive problems you can work in each lesson. To support this channel, go to brilliant.org/practicalengineering
and sign up for free. The first 200 people will get 20% off the
annual Premium subscription. Again, thank you for watching, and let me
know what you think!

Comments (100)

  1. The lack of a intergenerational contract is the reason why we do not make building ment to last thousands of years.
    This is sad that the modern people can not build things that will only pay of in the lives of there grate grate grate grand children.

  2. Roman structures didn’t have tens of thousands of cars driving over it every day

  3. Often brick-layers will add plaster-sizing agents (orange/brown) liquid to mortar mix to stop it going off or drying, I've mixed many times with this stuff and its amazing, sometimes when its all ran out they will use washing up liquid as a substitute and it works fine but not to code

  4. The Roman buildings of 2000 years ago are in better shape than the African huts of today.

  5. i dont know if u will ever see this but u are doing amazing work huge fan

  6. Romans didn't have 10 ton trucks driving on there roads 24/7

  7. Wonderful lesson, I dare say the tamping process employed during the construction of the Pantheon's played a role in the dome's solidity. All of the interlocking and compacted little patches of concrete getting the air as dry and helping it all go off evenly. Creating a dense complex conglomerate resistant fissures and cracks. Also the aggregate used on the dome was pumice. A volcanic rock that's very light. So the mix towards the top of the dome has more pumice in it than the base of the dome. The top of the dome is lighter than modern mixes. Its 1700 years old and still looking good.

  8. Romans built to glorify their empire regardless of cost. While today buildings are built for business reasons

  9. I feel better now that with chemical engineering we upped the Romans.

  10. I have just made some,come back in 6 to 7 hundred years and you can see how it worked out.

  11. Concrete sidewalks in KC from before the 1970's (they are marked) appear to outlast newer sidewalks, curbs, bridges, etc. The newer the concrete, the more I expect it to fail. This is especially true in government projects for some reason and less so on residential concrete.

  12. Today… technogy is at the finger tips and they can't perfect building a simple paved road…

  13. What I think is that you talked about the ratio of water to concrete, but in modern concrete you did not talk about the ratio of sand to cement in the concrete.

  14. There is also concrete filled with hemp, which is seldom spoke of, it has very good characteristics, is very renewable and cheap,

  15. Use a liquid rubber coating that you pass the rebar wiring through before bending it into the shape it will be prior to pouring concrete. That way the rubber coating acts like a coat for electrical wiring aka it makes a air tight skin protecting the rebar from oxidation caused by contact with air. Liquid rubber is used extremely common in waterproofing basement concrete walls. There’s no excuse to not use it for making rebar for use in concrete reinforcement phases of civil construction.

    Thank me later.

  16. So the Romans may of had a different recipe for concrete.
    Lost to history – how convenient –
    Perhaps they included the ground bones of all those that opposed them.
    Or maybe it was the addition of volcanic rock.
    Pumice – Concrete – Bone –
    All have similarity in structure.
    I assume plenty of material on hand.
    Just a gruesome stab in the dark.
    🐣

  17. Just a tip for your otherwise informative video. Point your camera down a little. You have too much "dead" space above your head. It will just make your video look better. I am critiquing not criticising.

  18. I read once that Roman concrete got better underwater. Their concrete bridges are best conserved in the parts underwater. Which I hear is the opposite of modern concrete.

    "According to the findings in the journal American Mineralogist, the secret lies in the chemical properties of two of the mixture’s components: lime and volcanic ash, which contained a rare mineral known as aluminium tobermorite. When exposed to sea water, the substance would crystallize in the lime while curing. Rather than be eroded by the water, its presence actually gave the material additional strength.
    "

  19. I love this information.

  20. Where girls cried titanic
    Where boys cried fortnite
    Where men cried Minecraft
    Where lords cried the fall of the Roman Empire

  21. I bloody love this channel

  22. Bullshit!No modern structure, paid by taxes, will out last the ancient ones. Modern contractors are all about cutting corners.
    The ancients had..a different philosophy. They built a thing to last and only then called it done.
    Too damn difficult to have to rebuilt the damned thing every decade or so. Slaves don't come out of an assembly line, you can't really work them to death,not if you're sane. (The CCP being a prime example of insanity)
    Machines …machines are cheaper and their operators,not being their owners, don't really care.

    Good enough for government work. The doom of our civilisation. Politicians meddling , contractors cutting corners, crews that don't really care.
    Engineers may discover or invent whatever, unless its the only material available,with no way to"stretch" it,…constructors wont use it.
    They'll go for the cheap stuff and charge the moon.
    The classical and pre-classical people had other ideas. Among them executing those who stole public money.

  23. I've seen plastic coated rebar being used. When they refurbished the Memorial Bridge between Springfield and West Springfield MA, they used rebar with green or yellow coated steel. It's most likely some type of rubberized plastic coating.

  24. That makes it a modern Marvel.

  25. mystery behing roman concrete must be conected with lava rock, but the problem is that strong crystals are made after lava cooling off and concrete is made by hydration, it is two different things, something must provoke silica from the mix to cristalize during or after the proces of hydration,

  26. Maybe if the costs aren't being used to the sheer large amount of meetings, drafting meetings, redraft meetings, redrafting the redraft meetings, backchannel dealings, ratification meetings, etc. We'd have more features that can be added with the same costs.

  27. Surprised you didn't get into lime mortars and limecrete vs. Ordinary Portland Cement. Also, no mention of Pise d terra or rammed earth, which the Romans seem to have perfected. My old church was built of this in 1850 and it is a viable building material when clad with stucco or other system.
    Lime is making a comeback because it doesn't have the faults of OPC.

  28. "Most infrastructure is paid for by taxes, and the cost of building to Roman standards is rarely impossible, but often beyond what the public would consider reasonable"
    Laughs in 23 Trillion Federal Debt

  29. Romans used animal blood in their concrete. The fats in the blood react with the other ingredients to stabilize the mixture.

  30. If houses in America were built to European standards of stone and plaster, they would last much longer, but the economy would not grow nearly as much and houses would cost far more. Speed is just as important as quality when building. Sometimes you don't need the perfect, just the good.

  31. Why not just galvanize the rebar?

  32. Did The Roman use Greeks to build the pantheon. Yes, the Colosseum also, using all three Greek styles. The Corinthian capitals on the pantheon gives the first clue.

  33. Our buildings and infrastructure, water and sewage, skyscrapers and bridges, all wouldn't survive very long if we didn't maintain them or weren't around to do so. Our structures have a survival rate of 50 to ~100 years and not much more. The Roman structures lasted 1,000-2,000 years of no one maintaining them and still worked or only needed repairing from vandalism, like the Cloaca Maxima (still functioning today after 2,500 years) or the aqueducts. Sure your sacrificing some time in building but your gaining centuries or millennia of usefulness and efficiency, the pantheon took 8-10 years with Roman technology to build and the Hagia Sophia of the eastern empire took 6 years, as compared to the largest buildings of the dark and medieval periods following which took a century or more to construct in a great many cases, even castles of that later time would take more than 2 decades to build. Of course even in Ostia you can see the brick and concrete ruins of the many apartment blocks of the city which would've gone up to 6 floors or 8 in rare cases (the emperors did introduce height regulations for many cities including Rome itself so they could've built up higher if they wanted), so even the civilian structures still exist in Rome and some of its cities which would defiantly not be the case for our homes of today built out of timber or concrete and brick not of the Roman quality for survival.

  34. You went full circle on this all a tad wiser no new. Information. Liked your vid look for more

  35. Do this test with geopolymer!

  36. They used blocks of limestone to build these structures.

  37. The Romans didn't invent concrete, the Carthaginians did.

  38. Gravity doesn't exist. It is merely a theoretical construct to support a false premise. Weight and relative density are the known measurable variables.

  39. You can also make a roof that will last hundreds of years. Some churches in Europe for example, are hundreds of years old. But the cost is staggering.

  40. I think that it needs addressing that many modern structures undergo far larger stresses than many Roman structures. Both us and the Romans have bridges, but our bridges support 2-3 thousand pound loads several thousand times per day, whereas Roman structure likely did not face the same fatigue stress.

  41. 5:20 Preview of next episode: Was Roman Heroin Better?

  42. How did the Roman's have better concrete then modern man? ALIENS!!

  43. Velkam tu tö Haidroolik Pres Tsänel.

  44. the French successfully emitted the production of antique concrete from Egypt https://www.youtube.com/watch?v=znQk_yBHre4

  45. the Romans may have used no slaked lime in their concrete more than volcanic ash.Although St. Sophia Cathedral in Istanbul used fine powder from old baked pottery.while for the reinforcement they had specially shaped bricks with openings but it was possible to use human ор horse hair and wrought iron rods from old barrels.

  46. I understand your explanation about the water to concrete ratio affecting strength but I also know that a long curing time also increases hardness, which is lengthened by having more water in the mix or added after the concrete is placed in its form. But you make no mention of curing time nor the means of lengthening it.

  47. The biggest enemy for building something is water. The same goes for using concrete. The driest mix is the best, and plasticizes are allowed. Compaction is what the Romans did. Yes, I know that is hard to do, but if you want the best, it takes physical or mechanical effort. Sloppy slurry is not what I recommend. Low slump and compaction is the key.

  48. Modern engineers suck.

  49. I don't see any comments from year 4000 or so.
    I don't know what it means.

  50. Grady: Hey, I’m Grady
    Me: Hey Grady!

  51. I wish we made things to last. It would be better than constantly having to deal with a crumbling infrastructure.

  52. Judging by Pittsburgh's concrete bridges, they didn't last more than a few decades.

  53. What about other types of cement? The 4th Eddystone Lighthouse was made with an experimental hydraulic lime – it hardened so much that, when they replaced it with an automated lighthouse in 1982, the grout was harder than the stones, and they left the lower 1/3 in the sea. The upper 2/3 are in a nearby park – The Hob, I think.

  54. I disagree with your assertion that the public has any say in what our taxes go to. There are bills in congress with 90% support that will never see a vote.

  55. Up north we use salt in the winter. That cuts way down on longevity.

  56. That crete looks terrible.

  57. You explained in (in another video, I think) that covering the re bar is important, but the concrete being poured in this video shows it resting on the ground, putting it at the lower edge of the concrete.
    What protects this re bar? It seems to be laid on plastic. Is that its protection?

  58. I love mixing concrete as much as you do 🙂

  59. Maybe Austalian high rise apartment builders should watch this lol

  60. I just learned something, Thank You!!!!

  61. Maybe 99% of the Roman concrete building actually crumbled to the ground, and the Pantheon is just an outlier…a freak accident. LOL

  62. That's why we cant use Roman concrete because you have to wait 100 or more years just to take volcanic ash when the volcano erupts.

  63. There's also a very heavy survivor bias.
    For the uninitiated, the bias goes like this:
    During WWII many planes were being shot down, so armor was to be added in the most important parts. So they started logging every bullethole in every returning plane to log where the planes got hit the most. They determined thevmost hit areas were the wings and tail.
    They armored said areas but planes kept going down. How could this be so! They were armoring every single sq inch that planes got hit in! Baffled they went back to the drawing board
    Then someone postulated that maybe, hits were distributed evenly, and that they could try armoring the areas that remain un hit in the returning planes. Said person theorized that no plane returned with hits in the cockpit or fuel storage areas because a hit there would cause the plane to go down. therefore creating these "missing hits"
    Desperate, they tried it and immediately they saw more and more pilots returning to base safely.

    This is the survivor bias. they saw the bullet holes of the survivord and thought "this is why planes go down" instead of "a hit here is not fatal, but that area with no survivor having a hit means that it must be vital"

    Now, we see these structures and compare it with any old building from today. However, these building are not any regular buildings; those are the building that survived.

  64. Observation bias: we have no idea how many Roman concrete buildings fell apart…

  65. I thought you used plasterciser to save on water, never knew it would also make it stronger, we used a liquid type on site, probably a weaker version

  66. "Taxpayers might not want to pay for…"?? RIDICULOUS! Taxpayers aren't allowed to choose. Nothing has changed politically since The Roman Empire. The US Empire/Police State is just as corrupt maybe more so because our infrastructure more quickly crumbles, creating more graft, more crony capitalism. With modern chemistry better concrete exists, but where's the profit in making it last? Remember, public works have the opposite incentive as private. The more wasteful, incompetent, and time-consuming, the more profit.
    Whatever product or service, EVEN security, private enterprise provides it faster, better, cheaper, because of competition. Remove monopoly and you get efficiency. Govt. is a monopoly that grants monopolies to others. IT creates TRUSTS, it doesn't break them up. No govt. – No monopolies.

  67. Traffic is another variable. Waaaaay more people have access to traveling. Even BIRDS change the chemistry of concrete. I.E. Pigeons to Quakers in New York.

  68. REBAR is why modern concrete is shit by comparison to ancient Roman concrete. No matter how hard you try, REBAR WILL RUST and start reducing the strength of the modern concrete.

  69. Americans:We made best concrete.
    Romans:Hold my beer

  70. Is this even a question?!?!

  71. Got to put some blood, in the concrete… like the Romans did………

  72. "brilliant" is bad at geometry. Look at their logo. Those pentagons do not tessellate and all the pentagons that are not the central pentagon have 8 triangles within rather than the 10 of the central pentagon. It's like someone wanted to feature a reverse pentacle without thinking about any of the exterior.

  73. Brilliant, thanks 🙂

  74. Would the drying mix not cure more in that week than the wetter mix and that is why it's stronger?
    Give the wet mix a extra 2 days of curing and see what happens.

  75. Less water, stronger thee Impact that goes over on Top. Great Conversation to have during pouring… especially on different Stages.🇺🇸

  76. So if you add more water and give the concrete more time, will the tensile strength improve and be equal to the dryer mix.

  77. What the hell are you talking about? Corporals Corner has the recipe for Roman Concrete and it's very simple combination of broken down limestone (by creating an exothermic reaction with citric acid until it's the consistency of paste) and mixing volcanic ash and terracotta – all classic materials of Roman lifestyle and technology that the Romans had direct access to. Why do you think they discovered glass blowing technology after observing the effects of volcanically-formed black glass known as "Obsidian"? They were scientific-minded from the get-go (asked the Etruscans how that helped them out to figure out how lightening isn't formulated because two clouds came together to create lightening bolts, but the inverse, rather)

  78. Learnt something…. Tq sirr

  79. My friend's grandpa build few concrete garages near his summer house (Russia). For one garage he used some chemicals to make concrete very tough. Because he just could. Very soon he undestood problem when he decided to make new ventilation hole. Concrete was so strong that it was impossible to drill. In Soviet times we didn't have powerful hammer drills, so he broke some drilling handheld instruments and gave. Next garage (he really loved to build) he made of normal concrete.

  80. I was taught in school cement won't allow metal to rust yet I think I should ask my money back it seems.

  81. woot woot mix design tech niggas

  82. Doesn't the regular cement Portland also comprise ashes?

  83. @ 4:58 If you want concrete to flow better, it would need to be less viscous. Viscosity refers to how thick or gummy a substance is.

  84. Personally not a fan with architecture in the 20th, so no loss if they don't last. Now Ancient Roman architecture… 🤩

  85. Maybe you could look at different basement floor substrate options for tile and other flooring. I've been thinking of a dry mix mortar or strata type design (that eliminates mortar all together). Concrete as a basement floor may not be necessary in many cases.

  86. The size of the aggregate also effects the strength greatly, also contrary to using its own weight for structural integrity Romans were also genius at making it light when needed, such as the pantheon

  87. Another major issue is usage. The pantheon is a self-supporting structure that's sorta just there. People visit it but don't climb on it. Meanwhile bridges suffer structural damage frequently because we're driving trucks across them all the time.

  88. There's also corruption in design. Cutting corners to make projects more profitable for contract holders.

  89. Nice job on the video 🤓. I use RCC in my design of stepped spillways (30-50ft in height), where there is initially high velocities. We can get the same strength in RCC in less than 7 days rather than 28 plus no need for forms.

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  91. They used coconut fiber or pubic hair to volcanic ash concrete. Roaming concrete baby!!!

  92. What a solid explanation of a complex topic. The real-world examples reinforce abstract concepts brilliantly. All this ensures a concrete understanding of the situation.

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  95. 1. Ancient Western Roman Concrete: Lime + volcanic ash + river sand
    2. Ancient Eastern Roman Concrete: Lime + powdered brick + river sand
    3. Ancient Chinese Cement : Quicklime or slake lime + stick rice glue + sand or gravel or both.
    4. John Smeaton Cement: Lime + iron slag powder + clay powder
    5. Upgraded ancient cement: lime + water glass combined with lime + sticky rice glue. The water glass is pre-dissolved in water
    and the lime is pre-dissolved in water as slake lime or quicklime, and the sticky rice glue is in the form of rice glue water.
    Aggregate as sand or gravel or both is added to make a concrete.

  96. hmmm, why not just chrome plate the steel reinforcement parts so as not to rust? Expense maybe?

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