[HN Gopher] Why was Roman concrete so durable?
___________________________________________________________________
Why was Roman concrete so durable?
Author : geox
Score : 587 points
Date : 2023-01-06 20:05 UTC (1 days ago)
(HTM) web link (news.mit.edu)
(TXT) w3m dump (news.mit.edu)
| dang wrote:
| Related:
|
| _Why Ancient Roman Concrete Outlasts Our Own (2017)_ -
| https://news.ycombinator.com/item?id=29366911 - Nov 2021 (67
| comments)
|
| _2,050-year-old Roman tomb offers insights on ancient concrete
| resilience_ - https://news.ycombinator.com/item?id=28833525 - Oct
| 2021 (101 comments)
|
| _Why Roman concrete is stronger than it ever was, while modern
| concrete decays_ - https://news.ycombinator.com/item?id=25690803
| - Jan 2021 (7 comments)
|
| _A chemical reaction in ancient Roman concrete makes it stronger
| over time (2017)_ - https://news.ycombinator.com/item?id=22580920
| - March 2020 (64 comments)
|
| _How Ancient Rome's Concrete Has Survived 2,000 Years (2017)_ -
| https://news.ycombinator.com/item?id=20482050 - July 2019 (81
| comments)
|
| _How Did the Romans Make Concrete That Lasts Longer Than Modern
| Concrete?_ - https://news.ycombinator.com/item?id=15544128 - Oct
| 2017 (3 comments)
|
| _The Rock Solid History of Concrete_ -
| https://news.ycombinator.com/item?id=15480165 - Oct 2017 (12
| comments)
|
| _Why Roman concrete still stands strong while modern version
| decays_ - https://news.ycombinator.com/item?id=14699652 - July
| 2017 (1 comment)
|
| _Ancient Romans made world's 'most durable' concrete_ -
| https://news.ycombinator.com/item?id=14695876 - July 2017 (4
| comments)
|
| _New studies of ancient concrete could teach us to do as the
| Romans did_ - https://news.ycombinator.com/item?id=14690329 -
| July 2017 (72 comments)
|
| _Ancient Roman Concrete Is About to Revolutionize Modern
| Architecture_ - https://news.ycombinator.com/item?id=5883443 -
| June 2013 (23 comments)
|
| _How the pantheon has lasted 2000 years without steel in its
| concrete_ - https://news.ycombinator.com/item?id=1852000 - Oct
| 2010 (35 comments)
|
| Also:
|
| _The problem with reinforced concrete (2016)_ -
| https://news.ycombinator.com/item?id=27282927 - May 2021 (186
| comments)
|
| _The problem with reinforced concrete_ -
| https://news.ycombinator.com/item?id=11975695 - June 2016 (147
| comments)
| russellbeattie wrote:
| I was thinking as I read this, "Wait, don't we already know
| this?" Now I know why.
| jonnycomputer wrote:
| our obsession with Roman concrete.
| TheMagicHorsey wrote:
| Some day in the very far future, our descendants will ask, why is
| the code manually made in the 2020s with Rust so durable, while
| our modern PHP20457 code that is spit out by Tardpilot100 is so
| fragile? Our modern operating systems need to reboot 1000 times
| per hour just to function while ancient operating systems could
| stay on for months at a time without rebooting!
| BirAdam wrote:
| Nah. Rust evangelists of the future will still be fervently
| rewriting everything in Rust, and they'll be researching why
| ancient code worked without being written in Rust.
| bachmitre wrote:
| It looks like ChatGPT already knew that (or I skimmed too
| quickly):
|
| Why was Roman concrete so durable?
|
| Roman concrete, also known as opus caementicium, was a highly
| durable construction material used by the ancient Romans for a
| variety of structures, including aqueducts, bridges, and
| buildings. There are several factors that contributed to the
| durability of Roman concrete:
|
| The use of lime and pozzolanic materials: Roman concrete was made
| from a mixture of lime, water, and an aggregate such as sand or
| crushed stone. The lime was derived from the heating of
| limestone, which produced a highly reactive form of calcium
| oxide. The Romans also added a pozzolanic material, such as
| volcanic ash, to the mixture, which improved the durability and
| strength of the concrete by reacting with the lime to form a
| cementitious material.
|
| The inclusion of a reinforcement material: Roman concrete was
| often reinforced with a material such as iron or lead, which
| helped to increase its structural strength and resist cracking.
|
| The use of a hydraulic setting process: Roman concrete was able
| to harden underwater due to its hydraulic setting properties,
| which allowed it to set and cure even in the presence of water.
|
| The construction of thick, monolithic structures: Roman concrete
| was often used to build thick, monolithic structures such as
| walls and foundations, which were able to withstand the forces of
| nature and resist deterioration over time.
|
| Overall, the combination of these factors made Roman concrete a
| highly durable construction material that has stood the test of
| time.
| itsthecourier wrote:
| Read the article, they discover they should use a particular
| state of lime, quicklime. That's new
| dgoldstein0 wrote:
| > The inclusion of a reinforcement material: Roman concrete was
| often reinforced with a material such as iron or lead, which
| helped to increase its structural strength and resist cracking.
|
| Sounds like chatgpt messed up it's facts? If this means
| reenforced like with rebar, the Romans didn't do that - and
| that's part of why their concrete structures lasted so long -
| when designed to be under compression rather than tension
| (arches, domes, etc)
| buttofthejoke wrote:
| [flagged]
| af78 wrote:
| Relevant thread:
| https://twitter.com/cleptok/status/1611622181665923075
|
| Ok. Let's do a short thread on Roman cement for the 3 people out
| there that might be interested. You often hear that the Romans
| had some sort of superior and arcane knowledge on superior cement
| mixes that has been now lost. And still today we cannot replicate
| it. This is complete nonsense. Modern day cement (and any other
| building material, really) is far, far superior than anything
| from the past. There is simply no comparison. Above everything we
| understand the chemical composition, interaction and quality
| control for consistent results.
|
| Romans were making mortars based on volcanic ashes. There was no
| set recipe. Every builder had their own. Volcanic ash from
| Pozzuoli, crushed brick, slaked like, animal fat, hair etc. Some
| basic rules existed (as recorded by Vitruvius on the 10 books on
| Architecture).
|
| Millions of structures were constructed these way. With the
| exception of a handful, most of these do not exist anymore. But
| why the ones that exist are still standing strong?
|
| Usually via a simple Darwinian process. Most of these times those
| builders got it wrong. But in a few cases, out of luck, they got
| the chemistry just right. This would result in a ok-ish material,
| with decent properties. Not only that. Unreinforced (without
| steel) concrete will not suffer any serious deterioration, with
| few exceptions. (Pantheon in Rome) Also the very coarse pozzolan
| they were using, will chemically react very very slowly producing
| low initial strengths Vs any modern material.
|
| In the long term (centuries) though, it will continue gaining
| strength. Totally useless for the original purpose of the
| builders, but quite good for the few surviving buildings.
|
| So what the latest MIT research told us? That lime in very small
| quantities will be "self-healing'. And this somehow is something
| that the Romans knew and used to create a superior cement.
|
| This is simply not true. It is well known that lime expands (the
| pompous "self-healing" tag), so in very small and precise
| quantities it will counteract the shrinkage and cracking
| behaviour of cement binders. But you have to be pretty lucky to
| get it just right.
|
| So not intentional. Just survivor bias in the remaining Roman
| cement structures. Beyond this, lime is a definite no-no for any
| concrete with steel in it -it corrodes it. The reason we use
| concrete today is precisely the embedded steel. It allows to
| build all modern structures.
|
| And steel is the reason modern concrete deteriorates. It
| corrodes, expands and cracks the surrounding concrete. An
| unreinforced concrete (like the ones Romans used) with modern
| materials and understanding would last forever. But you wouldn't
| build anything worthwhile.
|
| Final. Remember. Cement = the glue, the binder that holds
| everything together, activated by water. Concrete= the actual
| building material with binder, water, sand and stones. Mortar=
| only binder, sand and water (maybe small stones)
| MayeulC wrote:
| That reads as somewhat misguided and dismissive. You don't have
| to understand the chemistry to improve recipes by trial and
| error, over multiple generations, and learn from the still-
| standing structures.
|
| And there is still value in studying today those that survived
| in order to improve ours. The way lime healed cracks is new to
| me at least, but it's taken as a given here.
|
| > you wouldn't build anything worthwhile
|
| You just need more cement, it could be replaced with fibers. We
| still use unreinforced concrete in some cases.
| amai wrote:
| And the real deal is modern
| https://en.m.wikipedia.org/wiki/Textile-reinforced_concrete.
|
| Especially the combination of carbon fiber and concrete is a
| very promising solution, which is researched in Germany:
| https://de.m.wikipedia.org/wiki/Carbonbeton
|
| This stuff is superior to anything the romans did in every
| aspect.
| imtringued wrote:
| Honestly, I think a much bigger factor than random chance is
| the designed lifespan of these buildings. Some of them took
| decades or even centuries to build. So they must not only last
| throughout the construction process, they must also last long
| enough to make the construction process be worth it.
|
| Spending a few decades on experimentally determining an optimal
| cement mixture is also worth it.
|
| The by far biggest problem is that the vast majority of
| buildings get demolished and replaced by something else so
| making them long lasting is not very useful.
| avereveard wrote:
| sea water + quicklime was known to be the "secret" for concrete
| for a while, this is a 2017 article
| https://www.washingtonpost.com/news/speaking-of-science/wp/2...
| can we put this to rest already?
| [deleted]
| ricardobeat wrote:
| If you pay attention to the article, the previous theory of
| seawater + volcanic ash turns out to _not_ be the main reason
| for it 's durability. The lime clasts being a feature, not a
| bug, and hot mixing, are the new discoveries.
| [deleted]
| johnohara wrote:
| Disappointed that this article didn't at least give a "tip of the
| hat" to the dogged research done by Dr. Marie Jackson, et.al.,
| over her career at multiple universities.
|
| Here is an excellent read on this subject from 2013:
| https://cedar.wwu.edu/geology_facpubs/75/
| urthor wrote:
| Says a lot doesn't it.
|
| Marie Jackson makes it into the citations twelve times.
|
| Otherwise not mentioned by name.
|
| Academia:
|
| You thought capitalists were greedy for mere money? Come meet
| academics.
| trynewideas wrote:
| The lead author of this study, Linda M. Seymour, worked with
| Jackson on reference 29, on the mortar of the Tomb of
| Caecilia Metella, which is referenced repeatedly and the
| samples from which form a significant part of the hypothesis.
|
| That study: https://ceramics.onlinelibrary.wiley.com/doi/10.1
| 111/jace.18...
|
| Story on that study: https://als.lbl.gov/unexpected-
| transformations-reinforce-rom...
|
| Jackson is quoted, if briefly, by _Science_ 's article on the
| new paper.
| https://www.science.org/content/article/scientists-may-
| have-...
|
| Jackson's work is focused on pyroclastic volcanism. Seymour's
| work has focused on Roman water infrastructure.
|
| Jackson works for the University of Utah, Seymour works for
| MIT. The linked source is MIT's PR department.
| johnohara wrote:
| Thank you for pointing this out.
|
| A common thread, and no doubt mutual fascination behind
| Jackson's and Seymour's research, is the use of specific
| pozzolans found in and around Campi Flegrei volcano west of
| Naples.
| urthor wrote:
| That's true, I'm not giving any credit at all to the fact
| the article isn't written by the paper's authors, and is at
| best a summary.
| [deleted]
| next_xibalba wrote:
| Agreed. But is this not an example of a fundamental
| attribution error? The structure and incentives of academia
| creates all the credit grabbing and back stabbing (IMO).
|
| https://en.wikipedia.org/wiki/Fundamental_attribution_error
| [deleted]
| t3estabc wrote:
| [dead]
| hinkley wrote:
| I think the bigger question for me, and it comes up about half
| the time when the topic of Roman concrete comes up, is to what
| extent Roman concrete has a lower or higher lifetime carbon
| footprint than modern concrete.
|
| Stronger concrete means either less concrete or a slower
| replacement schedule, and the Roman formula absorbs a certain
| amount of CO2 out of the air as it ages.
|
| The second to last paragraph of this article talks about it:
|
| > 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.
|
| As we reach the end of the petroleum economy we are going to have
| a problem with making asphalt, as it is essentially diverting a
| waste stream from oil refining. When we only use petroleum for
| materials instead of setting it on fire, that's not going to be a
| 'free' stream of materials anymore.
| thowei2i34234 wrote:
| Reminds me of the Wootz Steelmaking (and much else) in classical
| India which was lost during the period of Anglo-Islamic
| colonization. Roman empire, Egypt and Greece, IMO is, contrary to
| current myths, is far closer in spirit to India than to anything
| of the 'modern West'. Indeed, the Greeks ruled parts of India for
| many centuries, and Rome had a great amount of trade with it.
|
| The loss of so much rich tradition across the world due to birth
| of religion and its obsession with tyrannical power over
| everything is such a tragedy on humankind... this was recognized
| by the thinkers of Europe during the wee end of the
| 'renaissance', but in light of post-WW2 plebification of
| intellectuals, is being rolled back because of the current crop's
| moronic obsession with another religion: Marxism.
|
| Such tragedy. tck. Such tragedy.
| kaesar14 wrote:
| What an atheist meme. These things were 'lost' because of
| breakdowns in trade networks caused by breakdowns of central
| authority and invasions by outside powers. If anything, the
| Church is what's kept the Classics alive through its usage of
| Latin in the clergy and its preservation of Roman structures as
| churches.
| ziotom78 wrote:
| The Pantheon is a perfect example. It has survived for 2000
| years because it was repurposed as a church.
| pigsty wrote:
| And lots of other Roman buildings didn't survive because
| they were destroyed so the blocks could be repurposed into
| churches in other locations.
|
| The Parthenon is one (1) building that survived basically
| as-is while countless others were actively demolished.
|
| One thing that surprised me when visiting Rome is how
| little original buildings existed. But when you get
| increasingly far from the city of Rome, you'll find quite a
| few well preserved Roman buildings that were out of reach
| of the long tentacles of the Catholic Church.
| ziotom78 wrote:
| The Pantheon is just an example, but many other instances
| can be found in Rome: the Church of Santa Maria degli
| Angeli, the Basilica of Saints Cosmas and Damian, etc.
| (These are just examples you find in Rome, there are
| plenty of other examples here in Italy.)
|
| The OP suggested that the loss of architectural art is
| mainly due to a clash of different cultures and to
| religion. While there were cases where this was surely
| true (the many churches destroyed during French
| Revolution!), in most of the cases the reasons were much
| more practical and did not involve conflicting cultures
| or the <<long tentacles of the Catholic Church>>.
|
| Before the concept of <<historical preservation>> was
| invented, what should have been the point to keep a
| temple to Venus in the crowded center of a city, when
| nobody worship her any longer and that very space could
| have been used for something more useful?
|
| These acts of destruction happen all the time even
| _within_ the same cultural context. For instance, the old
| Vatican Basilica, built in the IV century, was destroyed
| and rebuilt in the XVI century by the Pope himself! And
| the same applies to countless of other important ancient
| churches and public buildings (My favourite example: the
| astonishing church of St. Clemente [1], well worth a
| visit if you 're in Rome! The XI-century building was
| erected over the old VI-century church.) Not only
| churches, but frescoes in churches have been continuously
| covered by newer frescoes, once the taste of the church
| goers changed. A few days ago I visited the beautiful
| church of Sant'Abbondio in Como [2]: the church dates
| back to the XI century, but the old frescoes were covered
| by newer ones in the second half of the XIII century.
|
| Even the Romans did the same for many of their buildings:
| once they realized that they were no longer useful or
| usable, they either repurposed them or destroyed and
| built something else on the rubble. The Colosseum was not
| built on pristine land! And Nero destroyed a lot of
| houses to build his Domus Aurea, which was later
| destroyed by Vespasian and Titus and covered by newer
| constructions, with the intent of make people forget
| Nero. (No, as far as I know neither Nero nor Vespasian or
| Titus were catholic.)
|
| It's a pity for scholars, but before historical
| preservation was a thing, it was often the best thing to
| do, as the older buildings did no longer fit their
| purpose. These acts of destruction made the world lose
| important pieces of art, but they were meant as a way to
| repurpose the spaces of the city according to the evolved
| needs of its inhabitants. This is particularly true for
| cities like Rome, which have been populated continuously
| for ~2500 years.
|
| [1]
| https://en.wikipedia.org/wiki/San_Clemente_al_Laterano
|
| [2]
| https://it.wikipedia.org/wiki/Basilica_di_Sant%27Abbondio
| kaesar14 wrote:
| Exactly my point as well. The ancients didn't think to
| not tear down buildings so we could discover them 2000
| years later. It's a miracle anything of that time is left
| at all in terms of physical structures, and the best
| preserved have been buildings repurposed by the church.
|
| This isn't even touching on the subject of the Latin
| corpus which is ONLY extant because of the Church.
| ReptileMan wrote:
| Wootz steel was never lost. Just the contaminated with vanadium
| ores they used disappeared. We know quite well what happens to
| a carbon steel with vanadium. Most high performance steels
| today are made with it in the alloy.
| legitster wrote:
| Chemistry might be important, but we don't necessarily need that
| deep of an analysis.
|
| Romans didn't mind over-engineering with massive, inefficient
| structures. They didn't worry about complex/thin shapes, or any
| tensile elements. No rebar, no "piping" cement, etc. And they
| could put up with extremely long cure times.
|
| The end result is very, very dense concrete.
|
| We could probably recreate the durability of their concrete if we
| were actually willing to put up with the compromises they
| represent.
|
| https://practical.engineering/blog/2019/3/9/was-roman-concre...
| titzer wrote:
| [flagged]
| DenisM wrote:
| Please don't do this, it's against the rules:
|
| https://news.ycombinator.com/newsguidelines.html
|
| _Please don 't comment on whether someone read an article.
| "Did you even read the article? It mentions that" can be
| shortened to "The article mentions that"._
| starfallg wrote:
| In this case, the original poster went on a complete
| tangent without addressing the topic of the article at all.
|
| So my vote is for the person who pointed this out as he's
| most likely right in his deduction.
| ghshephard wrote:
| I don't think there is any requirement to read an article
| - that's implicit in the guideline that you don't comment
| on whether a poster read the original article.
|
| I would say 75-80% of the time I read the comments first,
| and probably close to 25% of the time I never read the
| posted article. Also - I found that comment regarding
| modern concrete, and the pointer to PracticalEngineering
| to be, by far, the most interesting comment so far -
| significant contribution. (And yes, I did read both in
| their entirety)
|
| Perhaps a better response might have been, "The
| PracticalEngineering article is missing the key detail
| regarding the exothermic hot baking associated with using
| quicklime instead of, or in addition to, the slaked lime,
| and the self-healing properties associated with that.
| Though the lack of corrosive iron, long curing times, and
| large structures might be more important - and its
| unfortunate the original article doesn't mention those as
| an important detail to at least demonstrate the authors
| were aware of this."
| starfallg wrote:
| That link is 'old news'.
|
| What the poster of that link effectively said is that I
| know all there is about this topic, then post an
| 'interesting' link as his source, without realising that
| the current topic is new development not covered by it.
| bob29 wrote:
| Please don't do _this_ it's also against the rules:
|
| _Don 't feed egregious comments by replying; flag them
| instead._
|
| Live by the sword die by the sword
| maximus-decimus wrote:
| But... you also just did it
| silisili wrote:
| But, you replied pointing out that he did it. It's flags
| all the way down.
| bob29 wrote:
| All this pedantry is turning this place into Reddit
| samstave wrote:
| 100% disagree with flagging.
|
| Have the knowledge balls to respectfully disagree.
| flagging just looks like throwing rocks as opposed
| knowingly refuting something.
|
| its also why I am very conservative upvoting anything,
| anywhere, any site.
| Zircom wrote:
| [flagged]
| mortehu wrote:
| I think we can make an exception when someone essentially
| says "we don't need this article" without addressing its
| contents.
| samstave wrote:
| I dont know if in a minority ; I always read the comments
| on a post before I read the article...
|
| I do this here and on reddit as well...
|
| I still read the articles, but I like to grab the gist
| from comments first, it allows me to be able to read the
| article faster as I can skim and search at the same time.
| gerdesj wrote:
| "Chemistry might be important"
|
| Conc is nearly all about chemistry. You mention curing rather
| than drying so you surely have some idea about what is going
| on. The Romans did not have electron microscopes so could not
| watch the way the matrix develops around the aggregate etc etc
| from the get go. To be fair, I fried my first sample in the
| beam at college by over focussing.
|
| They didn't use rebar because they generally built in
| compression - arches etc. Rebar and pre-stressing enables
| members to cope much better under tension. A PS beam or slab is
| a modern marvel and even protects the steel from fire - bonus.
|
| Cure times: weather/environment. In hot climes you need to stop
| the water buggering off the surface and leaving cracked and
| spalling surfaces before it even cures. It may also over heat
| (exothermic reaction). Cold - slower curing, too cold - no cure
| and frozen water (total disaster). Underwater - watch your
| fines wandering off and going for a smoke behind a reef and
| your structure collapsing, unless you keep them in place.
|
| Concrete curing is not like smoking a joint of meat! A quick or
| slow cure may be indicated depending on conditions. We have
| admixtures and all sorts to fiddle with parameters. Then you
| have things like grading and composing your agg. and other
| exciting stuff.
|
| I could go on at some length - it is really, really
| complicated. Roman engineers managed to invent an ancient
| wonder of chemistry and physics that was concrete. Their
| approach to its use and improvements was obviously rather
| better than what passed for science and medicine at the time!
| They do seem to have experimented and gone with what worked
| best but it was never deliberately developed from first
| principles. The self healing thing was probably a happy
| accident.
|
| A Roman engineer had some rather different design constraints
| than a modern Civil. For starters, failure could quite
| legitimately be blamed on the god's displeasure. "When that
| bridge was commissioned, we made all the correct sacrifices and
| anyway, you are holding it wrong, I mean walking on it
| incorrectly".
|
| (sp)
| UncleEntity wrote:
| > Roman engineers managed to invent an ancient wonder of
| chemistry and physics that was concrete.
|
| Technically, the ancient Egyptians used concrete in
| construction long before the Roman engineers were a thing.
| The difference is they used it for mundane things like wine
| cellars while the Romans integrated it into their whole
| architecture system.
|
| Once in a while that art history degree comes in handy...
| fpoling wrote:
| In Ancient Rome blaming gods was never an excuse. For
| example, there an architect or a chief builder had to spent
| several nights under the bridge after its opening. In general
| they followed a rule similar to one in ancient Babylon which
| explicitly required to put the architect to dearth if a
| building collapse would kill the owner. And if the collapse
| would kill a son of the owner, then the son of the architect
| would be put to death.
|
| That puts rather different perspective on the quality and
| longevity.
| Spooky23 wrote:
| I worked on a campus where they were building a building that
| had to be incredibly stable - they had to coordinate arrivals
| of like 30 trucks making 4-5 trips a day. Each truck had like
| 180 seconds to unload.
|
| Because of the coordination requirements, they embedded
| sensors in the structure and adjusted the water for curing
| and would slow down or speed up the flow of trucks based on
| how the process went.
|
| One of the engineers told me that a thousand years from now,
| someone would wonder why this slab is here. I'm sure he was
| mostly kidding, but it seemed believable.
| trynewideas wrote:
| https://www.science.org/doi/10.1126/sciadv.add1602
|
| > ... evidence that the Romans employed hot mixing, using
| quicklime in conjunction with, or instead of, slaked lime, to
| create an environment where high surface area aggregate-scale
| lime clasts are retained within the mortar matrix. Inspired by
| these findings, we propose that these macroscopic inclusions
| might serve as critical sources of reactive calcium for long-
| term pore and crack-filling or post-pozzolanic reactivity
| within the cementitious constructs. The subsequent development
| and testing of modern lime clast-containing cementitious
| mixtures demonstrate their self-healing potential ...
|
| Or, this study finds that Roman concrete regenerated using
| water-reactive calcium carbonate introduced through hot mixing-
| transformed lime clasts. This included observations of Roman
| concrete used in structures that weren't characteristically
| massive or inefficient, and reproducible in reformulated modern
| concrete.
|
| > In the present study, we demonstrate the calcium enrichment
| of matrix phases adjacent to the lime clasts, supporting the
| hypothesis that the lime clasts are a source of calcium for
| leaching and recrystallization within the pore space of the
| mortars. Microcrack filling by calcite has been recently
| observed in ancient Roman mortars from the tomb of Caecilia
| Metella (29), and the self-healing tests carried out on our
| modern samples described in the present study further support
| this hypothesis.
| marcosdumay wrote:
| Interestingly, the article founds out that their concrete cured
| quickly.
|
| Anyway, no, our usual concrete completely breaks down in a few
| centuries. No matter how it's structured, it does not match the
| durability of that concrete without ongoing maintenance.
| samstave wrote:
| >> _A few centuries_
|
| Sounds good to me?
|
| Although, many centuries old _sound_ structures also sounds
| better to me...
| User23 wrote:
| Like the Pantheon[1]? It's still got the world's largest
| unreinforced concrete dome and it's in active use as a
| church not to mention major tourist attraction.
|
| [1] https://en.wikipedia.org/wiki/Pantheon,_Rome
| User23 wrote:
| Yeah, I can't imagine a municipality letting their concrete
| roads cure for a couple years before letting cars on them.
| teilo wrote:
| We do need a deep analysis. Roman concrete is self-healing, and
| this article explains why. And the reason is exactly the
| opposite of the one you postulate.
| knodi123 wrote:
| "Anyone can create a bridge that will hold up under a maximum
| load. It takes a real engineer to create a bridge that _barely_
| holds up under a maximum load. "
| sph wrote:
| It takes an accountant with a tight budget, you mean.
| Engineers will tend to make the most durable thing ever, if
| given enough time and money.
| NegativeLatency wrote:
| Sounds like the chemistry is important
|
| > 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.
|
| > 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.
| interfixus wrote:
| > _massive, inefficient structures_
|
| How does a building, an aqueduct, or a bridge still in use
| after 2000 years manage to be inefficient?
| [deleted]
| [deleted]
| twelve40 wrote:
| > following all of the detailed recipes that had been optimized
| over the course of many centuries
|
| i wonder how all those detailed recipes were passed around for
| many centuries and now all is gone. Was it all passed down
| verbally?
| coryrc wrote:
| Some of it was "stone from this volcano" and then it was mined
| out. They didn't know how to choose a substitute.
| dreen wrote:
| I don't think the knowledge is gone, we could make that or
| maybe even better. The point is nobody wants it, most things we
| build need to be torn down after at most a few decades anyway.
| ricardobeat wrote:
| The knowledge is actually gone, like Damascus Steel (what we
| have today is just a visual reproduction) and Greek Fire.
|
| For a more recent example: we already "forgot" how to make
| the spaceships and rockets that went to the moon. Even if you
| had the full plans - and apparently we don't, a lot of the
| materials and processes are not around anymore and would have
| to be 'reinvented'.
| aidenn0 wrote:
| We have a pretty good idea of Damascus steel at this point:
|
| - We know that early Damascus examples were made from
| imported Wootz ingots, which we absolutely can recreated.
|
| - The high quality of the blades were due to naturally
| occuring impurities of molybdenum, vanadium, and chromium,
| all of which are used in various modern alloys.
|
| - Forging and heat treating processes varied greatly across
| historical blades called "Damascus" and we have sequences
| that create both visually and metallurgically similar
| results.
| NineStarPoint wrote:
| For the spaceship example, I'm fairly certain that we do
| know the theory behind how all those materials and
| processes are created though. It isn't that we lost the
| knowledge, but the infrastructure. Recreating the
| infrastructure to create the materials to create the
| rockets is possible, it's just that recreating entire
| processes from scratch when they had already been phased
| out of our modern structures would be outrageously
| expensive, especially just to construct rockets.
| dreen wrote:
| I was referring to the knowledge of how to make long
| lasting concrete, not necessarily specifically how the
| Romans did it, but I guess I could've been clearer.
| ricardobeat wrote:
| The answer is still no, we don't know how to make long
| lasting concrete with modern techniques either
| apparently. Hence the research.
|
| Especially steel-reinforced concrete, the lifespan is
| only 50-100 years. The only exceptions are massive
| structures like dams that will probably last a couple
| millennia.
| adgjlsfhk1 wrote:
| Right but the thing is neither did the Romans. The only
| reason roman concrete lasted so long is it didn't use
| steel reinforcement. All of the structures we have from
| them are carefully designed to only use compression.
| dale_glass wrote:
| Not quite.
|
| For Damascus steel and Greek Fire we almost certainly still
| have the knowledge. We just lack a document to tell us that
| "Greek Fire" matches formula #44 of napalm specifically, or
| what specific process an ancient smith actually followed.
|
| For the spaceships, no, we have the plans, but they're long
| obsolete. They're made for ancient, manual equipment nobody
| uses anymore, and old materials that have since been
| improved on. We technically could dig up and restore
| ancient manual milling machines, recruit retired engineers
| and special order obsolete materials and parts, but what
| for? Unless you're engaging in experimental archaeology
| what you want is _a_ rocket, not _the_ rocket that has a
| nostalgic feel to it, and it 'd make far more sense to make
| one with modern methods.
| mitthrowaway2 wrote:
| So why didn't the researchers just ask one of the people who
| knows how it's made, instead of wasting all this time
| conducting tests and doing spectroscopy?
| eole666 wrote:
| In the 6th century, big volcanic eruptions, low temperatures
| and plagues bringed a dark age in Europe and other parts of the
| world. A large part of the population died. Maybe those recipes
| were lost during this period.
| rootusrootus wrote:
| How does this concrete compare to a state-of-the-art mix -- not
| just the stuff they use to pour my driveway or the highway, but
| the best we know how to make?
| devoutsalsa wrote:
| Practical Engineering can answer all your questions with their
| series on concrete. It's extremely well done, including a video
| on "Was Roman Concrete Better?":
|
| https://youtube.com/playlist?list=PLTZM4MrZKfW90PdaBFt70BLTb...
| ogogmad wrote:
| For people who don't know the difference between cement, mortar
| and concrete:
|
| _Cement_ is a substance used for producing mortar and concrete.
| It 's never used on its own. It is a "binding agent". Note that
| the term "cement" is often not used correctly in everyday speech,
| with people talking about gluing bricks together with cement,
| when bricks are actually glued together with mortar.
|
| _Mortar_ is the glue between bricks. You can see it between the
| bricks in any brick wall. It is produced by mixing cement with
| sand. This results in a paste which hardens after being applied
| to a brick.
|
| _Concrete_ is a substance that can be put into any shape, and
| then hardens. The bricks in a brick wall can be made from it.
| (More examples?) It is produced by mixing cement with sand and
| gravel (which are larger rocks).
|
| There is also _reinforced concrete_ , which the Romans didn't
| have. While concrete by itself can in principle be moulded into
| any shape, this can sometimes fall apart after hardening.
| _Reinforcement_ refers to putting the concrete around metal
| wiring, which allows for more versatile shapes while maintaining
| stability.
|
| Feel free to provide corrections.
| sambeau wrote:
| Though most concrete is reinforced with steel rebar, it can be
| reinforced with all sorts of other materials to strengthen it
| under different conditions & loads: glass rods, plastic meshes,
| fibres, carbon nanotubes, etc.
| olau wrote:
| > The bricks in a brick wall can be made from it.
|
| I think "brick wall" usually refers to fired clay blocks:
|
| https://en.wikipedia.org/wiki/Brick
|
| But yeah, you can make concrete blocks and build stuff with
| those. They are usually larger than clay bricks. In my country,
| the stuff used for building is mostly concrete bricks filled
| with small air bubbles air so that it is lighter and also
| insulates better.
| duckmysick wrote:
| This type is called autoclaved aerated concrete.
|
| https://en.wikipedia.org/wiki/Autoclaved_aerated_concrete
|
| It's pretty good but it's also brittle. You have to use
| special screws and wall plugs if you want to attach
| something.
| LegitShady wrote:
| >There is also reinforced concrete, which the Romans didn't
| have. While concrete by itself can in principle be moulded into
| any shape, this can sometimes fall apart, even after hardening.
| Reinforcement refers to putting a concrete around metal wiring,
| providing more versatility.
|
| Not a correction per se, but some further explanation.
|
| The reason for reinforcement is because concrete is strong in
| compression and weak in tension - in fact for design purposes
| we disregard its tensile capacity entirely. What reinforcement
| does is handle the tensile stresses in a structural member.
| When a beam, column, or slab bends it often (based on the load
| placed and structural design) creates tension on one side and
| compression on the other, so we put the rebar in the structural
| member close to the tension side, or on both sides if there may
| be tension on both sides.
|
| In slabs reinforcing may also be used in some capacity just to
| limit cracking in an otherwise non structural capacity. In
| certain kinds of designs it may also provide confinement to the
| concrete which can be important for structural analysis reasons
| that are too technical to get into here (plastic hinging
| especially in earthquake design, etc).
|
| We have different kinds of reinforcement, depending on the need
| of the project, but for the most part we use steel because its
| reasonably durable, has similar temperature expansion
| properties to concrete (imagine if your concrete got cold and
| shrunk more than things embedded in it, or grew so much the
| things embedded in it weren't attached anymore), its behaviour
| is well understood, and it is reasonably priced.
|
| The design of steel reinforcing in concrete is also done in a
| way that reduces the likelihood of sudden failures, so that if
| something does happen, it happens slowly and with plenty of
| warning.
|
| There are alternative reinforcing materials that may be
| appropriate in some very specific situations, but civil
| engineering moves very slowly and adoption is slow because risk
| is high. Fiber Reinforced Polymer (FRP) and Glass Reinforced
| Plastic (GRP) are examples of these. They may have much higher
| tensile stress capacity per unit of area, and also are less
| susceptible to corrosion, but they cost a lot, their failure
| modes are sudden, greater deflections under load, and each may
| have other tradeoffs like worse compressive behaviour, or worse
| fire resistance, etc.
| Animats wrote:
| There's a small trend towards stainless steel rebar. It's
| expensive, but is now used for concrete structures near salt
| water.
|
| Epoxy coated rebar turned out to be a mistake. One scrape in
| the epoxy and it starts rusting. Exposure to UV prior to
| installation can damage the epoxy coating. Currently banned
| in Quebec.[1]
|
| [1] https://news.ycombinator.com/item?id=27676447
| dima_vm wrote:
| Well, technically, you can use cement instead of mortar (wet,
| but without sand). As far as I understand, sand is more like a
| neutral filler, to save money on cement. Various other things
| can be used to fill as well, like gravel. Sometimes even empty
| plastic bottles (reduces material and weight) are suitable
| (just make sure they don't float up). If one got very smooth
| bricks (e.g. precisely cut aerated concrete), then it might
| make sense, as there's very tiny amount of mortar (or even
| glue) is needed anyway.
| IIsi50MHz wrote:
| If the sand is properly coarse, it can add strength. However,
| finding coarse sand is increasingly difficult, resulting in
| misuse of smooth sand (from error or being defrauded).
|
| Tangent: coarse sand is also important for certain types of
| septic systems to function properly.
| ggm wrote:
| Reinforced concrete in part is designed to provide structural
| strength under tension forces. Concrete is stable in
| compression but has weak resistance to tension. Pretensioned
| reinforced concrete permits longer unsupported spans but even
| vertical concrete can benefit from reinforced bars, to prevent
| spalling. (I believe). Not all reinforcing steel has to be
| tensioned to be useful, that's a technique for long spans.
|
| Reinforced steel bars hence rebar.
| ComputerGuru wrote:
| > but even vertical concrete can benefit from reinforced
| bars, to prevent spalling. (I believe).
|
| I liked your comment but this bears correcting. (Corrosion
| of) rebar is actually the biggest _cause_ of spalling in
| vertical concrete structures.
| LegitShady wrote:
| >Reinforced steel bars hence rebar.
|
| More like reinforcing bars, rather than reinforced bars. And
| technically the overwhelming majority of what is sold today
| are actually deformed reinforcing bars, since the intentional
| addition of ridges on the outside of the bar helps the
| concrete adhere as compared to smooth mild steel.
| jacquesm wrote:
| The baths of Caracalla (sp?) had concrete reinforced with
| copper!
| jhallenworld wrote:
| There are different types of cement: Portland and CSA (Calcium
| Sulfoaluminate).
|
| https://caltra.com/wp/wp-content/uploads/2016/11/What-is-CSA...
|
| Portand is the cheap stuff- like the $6 Quikrete bag at Home
| Depot. CSA is more expensive, but also available at Home Depot-
| look for the "Rapid Set" brand (Rapid Set Cement All is like
| $28 a bag).
|
| It's kind of awesome, it's so fast you can sculpt vertically
| with it. You use more water with it than Portland, it starts
| out more mud-like. It tends to be preferred for repairs.
|
| https://www.youtube.com/watch?v=XO8wyQfjpt4
|
| https://www.youtube.com/watch?v=kaB22ceIrqk
| aidenn0 wrote:
| There are many, many, types of cement. Another common type of
| cement that people are probably familiar with is asphalt
| (a.k.a bitumen).
| LegitShady wrote:
| There are many types of even just portland cement, or
| portland cement with additives. Early strength development,
| sulfate resistance, air entrainment (trapping little
| bubbles of air in the concrete so that it cracks less in
| freeze thaw cycles), different heats of hydration, etc.
| hbarka wrote:
| Breaking down cement further, the raw materials are limestone,
| clay, and touch of iron ore ("red earth").
| [deleted]
| egberts1 wrote:
| Now onward to replacing the roads and bridges on freeways and
| highways with these new concrete.
| naikrovek wrote:
| modern roads and bridges are designed to decay at the rate they
| decay, because building in longevity is far more expensive than
| simply replacing the road surface or replacing the bridge at
| the end of its life.
|
| what we don't do today is follow through on the maintenance and
| replacement schedules, in an attempt to save money. we try to
| repeat our tradeoff after the infrastructure is built, again
| trading away longevity in favor of money. well, infrastructure
| decays if you don't maintain it or build it to last longer.
|
| skimping on maintenance after you skimped on longevity is
| trying to eat the cake, and still have it after you've eaten
| it. it doesn't work that way.
| cjohnson318 wrote:
| I worked at a geo-polymer start-up. One huge hurdle is sourcing
| the right kind of ash, and other ingredients, in sufficient
| quantities and with the right level of quality. Building a kiln
| or a launch pad is one thing, but building a road is orders of
| magnitude more expensive. Like, it's humanly possible, but it's
| not economically possible.
| AlexandrB wrote:
| Only some bridge designs can use un-reinforced concrete. Many
| (most?) modern bridges need reinforced concrete to allow the
| concrete to bear tensile loads. Reinforcing concrete introduces
| new ways that concrete can degrade such as rusting of the
| reinforcing elements. I'm not really sure Roman concrete would
| be much help here.
| marcosdumay wrote:
| The quick cure may be very useful for most construction. And
| the self-healing may be better enough for use on pavement.
|
| But most bridges and highways are quite demanding and can't
| simply adopt a new concrete chemistry based on an improvement
| in a single dimension.
| insane_dreamer wrote:
| cobblestones for the roads
| naikrovek wrote:
| for slow neighborhood roads I see no reason why brick isn't
| used more often. my hometown had brick roads everywhere and
| once every 3-5 years a few bricks would get replaced here and
| there. in the 1990s I'd look around and see a lot of the
| bricks on those roads that were made in the 1930s, and there
| were probably older bricks to be found if I'd looked harder.
|
| the rough ride kept speeding down a lot more than the police
| could, because I watched people scream through my
| neighborhood all the time after they paved over the bricks.
|
| plowing snow is harder on brick roads, but it isn't so hard
| that it is an unsolvable problem.
| mcguire wrote:
| Speaking as someone who grew up in a neighborhood with
| brick streets,...
|
| They're insanely slippery when wet. A freeze-thaw cycle
| tends to make them move, eventually leading to weird dips
| and ridges. They're expensive to install and more expensive
| to maintain.
| naikrovek wrote:
| they were not slippery that I noticed in my town. not
| sure why.
|
| my town used dirt as the "mortar" between bricks, so
| there was no solid joint to degrade over time. I do
| remember crews going around and spreading small amounts
| of dirt on those roads, to refill what little rinsed away
| after spring thaw. they'd just have a guy following
| behind the truck with a push broom moving the dirt so it
| fell between bricks.
|
| dirt is dirt cheap.
| mikeyouse wrote:
| It's not the plowing that gets bricks in winter, or not
| plowing exclusively, it's the freeze-thaw cycling that
| kills anything with joints. Every grout joint / polymeric
| sand joint is an opportunity for moisture intrusion and in
| any climate zone that gets cold enough to freeze, those
| joints are going to degrade incredibly quickly. Bricks may
| make sense in the South, but definitely not in most of the
| US.
| teucris wrote:
| I'm not sure how this applies. Most joints are meant to
| flex, reducing the breakage of actual paving elements
| significantly. It also means that an area with
| significant heaving can be repaired more easily by only
| needing to service the affected area, and the repair has
| minimal impact to the surface quality, unlike concrete
| patching or pothole filling.
| jcadam wrote:
| That is... not a smooth ride.
| [deleted]
| insane_dreamer wrote:
| it's not so bad; where I grew up in France many streets
| were cobblestone and it was fine. It's pretty rare in the
| US though except I've noticed it in streets where they have
| trams running--presumably to reduce the need for
| maintenance on those streets.
| cameronh90 wrote:
| Sounds like a good way to make people slow down.
| naniwaduni wrote:
| The problem with making people slow down is that it slows
| people down.
| r00fus wrote:
| Sometimes that's what's needed.
|
| https://en.wikipedia.org/wiki/Braess%27s_paradox
| naniwaduni wrote:
| But usually, it slows people down.
|
| > In 2012, Paul Lecroart, of the institute of planning
| and development of the Ile-de-France, wrote that "Despite
| initial fears, the removal of main roads does not cause
| deterioration of traffic conditions beyond the starting
| adjustments. The traffic transfer are limited and below
| expectations".[4] He also notes that some private vehicle
| trips (and related economic activity) are not transferred
| to public transport and simply disappear
| ("evaporate").[4]
|
| > The same phenomenon was also observed when road closing
| was not part of an urban project but the consequence of
| an accident. In 2012 in Rouen, a bridge was destroyed by
| fire. Over the next two years, other bridges were used
| more, but the total number of cars crossing bridges was
| reduced.[4]
|
| It seems a lot like the real-world examples of the
| phenomenon look like close cousins of "if you remove the
| smallest values in a set, the average goes up".
| [deleted]
| Retric wrote:
| Modern roads are designed to take serious abuse. 50 years of
| load cycling 20 ton semi at highway speeds causes mechanical
| damage which Roman concrete wouldn't be effective in
| preventing. In ancient sites you can sometimes see the walls in
| high traffic areas have gotten smoothed and indented from
| hundreds of years worth of people gently dragging their
| fingertips across the surface as they walk by, tires are less
| gentile.
|
| Also, people vastly underestimate how cheap road surfaces need
| to be. Try and calculate the volume of material making up the
| US road system.
| magicpin wrote:
| A fun exercise is to calcualte the cost of some road in a
| neighboorhood, and compare that to the total collected
| property tax of all the homes along that road.
| nemo44x wrote:
| Then multiple that by 20 (the lifetime of the road surface)
| and factor in that the resurfacing is significantly cheaper
| than the initial build and you quickly find roads are
| easily subsidized by property taxes.
| elzbardico wrote:
| They are not subsidized, they are an infrastructure
| common good that is financed with taxes.
| nemo44x wrote:
| It depends. Where I live the roads in our neighborhoods
| are paid for by the town (property taxes) and many roads
| that run through the town are paid for by the county
| (income taxes) and then the highways are paid for by the
| state in part via tolls and other ones by the Federal
| Government via taxes.
| avidiax wrote:
| There are two sides to this coin. The roads need repair
| continually and resurfacing eventually, yes. What happens
| when property values and the local economy begin to
| deteriorate instead of prosper? All those utilities and
| public rights of way still need those repairs, but
| there's no appetite to raise property taxes, and the tax
| base is dwindling, and there's little reason to keep
| paying the mortgage on a depreciating house, especially
| once 2/3rds of your street is gone.
|
| How sustainable is a system that requires perpetual good
| times?
|
| Calling it a ponzi scheme is a stretch, but this guy
| seems to be the only one talking about this:
| https://www.strongtowns.org/journal/2020/8/28/the-growth-
| pon...
| nemo44x wrote:
| You abandon it. Detroit did this for example.
|
| Also easy expansion is more a function of interest rates
| than anything. Municipal bonds buy everything and there's
| been very little interest on them. This means fewer taxes
| to buy things. And new bonds can be sold down the road as
| the town increases tax base and interest rates fall.
| MalcolmDwyer wrote:
| NotJustBikes covered this too:
| https://www.youtube.com/watch?v=7IsMeKl-Sv0
| dwater wrote:
| Even in rural areas? Even if we add in the cost of
| maintaining infrastructure that runs under the road
| surface (water, sewer, and gas)?
| toast0 wrote:
| I live in a semi-rural area. There's no utility gas near
| me; we're too sparse for that to make sense. I'd guess
| most of the houses have big propane tanks (i've got two
| 250 gallon tanks) and there's several different companies
| that will come out and fill the tanks. In the nearby
| urban area, there's utility gas, but then they're trying
| to outlaw that for indoor air quality reasons.
|
| I don't have utility water; it's available on my street,
| but it doesn't run by my house, it stops at a much lower
| elevation, our well water is fine (although we had to
| replace the well pump recently which was expensive). No
| utility sewer either, that's available in parts of my
| area, but mostly places with density or poor site
| conditions for septic or both.
|
| Electricity is mostly overhead, with a little bit of
| underground telephone has a lot of undergrounding, but
| some overhead, cable and municipal fiber are almost all
| overhead. But when those are undergrounded here, they're
| on the sides of the road (directly under the overhead
| path) not under the road. That way it's easier to get to
| them for maintenance when needed.
| eppp wrote:
| I live in a very rural area and I had a few minutes so I
| calculated it.
|
| I live at the end of a deadend road that is 0.9 miles off
| another very rural road.
|
| The road is chip sealed, which according to google in
| 2022 is $25,000 to $42,000 per mile.
|
| There are 7 parcels that collect $6396 per year in
| property taxes.
|
| At the low end of the chip seal price, it would take 3.53
| years to pay it off and 5.9 years at the high end.
|
| This assumes that no sales or gas taxes are used to fund
| any of the road construction, which isn't true.
| nemo44x wrote:
| > (water, sewer, and gas)?
|
| Over their lifetime, easily. The pipes for those will
| last 100 years, easily. The maintenance of them are paid
| for by the delivery costs you pay in your bill.
|
| As for rural I think there's 2 distinctions. 1 is we need
| rural communities because they produce our food and other
| things. Secondly, rural areas are between 2 or more
| populated areas. We need to connect populated areas so by
| necessity there are roads. Rural communities are built
| off of those.
|
| The other distinction where you may be closer is
| exuburban communities built into rural areas. These may
| or may not be fully covered. Not initially anyways, but
| you'd assume the property taxes would cover in time.
| toast0 wrote:
| > pipes for those will last 100 years, easily
|
| My wife served on a sanitary district board. Decent
| underground sewer mains have an expected service life of
| 70 years. Some will last longer, some won't hit the
| expectation. It depends on site conditions, materials,
| etc, etc. Many will probably last to 100 years, but I
| wouldn't expect it to be easy. Especially if you had any
| of the not decent materials (Orangeburg pipe was common
| in some areas and is basically wood pulp/fibers mixed
| with hot tar; service life could vary between 10 and 50
| years; the major manufacturer went out of business in
| 1974, as PVC and ABS pipes rapidly replaced Orangeburg in
| the materials markerplace).
|
| Actually there was a huge nationwide boom in sewer
| building post WWII, especially in the 50s, and you can
| expect that infrastructure to need some largescale
| replacement over the next 20 years or so. Depending on
| system design and how housing and industry developed,
| some systems will be able to just inspect periodically
| and replace as needed, and some systems will probably
| take the opportunity to do a more modern redesign (older
| cities tend to have combined sanitary sewers and
| storm/runoff drainage; if you're tearing up all the
| streets to replace the sanitary sewer, it might be a good
| time to put in a parallel storm drain system)
|
| I'm not sure about water mains, I'd guess they need more
| frequent replacement since they operate at pressure.
| mikeyouse wrote:
| A relative of mine who's otherwise a smart guy was
| lamenting rural broadband as an Obama boondoggle since it's
| never going to pay for itself to run fiber to all of the
| remote communities in our state... he didn't want to hear
| about the "P&L" for the road capital/maintenance costs.
| JanSolo wrote:
| I live in Montreal; many of the concrete structures in my
| city are crumbling and decaying due to the constant
| freeze/thaw temperature cycling that they're exposed to. I
| wonder if the self-healing property of this new advanced
| concrete would help to avoid some of the cracking & flaking
| we're seeing in constructions from the 60s & 70s.
| kibwen wrote:
| Only if you take out the rebar. Concrete is porous, water
| penetrates to the rebar inside, the rebar rusts and
| expands, cracking the concrete. But if you remove the
| rebar, you remove much of the tensile strength of the
| structure, which means you need to use way more concrete to
| compensate (via the sheer compressive force of its own
| weight).
| elzbardico wrote:
| What about those new materials for rebar? Like
| fiberglass? What do you think of them?
| bombela wrote:
| Not the parent. My understanding is metal rebar is the
| cheapest. You need a lot of rebar in modern concrete
| construction.
| betaby wrote:
| I live in Montreal too, and while all what you say is true
| ... the same is not true for the xUSSR cold cities I lived
| before immigration. So quality makes difference. Also
| planing and designing for _less_ maintenance. Concrete
| structures from the same era across xUSSR are in way better
| shape.
| newsclues wrote:
| Montreal has infrastructure problems because of systemic
| corruption with the local Mafia.
|
| To think that the USSR had better infrastructure (less
| corruption) than modern day corrupt places like Montreal
| is a brutal shock.
| [deleted]
| beezlewax wrote:
| There is a Greek Hellenistic breakwater or port ruins in Sant
| Marti near L'escala in Catalonia, Spain that is sitting in the
| sea. It is still standing. Always amazes me that it's still there
| though I'm sure some minor restoration work has probably been
| done.
| w1nst0nsm1th wrote:
| Dawn, I just wanted to patent it.
| [deleted]
| naikrovek wrote:
| the article talks about evidence which has always been present in
| evaluations of Roman concrete which was "disregarded as merely
| evidence of sloppy mixing practices, or poor-quality raw
| materials," and this kind of thing REALLY infuriates me, as a
| layman.
|
| if you don't know how to make Roman concrete, don't assume
| _anything_ about what you see in Roman concrete while you 're
| trying to figure out how it was made.
|
| The modern-day belief that we are superior to humans thousands of
| years ago is just an absolutely insane idea, to me. we are more
| technologically advanced because we have more shoulders of giants
| to stand on, and we are NOT smarter or more clever than humans of
| 5000-10000 years ago. we just aren't.
|
| as soon as you believe that we are superior to our ancestors, you
| dismiss the evidence you are looking for as "sloppy mixing
| practices, or poor-quality raw materials" and you prove modern-
| day humans as inferior, or at least you prove your own efforts as
| careless and incomplete.
|
| leave no stone unturned when you are trying to understand
| something you do not understand; your lack of understanding could
| be due to your false assumptions.
| spacemark wrote:
| I agree with the spirit of what you're saying but you go too
| far, ironically asserting without any supporting logic that the
| intelligence of homo sapiens has remained static for the last
| 2,000 years. But I suppose the disagreement hinges on what is
| meant by intelligence.
|
| Here's a thought experiment: if you removed all technology
| (tools, writing, vast stores of knowledge) from a human child
| and raised them in this vacuum, would they be more or less
| intelligent? Would they understand their place in the solar
| system and the structure of the cosmos? Would they know how to
| protect themselves from sickness (germ theory)? Would their
| vocabulary and ability to express themselves be less or more?
|
| Of course these questions don't have definitive answers and you
| can play the game the other way, arguing that modern humans
| would die in a couple weeks if transported back to caveman
| times.
|
| But it's a poor model to view intelligence as some static
| property independent of technology, environment, gene mutation,
| sexual selection and all the other strings in the web of
| existence.
| naikrovek wrote:
| "intelligence," as I used it, is the ability to learn, to use
| what you've learned to solve problems, and to accurately
| predict the future outcomes of today's decisions.
|
| my knowledge of the horsehead nebula has no positive or
| negative effect on my ability to learn how to make concrete
| or to use that knowledge to actually make thae concrete.
| intelligence is not simple memorization of fact, it is a
| collection of understanding, and the ability to both grow
| that understanding and to use it to accomplish things that
| you don't yet know how to do.
|
| we are continuously surprised by what we learn about ancient
| cultures, because we assume they were intellectually inferior
| to us.
|
| the Lycurgus Cup is a great example of something that some
| people still view as a lucky accident. Anyone who has
| actually learned to make physical things and worked to refine
| their skill in making things will know in their soul that the
| colors in that cup are clearly intentional and the product of
| intelligence and time.
|
| our belief that only contemporary humans have control over
| and understanding of the their world is just simply wrong, I
| think.
|
| we discover new evidence from ancient civilizations which
| surprise us all the time. is there enough evidence to _prove_
| that we aren 't smarter than people 100-200 generations ago?
| I don't know.
|
| there certainly is a lot of evidence that ancient
| civilizations knew more than we believe they knew, and that
| is significant when you think about how long that evidence
| needs to last to be discovered today, and that those things
| which do last long enough are recognized for what they are
| before they are discarded because of a bad assumption. how
| much evidence has been lost? we only see a tiny fraction of
| the evidence that would have existed at the time.
|
| these discoveries happen frequently enough for me to have no
| problem believing that there is a great deal about ancient
| civilizations that we think we know which we actually do not
| know.
|
| that's a rambly comment but it's all I have time for before
| the edit window closes.
| c7b wrote:
| > if you don't know how to make Roman concrete, don't assume
| anything
|
| That's not useful guidance for doing research at all. It's
| similar to some 19th-century physicists/philosophers saying 'if
| you can't see atoms, you can't possibly know anything about
| them or whether they even exist'. We also can't _make_
| supernovae or supermassive black holes, yet we can still try to
| learn about them through a combination of available data and
| educated 'assumptions' (ie theories).
|
| What this research has done is replace one theory with another,
| and that theory might be replaced by another one later, that's
| just how science works.
| naikrovek wrote:
| eh, I disagree.
|
| hypothesizing that atoms exist allows and encourages you to
| design experiments which can prove or disprove their
| existence.
|
| assuming that they exist, and never experimentally verifying
| that is not research and it is not science.
|
| assuming that some feature of a product that you do not
| understand exists for any reason is at most an hypothesis,
| and dismissing the hypothesis without experimental evidence
| disproving it is simply bad science.
|
| Roman concrete is not something far away that we can not
| interact with. we can verify by experiment. for years we
| chose not to validate the assumption that the white specs
| were accidental, and that delayed our understanding of Roman
| concrete.
|
| I just want scientists and historians that take the time to
| recognize their assumptions and to prove them correct or
| incorrect, if possible, instead of just relying on them as
| immutable facts; assumptions are often wrong.
|
| I write software for a living, and the number of times that
| my assumptions about the cause of any particular problem have
| been correct approximately 0% of the time. whether it's a
| logic bug or a performance problem or a usability problem.
| despite decades of experience in this field, I am still
| almost always wrong about the cause of any particular problem
| I encounter, unless I have seen that exact same issue
| previously, which is rare.
|
| historians, some of them at least, would probably benefit
| quite a bit from making fewer assumptions and by
| experimentally proving the assumptions they do make. if it
| isn't possible to prove or disprove your assumption, then you
| must never forget that it is an assumption and not proven
| fact.
|
| I've seen so many scientists and historians say they know
| things which they simply do not know. things like "we know
| dark matter exists." no, we don't. we know that the currently
| accepted theories of our observations require dark matter to
| exist in order for our observations to make sense. that is
| not proof of dark matter.
|
| dark matter may exist! I don't know, but for a scientist to
| say that it exists is incorrect because we've never observed
| it directly, and have devised no tests which can prove that
| it does exist.
|
| our theories which require it in order for our observations
| to make sense could be wrong. our observations may not be as
| accurate as we assume. we may be observing things that we
| aren't aware of which look like something that we are aware
| of. etc.
|
| I'm saying that professing that you know something without
| proof is folly. just like the white specs in the concrete
| were assumed to be accidental impurity without that
| hypothesis being proven is folly. these things set us back as
| a scientific community that wants to understand its
| environment.
| trynewideas wrote:
| From the study:
|
| > In addition to the features described above, aggregate-scale
| relict lime clasts, also referred to as remnant lime or lime
| lumps, are a ubiquitous and conspicuous feature of both
| architectural and maritime Roman concretes. The presence of
| these distinctive bright white features has been previously
| attributed to several scenarios including incomplete or over-
| burning during the calcining of lime (20), carbonation before
| concrete preparation (30), incomplete dissolution during
| setting (12), or insufficient mixing of the mortar (14).
|
| 20:
| https://www.sciencedirect.com/science/article/abs/pii/S00088...
|
| 30:
| https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1475-4754....
|
| 12: https://www.amazon.com/Building-Eternity-Technology-
| Concrete...
|
| 14: https://www.cambridge.org/core/journals/journal-of-roman-
| arc...
| insane_dreamer wrote:
| > modern-day belief that we are superior to humans thousands of
| years ago is just an absolutely insane idea, to me
|
| totally agree that kneejerk response when we see something that
| doesn't match our current methods is "those people didn't know
| what they were doing" is both potentially incorrect and
| certainly unhelpful to the advancement of science
| sogen wrote:
| An extremely good example of Chesterton's fence?
| sarchertech wrote:
| That depends on the what you mean by smarter. At least some
| component of what we consider intelligence is cultural.
|
| Just one example is that the ability to write/draw allows you
| to solve problems that are impossible without it.
| HPsquared wrote:
| Being literate definitely means some faculties get less
| practice. Practically nobody today can recite epic poetry
| like the Odyssey, for example. That lack of rote memorization
| skill may have unexpected side-effects.
|
| https://daily.jstor.org/how-do-we-know-that-epic-poems-
| were-...
| sarchertech wrote:
| That's possible, but unlikely considering that numerous
| studies of literate vs illiterate people have shown that
| literacy correlates with improved working memory not the
| inverse.
|
| Studies of using mnemonic techniques to memorize long
| sequences (similar to what oral performers were doing) have
| also not shown much promise in increasing cognitive
| abilities.
| samstave wrote:
| Thats a really good, succinct, statement that triggers
| thought - where ironically - being literate is required to
| reply to via the most advanced machine I have ever used...
|
| But there are so many skills lost due to the privilege of
| technologically enabled sedentary life-styles...
|
| can you imagine attemting to found a town/village/city in
| flat/cold/resource-constrained climates without
| electricity/supply-lines?
|
| Those people before us had balls and conviction of steel -
| and even more-so for the women. You would not exist without
| a woman (mother) and women are stronger than men.
| [deleted]
| jesuspiece wrote:
| It is a testament to the ingenuity and expertise of the ancient
| Roman engineers. It will be interesting to see what other
| insights this research may lead to and how it could potentially
| be applied to modern construction techniques.
| I_complete_me wrote:
| The subject is complicated. For example see this paper[0]. The
| setting of concrete goes on for a long time and the Romans were
| probably not aware of how long their concrete(s) was/were going
| to last. There is a type of 'survivorship bias' going on here.
| But still, I guess, they knew something important. Adding
| reinforcement to concrete may well be a source of shortevity -
| or what ever the complement to longevity is.
|
| [0]
| https://www.sciencedirect.com/science/article/abs/pii/S00225...
| UncleEntity wrote:
| It's not like the Romans started out in a place where there
| weren't thousands of years old structures nearly everywhere
| they went.
|
| Assuming they didn't want their structures to last as long as
| the ancient ones (at their time) is just laughable.
| [deleted]
| akolbe wrote:
| Here is a nice picture of the Pantheon, mentioned in the article
| as a prime example of these incredibly durable Roman concrete
| structures:
|
| https://commons.wikimedia.org/wiki/File:Pantheon11111.jpg#/m...
|
| Not bad for something built nearly 2,000 years ago.
| pachico wrote:
| It doesn't matter how many times I see it, every time I go to
| Rome and find myself in front of the Pantheon, I get
| overwhelmed by it.
| benreesman wrote:
| With zero sarcasm, when I read "every time I go to Rome" I
| feel that I took a wrong turn in life somewhere.
|
| Fucking awesome mate.
| krisoft wrote:
| Worth remembering that "Going to Rome" has a very different
| feel to it if you live in Terni vs if you live in Whichita,
| Kansas. One is a day trip to shop, the other might be an
| adventure of a lifetime.
|
| I was born in an East European country and I worked a few
| years in New York. Many people back at home react to this
| fact as if I made it. As if shoveling software on Lafayette
| street makes you a better software engineer than doing the
| same on the Rakoczi Korut. On the other hand for many
| people living and working in New York is nothing special.
| They were born there, it is their normal.
|
| I for one think where you were is not as important as what
| you made of your time there.
| pachico wrote:
| Well, I lived in Italy for 10 years. Going to Rome from
| time to time wasn't that hard.
|
| Now I live in Spain and I continue to fly to Rome now and
| then.
|
| In Europe, distances are easy to overcome.
| rollcat wrote:
| In Europe, 100km is a long way; in the US, 100 years is a
| long time.
| KptMarchewa wrote:
| Unless you fly ryanair for 10$
| jjeaff wrote:
| If you fly Ryanair, 20 minutes is like 100 years.
| hgsgm wrote:
| Do you mean 1000km? The thread is about Rome being easy
| to reach.
| rollcat wrote:
| It's just a saying, having the same number on both ends
| (but measuring different things) is the part that is
| supposed to make you think it's clever ;)
| mgaunard wrote:
| Italy is wonderful, you should go, only problem is that
| they speak Italian.
| junga wrote:
| I think this is meant to be funny but it upsets me a
| little bit to be honest. Learning at least some basics of
| the country's language is travelling 101 to me. Going
| abroad and expecting the locals to speak my language is a
| very rude thing and a display of disrespect in my
| opinion.
| julenx wrote:
| Well, it's also wonderful they speak Italian!
| jylam wrote:
| But they drive Italian too. Ho well.
| _nalply wrote:
| Drive confidently but attentively and you fit in
| beautifully.
|
| Source: tried it myself.
| jupp0r wrote:
| Can't confirm. Drive unsafely like the worst drivers in
| LA and you'll fit right in but still be miserable.
| beebeepka wrote:
| Spanish and Italian sound great to me, even though I
| don't speak them. They sound, well, human. Can't say the
| same about English or German
| insane_dreamer wrote:
| I wonder what percentage of the original stones are left (given
| that it was repaired and restored over the centuries)
| helloworld11 wrote:
| Unlike many ancient structures, the Pantheon has mostly been
| left intact across the millennia. The Dome is entirely
| original and so is most of the remaining structure. From what
| I know, the majority of the restoration and renovation work
| has been to the interior ground-level walls and some of the
| exterior along the ground level, but even these are mostly
| minor renovations. In this case, what you see truly is for
| the most part what always was, and especially for the main
| awe-inspiring part, the great dome.
| Bayart wrote:
| The Pantheon is very notable among Roman monuments for having
| little done over the years other than cosmetic upgrades.
| peoplefromibiza wrote:
| of the original Pantheon from 27 B.C. very little remained.
|
| It was rebuilt after the fires of 80 A.C. and 110 A.C.
| damaged the original structure.
|
| It's been mostly unchanged after that.
| ggm wrote:
| I don't believe the dome structure was radically altered
| across time. It's possible I misunderstood but my belief was
| it was only cosmetic changes to the dome itself. Other
| structural changes were made to the portico and doorways.
| Maursault wrote:
| > Not bad for something built nearly 2,000 years ago.
|
| According to the Pyramids, Stonehenge, Newgrange, Watson Brake,
| et al., it's a little premature to suggest that. Let's check
| back in 3,000 years.
| [deleted]
| jacquesm wrote:
| Hehe, that's funny. But the OP clearly meant it relative to
| other stuff built 2000 years ago, most of which has vanished
| without leaving a trace, maybe a couple of foundation stones
| buried under a meter of new topsoil.
|
| Have an upvote, it's sad to see you grayed out.
| GuB-42 wrote:
| The pyramids are essentially just piles of rocks. The
| impressive part about them is not really how they stood out
| the test of time, in fact they lost most of their finer
| details, but how an ancient civilization managed to make
| piles of rocks that big.
|
| The Pantheon is not a pile of rocks, it is made of engineered
| materials (concrete), with domes and overhangs. Unlike "pile
| of rocks" architecture that essentially can't fail, if it
| wasn't well engineered, it would have collapsed into
| something unrecognizable.
| peoplefromibiza wrote:
| stone != concrete
|
| edit: we have a > 2,000 years old pyramid in Rome too, and
| it's in perfect shape, because stone != concrete
|
| https://upload.wikimedia.org/wikipedia/commons/thumb/9/9d/Ci.
| ..
| moloch-hai wrote:
| Funny, its perimeter vs. height approximates pi, rather
| than the originals' 2pi.
| ectopod wrote:
| What it is:
| https://en.m.wikipedia.org/wiki/Pyramid_of_Cestius
| ggm wrote:
| Uses pumice in aggregate as aerated mass to lighten the
| concrete and also varies concrete thickness by height in the
| dome to reduce load
| ggm wrote:
| Cannot recommend enough "the new science of strong materials: or,
| why you don't fall through the floor" by JE Gordon. Old, but
| amazing.
| nkurz wrote:
| The formatting is a little off, but a fully text PDF is here:
| https://edisciplinas.usp.br/pluginfile.php/3975708/mod_resou...
| FairDune wrote:
| Thanks for the suggestion
| adrian_b wrote:
| The research paper:
|
| https://www.science.org/doi/10.1126/sciadv.add1602
| adolph wrote:
| _One method to reduce cement's carbon footprint (which accounts
| for up to 8% of total global greenhouse gas emissions), is to
| improve the longevity of concrete through the incorporation of
| self-healing functionalities. The resulting extended use life,
| combined with a reduction in the need for extensive repair,
| could thus reduce the environmental impact and improve the
| economic life cycle of modern cementitious constructs._
|
| I wonder:
|
| How much of an environmental impact this would make given the
| number of structures that are not useful before the concrete
| requires repair?
|
| How much of Roman concrete's reputation for durability comes
| from survivorship bias--the structures that lasted were just
| lucky?
| ryanwinchester wrote:
| if we built these aquaducts now using common concrete,
| without steel reinforcement, they'd be in shambles in a few
| years.
| imtringued wrote:
| Our dams don't appear to be that fragile.
| mitthrowaway2 wrote:
| Survivor bias comes up every time this topic is mentioned,
| but it really has less explanatory power than most people
| think. If you meet a man born in 1932 who is still running
| marathons and doesn't need glasses, it's probably luck,
| although he might have some valuable diet tips to share. If
| you meet a man born in 1732 running the same marathon, it's
| time to rule out luck, and start collecting blood samples
| because he might _actually_ be some kind of vampire.
|
| Furthermore, the "survivor bias" idea, as an attempt to
| explain the longevity of Roman concrete as a building
| material, implies that the buildings that survived were
| stronger than the ones that did not, so we're just seeing the
| upper end of structural strength. But that's not even
| necessarily the case. Many more were lost because they were
| deliberately demolished for other reasons (honoring the wrong
| gods, etc). And it's not like these buildings only survived
| in ideal environments for preservation; as the article
| mentions, they have survived in many different climates
| across a vast empire, standing in seawater, through
| earthquakes, and so on.
| moloch-hai wrote:
| Right. Romans experimented with the formula for concrete
| for centuries, and learned a lot about how centuries-old
| concrete structures deteriorated. They didn't have modern
| chemistry, but they had observational skills and were
| serious about their work.
|
| It would not be surprising to find that most structures
| weren't built to last any longer than ours, but that some
| were meant for the ages. An important difference today is
| we don't build the latter sort, excepting maybe the Sydney
| Opera House. Many people act personally offended that it
| doesn't have steel inside.
| hprotagonist wrote:
| The cathedral of st. john the divine in new york city has
| yet to be completed.
|
| we just don't build a lot of them.
| imtringued wrote:
| We build dams to be long lasting.
| moloch-hai wrote:
| More of them, anyway, than of other types. Some have not
| lasted, with typically regretted consequences.
| saalweachter wrote:
| I wonder if generational reputations and transmission of
| methods from master to apprentice is sufficient.
|
| "Secundus was an apprentice to Marius who was an
| apprentice to Darius, who built that awesome aquaduct;
| Marcus was an apprentice to Felix who who was an
| apprentice to Marcellus, whose shit bridge fell down
| after twenty years. We're going to hire Secundus instead
| of Marcus."
| rerdavies wrote:
| Real Roman engineering theory came from Marcus
| Vitruviouss Pollio's De Archetectura. Considered to be
| the ultimate reference text for building and engineering
| projects in Rome in 32bce, It's ten volumes cover how to
| build everything from temples, to aqueducts, to water
| mills to machines used for construction. A fascinating
| read, if you're curious how Romans built things.
|
| De Architectura provides the sort of long-term
| perspective required to build and engineer projects that
| were meant to last for centuries, based on experience
| gathered from centuries of recorded experience.
|
| I'm not sure if De Architectura is the only book that
| Roman Architects used. But it was certainly the most
| important.
|
| Hundreds of pages of De Architectura list dimensions of
| older ancient buildings, the dimension and spacing of
| pillars, and failures encountered during or after
| construction. Something along the following lines (not
| actual text):
|
| ---
|
| _The second Temple at Delos was built in 432bce. It
| consisted of 13 x 29 doric columns, 6 ' in diameter, 22'
| high, spaced on 12' intervals, with two rows in the pro-
| cella. The cella measured ..... The entrance to the cella
| was 16' high and 12' wide with a granite lintel measuring
| 16' x 3' x 2'.
|
| The lintel above the entrance cracked and had to be
| replaced after an earthquake in 430bce. The front-right
| architrave cracked in 329bce, but was not repaired. The
| temple was subsequently abandoned and collapsed
| completely after an earthquake in 327bce.
|
| The temple of Apollo at Thebes ....
|
| The main architrave cracked while it was being mounted,
| and further construction was abandoned._
|
| ---
|
| Given a hundred or so such examples, a Roman architect of
| a new temple could make somewhat informed decisions about
| how high, how wide, and how thick he would need to build
| a new temple, and how afraid he should be when he was
| commissioned to build a new temple that was higher,
| wider, or taller.
| jacquesm wrote:
| That's a combination of 'Risks Digest' and the
| 'Engineering handbook' all in one. I'll have to go read
| this, thank you so much for the pointer.
| yawboakye wrote:
| as far as i know, vitruvius wasn't original: he aped the
| meticulous and more successful greeks. the ten volumes
| regularly refer to greek knowledge or practice to cement
| its authority. the method of construction that is
| uniquely roman is mixing concrete and bricks, usually to
| produce aqueducts. and here the simple theory was:
| everything in excess. in fact, the romans may have been
| unique in their construction of military camps. for more
| on that see _de re militari_
| agumonkey wrote:
| meta comment: I'd love to see the stats about all bias and
| fallacies mentionned in conversations in the last 20 years.
| Something tells me wikipedia got deep into people's head.
| jacquesm wrote:
| > start collecting blood samples because he might actually
| be some kind of vampire.
|
| In which case your first worry would be to make sure he
| doesn't collect _your_ blood samples.
| amai wrote:
| > One method to refuce cement's carbon footprint...
|
| ...is to simply use less concrete by making it much stronger.
|
| Very promising in that respect is
| https://en.wikipedia.org/wiki/Textile-
| reinforced_concrete#Su...
|
| Especially carbon concrete can be up to 4 times stronger than
| steel concrete, so one can reduce the amount of material
| necessary by 4 times.
| imtringued wrote:
| Don't worry the engineers will use five times less concrete
| and sacrifice longevity.
| asah wrote:
| very exciting! and I imagine there will be follow-on work
| delivering even greater results.
|
| There's also an interesting finance project here, to integrate
| the impact of this material into projects budgets, so that
| designers and investors can justify this material over cheaper
| alternatives. In particular, different construction projects have
| very different expected lifespans.
| HPsquared wrote:
| I wonder if it could have relevance for nuclear waste
| installations.
| canadianfella wrote:
| [dead]
| insane_dreamer wrote:
| I read the article quickly but couldn't see whether this
| discovery is applicable to modern concrete (in other words, could
| the same technique be applied to modern methods for making
| concrete that would make it more durable)?
| novosel wrote:
| "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, [...] cracked them, and then ran water through
| the cracks. [...] Within two weeks the cracks had completely
| healed [...] As a result of these successful tests, the team is
| working to commercialize this modified cement material."
| insane_dreamer wrote:
| thanks
| [deleted]
| nimbius wrote:
| on the other end of the spectrum, did you know concrete can be
| used to demolish concrete?
|
| dexpan is a special demolition concrete mix that, when poured
| into holes, expands at 18kpsi. it gets used when jackhammers and
| explosives cant be used, for example, in refineries and explosive
| atmospheres.
| amelius wrote:
| Won't it expand out of the holes you poured it into?
| jaclaz wrote:
| In some cases (particulary with modern, faster, formulations)
| it can, actually projecting (powder/smoke) out of the holes
| but it is not usually an issue.
|
| When it happens is because the expansion is too fast (and
| consumes all the water available), making the grout itself
| fragile, with slower formulas, after the initial setting of
| the grout, you should water/keep the surface wet.
|
| It is surprisingly difficult to find actual videos of it
| working (most are just a set of photos) because it is very,
| very slow (between 6 and 48 hours, usually), here is one from
| one of the many producers:
|
| https://www.youtube.com/watch?v=CYAcHc9rP9o
| Jensson wrote:
| Not if it hardens before it expands.
| hinkley wrote:
| Presumably dexpan has lower tensile strength so it can be
| disposed of easily? Or is the piece excavated and hauled away
| intact?
| barathr wrote:
| It expands in the holes you make in the to-be-destroyed
| concrete, cracking it. You can haul it off in chunks at that
| point.
| hinkley wrote:
| The destroyed concrete, yes, but what about the dexpan?
| <Peregrine Took>
| Dylan16807 wrote:
| The dexpan never existed as big pieces.
| masklinn wrote:
| The dexpan is not a huge concrete structure, it's just a
| cylinder the size of the hole it was poured in.
| hinkley wrote:
| Oh, I see, just a bore hole and hydraulic concrete. Sort
| of like the metal shims you see used in pre-industrial
| stoneworking.
|
| I was picturing pouring it into a void for some reason.
| [deleted]
| barathr wrote:
| It's also useful if you want to do concrete demolition yourself
| using only hand tools. You drill holes, pour, wait for cracks,
| and then use a pick and hammer to remove the remaining chunks.
| Often sold as "expansive grout".
| dsfyu404ed wrote:
| If you can drill holes you can use stone splitting wedges.
|
| A lot of these high dollar modern miracles of chemical
| engineering are purely for use in situations where it's
| cheaper to just buy the $100/tube stuff than it is to try and
| get the approval to do something sensible. Basically you're
| paying to get around process tech debt.
| VLM wrote:
| Not in a refinery, or you have to buy weird/expensive non-
| sparking hammers and wedges. Aluminum bronze wedges are
| commercially available but the liability insurance is
| incredible so you're better off cutting your own (its a
| wedge, not a rocket engine...). It ends up being cheaper to
| use the expansive grout.
| dsfyu404ed wrote:
| This is exactly what I mean by "paying to get around
| process tech debt"
|
| Facility has a "no sparks" in buildings A, B and C rule.
| Rule obviously doesn't apply to contractors doing a ton
| of welding during a holiday shutdown. Non-contractors in
| maintenance dept want to fix some other crap at the same
| time. Sure they could try and get approval to use a
| jackhammer concurrent with the other work but in reality
| there's a 75% chance the safety department will
| intentionally stonewall until after the shutdown rather
| than set the precedent of a sensible exemption and the
| maintenance manager knows it so they buy the expensive
| grout.
| swayvil wrote:
| I've used that. Drill holes. Fill holes with gunk. Come back in
| the morning and the concrete is all cracked up. Silent and
| easy. Works great.
| boogoob wrote:
| Isn't the particularly short lifespan of modern concrete
| construction mostly a combination of its use in areas with
| regular freeze-thaw cycles and using a reinforcement material
| that rusts (and in doing so expands, damaging more concrete and
| hastening further water inclusion)?
| oakwhiz wrote:
| The rusting and getting wet is cyclical in nature and part of
| what accelerates that is the formation of cracks in the first
| place. Part of the maintenance of concrete is to fill any
| cracks that you can find to prevent it from getting worse. The
| cracks typically start small, and they might form in places
| that are hard to get to as well as being too small to see, so
| if the concrete is self-healing it will prevent some of these
| small cracks from getting worse on their own which should
| reduce the effect of expanding water (ice) as well as expanding
| rust.
|
| The reinforcement material (rebar) already has a very close
| thermal coefficient of expansion to concrete and this can be
| thought of as kind of a lucky coincidence.
| masklinn wrote:
| > as well as expanding rust.
|
| Ideally they'd seal before the rebar is exposed and _can_
| rust. As long as the rebar is encased, unless you fucked up
| dramatically it should be safe.
| anonuser123456 wrote:
| Steel gives concrete tensile strength. Unfortunately,
| defects in the epoxy coating become a focal point of
| oxidation, often pitting that single point more than
| otherwise uncoated steel. The result is, the pitted area
| fails quickly and the integrity of the entire member is
| compromised.
| moloch-hai wrote:
| The rust is essential to bind it to the cement. Without, it
| adds little strength.
|
| Modern concrete isn't expected or designed to last more
| than a century. It could have been made to last longer, if
| they wanted, but that would cost a little more. Making no
| provision for when it will predictably fall apart is a
| modern failing. That major construction with concrete is
| about a century old should worry everyone.
|
| We have a very great deal of infrastructure that will fail
| on a predictable schedule, with nothing budgeted to replace
| it all.
| LegitShady wrote:
| > The rust is essential to bind it to the cement.
| Without, it adds little strength.
|
| Do you have a citation for this? As far as I know this is
| entirely not true.
|
| Rust is an expansionary product - when steel rusts its
| volume increases something like 10x, which reduces the
| connection between the concrete and the steel and causes
| issues like cracking and spalling. Minimizing rust
| improves the long term performance of rebar.
| IgorPartola wrote:
| Rust is perfect. We don't criticize rust on HN.
| moloch-hai wrote:
| They leave the rebar out to rust a bit, on purpose,
| before they pour. Surface rust is good, but more is bad.
| Like many things in life.
| zoklet-enjoyer wrote:
| I read your comment as I finished eating my third slice
| of pie and wondering why I cut myself 3 slices.
| imron wrote:
| Perhaps you're just mathematically inclined.
| moloch-hai wrote:
| You could have cut one big slice instead.
| PakG1 wrote:
| 3 is the limit. More than 3 is bad.
| aborsu wrote:
| One would think the limit for pie is closer to
| 3.14159265359
| PakG1 wrote:
| It is, but it's not easy to cut pi slices of pie without
| being unfair to others who want to have equal slices of
| pie. Plus, the effort to be so exact may not be worth the
| utility. You may hit the true pi limit by random luck
| too.
| oakwhiz wrote:
| Yes although it is true what the grandparent comment said
| about sealing - that keeping things dry, using coatings
| or topper materials, dewatering, etc. will all help
| extend the longevity and reduce maintenance requirements
| a bit.
| saalweachter wrote:
| On the plus side it makes for some wicked post-
| apocalyptic ruins. Remove maintenance, add 20 years, and
| you get the most photogenic wasteland you could ask for.
| jcampbell1 wrote:
| > The rust is essential to bind it to the cement
|
| What? This is total nonsense.
|
| > Modern concrete isn't expected or designed to last more
| than a century. It could have been made to last longer,
| if they wanted, but that would cost a little more.
|
| Is hacker news a conspiracy theory website now?
|
| > We have a very great deal of infrastructure that will
| fail on a predictable schedule
|
| Wood rots in a few years under certain conditions and can
| last hundreds in others. Concrete works similarly.
|
| The 3rd pantheon is currently standing, but it is a huge
| mix of repairs across centuries. The Romans built many
| structures that are similar but now are in ruins because
| the Catholics didn't maintain the roofs on bathhouses.
| moloch-hai wrote:
| It is a conspiracy theory that engineering construction
| is optimized for cost against requirements? Maybe ask
| literally any civil engineer how much cost matters.
| chrisdhoover wrote:
| So the Hoover dam will fail in 10 years?
| moloch-hai wrote:
| Fortunately, Hoover Dam is under compressive load.
| anamexis wrote:
| Only if the Hoover dam was made with standard concrete
| using standard building methods, I suppose.
| [deleted]
| adgjlsfhk1 wrote:
| Concrete lasts a really long time when it's under pure
| compression. You only run into issues when you try to
| build structures that need to survive in tension. That's
| when you start having to add rebar and lower weight and
| you run into issues.
| LegitShady wrote:
| this isn't really possible. For the rebar to take up
| meaningful tensile stresses, the concrete nearby must have
| cracked.
|
| Reinforced concrete ALWAYS cracks.
|
| If you want better corrosion resistance, you do other
| things - lower water ratios, increased concrete cover,
| sulfate resistant concrete with lower permeability,
| different reinforcing or epoxy coated reinforcing, etc.
| dima_vm wrote:
| Not always, if rebars are pre-tensioned before concrete
| solidifies. So the rebar is always under tension. Pretty
| common in prefab parts, like bridge bars.
| sporkland wrote:
| For someone totally outside this space I had assumed
| concrete is rigid and brittle and rebar reinforcement
| allows for it to bend and flex without breaking. But your
| comment makes it feel like it keeps the concrete in
| tension with compression forces to make it sturdier. Can
| you ELI5 what the rebar does to help?
| walty wrote:
| You're going to love this playlist from Practical
| Engineering [1]. Grady explains all of this much better
| than I could. The second video explains reinforcement and
| the fifth explains pre-stressing.
|
| [1] https://www.youtube.com/watch?v=UOHURuAf5iY&list=PLTZ
| M4MrZKf...
| LegitShady wrote:
| pre-stressed concrete is great, and has many advantages
| over regular reinforced concrete and is more efficient in
| terms of cross section so cracks less. It still cracks,
| though, and in different locations like on the ends
| horizontally instead of at high moment/deflection areas
| vertically. Pre-stressed does experience fewer shrinkage
| cracks, which is nice. It's more expensive to build and
| repair.
|
| And while you absolutely have pretensioned girders on
| bridges commonly, the bridge decks generally aren't,
| although they're almost always completely in compression
| and the steel is there for shrinkage cracks etc.
| PicassoCTs wrote:
| Another method is to connect all the rebar and add a
| https://en.wikipedia.org/wiki/Galvanic_anode
| tuatoru wrote:
| > expanding rust
|
| The alkaline environment inside concrete "passivates" the
| reinforcing bar, greatly reducing the rate of oxidation and
| changing its form.
|
| The problem exists only in concrete that is badly made with
| poorly chosen aggregate, and in corrosive environments.
|
| 1. https://en.wikipedia.org/wiki/Passivation_(chemistry)
| riversflow wrote:
| I'm just going to throw it out there to spread the word; GFRP
| Rebar (Glass Fiber Reinforced Polymer) is a thing, and you can
| buy it today at your local hardware store. I really wish I
| would have known about it on my last project, probably the last
| time I will buy steel rebar to put in concrete.
|
| I'm not an ME, but my understanding is that it is a comp in
| terms of structural reinforcement. I'd be really interested to
| do a deep dive on how these technologies stack up against each
| other, it seems like a win for construction longevity, it would
| be pretty cool if the ecological impact of production penciled
| out as a win too. My understanding is that there are some trade
| off when being used in large projects.
|
| My cursory research has indicated that this stuff first hit
| production in the 80's and was used in a bridge in the US in
| 96. Still haven't figured out why it hasn't taken over.[2] Is
| it just for a lack of evangelists?
|
| [1]https://www.lowes.com/pd/Owens-Corning/5013333093
|
| [2] https://www.fiberglassrebar.us/gfrp-rebar-from-the-
| beginning...
| _jsnk wrote:
| I recommend Tyler Ley's youtube channel[0] entirely devoted
| to concrete. He has an episode[1] addressing GFRP that might
| interest you.
|
| [0] https://www.youtube.com/@TylerLey
|
| [1] https://www.youtube.com/watch?v=thUZImUTZn0
| xattt wrote:
| Mike Holmes, a home reno personality in Canada, had been
| touting its benefits in about the mid-2000s for home
| foundation re-pours.
| iamgopal wrote:
| Any comparison in tensile strength?
| scarier wrote:
| The main reason is stiffness--off the top of my head, it's
| roughly a quarter as stiff as typical steel, so it needs
| significant engineering and often much more reinforcement to
| keep the concrete within allowable deformation limits. Basalt
| and carbon fiber are more promising replacements, but are
| significantly more expensive.
| prometheus76 wrote:
| And being driven over by semi trucks full of heavy cargo 24/7.
| tuatoru wrote:
| > Isn't the particularly short lifespan of modern concrete
| construction mostly a combination of its use in areas with
| regular freeze-thaw cycles and using a reinforcement material
| that rusts
|
| No. It's a consequence of designing to requirements of minimum
| cost and a 50-year lifespan. It'd be easy to make concrete with
| much longer lifespan, but it costs more.
| raspberry1337 wrote:
| It's a nice thought that all these depressive
| brutalistic/modernist builduings will all soon crumbly by the
| same mechanism that spawned them!
| stephencanon wrote:
| Most brutalist buildings are already 60+ ish years old and
| doing great (actual brutalism, rather than "concrete
| buildings I don't like," was mostly a style of the 1950s
| and 60s in the west, though it lasted quite a bit longer in
| Eastern Europe). Even the Boston government services
| center, everyone's most hated brutalist building in the US
| is already past 50.
| bpbp-mango wrote:
| for many people, myself included, actual brutalism _is_
| "concrete buildings I don't like"
| stephencanon wrote:
| Eh, there's no accounting for taste, but there have
| always been shitty buildings in every vernacular. We tend
| to not see the worst buildings in older styles because
| they've long since been torn down.
| ithkuil wrote:
| "Any idiot can build a bridge that stands, but it takes an
| engineer to build a bridge that barely stands." - Unknown
| colechristensen wrote:
| Tl;dr:
|
| Old "riddle solved": Romans used volcanic ash as an ingredient
|
| New "riddle solved": the good stuff also includes tiny lumps of
| calcium carbonate that self heal cracks
| [deleted]
| georgyo wrote:
| > the good stuff also includes tiny lumps of calcium carbonate
| that self heal cracks
|
| According the article, they didn't use calcium carbonate
| directly. They use quicklime (Calcium oxide) which must be
| mixed in at very hot temperatures.
|
| When a crack forms, that stuff melts and forms calcium
| carbonate that seals the crack.
| taetaset wrote:
| > which must be mixed in at very hot temperatures
|
| It gets hot when you mix it.
| georgyo wrote:
| It's a little unclear to me about that, it is what I
| thought at first. But it appears that quicklime is not
| stable at ambient temperatures and recombines with CO2 to
| make Calcium Carbonate; which is how the self healing
| works.
| longt1melurker wrote:
| they used saltwater and added volcano ash. thats the secret sauce
| ShredKazoo wrote:
| >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.
|
| So this method wouldn't necessarily work in a dry climate without
| much rain?
| simonblack wrote:
| They didn't reinforce it with iron.
| [deleted]
| Toutouxc wrote:
| This is from the article:
|
| > Masic wondered: "Was it possible that the Romans might have
| actually directly used lime in its more reactive form, known as
| quicklime?"
|
| And this is from Wikipedia, with the source dated 2011:
|
| > Gypsum and quicklime were used as binders. Volcanic dusts,
| called pozzolana or "pit sand", were favored where they could be
| obtained
|
| Is it just me or are popular science articles really so
| simplified that they often completely misrepresent the point of
| the research?
| sebmellen wrote:
| Gell-Mann Amnesia is real.
| [deleted]
| [deleted]
| kazinator wrote:
| Roman concrete was durable mainly because they didn't yet hit
| upon that silly idea of adding steel rebar.
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