[HN Gopher] Why was Roman concrete so durable?
___________________________________________________________________
Why was Roman concrete so durable?
Author : geox
Score : 241 points
Date : 2023-01-06 20:05 UTC (2 hours 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)
| 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!
| buttofthejoke wrote:
| [flagged]
| 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.
| 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.
| [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]
| 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)
| 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...
| 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. "
| 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.
| [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'.
| 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?
| 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.
| 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.
| 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.
| [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.
| [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)?
| 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.
| 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?
| 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]
| 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, and to
| use what you've learned to solve problems.
|
| 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.
|
| 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, whereas anyone who has
| actually learned to make 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
| their environments is just simply wrong, I think.
|
| we discover new evidence which surprises us all the time. do
| we have enough 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
| 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.
| 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-...
| 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.
| [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.
| 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.
| 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.
| 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.
| 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?
| 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, perhaps most, of the buildings
| that did not survive were lost because they were deliberately
| demolished for other reasons (honoring the wrong gods, etc).
| 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.
| 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.
| [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".
| 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.
| 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.
| 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.
___________________________________________________________________
(page generated 2023-01-06 23:00 UTC)