[HN Gopher] Experts revive ancient techniques to make concrete m...
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Experts revive ancient techniques to make concrete more sustainable
Author : PaulHoule
Score : 75 points
Date : 2023-12-04 04:08 UTC (18 hours ago)
(HTM) web link (techxplore.com)
(TXT) w3m dump (techxplore.com)
| InCityDreams wrote:
| Perhaps the UK 'construction' industry could provide some
| er....support.
|
| https://www.theguardian.com/uk-news/2023/sep/05/raac-and-rui...
| adamjc wrote:
| > "For centuries, builders tried to cut costs by limiting how
| much cement they used and incorporating recycled waste materials
| into their concrete," says Salvatore Aprea, head of the Acm
| research group. "The challenge now is to revive these old methods
| --not for financial reasons but for the sake of our planet."
|
| I put it to you that if it was financially viable and simple
| ("ancient methods"), it would already be done.
|
| Good luck to them
| ChatGTP wrote:
| I find it a bit hard to imagine you're the first person to
| think of this, let alone those people working on it who I'm
| sure are a bit familiar with concrete then you ?
| beAbU wrote:
| The article is about increasing sustainability, not financial
| viability.
| SV_BubbleTime wrote:
| Those are the same thing in reality.
| baq wrote:
| Financial viability is _just_ (ahem) a question of pricing in
| externalities correctly (i.e. tax CO2). It must happen, when
| exactly and on what schedule is a very good question.
| icegreentea2 wrote:
| These old techniques come from a time with completely
| constraints. Modern techniques are generally all about creating
| uniformity as far upstream as possible to them deploy cheaper
| labour/logistics systems/automation downstream. Think about
| modern masonry. The "bricks" are uniform, the mason man knows
| exactly how they can be shipped, moved around the site, and
| individually placed. Concrete mixes are standardized as much as
| possible and the optimized so that the man with the trowel can
| work as efficiently as possible.
|
| Working with off cuts/minimally processed stone is harder. You
| need to be able to manipulate a greater variety of shapes and
| sizes. Stuff doesn't stack. It takes way more brain and finesse
| on the work site to make things work well.
|
| These ancient methods are in many ways much more complicated
| (not simple) than modern methods. But they are complicated in
| ways that we're just starting to be able automate well
| (computer vision systems to sort/group/place irregular blocks
| for example).
| wconrm wrote:
| Ancient methods were lost because...earthquakes?
| devoutsalsa wrote:
| A big reason the Romans stopped using concrete is because they
| no longer wanted to build projects that needed concrete.
| r/AskHistorians has a good post on this...
|
| _Why Was "Roman Concrete" Not Used for Centuries After the
| Fall of the Empire?_
|
| https://www.reddit.com/r/AskHistorians/comments/d79rpp/why_w...
| hliyan wrote:
| Is this related to the technique that this group recently claimed
| to have rediscovered:
| https://www.sciencenews.org/article/chemists-long-lasting-ro...?
| Although that is more about much longer lasting concrete:
|
| > Masic and his colleagues were trying to re-create an ancient
| Roman technique for making concrete, a mix of cement, gravel,
| sand and water. The researchers suspected that the key was a
| process called "hot mixing," in which dry granules of calcium
| oxide, also called quicklime, are mixed with volcanic ash to make
| the cement. Then water is added.
|
| > Hot mixing, they thought, would ultimately produce a cement
| that wasn't completely smooth and mixed, but instead contained
| small calcium-rich rocks. Those little rocks, ubiquitous in the
| walls of the Romans' concrete buildings, might be the key to why
| those structures have withstood the ravages of time.
| semi-extrinsic wrote:
| While it's interesting to explore ancient concrete, actually
| scalable improvements of concrete production will be made
| elsewhere.
|
| For instance HeidelbergCement has successfully piloted and is
| currently implementing technologies that bring the CO2 emissions
| from cement production close to zero. The OxyCal hybrid process
| that they are deploying in Bulgaria and Belgium will capture >97%
| of all emissions from the cement production process.
| culi wrote:
| I tried looking it up but don't fully understand. What exactly
| is the OxyCal hybird process?
| semi-extrinsic wrote:
| It's their name for combining oxyfuel combustion with amine
| capture.
|
| Oxyfuel is where you feed the combustion process using pure
| oxygen mixed with exhaust gas, instead of air. Since you're
| not pulling in all that nitrogen gas from the air, the
| exhaust is much richer in CO2, which is then easier to catch.
|
| Amine capture is where you use an amine solvent liquid that
| is sprayed as droplets into a large column, where the
| droplets fall down and absorb CO2 into the liquid, while the
| exhaust gas flows up and leaves the column free from CO2.
| Then the liquid that collects at the bottom is moved to a
| stripper cylinder, where the liquid is heated up and the CO2
| is released as pure gas.
|
| Specifically for the cement process, using both of these
| technologies together, it turns out you can do some cool
| process integration where the byproduct of one is the
| requirement of the other, and vice versa, so you can make the
| whole setup a lot cheaper in both CAPEX and OPEX.
| willmadden wrote:
| Does it turn into rusted out rubble in 100 years like the
| reinforced concrete we use today?
|
| I remember reading an article about the longevity of Roman
| concrete. The best they could come up with was the use of
| volcanic ash and much slower curing in salt water.
| semi-extrinsic wrote:
| You are correct that reinforced concrete will corrode,
| generally the service life of reinforced concrete is around
| 50 years if no special measures are taken. This is because
| the initial alkalinity of the concrete, which protects the
| steel, will be neutralized over time. This is the same for
| modern and for Roman concrete.
|
| But many methods are available both to extend life, and to
| monitor the health of reinforced concrete. The failures that
| do occur are typically due to negligent maintenance.
|
| The Romans didn't use steel reinforcement, of course, they
| just used massive concrete structures. We can do the same
| today, but it would mean no skyscrapers, no long span
| bridges, etc.
|
| To be able to build the Pantheon, at 43 meters height, they
| used walls with a thickness going from 6.4 meters at the base
| down to just 1.2 meters at the top. In addition they reduced
| the density of the concrete by almost 50% towards the top, by
| using very light aggregates.
|
| In comparison the Burj Khalifa at 828 meters heigt has _less
| than a tenth of the wall thickness at the base_ , just 0.6
| meters of reinforced concrete wall thickness in the hexagonal
| frame.
| greenpresident wrote:
| Their CFO gave a talk this summer that I went to. He noted that
| green energy does not solve their sustainability goals, as
| about a third of the CO2 emissions are process related. He
| talked about their capture plans but noted that they are
| unlikely to be big enough to capture ongoing emissions,
| essentially admitting that this looks good on slides but would
| work at scale.
| cm2187 wrote:
| I was a bit shocked when I learned that reinforced concrete only
| has a lifespan of about 100 years. That means that if you buy a
| condo in a building built in the 1970s, the building will become
| unsafe and need to be demolished in your life time. I don't know
| if people are pricing this consideration.
|
| It also means there will be pretty much nothing left of our
| architecture, all those appartments, offices, museums, bridges,
| will all need to be destroyed and rebuilt. Not that modern
| architecture is really worth preserving. But it feels the only
| thing our era will leave behind is financial debt and bits in the
| cloud!
| adhesive_wombat wrote:
| Considering the astounding cost of building anything now, I
| guess being in the mitigation industry (retrofits, shoring-up
| and general can-kicking) will be rather profitable.
|
| But I can see at least some buildings being profitable even
| then. A modest London property can easily cost 500k, most of
| which is the land itself. If it lasts 100 years, that's "only"
| 5k per year, and you keep the land. Obviously the calculation
| is different if you're _buying_ a 95-year-old concrete
| property, rather than building a new one. I imagine mortgage
| providers are paying attention, they already strongly dislike
| lending against steel-framed houses.
|
| I don't think we'll be seeing mass demolitions of 100 year old
| properties and infrastructure, except probably quite a bit of
| useless office space if RTO continues to not really happen over
| the next few decades. But we will see some very expensive and
| disruptive repairs-in-place to infrastructure when it can't be
| ignored any more.
| gumby wrote:
| In the US the accounting treatment of a building (depreciation)
| is, IIRC 40 years. So a century is considered longer than the
| typical lifespan.
|
| Looking around Palo Alto, there are a fair number of wood frame
| building ps of about a century in age, and a LOT built in the
| 1950s. I dont know about survivorship bias, but a century seems
| like a pretty reasonable assumption.
|
| (I was built in the 1960s so appreciate the thought that I
| might still be going strong in the 2070s, thanks!)
| __MatrixMan__ wrote:
| The majority of our debt, and the majority of our bits, are not
| really aligned with especially meaningful goals. Why would the
| future keep them around?
| 101008 wrote:
| > That means that if you buy a condo in a building built in the
| 1970s, the building will become unsafe and need to be
| demolished in your life time. I don't know if people are
| pricing this consideration.
|
| Isn't possible to do some repairs to make it safe again,
| instead of completely demolish it? I live in a big city (South
| America) with a lot of old buildings. People treats property as
| something that will last forever, but if this is the case, a
| lot of people are going to lose assets - and I am also scare of
| the gov to check that these buildings are still safe.
| droopyEyelids wrote:
| > Isn't possible to do some repairs to make it safe again
|
| This ends up being a complex question that's unique to every
| building, and needs to take into account the architecture,
| the soil (reinforced concrete is used in footers/pilings) and
| a ton of other factors.
|
| But what makes it extra scary? In most countries there is
| _always_ a company that will tell you "Yes, it can be done,
| and for less than the cost of replacing the building". Even
| in the USA this happens and then we have deadly condo
| building collapses.
|
| I say "most countries" because I hope that there's some
| country where they have tight enough regulations to prevent
| it. Like maybe Norway or Luxembourg or something.
| high_5 wrote:
| Imagine the shock for those poor bastards then:
| https://en.wikipedia.org/wiki/Ponte_Morandi#Collapse
|
| 51 years.
| axus wrote:
| Or these guys
| https://en.wikipedia.org/wiki/Surfside_condominium_collapse
|
| 42 years... and some poor maintenance
| p1mrx wrote:
| > reinforced concrete only has a lifespan of about 100 years.
|
| Currently, less than 1% of rebar is made from stainless steel:
| https://www.youtube.com/watch?v=zn9SzyDhfj8&t=140s
| scythe wrote:
| Stainless steel contains a necessary 12% (often more, usually
| 18%) chromium, which is relatively scarce from a building
| materials perspective. Already 85% of available chromium is
| used for stainless steel; many other metals are primarily
| supplied as byproducts of chromium extraction because of the
| extensive efforts [1, 2] made to locate and exploit deposits.
| In fact, total rebar production is roughly the same scale (if
| not larger) as total stainless steel production, meaning that
| practically the entire world supply of stainless steel would
| have to be diverted to rebar in order to use it for this.
|
| In general only the 12 or so most common elements can be used
| for construction. Copper is the rarest material used in major
| applications, but this is relatively less total mass consumed
| than rebar.
|
| 1: https://en.wikipedia.org/wiki/Bushveld_Igneous_Complex#Min
| in... (50% of world supply)
|
| 2: https://en.wikipedia.org/wiki/Ring_of_Fire_(Northern_Ontar
| io...
| p1mrx wrote:
| > Copper is the rarest material used in major applications,
| but this is relatively less total mass consumed than rebar.
|
| At 43:51 in the video, he claims that an outer layer of
| stainless steel rebar is sufficient to protect the
| interior, so the goal is not 100% stainless.
|
| https://en.wikipedia.org/wiki/Abundance_of_elements_in_Eart
| h... says chromium is slightly more abundant than copper.
| quickthrowman wrote:
| It's probably close to 10x the price.
|
| I occasionally buy stainless steel strut and a 10' stick of
| 12ga 1-5/8" deep SS 316 strut is around $250. The same strut
| made of galvanized steel is around $40.
| alentred wrote:
| Worth noting that 100 years is not exactly the hard deadline,
| but a typical (default) *target* for the calculations made by
| the engineers planning the construction.
|
| What I mean is that this number is defined by design, although
| they are of course also constrained by what is possible within
| the set budgets.
|
| Reinforced concrete lifespan depends on a lot of factors,
| including some that can be controlled, such as isolation of the
| reinforcement, materials used, various qualities of the
| concrete itself. When the new structures are designed,
| engineers do the calculations to achieve a specific goal in
| terms of lifespan, construction cost and maintenance cost.
|
| I don't know how this works in practice, but I would hope that
| various factors such as the total cost and environmental impact
| (yes, I can hear my inner self laughing at my naivety here) are
| taken into account to arrive to the optimal target.
| culi wrote:
| The oldest buildings in the world[0] are as old as they are
| because they use materials with lifespans of much less than 100
| years. Instead they make them modular. Make it so that you can
| take out parts of the building to replace them without
| collapsing the whole thing. Instead we build our buildings in
| such a way that makes maintenance very hard and costly. We
| prefer to pretend like our buildings will last forever rather
| than actually plan for the inevitable degradation
|
| There's small scale movements towards changing this. Some
| cities are specifically building buildings in a way that makes
| them modular and reusable[1]
|
| [0] https://en.wikipedia.org/wiki/H%C5%8Dry%C5%AB-ji
|
| [1] https://www.bbc.com/future/article/20230207-can-we-design-
| ci...
| scythe wrote:
| Also in Japan, there has been an increasing use of aluminum
| (!) in construction, since it will generally be melted and
| re-used after the structure is no longer useful.
|
| https://www.acsa-arch.org/chapter/toyo-itos-second-age-of-
| al...
| rowanG077 wrote:
| What's the problem with aluminium? I would always build
| structures out of aluminium if aluminium would be strong
| enough. It has extreme corrosion resistance, it's cheap,
| it's easy to handle, you can easily make almost any
| imaginable shape with it, you can cheaply reuse it, it's
| very light.
| cm2187 wrote:
| Also the low melting point in case of fire.
| hef19898 wrote:
| Aluminiums corrosion resistance is mostly myth so.
| more_corn wrote:
| Aluminum corrosion resistance is caused by a thin film of
| aluminum oxide which protects the rest of the material.
| davidgay wrote:
| > The oldest buildings in the world[0] are as old as they are
| because they use materials with lifespans of much less than
| 100 years.
|
| Rather apropos counter-example: Rome's Pantheon is several
| hundred years older and built in part of concrete.
| iwwr wrote:
| The ancient Roman concrete was very different from modern:
| it was more thick, could not ne poured etc. But more
| importantly, it had no rebar, which is the main thing that
| corrodes over time. Ancient buildings could use molten lead
| to join together pieces of stone, but steel could not be
| made in the volume needed for reinforced structures.
| smegger001 wrote:
| Thing is we can use rebar in concrete for indefinately
| long use if we plan ahead, use sacrificial annodes to
| stave off corrosion or use stainless steel or use
| carbonfiber rebar as they won't rust. Hell using a
| polymer coating on rebar can prevent moisture contacting
| the surface of steel and rusting but that would require
| added cost and care when preping to prevent the polymer
| from being damaged prior to being embedded in concrete.
| anonymouskimmer wrote:
| Are the thermal expansion characteristics the same as for
| regular steel rebar?
| Modified3019 wrote:
| Reinforcing rebar and fibers can also be made out of
| basalt, which takes care of both corrosion and thermal
| expansion issues.
| more_corn wrote:
| Un reinforced.
| chalcolithic wrote:
| > if you buy a condo in a building built in the 1970s, the
| building will become unsafe
|
| OTOH if I buy a condo in a building built in the 1970s....
| scythe wrote:
| CFRP rebar has been developed with a much longer lifespan.
| However, it is currently considered non-economical, possibly
| because design lifespans are not long. Aramid FRP has been
| considered for rebar as well; glass fibers are attacked by
| cement alkali; basalt fibers have good performance dependent on
| the source of basalt (rocks with varying composition).
|
| One issue with a long-lived building is that you never know
| exactly when it will fail. 700 years down the line, it starts
| to crack: now what? The evolution of biological systems has
| strongly preferred regular replacement to longevity.
| foobarian wrote:
| European acquaintances often poke fun at our North American
| wood frame construction, noting their concrete houses are
| stronger and "will last for centuries." Are they wrong? I know
| there are a lot of stone buildings that had excellent longevity
| but those are made of large stone blocks instead of reinforced
| concrete. And that's just walls, floors in old houses are
| usually spanned by wood beams (there goes the wood again).
| cm2187 wrote:
| I think a lot of houses are made of bricks, not necessarily
| reinforced concrete. Appartement blocks on the other hand is
| all reinforced concrete I believe.
| foobarian wrote:
| Good point - yes the walls not necessarily, but floors.
| There used to be a common community activity similar to
| "barn raising" - "building the plate" where after the
| homeowner DIYd the molds and rebar, the neighbors would
| come together and mix and pour concrete over the span of
| one day. Fun times.
| gnopgnip wrote:
| In the US four to five stories of wood framed apartments
| over a primarily wood podium garage is a common
| construction technique. Type IIIA construction.
| cm2187 wrote:
| I can't imagine what the sound insulation between floors
| must look like.
| quickthrowman wrote:
| > Appartement blocks on the other hand is all reinforced
| concrete I believe.
|
| Five-over-one is probably the most common new residential
| apartment building variant in the US today, it's a single
| story of concrete (commercial space or common areas) with
| 4-5 floor of stick built (wood-framed) apartment housing on
| top. Developers only build apartment towers when the land
| is expensive enough to force them to.
|
| https://en.m.wikipedia.org/wiki/5-over-1
| sudobash1 wrote:
| On the west coast of America, I would much rather be living
| in a wood frame house when an earthquake hits. Depending on
| construction, the house may not survive, but I probably will.
| Cement, stone, or brick all seem much riskier to me in an
| earthquake zone.
| AlbertCory wrote:
| It can be much less, if water gets in and corrodes the rebar.
|
| https://www.npr.org/2021/08/26/1031245430/surfside-condo-col...
| joelegner wrote:
| Where did you hear that reinforced concrete has a lifespan of
| 100 years?
|
| As a structural engineer, I can tell you this is not correct as
| a general rule, but is true for structures subject to
| chlorides, especially marine structures like bridge piers.
|
| One of my now-retired professors at the University of South
| Florida studied concrete durability for FDOT. He told me FDOT
| is now using a 100-year design basis for bridges. The concrete
| materials and additives have gotten quite good over the past 2
| decades. We are learning a lot and still improving our
| concrete.
|
| The key is to make a tortuous path for the chloride ions so it
| takes them decades to build up enough to overcome the passive
| film at the steel-concrete interface. The high pH of the
| concrete matrix causes this passive film, and it takes either
| acidification or chlorides to defeat it. Concrete bridge decks
| and roads in cold regions that use deicing salts are also
| damaged by chlorides.
|
| Reinforced concrete protected from the weather in buildings
| would not have a 100-year lifespan forecast. If the building is
| properly maintained, the concrete should last much, much longer
| than that. I say "properly maintained", because of the Surfside
| Condo collapse in Florida. There a leaking plaza deck, lack of
| maintenance, and design flaws (columns too skinny) led to a
| tragic collapse of a building.
| toss1 wrote:
| What baffles me (as someone working in Advanced Composites)
| is why not simply get rid of the steel, the steel-concrete
| interface, the chloride ion and corrosion problem altogether
| -- by instead using rebar made of composites?
|
| Rebar of fiberglass, carbon fiber, basalt, and other
| combinations is all redily available and has known
| properties.
|
| The key issue is that steel will corrode, then expand and put
| the concrete in tension (which concrete sucks at reacting),
| causing the concrete to crack, then spall off. None of the
| composites do this.
|
| Yet, despite composites being available for years, and even
| being cheaper than steel [0], they are being picked up at
| remarkably slow rates.
|
| It seem blindingly obvious to me that everyone should have
| just switched some time ago. Yet, this has not happened. Why?
|
| [0] https://ernestmaier.com/is-fiberglass-rebar-more-
| affordable-...
| gumby wrote:
| The proposed approach (stacking irregular rocks) is much more
| labor and probably time intensive, one of the reasons it's not
| done any more. Another is the difficulty of estimating the load
| bearing strength when you don't have predictable uniformity in
| the structure. And transporting irregular large rocks is less
| efficient than gravel.
|
| The good news is these problems can be solved down the road! On
| the labor side, I imagine robots can be used to do the stacking
| and transporting. Probably 20 years down the road but definitely
| within the realm of serious possibility. As for the strength, you
| can watch and assay each large rock as you place it, and use some
| test + statistical methods to estimate structural integrity (the
| current model of pouring slurry into a wooden form is just a
| simplified version of this anyway, one that can be computed with
| a slide rule). As a bonus the result could be _stronger_ due to
| its amorphous structure.
| thejohnconway wrote:
| There was a rock stacking robot on HN a couple of days ago.
|
| https://wonderfulengineering.com/this-new-monster-robot-can-...
| gumby wrote:
| Nice!
| tantalor wrote:
| Incidentally, both the rock stacking robot and this
| sustainable-concrete resarch are at ETH Zurich.
|
| https://rsl.ethz.ch/robots-media/heap.html
|
| https://sc.ibi.ethz.ch/en/
| kderbyma wrote:
| Hemp based concrete
| dang wrote:
| Related - others?
|
| _The ancient Roman secret to concrete resilience in seawater
| (2017)_ - https://news.ycombinator.com/item?id=36585331 - July
| 2023 (76 comments)
|
| _Making Concrete That Lasts 1k Years_ -
| https://news.ycombinator.com/item?id=34644295 - Feb 2023 (3
| comments)
|
| _The Mystery Finally Solved: Why Has Roman Concrete Been So
| Durable?_ - https://news.ycombinator.com/item?id=34456323 - Jan
| 2023 (1 comment)
|
| _Mystery of Roman Concrete Unraveled_ -
| https://news.ycombinator.com/item?id=34353330 - Jan 2023 (1
| comment)
|
| _The New Science of Strong Materials (1968)_ -
| https://news.ycombinator.com/item?id=34287101 - Jan 2023 (11
| comments)
|
| _Why was Roman concrete so durable?_ -
| https://news.ycombinator.com/item?id=34280239 - Jan 2023 (270
| comments)
|
| _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)
|
| _The problem with reinforced concrete (2016)_ -
| https://news.ycombinator.com/item?id=27282927 - May 2021 (186
| 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)
|
| _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)
|
| _The problem with reinforced concrete_ -
| https://news.ycombinator.com/item?id=11975695 - June 2016 (147
| 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)
| ChuckMcM wrote:
| C'mon it was right there! From the article -- _consisting of
| experts from EPFL 's Archives of Modern Construction (Acm)
| research group,_
|
| Archives of Modern Construction Engineering (ACME) :-)
|
| I am glad that this is being investigated. One of the effects of
| climate warming is going to be a requirement for a lot of walls
| and being able to make those walls without aggravating climate
| warming as much as concrete use does now, is good for us. (it
| sucks the walls will be needed but alas that ship appears to have
| sailed).
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