Concrete Thinking

September 16, 2021 7:14 PM

"What’s the most underrated material in the modern world? How about CONCRETE? Often dismissed as boring, ugly & inert. Concrete is actually surprising, dynamic & incredibly complex. With that in mind here are a few reasons why we need to start talking about concrete" (a Twitter thread from Ed Conway; Threadreader version).

But wait! It gets even better! Meet Dr. Steve Ressler, who would like to know if you have a few minutes to learn about The Beauty and Versatility of Modern Concrete (YT; this lecture and the rest of Understanding the World's Greatest Structures are also available through Kanopy). Because concrete isn’t just for sidewalks.

posted by MonkeyToes (48 comments total)

You'll see a lot of nonsense in "green" discussions about concrete absorbing CO2, which is technically true but extremely deceptive. What the thread talks about, making the clinker, is basically starting with stuff that will decompose under heat, and in that decomposition process it emits CO2, and becomes a more chemically active product. When you mix it up and pour it, the curing reaction is driven by the potential energy you put into the material by driving the CO2 out, as it absorbs CO2 back into the material. So all that CO2 it's absorbing is CO2 that you put into the air in the first place when you turned it into clinker.

And that isn't even talking about the huge amount of CO2 from whatever fuel you burned to heat it up enough to drive the decomposition reaction forward in the first place. But if you somehow did the clinker step without using any fossil fuels (which feels unlikely because it takes a LOT of concentrated heat to do it, which would be quite challenging to do with pretty much anything besides fossil fuels), then you'd still have the emitted CO2 to deal with, which only gets reabsorbed into the concrete on an extremely long timeline. They touch on this by talking about how the Hoover Dam is still curing, and that's because there's still a whole lot of chemical potential energy residing there, each bit of which is attached to some bit of CO2 that had been driven off and which has not yet come back home to roost. So even if you made the clinker with 100% renewable energy, you'd still have CO2 that would need sequestering somehow if your mandate was truly zero-emissions on anything resembling a realistic timeline.
posted by notoriety public at 7:30 PM on September 16, 2021 [22 favorites]

Ed Conway thankfully mentions that cement production creates 7% of global CO2 emissions (although I thought it was 8%).
posted by BrotherCaine at 7:36 PM on September 16, 2021 [6 favorites]

Water Use in Concrete Production Higher Than Expected

(I recalled reading about this when the study first came out. My quick search didn’t find a comparison of relative water use versus other building materials though - that is, is total water usage by concrete production so high just because concrete is the most widely used building material worldwide, or is it higher than what water use would be if the same buildings and infrastructure were constructed of other materials?)
posted by eviemath at 7:36 PM on September 16, 2021

This is really interesting. Thanks, MonkeyToes.

Don't miss this link which I thought was at least as interesting as all the fascinating stuff about concrete and cement: Why It's Hard to Innovate in Construction
posted by straight at 7:40 PM on September 16, 2021 [13 favorites]

Neat!
I'm curious to know though - if concrete is more economical than bricks and mortar why don't we have more concrete houses built? It would seem to be more enduring and maintenance-free?
posted by storybored at 8:17 PM on September 16, 2021

I met a woman who is making concrete earrings, they look like little cinder blocks. She discussed making concrete and additives and how to make it weigh less. I realized I could make myself an aggregate window sill for my kitchen. Anyway.
posted by Oyéah at 8:21 PM on September 16, 2021 [3 favorites]

Here's a nice video from Practical Engineering that looks at the problems presented by reinforcing concrete with rebar, and how reinforcement was handled in Roman times.
posted by cooper green at 8:32 PM on September 16, 2021 [4 favorites]

I'm curious to know though - if concrete is more economical than bricks and mortar why don't we have more concrete houses built? It would seem to be more enduring and maintenance-free?

I have no special knowledge here, but at least in the US neither masonry nor concrete are used often as stick building remains cheaper. Builders certainly don't care about longevity beyond a warranty period.

Personally, I'm always surprised that structural steel isn't used more often as it would be quick to erect and leave the exterior as curtain walls which would be easy to install however you liked. I imagine that's still a cost issue though.
posted by Ickster at 9:06 PM on September 16, 2021

See also; Concrete: the most destructive material on Earth
posted by krisjohn at 9:22 PM on September 16, 2021 [3 favorites]

if concrete is more economical than bricks and mortar why don't we have more concrete houses built?

Concrete walls have to be shaped within a mould. It's hard to do that with a vertical wall, because the base of the mould would be under a lot of pressure; and you'd run the risk of bubbles and cavities within the mould. So concrete walls are generally moulded offsite, except for basement walls which are intrinsically braced by the outside earth, don't generally have many openings (which take more work to shape) and are less aesthetically important.

So concrete walls are basically panel walls. Concrete is definitely used for walls, but it's not necessarily cheaper if you're doing one-off plans and have to rent a crane to place the panels. They are used extensively for apartment construction, but composite panels ("structural insulated panels") incorporating insulation, bracing, and an external coating, can be lighter and better for the occupants.
posted by Joe in Australia at 9:25 PM on September 16, 2021 [6 favorites]

thank you for posting, this is extremely my shit
posted by capnsue at 10:56 PM on September 16, 2021 [3 favorites]

Concrete for housing also has the downside of being bloody hard to put any holes in afterwards with consumer-grade tools. My building thankfully only has a concrete frame, but the load-bearing walls are murder for drilling. Guess who put up cat shelves this year that had to withstand several 7kg cats...
posted by I claim sanctuary at 10:56 PM on September 16, 2021 [1 favorite]

Ecological or not, I prefer concrete over wood-framed rental apartments in order to ensure sound insulation and neighbour unity (and not having to move every fucking year.)
posted by neon909 at 11:49 PM on September 16, 2021 [1 favorite]

Concrete.
posted by vrakatar at 12:25 AM on September 17, 2021 [3 favorites]

Oh my golly, MonkeyToes, this is a fascinating post. Thanks so much!
posted by Bella Donna at 12:40 AM on September 17, 2021 [2 favorites]

Great post.

Cement and steel often get mentioned together in terms of driving industry to reduce the carbon emissions from them but there's actually some big differences. Specifically, cement is very low value per weight and is almost never transported very long distances so you can incentivise the production of low or zero emissions cement without the carbon leakage concerns of steel and therefore don't need to have any kind carbon border adjustment mechanism.

That means that the EU could put a substantial and rising price on cement CO2 emissions immediately without waiting to set up a complex CBAM - there is no risk of cement being imported from China.

This will do a few things:

-drive the adoption of some kind of CCS for portland cement production (if this is possible... but it is definitely not possible while CO2 emissions are free!)

-drive the adoption of alternative concretes which will never happen without a financial incentive

-potentially reduce the use of concrete in favour of other structural materials like steel (it is well known to structural engineers that designs can trade-off between concrete and steel and that this tradeoff is driven by long term commodity price trends), timber (heavily used in the form of light framing in North America where it is cheaper and as CLT in Europe for medium-rise buildings), and other materials.

-reduce the amount of construction as a whole to the degree that the above factors lead to higher costs.
posted by atrazine at 3:18 AM on September 17, 2021 [2 favorites]

There's also the illegal sand mining cartels Destroying marine habitats by sucking up huge quantities of sand from the sea floor around tiny Indonesian islands….because of course, desert sand doesn't have the right geometry to make good concrete.
posted by brachiopod at 4:16 AM on September 17, 2021 [5 favorites]

What? I wouldn't say concrete is "generally" shaped offsite in a mold and then carried in by crane. Precast concrete panels exist, sure, but cast-in-place is also common. You build the mold on site, pour the concrete, then remove the mold.

I design water and wastewater treatment plants and I specify cast in place for everything unless it's a deep water tank where something like precast post-tensioned construction is more economical or needed for strength.

Houses aren't made of concrete because it's cheaper to build them other ways. You'd also have a hell of a time modifying them so you'd better like every detail of your house layout.

Concrete houses if you're into that sort of thing.
posted by The Monster at the End of this Thread at 4:33 AM on September 17, 2021 [7 favorites]

My background is civil engineering, and in undergrad, I was part of a student chapter of the American Society of Civil Engineers. Every year, ASCE holds regional/state competitions and then a national competition for concrete canoes. Student chapters have to figure out to make strong and light canoes out of concrete and then race them. It was super cool telling people our 10-foot canoe - which used microfibers, glass beads, and fiberglass mesh rather than traditional aggregates and admixtures - weighed a little under 100 pounds.
posted by TheKaijuCommuter at 5:25 AM on September 17, 2021 [4 favorites]

Concrete? Heck, yeah! That's concrete baby!
posted by JDHarper at 5:56 AM on September 17, 2021 [1 favorite]

I'm curious to know though - if concrete is more economical than bricks and mortar why don't we have more concrete houses built?

Disclaimer, house building technologies vary wildly between different regions - but local to me, the catch is that almost all "bricks and mortar" houses are actually timber framed, with a brick veneer on the outside.

The reason for that is that all the stable soil was already been taken for building over a hundred years ago. What's left is soil that's mostly clay, which expands / contracts by about 6cm between wet and dry. So you need timber construction, because timber can flex as the ground shifts. Masonry or concrete would just straight up crack in half because it can't flex. But people really like the look of brick, so they attach a brick veneer to the outside of the timber framed house, just for looks.

So it's not so much a matter of why don't we use concrete instead of bricks and mortar, but why do people prefer the exterior look of brick vs the exterior look of concrete.
posted by xdvesper at 6:09 AM on September 17, 2021 [3 favorites]

The reason for that is that all the stable soil was already been taken for building over a hundred years ago. What's left is soil that's mostly clay, which expands / contracts by about 6cm between wet and dry. So you need timber construction, because timber can flex as the ground shifts. Masonry or concrete would just straight up crack in half because it can't flex.

Maybe it depends on where you are, but in the US, and I suspect many other countries, it's about labor costs. A wood frame structure can go up really quick with just a couple people working on it. Clay soils can be mitigated, but you generally don't build on them without mitigation (which means extra cost) no matter what the building construction type, since your foundations are going to be concrete anyway. There are plenty of decent building sites left.
posted by LionIndex at 6:20 AM on September 17, 2021 [2 favorites]

I'm curious to know though - if concrete is more economical than bricks and mortar why don't we have more concrete houses built?

Disclaimer, house building technologies vary wildly between different regions - but local to me, the catch is that almost all "bricks and mortar" houses are actually timber framed, with a brick veneer on the outside.

And in my region, most houses built in at least the last 40 years have walls of concrete block. We build with concrete, just not by pouring it into walls.
posted by Aardvark Cheeselog at 6:56 AM on September 17, 2021

I'm curious to know though - if concrete is more economical than bricks and mortar why don't we have more concrete houses built? It would seem to be more enduring and maintenance-free?

Bricks (or at least what you see on modern NA houses) are just there to protect the inner structure and enveloppe of the house, they do not and cannot support anything, which is quite different from concrete which can actually support things.

Concrete is also a poor insulator, so depending on the local climate it's much better to frame with wood and put insulation material in the walls.

Clay soils can be mitigated, but you generally don't build on them without mitigation (which means extra cost) no matter what the building construction type, since your foundations are going to be concrete anyway.

Ha.... I wish that was true, it's certainly truer now, but there's a huge amount of old real estate built on clay without proper support. A few years ago they fixed an old leaky water pipe around where I live, and in the following years, almost everybody on the street had to have piles added to stabilize their foundations, turns out the water pipe leak was acting as a stabilizer by keeping the clay wet...

Climate change is also really amplifying the issue, it's hotter/dryer so the clay dries quickly and buildings are moving more and more.
posted by WaterAndPixels at 7:15 AM on September 17, 2021 [5 favorites]

Americans use too much concrete. We use it to pave sidewalks for some reason. It looks great at first, but it takes so much machinery to build it, it's quite expensive and labor intensive. Then over the years it forms cracks and gets shifted by trees or ground movement.

At some point it will need to be repaired or someone will need to work under it to get to a sewer line or something. At that point they need to block off part of the street and work with jackhammers, at dump truck, a cement truck, etc. It needs to be scheduled carefully and it needs a big crew.

Contrast this with what I've seen in many European and Asian countries: sidewalks can be paved with... Pavers! This may require more labor up front but it leaves you with a very nice looking sidewalk. If done nicely it won't be quite as smooth as concrete but it's close. The big benefit is when you need to do that maintenance. At that point it's just a couple guys pulling up the pavers, doing whatever work needs to be done, and then replacing them. No large tools are required. I don't really get why you don't see this more often in the US, except that I think there might be some bias against an installation that requires much more manual labor at first.

Anyway here's the great Mike Hadduck making the same point in a much better accent: sidewalks in Denmark
posted by cman at 7:24 AM on September 17, 2021 [7 favorites]

Cool post, monkeytoes. A lifetime ago I worked on a concrete crew, it was a very No Country for Old Men experience. I think the University of Manitoba is/was a site of considerable research on fabric forms and the like, this was way beyond the flatwork I was involved with.. but yeah, concrete is a dynamic material for sure.
posted by elkevelvet at 7:24 AM on September 17, 2021

cman, I'm pretty sure it's because paver cost more upfront and also requires more ground prep / work than just pouring concrete. And as a whole, we're not good at projecting maintenance costs and making smart decisions upfront in NA (no idea about Europe), we just keep building stuff but never seem to realize it'll have to be maintained and budget money over decades for that maintenance. Or at least, around here we're no good.

In general I don't understand why houses and infrastructure aren't built with servicing in mind, but it's probably because its cheaper/easier to design something hidden behind drywall or buried in the earth. To me if I need to access something behind drywall it's a huge pain in the ass to fix later on, but for a real construction crew it's probably quite easy/quick. And I guess building actual tunnels under every street so that gas/water/electricity can be accessed without digging would cost an unreasonable amount of money.
posted by WaterAndPixels at 7:45 AM on September 17, 2021 [1 favorite]

We use it to pave sidewalks for some reason. It looks great at first, but

also, concrete may be good for sidewalks in terms of strength, durability but it's terrible for humans in terms of foot, knee, hip, back injury due to pretty much unavoidable repetitive use (they're EVERYWHERE, and they offer way less "give" than even asphalt). I'm pretty confident that future humans will look back on the mass concretization of our foot paths as one of the dumber moves humans ever made in the name of "progress".
posted by philip-random at 7:48 AM on September 17, 2021 [2 favorites]

Contrast this with what I've seen in many European and Asian countries: sidewalks can be paved with... Pavers!

Pavers are used in the US too for fancy sidewalks, but for regular sidewalks they are not smooth enough to support ADA requirements, unless they are laid on a concrete base.

And in my region, most houses built in at least the last 40 years have walls of concrete block. We build with concrete, just not by pouring it into walls.

Concrete block houses are very common in coastal Florida.

Bricks (or at least what you see on modern NA houses) are just there to protect the inner structure and enveloppe of the house, they do not and cannot support anything, which is quite different from concrete which can actually support things.

This is way too simplistic. A brick-veneer protects the house from weather, and it 'supports' the windows and doors, especially those above the first floor. A double brick wall across most of the US would be terrible from an insulation perspective and take longer to build. That's why most houses are just brick veneer. It's a better way of building.
posted by The_Vegetables at 7:49 AM on September 17, 2021 [2 favorites]

Brick and concrete both also suck in massive amounts of moisture, such that brick veneered homes have a huge space between the frame of the home and brick to allow water to drain. Without that, in some climates the walls would weep water and mold quickly. Brick is just not a real great building material if you have things like central AC without a lot of water mitigation and other modern building techniques.
posted by The_Vegetables at 7:54 AM on September 17, 2021 [1 favorite]

I spent my youth building forms for pour in place concrete and then pouring. It was basically the worst job you can have as a teen, and why I work inside now. Hot, everything is sharp, endless repetitive, but also fussy -- think all the worst aspects of any office job but done in the hot sun and you really have to be up on your tetanus shot..
posted by The_Vegetables at 7:57 AM on September 17, 2021 [3 favorites]

Really happy to see folks enjoying this! Please do give the linked Ressler lecture a chance--I was skeptical about the prospect of enjoying hours of someone discussing civil engineering, but was pleasantly surprised at how interesting Ressler's presentations are.
posted by MonkeyToes at 8:38 AM on September 17, 2021

Concrete walls have to be shaped within a mould.

Not necessarily, because shotcrete is a thing.
posted by flabdablet at 8:40 AM on September 17, 2021 [4 favorites]

this is extremely my shit

If you're inclined to compare your shit to concrete, consult a physician.
posted by Greg_Ace at 8:50 AM on September 17, 2021 [4 favorites]

or take Barker's Microscopic Liver Pills.
posted by flabdablet at 9:01 AM on September 17, 2021

Concrete walls have to be shaped within a mold.

In Silicon Valley, Tilt-Ups were a thing. Cast the wall on the ground, then tilt it up into position. Many office parks were built like that.

in the US neither masonry nor concrete are used often as stick building remains cheaper. Builders certainly don't care about longevity beyond a warranty period.

Makes me crazy -- why is wood-framed housing built in termite zones? Why is it even allowed? In my perfect world, that would be a code violation.

I prefer concrete over wood-framed rental apartments in order to ensure sound insulation

Yeah, they're the best; unfortunately extremely rare, where I've wanted to live.
posted by Rash at 9:16 AM on September 17, 2021

Front porch drinkin’ Hamm’s in the summertime stay out all night ‘n avoid the heat 2:30 rolls around biker bars shuttin’ down all he biker barrin’ yuppies roll out into the street. Concrete.
posted by snofoam at 9:26 AM on September 17, 2021

Great discussion on this topic! Concrete gets a lot of attention in sustainable construction because of resource use, but for concrete frame vs steel frame there is no clear-cut winner as the variance in individual system is greater than the difference between them. I’m also holding a tiny amount of hope that the experiments with carbon-cured concrete will pan out and scale in a way that make it a feasible material - would solve the water and carbon issues neatly.

Concrete, like steel, has the advantage of being and extremely durable and long-lifespan structure, which ultimately can be more important than first cost as nothing is more sustainable than an existing building.

My favorite structural concrete is type 1L, which gets a lower carbon load by using limestone as part of the cement mixture, which also has the nice side effect of a buttery white color.
posted by q*ben at 9:32 AM on September 17, 2021 [2 favorites]

When I was in school, concrete and the fascination therewith in the Civil Engineering department was a large source of derision from all of the EE and ME students.
posted by Dr. Twist at 11:21 AM on September 17, 2021

Here's an explanation I found helpful in understanding the CO2 emissions involved in Portland cement production:

From the standpoint of CO2 emissions, the most important characteristic of [minerals used in Portland cement] is the calcium content. The calcium comes from calcium carbonate (limestone) and the first step of producing clinker is the decarbonation of the limestone:

CaCO3 → CaO + CO2

This is the chemical reaction that accounts for some 60% of CO2 emissions from the manufacture of traditional Portland cement. Since no large-volume concentrated sources of calcium exist other than limestone, the manufacture of calcium-based cements inevitably leads to substantial “chemical” CO2 emissions associated solely with the decarbonation reaction, and not with the fuel burned in the process. It is exactly for this reason that the cement industry is such a significant CO2 emitter. This also a cause for optimism — it is clearly possible to reduce these emissions in a relatively inexpensive way, simply by changing the composition of cements.

This is what the "37% clinker substitution" wedge of the "key levers for CO2 reduction" pie chart is referring to, from the china national building material group slide quoted in Ed Conway's thread.

source: UN report on Eco-efficient cements 2017 (PDF, unep.org))
posted by are-coral-made at 2:26 PM on September 17, 2021 [4 favorites]

atrazine, thanks for your excellent insight re: cement having low value per weight => cement more likely to be manufactured locally => more opportunity for states to unilaterally incentivise emissions reduction for local concrete production within their borders without needing to negotiate international carbon treaty stuff.

On another hand, one could argue that a state adding carbon taxes for local concrete production makes that state incrementally less attractive on the global state for business etc due to higher construction costs, so it still puts the state at a disadvantage to other competitors that do not discourage high-carbon intensity concrete production -- or is that complete nonsense? i imagine many businesses would be insensitive to this, they'd go where the business is.

On a national or international level, it's all very well to imagine entirely different other ways for how society or economies could operate, that would be much better from a environmental perspective and for humanity in the long run, but it's a whole other matter of which of those ways of operating might be feasibly reachable from where we currently are, given politics, vested interests, human nature, etc. Any opportunity for incremental "moves" in a vaguely right direction that can be made locally without international agreements are promising.
posted by are-coral-made at 2:46 PM on September 17, 2021 [3 favorites]

this is making me want to rewatch Locke so dang bad. seriously great movie and it will make you really care about concrete (but in a different way than this post)
posted by capnsue at 10:33 PM on September 17, 2021 [2 favorites]

When I was in school, concrete and the fascination therewith in the Civil Engineering department was a large source of derision from all of the EE and ME students.

At least in the case of EE, a bit hypocritical given their obsession with silicon.
posted by notoriety public at 8:15 AM on September 18, 2021 [1 favorite]

I saw this post a few days back but couldn't get here.

ETH Zurich's A world of construction without cement.

I'm into de-carbonising/de-oiling as much as much as possible, there are many, many cement alternatives, from Africa, Iran, Germany - but they are hard to find. It does depend on what you need your concrete for, e.g. parking, driving, steps/ramps, walls, floors, roofs, rather than one (semi)-generic material design should be expected to shift to task-appropriate.

Joe in Australia have you heard of concrete canvas? I contacted manufacturer about using it as a combined fire-barrier/noise-barrier/party-wall for a large industrial workshop to create a heavy draped curtain - fabric formed concrete is the same technology.

Eliminates many steps (formwork is so, so expensive) but building is stuck in the past; getting easier to drag them forward now though. Even Holcim are promoting it - it does result in a lot less cement used so this is a good sign of a leader taking a better path.
posted by unearthed at 8:01 PM on September 18, 2021 [2 favorites]

neon909 I prefer concrete over wood-framed rental apartments in order to ensure sound insulation and neighbour unity

Around here, older towers indeed have concrete walls between units. The vast majority of new tower builds does away with this to save costs.

Also, minimal sound abatement for the hard flooring, and carpets have fallen out of style.

Modern glass for better insulation is nice, though, to block outside noise a little bit better.
posted by porpoise at 4:54 PM on September 19, 2021

Sigh. Concrete and cement are not synonymous. Cement is to concrete as flour is to cake. Please writers. PLEASE. Write this down. - Roxane Gay

(I say this not to point fingers, but because I was delighted to learn yet another area that Roxane Gay is knowledgeable about.)
posted by The corpse in the library at 7:53 PM on September 19, 2021 [2 favorites]

Need a 2000 ft. long aircraft carrier to fight Nazi Germany? Try creative thinker Geoffrey Pyke’s recipe using Pykrete: mix a big bowl of 14% sawdust with 86% water; mold and freeze it; hollow it out a bit; add refrigeration, propulsion, and aircraft; and you get HMS Habakkuk.
posted by cenoxo at 8:24 AM on September 20, 2021 [1 favorite]

A longer version of this is Robert Courland’s book “Concrete Planet.”
posted by fantabulous timewaster at 12:40 PM on September 20, 2021