Waste coffee grounds make concrete 30% stronger

October 2, 2023 8:20 PM

Waste coffee grounds make concrete 30% stronger. Researchers have found that concrete can be made 30% stronger by replacing a percentage of sand with spent coffee grounds, an organic waste product produced in huge amounts that usually ends up in landfill. The method also reduces the use of natural resources like sand, further contributing to a greener circular economy approach to construction.
posted by chariot pulled by cassowaries (56 comments total)

Awesome! This absolutely makes sense as a study coming out of Melbourne, too.

I wonder which Council will be the first to implement a separate coffee waste collection for households? They'll have to give us brown bins to round out the red, yellow, green and purple...
posted by Athanassiel at 8:42 PM on October 2, 2023 [3 favorites]

They'll have to give us brown bins to round out the red, yellow, green and purple...

What are the purple bins for?
posted by chariot pulled by cassowaries at 8:44 PM on October 2, 2023

Does this mean I have to think about the Roman Empire again?
posted by Chuffy at 8:51 PM on October 2, 2023 [32 favorites]

Does this mean I have to think about the Roman Empire again?

I lost The Game.
posted by ChurchHatesTucker at 9:02 PM on October 2, 2023 [13 favorites]

What are the purple bins for?

leftover grape kool-aid, which makes an excellent industrial abrasive and salon exfoliator
posted by They sucked his brains out! at 9:11 PM on October 2, 2023 [20 favorites]

This is great news, and it explains my kidney stones.
posted by MonsieurPEB at 9:21 PM on October 2, 2023 [5 favorites]

And I’ve been putting waste concrete in my coffee all this time.
posted by atoxyl at 9:21 PM on October 2, 2023 [20 favorites]

We've secretly replaced his concrete with Folger's Crystals...
posted by Saxon Kane at 9:33 PM on October 2, 2023 [40 favorites]

Play the Hills Bros. game of grind shipping and economic inanity.
posted by clavdivs at 10:06 PM on October 2, 2023

This is extremely relevant to my interests. :D
posted by LionIndex at 10:16 PM on October 2, 2023 [1 favorite]

Purple is for separated glass, where catered for (I know they are in Fitzroy... haven't seen them much in the West).
posted by pompomtom at 10:41 PM on October 2, 2023 [3 favorites]

(someone please come and make buildings from my coffee waste, because I just keep buggering up the compost heap...)
posted by pompomtom at 10:43 PM on October 2, 2023 [2 favorites]

Purple is for separated glass, where catered for (I know they are in Fitzroy... haven't seen them much in the West).

Thanks, pompomtom! ^_^

We just have
red (rubbish);
green (food waste and plant waste for composting, also paper with traces of food or oil on it); and
yellow (clean paper, clean cardboard, clean tins, clean glass, clean plastic.)
posted by chariot pulled by cassowaries at 10:51 PM on October 2, 2023

pompomtom beat me to it, yes purple are separated glass. My units don't have them - we don't even have the green ones for some stupid reason - but some of the inner/northern Melbourne councils have the purple ones now.

At my units the shared yellow bins are apparently also for wood, broken electrical goods, coat hangers, old pots and pans, Styrofoam, etc. I honestly don't know why I even make a pretence of recycling.
posted by Athanassiel at 11:15 PM on October 2, 2023 [1 favorite]

CO2 has also been shown to increase concrete's strength. Leading to proposals to use it for carbon sequestration.
posted by joeyh at 12:30 AM on October 3, 2023 [1 favorite]

There's a sand shortage where I'm from so this is great.

Re the bins I've long thought that this will soon be reality and not satire.
posted by pianissimo at 12:37 AM on October 3, 2023

Fine. Give me 36 bins, as long as you assure me the fuckwits next door aren’t ruining 36 truckloads of sorting done by everyone else on the route.

Or string them up. I’m easy.
posted by pompomtom at 1:05 AM on October 3, 2023 [3 favorites]

I'm pretty sure all Victorian councils are going to move to the four bins as the requirement is coming from state government. Not 100% on that but fairly sure.
posted by deadwax at 1:26 AM on October 3, 2023 [1 favorite]

Because we live in a clatter of, mostly granite, buildings built as "rubble in courses", lime mortar should be used between the stone lumps. Lime mortar is made from 1) slaked / hydraulic lime = calcium oxide = CaO, 2) sand and 3) water. In regular Portland cement CaO is adulterated with ~30% Si Al Fe S oxides which make it super strong. In building material such as ours the coefficient of thermal expansion differs for different rock-types so trad lime mortar is preferred because it retains plasticity. !tmi tmi they cry! The point relevant to the OP is that our olde time builder recommended adding 5% organic runny cow shit to the mix for re-pointing.

Also on message is that I went to Starbucks for the first time in September when it was the only choice at a Welsh motorway service station. Picked up a 2kg bag of spent coffee grounds SCG for nothing, intending it for compost; but I'll try it now when I'm next re-pointing.
posted by BobTheScientist at 1:31 AM on October 3, 2023 [5 favorites]

I was also wondering if this could also be used in plasters for natural building (adobe, straw bale, cob, etc., or various plaster surface treatments). Sounds like it’s too soon to know since they’ve only done the one experiment with concrete so far, but I’m sure lots of people will be experimenting once they hear about this.
posted by eviemath at 1:43 AM on October 3, 2023 [2 favorites]

“There's a sand shortage where I'm from so this is great.”

NoHo Hank and Cristobal will hook you up.
posted by Ivan Fyodorovich at 1:46 AM on October 3, 2023 [6 favorites]

Jim never casts concrete slabs for brutalist architecture at home.
posted by Mr. Bad Example at 2:34 AM on October 3, 2023 [21 favorites]

Note well:

"Wet quick-drying concrete – being used by contractors upgrading Victoria Station – appears to have escaped through a void in the escalator machine room into the Victoria line signal control room. The room, and its equipment, rapidly became submerged in 30 cm of wet concrete. The equipment was immediately shut down, along with the tube line it controls. Damage limitation came from the engineers’ quick-thinking and chemical knowledge. The solution was surprisingly simple: as many bags of sugar as they could lay their hands on.

Sugar is already extensively used in the handling of concrete – normally as one component of a chemical retarder added when it is being mixed. The sugar slows down the setting of the concrete, and is used in hot conditions or when large amounts of concrete must be poured out before setting occurs.

Very small amounts of sugar delays the hardening of concrete without influencing its strength or other properties once finally set. For example 0.05% by sugar weight of concrete will retard setting by a few hours, while just 1% will almost completely inhibit hardening."

Royal Society of Chemistry - Soundbite

posted by sebastienbailard at 3:05 AM on October 3, 2023 [11 favorites]

Why would you use coffee grounds in concrete when they are such good fertilizer? They’re 2% Nitrogen!
posted by goingonit at 4:04 AM on October 3, 2023 [3 favorites]

We extract roughly 40 to 50 billion tons of sand and gravel each year for use in construction.
vs.
the total amount of spent coffee grounds (SCG) produced annually is 60 million tons

I won't call it green-washing, more a little sneeze of engineers disease. And I actually like this type of project, it's fun! My only beef with it is that it is presented as a solution to a huge problem, which it isn't
posted by mumimor at 4:08 AM on October 3, 2023 [8 favorites]

This sounds horrible, like the corn-for-ethanol situation but multiplied by an even higher carbon footprint and a crop that has to be picked by hand.
posted by clawsoon at 4:17 AM on October 3, 2023 [3 favorites]

I don't think anyone is realistically suggesting making extra coffee grounds for this.
Just using up the ones that are already produced en masse where available.
posted by Just this guy, y'know at 4:31 AM on October 3, 2023 [7 favorites]

You have so little faith in the dystopian power of capitalism.
posted by clawsoon at 4:42 AM on October 3, 2023 [6 favorites]

Presumably replacing 30% of your coffee with concrete would make it stronger, too.
posted by NotMyselfRightNow at 4:52 AM on October 3, 2023 [7 favorites]

i doubt these findings will hold up to long-term testing. i was under the impression from the masons i've worked with that generally you don't want organic material in concrete cuz uh it decays over time, leaving gaps. looks like these tests were performed over a short time frame? a grain of sand 50 years from now is still a tiny piece of rock, what is a grain of ground coffee going to be?
posted by glonous keming at 4:53 AM on October 3, 2023 [1 favorite]

The significance of this discovery long term will probably be boost scientific interest in other possible additives.
posted by SemiSalt at 5:15 AM on October 3, 2023 [2 favorites]

The UK is in the middle of a crisis that has closed a large number of schools and hospitals built in the 1960s and 1970s, after it was found that the reinforced autoclaved aerated concrete (RAAC), essentially concrete+bubbles, used in their construction has deteriorated over time and is now prone to collapse. (Actually people have known for a while that there was a problem but the Government ignored it until buildings actually started collapsing, hence the crisis.)

I imagine that there are ways of simulating aging on concrete+coffee mixes, and that will show up potential problems, just as RAAC was known to have a safe lifespan of about thirty years. If there is an economic case for making and selling the stuff then that will be conveniently ignored and maintenance budgets will be kicked down the road until things start falling apart.
posted by Hogshead at 5:22 AM on October 3, 2023 [5 favorites]

I'm reminded of that walking on water episode of Mythbusters where they make the joke about the ninja assassin who owns a cornstarch factory and has the ability to turn the castle moat into a non-newtonian fluid.

This probably won't lead to any global changes in how concrete is made, but if you're doing a bunch of cement work and have access to a few thousand pounds of coffee grounds that you aren't otherwise using for fertilizer it's good to know that you have options.
posted by RonButNotStupid at 5:26 AM on October 3, 2023 [4 favorites]

a grain of sand 50 years from now is still a tiny piece of rock, what is a grain of ground coffee going to be?

You don’t just use the coffee grounds as is — they are converted to biochar by anaerobic heating. Biochar is very stable.
posted by en forme de poire at 5:37 AM on October 3, 2023 [14 favorites]

ah i see, i missed that on skim. thanks
posted by glonous keming at 6:10 AM on October 3, 2023

Bob, you're a scientist...surely you don't believe all this superstitious nonsense! I don't think it's a good idea to put biological materials in your grout. They're kind of putting a misleading spin on this, seems to me. It's not really about coffee grounds. They found that charcoal bits in concrete is helpful, and it so happens that coffee grounds can be used for that.
posted by The Half Language Plant at 6:24 AM on October 3, 2023 [1 favorite]

The recycled use for coffee grounds I see around here is pressed into fireplace logs. I suppose you could press the grounds, burn them in the fireplace in the winter, and then use the resulting charcoal.
posted by Karmakaze at 6:28 AM on October 3, 2023 [1 favorite]

What fraction of paper waste and food waste can be used like this?
posted by sebastienbailard at 6:34 AM on October 3, 2023

I don't think it's a good idea to put biological materials in your grout.

My understanding is that people have been putting manure (an organic/biological material) in mud-based plasters (along with whatever organic material was just sort of the mud) since prehistory, and some of that construction is still around to be studied by archeologists.

Wooden (another organic/plant-based material) buildings can also last centuries. That’s probably a more similar comparison, since any wood exposed to weather in wooden buildings is typically treated somehow to prevent rot (either through charring, which sounds similar to the treatment applied to the coffee grounds, or by stains or painting). Similarly, I would only expect organic particulates on the surface layers of such concrete to be affected by environmental degradation. You need water or air (and thus microbe access) to break down organic material; and if water is getting into the interior of your concrete, you’ve got a larger and more immediate problem for the integrity of your building.
posted by eviemath at 6:47 AM on October 3, 2023 [3 favorites]

"...

Ever innovative in their methods, the Romans did not produce concrete as we do today.  They had forced labor and unique added ingredients – ox blood, volcanic ash and horse hair.

Today’s concrete professionals take note from our master builder Roman forefathers and add ingredients to concrete to get desired results as well.  Comparing a bit, in today’s world, ox blood is a fatty air entraining agent, volcanic ash is a pozzolin much like our fly ash today and horse hair a reinforcing fiber serving the same purpose as our various modern fibers.

..."

https://www.shelbymaterials.com/blog/romans-concrete-reinforcing-fibers/

posted by sebastienbailard at 7:07 AM on October 3, 2023 [3 favorites]

Added bonus: everything you build with the new concrete will smell GREAT!
posted by Paul Slade at 7:42 AM on October 3, 2023

Adding extra carbon to the concrete mix might be increasing the rate of curing, like adding carbon dioxide to fresh concrete in the CarbonCure™ process, or the natural curing and hardening of set concrete over time by the carbon dioxide in the air.
I don't know if you can pyrolyze coffee grounds greenly (that is, fixing more carbon than is used to create it), but it seems possible as long as you don't use any fossil fuel to do it.
posted by the Real Dan at 7:48 AM on October 3, 2023

Thinking of a Pantheon in the form of a French Press or Moka Pot.
posted by effluvia at 7:57 AM on October 3, 2023 [1 favorite]

i doubt these findings will hold up to long-term testing.

Maybe not, but there are grounds for further study.
posted by Gelatin at 8:03 AM on October 3, 2023 [20 favorites]

Mostly I wind up thinking about waste streams, as wags upthread have noted. Is it coffee shops that are throwing out grounds on the scale needed to make this a cheap byproduct without having to race around and collect it? This is like the fifth great initiative to use spent coffee grounds I've heard of in the past five years, but it seems to me that trying to get it from individual coffee drinkers is something of a Sisyphean task relative to just taking up a compost collection. So far, the only people talking about actually collecting the spent coffee grounds are doing so in theoretical terms: collecting them from "developing economies" just investing in chain coffee shops, for example, or more usually guides like this one that act as if these are fun new things to do with your garbage to save the planet.

None of this stuff is going to be worth using at scale unless someone is willing to regularly collect these grounds, store them appropriately, and sell them. Which is the usual problem with "one great trick!" to make new use of our trash: individual households are by and large too damn tired and distracted to do any of it, but unless you have very fine-grained, multiple-stream recycling and citizens willing to sort their detritus by planned function, it's hard to actually get the stuff streamed to you in bulk enough to turn it into a product pipeline.

(I do not drink coffee, so I always wind up being initially excited to suddenly be able to take advantage of this supposedly bountiful! waste! product! and then belatedly remembering that a) only my roommate drinks coffee in my house and b) she tends to go for instant coffee granules that, as far as I can tell, do not yield spent grounds. So I suppose it's all a bit of a moot point on my end, anyway.)
posted by sciatrix at 8:09 AM on October 3, 2023 [4 favorites]

The climate benefits will be offset somewhat when the largest-scale use of coff-crete turns out to be building a bunch of drive-through Starbuckses.
posted by box at 8:51 AM on October 3, 2023 [3 favorites]

Presumably replacing 30% of your coffee with concrete would make it stronger, too.

Maybe, but coffee already sits heavy in my stomach some days...
posted by Greg_Ace at 8:56 AM on October 3, 2023

None of this stuff is going to be worth using at scale unless someone is willing to regularly collect these grounds, store them appropriately, and sell them.

But there's another way of thinking about this. Let's say you have a factory that regularly bottles cold brew or does some other industrial production of a coffee derivative. It produces a ton of coffee grounds. Those grounds can be mixed into concrete applications nearby in lieu of shipping in other additives.

Around here you can usually spot the approximate location of a historic brick foundry by finding a cluster of houses made of bricks. Since it was expensive to ship bricks, only buildings near the foundry would get made out of bricks. And brick foundries were usually located where the materials to make bricks could be easily obtained.
posted by RonButNotStupid at 9:21 AM on October 3, 2023 [3 favorites]

We've secretly replaced his concrete with Folger's Crystals..

Correct! We also would have accepted: (Jim never has a second cup of concrete at home...)
posted by davidmsc at 10:01 AM on October 3, 2023 [1 favorite]

box, I worked for three years at a medium-volume coffee shop (not a chain) in a hospital in MD. At one point we had someone bringing a 5 gallon bucket for fertilizer for his garden. We would fill it in a day to a day and a half, and that was with people sometimes forgetting to use the bucket (since he only came in a few times a year and it was in an inconvenient place). I don't know for sure, but I would assume most Starbucks locations could fill a bucket in about 4-5 hours, and some are open 16 or more hours a day and may be even higher volume than I'm imagining. You're right that the collection efforts (and potential contamination from paper products like filters) are a problem for making this effective, but I can imagine a system being created that wouldn't be totally wasteful.
posted by Night_owl at 10:23 AM on October 3, 2023 [2 favorites]

Heineken once experimented with making square bottles that could be repurposed as bricks after they were emptied of beer. The idea was that every beer bottle meant one less brick had to be shipped somewhere.

If you've already got coffee grounds, you don't need as much sand. I see the 30% increase in strength as just being an added benefit. There's probably some other additive that yields the same performance increase. The real benefit is substituting materials that would need to be shipped in with materials that might be easy to come by.

If you're a ninja and you just happen to have access to industrial amounts of used coffee grounds, it's time to build a cement factory!
posted by RonButNotStupid at 10:44 AM on October 3, 2023

[taps mic] Coffee makes *me* 30% stronger, too.

[bows and immediately leaves room]
posted by heyitsgogi at 10:44 AM on October 3, 2023

What are the purple bins for?

He doesn't know how to use the three seashells purple bins!
posted by cmfletcher at 12:01 PM on October 3, 2023

Earlier this year I got to spend a day with my nephew who is a structural engineer. We looked at 2 skyscrapers that he designed under construction just a couple of blocks apart. He said that concrete can be made much stronger now compared to just 20 years ago; I forget the numbers but perhaps twice as strong. A big focus of concrete research now is reducing its carbon footprint which is very high.

Interesting, concrete is extremely strong against compression; you could build a tower 7000 meters (21,000 feet) tall if you could balance it But it is weak against tension. So horizontal elements in building have to have steel reinforcement and must be stressed before installation.

The 1978 book Structures: Or Why Things Don't Fall Down is fantastic.
posted by neuron at 11:31 AM on October 4, 2023 [2 favorites]

He said that concrete can be made much stronger now compared to just 20 years ago;

Theoretically stronger - I'm not sure how well modern concrete PSI fiddling is working out in actuality - go see for yourself the recently poured but cracked and broken sidewalks and streets around your neighborhood. That could also be due to less base material, which theoretically can also be adjusted due to stronger concrete.
posted by The_Vegetables at 2:08 PM on October 4, 2023 [1 favorite]

It makes so much sense to me that this is coming out of australia- I met someone recently who was working for a social enterprise called ReGround that had built a network of hundreds of coffee shops where they started collecting coffee grounds, and in the process created channels for two really clean waste streams (one of the main challenges in the recycling businesses in most places.

They started with the coffee grounds for composting and expanded into collecting + recycling soft plastics with a single partner who was willing to try it out. Now that australia is no longer allowing their plastic refuse to be shipped offshore, that original plastics recycling partner is way ahead of everyone else.
posted by wowenthusiast at 4:09 PM on October 5, 2023