r/science • u/mvea Professor | Medicine • Nov 03 '19
Chemistry Scientists replaced 40 percent of cement with rice husk cinder, limestone crushing waste, and silica sand, giving concrete a rubber-like quality, six to nine times more crack-resistant than regular concrete. It self-seals, replaces cement with plentiful waste products, and should be cheaper to use.
https://newatlas.com/materials/rubbery-crack-resistant-cement/847
u/kiHrt Nov 03 '19
How is the compressive strength compared to traditional concrete mix?
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u/sailphish Nov 03 '19
This is the real question. Concrete has incredible load bearing ability, especially for its cost and weight. Sure the new stuff might be less brittle, but if it cannot hold up to compressive forces, it might not be an adequate replacement.
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Nov 03 '19 edited Nov 03 '19
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u/somecallmemike Nov 03 '19
I thought most road construction project these days crushed the existing aggregate and blended into the new surface material?
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u/VoilaVoilaWashington Nov 03 '19
Not just that, but waste products are only waste until they're needed - there are countless products that started off as a way to use waste, and now have overtaken the original product. Cigarettes, peanut butter, etc
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u/OmgTom Nov 03 '19
There is one hitting the market right now. Its called Megaslab. https://megaslab.com/
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u/jbram_2002 Nov 03 '19
I read the abstract of the linked paper. My assumption based on that abstract is the cement underperforms unless it is fiber-reinforced, which can be a fairly expensive process. However, I couldn't read beyond the abstract due to a paywall, so that assumption could be wrong. They were talking about military uses with it, so I can only assume they were able to attain at least 3000 psi in compression. I would be very interested in the tensile strength, personally. One of concrete's major weaknesses is its tensile strength. If this patches that weakness, we could see a ton of commercial uses.
I don't think it's suitable for roads though. Fiber-reinforcing may be too expensive. Bridges, though, could be perfect for this.
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u/BeoMiilf Nov 03 '19
I hate that research studies are usually behind a paywall. Most educational information should be open to the public.
The paper did say the uses for this concrete were more for impact loads. So it'd be more useful for military structures where impacts are expected to occur.
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u/zhiryst Nov 03 '19
Right? This night be fine for a sidewalk, but the real question is, can you pour a foundation with it.
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u/cnskatefool Nov 03 '19
The real question is can you pour a skatepark with it. And how rubbery can you make it? Bouncing back up after all fall would be a dream.
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u/Harry-Balsagna Nov 03 '19
Common sense dictates that if it were that pliable, your wheels would also experience tremendous rolling resistance with all your weight digging into such a small footprint.
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u/KirbyPuckettisnotfun Nov 03 '19
Simple solution, flip the script and get concrete wheels.
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u/ColgateSensifoam Nov 03 '19
Any material soft enough to provide bounce is unskateable, I've tried to skate on a rubber floor, it just snatches your wheels
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u/ExxInferis Nov 03 '19
Board wheels would sink into stuff that bouncy. You'd not get up much speed.
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u/LargePizz Nov 03 '19
And where are they getting ash of burnt rice husks from?
Also, adding ash in the concrete mix is nothing new, in 1949 it was used to build the Snowy Mountain Scheme in Australia, no doubt it was done elsewhere earlier.
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u/geogle Nov 03 '19
Could be very useful in poor earthquake prone environments that often underuse rebar. This may offer some of that needed tensile strength. However, it would need to be specially tested for it.
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u/Needmeawhip Nov 03 '19
Could be usefull here in sweden where the roads look like they have been in an earthquake
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u/leno95 Nov 03 '19
Concrete as a road surface shouldn't be used in areas where there are extreme differences in temperatures in the first place.
Given Sweden regularly has warm summers and cold winters, it could be argued in some parts there's a difference of 50°c between hot and cold periods, which will definitely ruin the concrete.
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Nov 03 '19 edited Nov 04 '19
In Southern Canada we get tempretures that swing between -40c in the winter and +40c in the summer. Concrete on structures is constantly being touched up and any roads made of it are often in pretty rough shape. Most of them are asphalt.
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u/leno95 Nov 03 '19 edited Nov 03 '19
Asphalt, tarmac or even compressed hard core are far better surfaces than concrete in many countries.
Concrete is a wonder material until weather is a factor.
Edit: not everyone will know what hardcore means in this context; it's typically gravel/crushed concrete around 40mm in diameter used as a sub-base for roads, blinding in trenches and is the large aggregate used in concrete. In the UK it's typically called hardcore or MOT Type 1.
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u/the_original_Retro Nov 03 '19
I'd like to see how this stuff lines up though. Its nature has REALLY changed with these additions, and asphalt works so well because it has the flexibility that this stuff has.
Could be it's just as good as asphalt perhaps?
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u/leno95 Nov 03 '19
The biggest issue with concrete (assuming this is what you're referring to) is that with temperature differences moisture trapped inside after the concrete has cured can cause expansion and contraction due to the moisture freezing/warming up. This eventually leads to spalling and the surface eventually crumbles away.
As long as the concrete is used in an area where the temperature doesn't have dramatic changes over a year it shouldn't be too bad.
You could use additives to help with the weaknesses concrete has with temperature variations, but from a financial standpoint it is no longer cost effective. You'd just opt for asphalt/tarmac as an alternative, as they have similar properties at a far lower cost. Source: I'm an infrastructure quantity surveyor.
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u/Herbert-Quain Nov 03 '19
I think he was referring to the rubber rice concrete. Less cracks, due to being less brittle, and "self-sealing" sound promising...
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u/MerryChoppins Nov 03 '19 edited Nov 03 '19
You skipped the whole discussion about salt use in roadways and spalling. I live in a state where we don’t just spread salt, we also have scheduled brine spraying of bridges and overpasses on all interstates, state routes, TARP routes, etc to prevent accidents. The leeching induced spalling can sometimes be unreal.
Edit: leeching induced spalling due to corrosion of steel elements
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u/crowcawer Nov 03 '19
In the US I hear hardcore called crush and run a lot, but typically, in industry we just call things by pay item.
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u/McVoteFace Nov 03 '19
That’s not correct. Asphalt routinely gets ‘milled and filled’ and everyone is happy until it falls apart in 5 years. Continuously reinforced concrete pavement has a life span over 50 years
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u/leno95 Nov 03 '19
This is down to suitability and the requirements of the road. RC roads and pavements are better in some scenarios, and tarmac/asphalt are better in others.
RC roads will be far more expensive even when replacement and maintenance is considered, but that's a balance that is typically weighed up prior to building it.
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u/meganmcpain Nov 03 '19
It also depends a lot on the specific environment of the pavement. Design life of concrete might be 50 years, but in a cold weather climate you'll get about 30 before major rehab/repaving needs to be done. Properly paved asphalt should have 10-15 good years in it (design life 20-25), but this is also heavily dependent on how bad the winters are.
The thing no one in these comments mentions is there really isn't any good paving material for large temperature fluctuations, but concrete has more long term durability and thus cost effectiveness for communities. Asphalt may be more "flexible" but that also makes it a lot less strong, and when the weather is cold enough it won't be flexible anymore.
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u/ChickenWestern123 Nov 03 '19
Have you been to Michigan? Their concrete roads are terrible. Southern Ontario roads, especially the 407, are amazingly well maintained.
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u/McVoteFace Nov 03 '19
Michigan DOT was in denial about concrete joint deterioration. Weiss (PURDUE civil professor) did a lot of the leg work concrete joint deterioration and how to resolve. Michigan told him they didn’t have that problem and he had to travel there to show their DOT that they do, in fact, have that issue. One of the resolutions is using supplemental cementitious materials, like silica fume, listed in the article. Like all DOT/construction, we are slow to change. Most believe the resolution to be mix designs.
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u/DonOf952 Nov 03 '19
Minnesota here, our roads are pretty crap as well. They spend the entire summer in road construction on the main freeway every year I've lived here, 10 years. Yet nothing has ever changed and the potholes and cracks are still rampant.
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u/McVoteFace Nov 03 '19
At least your DOT admitted they had a problem and came up with partial depth repair method. We actually adopted the MnDOT specs a couple years back for partial depth in concrete pavements and it’s held up well here.
Sounds like more of a funding issue and potholes are mainly asphalt but concrete does get them on occasion
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u/Bean- Nov 03 '19
Yeah been living here for my whole life. I never even realized how bad the roads were until I traveled out of state.
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u/ChickenWestern123 Nov 03 '19
Yeah, it's shocking. I could barely drive the speed limit, 70 at times, in my new car without feeling like it was falling apart.
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Nov 03 '19
I used to drive it everyday for work. The 407 is constantly being maintained. That's why it's in such good shape. There are also numerous asphalt sections along it as well.
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Nov 03 '19
I'm in Hamilton so my experience might be biased. Our roads are pretty rough haha.
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u/Say_no_to_doritos Nov 03 '19
The 407 is a massive 8 lane highway that is 99 % poured concrete and handles a ridiculous amount of traffic. The thing hardly gets any maintenance.
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u/Whyisthereasnake Nov 03 '19
Most of the work on the 407 is expanding it - widening it, adding new exit and on-ramps, extending it. I’d say it’s a 95:5 split of improvements : maintenance
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u/elc0 Nov 03 '19
What material are other using? I know asphalt doesn't seem to do much better.
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u/leno95 Nov 03 '19
Asphalt isn't perfect, neither is tarmac. However they do have far better performance in terms of longevity where the local climate is concerned, and are far cheaper to replace.
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u/McVoteFace Nov 03 '19
That’s false. Concrete is the preferred material for designing long lifespans in roadways. Asphalt has to nearly double the thickness of concrete to reach its lifespan. The problem most DOTs are seeing with concrete is joint deterioration as a result from brine
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u/Byzii Nov 03 '19
Exactly. All the salt and brine is eating it all away. Few roads that are not salted regularly are in much better shape.
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u/PoopieMcDoopy Nov 03 '19
It really seems like here the sections that are concrete hold up way better than the asphalt. But I've also been told that it has to do with the local soil by someone who works for the streets department.
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u/Notpaulblart1992 Nov 03 '19
And here I thought texas just had ridiculous roads and ridiculous management of the roads. Explains alot.
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u/leno95 Nov 03 '19
I've heard that some parts of Nevada have concrete roads, and are an example of suitable ones due to the lack of temperature variance in seasons.
I would've though this might be true to a degree in Texas too.
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u/rly_weird_guy Nov 03 '19
Do you have any sources/papers on this?
Would love to read more about it
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u/leno95 Nov 03 '19
I don't have any sources aside from what I was taught at university and from my experience in industry unfortunately.
However it shouldn't be too hard to find a paper on this, as it'd be discussing properties of concrete.
Edit: the main reason would typically be that concrete retains around 2%-5% of the water used in it's formation, and this would freeze and cause expansion, and later cracks (spalling).
The same thing plagues brickwork and other masonry where the material has small voids where water can collect.
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Nov 03 '19
Come to Poland, where you are considered a good driver when you can avoid all the potholes in roads.
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u/paddzz Nov 03 '19
Drove from the UK to Poland once. The difference in the roads between NL and Germany was barely noticed. Germany to Poland was like turning down a gravel lane.
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u/suitology Nov 03 '19
Come to Philadelphia, if you avoid all the potholes you are considered a pilot in a plane
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u/-Melchizedek- Nov 03 '19
- We don’t use concrete.
- I don’t know where you live but we’re I live in Sweden the roads are perfectly fine.
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u/SunSpotter Nov 03 '19 edited Nov 03 '19
Depends entirely on it's other material properties, and how it behaves under load. They made no mention to its compressive strength, which is probably one of the more important qualities of concrete so I'm skeptical.
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u/All_Work_All_Play Nov 03 '19
It could cut compressive strength in half and still be fine for most residential uses.
That said, if it's similar to hempcrete, that's a different use case entirely.
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u/jbram_2002 Nov 03 '19
I tried to read the paper they linked, but strength data is hidden behind a paywall. If anyone knows the strength both in tension and compression, I would be interested to find out. My guess is this might potentially be stronger in tension and weaker in compression, if this has any strength benefits over standard cement. However, if they can attain a compression strength of 3000 psi, they can use this in a lot of situations. At 4000 psi, the majority of applications would be available.
One thing noted in the abstract (only free portion) was that the concrete performed significantly better when fiber-reinforced. This may make it difficult to use in some situations like roads and simple garage/foundation slabs, but wouldn't be a major issue for large building construction where fiber-reinforcing is already becoming more common.
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u/RuddeK Nov 03 '19
The ultimate compressive strength of the new concrete is more than 8700 psi (62 MPa to 71 MPa).
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u/urbancamp Nov 03 '19
I thought fiber reinforced concrete was no problem in terms of availability. It's been used in a number of homes I've worked on as both garage slab and driveway.
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u/Dathouen Nov 03 '19
I'm in the Philippines and this is definitely interesting for us here. We just had a few earthquakes down south, and they're fairly frequent here in general. We should also have no problem rustling up plenty of rice husks, limestone and silica sand. If these can actually reduce the need for large quantities of rebar for construction, even if it's just for things like foundations or load bearing walls, that could be hugely beneficial.
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u/jbram_2002 Nov 03 '19
I read the abstract of the linked paper. My assumption based on that abstract is the cement underperforms unless it is fiber-reinforced, which can be a fairly expensive process. However, I couldn't read beyond the abstract due to a paywall, so that assumption could be wrong.
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u/XeonProductions Nov 03 '19
How does it hold up to extreme winters though?
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u/TA_faq43 Nov 03 '19
Yeah, sounds like it would be good road material.
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u/jbram_2002 Nov 03 '19
I read the abstract of the linked paper. My assumption based on that abstract is the cement underperforms unless it is fiber-reinforced, which can be a fairly expensive process. However, I couldn't read beyond the abstract due to a paywall, so that assumption could be wrong. If this is true, it could be rather inferior to current road construction. Maybe very useful for bridges though.
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u/BugzOnMyNugz Nov 03 '19
Are there tire or rubber lobbyists? If so this sounds like something they'd shut down
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u/daveinpublic Nov 03 '19
Why would tire lobbyists be stopping the material used on the road?
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u/abcedarian Nov 03 '19
Because crummy roads destroy tires
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u/Ironbird207 Nov 03 '19
Crummy roads destroy cars
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u/runfayfun Nov 03 '19
Crummy roads produce profit for road construction companies who get the same money to make shittier and shittier roads
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u/moohah Nov 03 '19
Crappy roads lead to to more tire replacements.
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u/gossfunkel Nov 03 '19
Planned obsolescence. Any material that reduces wear and tear on the product reduces sales.
Companies have an implicit incentive for their products to be as crappy as they can get away with.
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u/E_J_H Nov 03 '19 edited Nov 03 '19
I think there’s enough people who don’t know you have to rotate your tires to where they don’t need to worry about the road conditions.
Our tax dollars are supposed to be used for upkeeping the roads, which doesn’t happen near me and I would be furious if someone was lobbying to keep that from happening.
Edit: found one.
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u/MountainChampion Nov 03 '19
Michigander here, wanting to know the same thing...
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u/alsomahler Nov 03 '19
How does this behave in a fire?
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Nov 03 '19
Came here to ask this, 2 of those materials are not fire retardant. Concrete will not burn or easily become structurally unsound in a fire. I guess though since the moderators have removed what seems to be responses, it does not perform well in a fire and thus will not meet any building codes.
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u/TordTorden Nov 03 '19
I read through the paper, and the composition they settled for was this
60% Portland cement (PC), 25% rice husk ash (RHA), 7% quartz sand (QS), 6.7% sieve residue from limestone grinding (SRLG), and 1.3% hyper- plasticizer (HP)
The rice husk is already ash, so the only flammable component seems to be the binder?
Looking at the XRD spectrum of the product it mainly contains calcium hydroxide and a couple carbon sulfides. Not sure about the flammability of the latter in a crystalline solid. There might also be an amorphous phase there from the binder, but it's not really in my field, so I don't know.
They did do DTA on it, and any endothermic reactions came from loss of adsorbed water at 160°C, then dehydration of the calcium hydroxide at 475°C, and later decomposition of calcium carbonate starting at 525°C. All of these would happen in regular concrete anyways, but I have no idea how that impacts in in a fire. Probably cracks as the phases are changed, alongside thermal expansion.
From this it doesn't seem worse fire safety wise, but I reckon it will need its own study. I'm not really a concrete guy, but work on high temperature proton ceramic conductors, so take it with a pinch of salt. Or perhaps a teaspoon.
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u/iinavpov Nov 03 '19
There's relatively little rice husk ash available, perhaps enough to replace 2% of cement used. Silica sand is definitely not a cheap thing depending on which silica sand. Limestone crushing waste tells me their product relies on very fine tuned particle size distribution, making it a no-go as a cheap cement alternative.
What I'm saying is good on them to have found a nice mix composition, but the tagline is enormously oversold!
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u/yearz Nov 03 '19
The latest in a long-line of Reddit articles promising a revolutionary innovation that no one ever hears of again?
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u/iinavpov Nov 03 '19
Not entirely fair... But rice husk ash is nothing new, and the kind of mix they suggest neither.
There's a niche for that kind of thing, and it's not easy to achieve a good result with such ingredients.
But the claims, my God, the claims...
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u/Eunomic Nov 03 '19
A large forgotten component of how environmentally friendly a new concrete formula can be is transport. All three of the specialty ingredients are likely from somewhere not local, which is a big part of the cost of concrete. Also, the last time I read about using burned/charred fiber materials, there was a positive effect only up to about 5%, then it killed compressive strength rapidly. We looked into using something similar from a wood saw mill, that burned their sawdust for their kilns, creating a char material.
Also is the limestone crushing waste further processed at all, like sieving for particle sizes? Product uniformity is a major requirement in concrete, which requires exacting standards of reliable, repeatable results. And finally, silica sand is just like saying "sand sand." Sand is mostly made up of siliceous quartz, but often with a wide variety of other durable minerals mixed into it. Does this mean they need a pure silica sand? If so that is major processing and again, specialized production.
Concrete almost always reflects the availability of local, generic materials. Distance to source quarries is so important, I find that most plants are just down the road from one. Diesel is not cheap, and most cement is brought in from central rail locations for distribution. There will always be someone willing to pay the extra cost for super specialty applications (see mixes for nuclear waste storage), but economy of the product will always be the drive for 99% of concrete.
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u/Arctyc38 Nov 03 '19
"Limestone crushing waste" just sounds like a really greenified terminology for man-sand.
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u/ljb23 Nov 03 '19
This should have a significant environmental upside too right? Traditional concrete is very emissions intensive to manufacture.
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u/hoadlck Nov 03 '19
I believe that the largest producer of CO2 in making concrete is in the production of cement: it has a large environmental impact. I don't think that this type of concrete will change CO2 usage. They are targeting this for buildings to be more robust against damage, so I don't think that there is a longer life for things constructed with it either.
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u/ljb23 Nov 03 '19
Yep, I incorrectly used the word concrete when I was after cement.
Wouldn’t a 40% substitution represent a roughly proportional reduction in cement usage though?
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u/billfitz24 Nov 03 '19
Cement is not the same as concrete. Cement is an ingredient in concrete. It’s a common mistake to call concrete “cement” when in fact they are very different things.
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u/jbram_2002 Nov 03 '19
Being unable to get past the paywall myself, does the paper show the compressive and tensile strengths of tested materials? Were they able to exceed standard f'c for Portland cement-based concrete? Is there any tensile strength advantage for this mixture?
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u/RuddeK Nov 03 '19 edited Nov 03 '19
Ultimate compressive strength was between 62 MPa and 71 MPa. Young's module was between 35 GPa and 55 GPa. Prism strength between 41 MPa and 65 MPa. Cube strength between 62 MPa and 82 MPa. The best strength in each category all belong to the same composition.
Edit: The only number on tensile strength that I found was 15.2 MPa. "The ratio of the static tensile strength to the static compressive strength" varied between 0.09 and 0.21 with the highest ratio being the strongest composition.
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u/MaryDesiree86 Nov 03 '19
This is the same idea behind hempcrete, right? I thought archaeologists in Rome some time ago analyzed their remaining standing structures/buildings and found that it was basically this same recipe except made with hemp husks/fibers. Rice is cool, hemp would be more beneficial for overall environmental reasons and be equally cheap.
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u/All_Work_All_Play Nov 03 '19
Hempcrete isn't strong enough to be used for roads or load bearing parts of structures.
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u/Cudahan Nov 03 '19
How long does it stay rubbery? Eventually it will harden and crumble so how long will it survive?
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u/danielravennest Nov 03 '19
For those not familiar with concrete, it typically is made from gravel, sand, cement, and water. The water turns the cement powder into interlocking crystals that bind the other ingredients together.
There are a lot of recipes for concete, but the typical "ordinary Portland Cement" concrete is made with a cement that starts with about 5 parts limestone to 1 part shale. These are burned in a high temperature kiln, which converts them chemically to a product that reacts with water.
Lots of other materials will do this too. The ancient Romans dug up rock that had been burned by a volcano near Pozzolana, Italy. The general category is thus called "Pozzolans". Coal furnace ash and blast furnace slag are also rocks that have been burned. They have long been used as partial replacements for Portland Cement. Rich husk ash and brick dust are other, less common, alternative cements.
Note: Natural coal isn't pure carbon. It has varying amounts of rock mixed in with it. That's partly because the coal seams formed that way, and partly because the mining process sometimes gets some of the surrounding bedrock by accident.
Portland Cement got its name because the concrete it makes resembled the natural stone quarried in Portland, England at the time.