Rubber concrete that self-seals and is cheaper and more environmentally friendly | Hacker News Reader

Rubber concrete that self-seals and is cheaper and more environmentally friendly

newatlas.com

111 pointsatombender41 comments

Rubber is a latex or elastomer, not the substance described here. The original article used rubbery in the title, an adjective that means tough and elastic. Better not to have been changed.

Another interesting material is Papercrete.[1]

"Papercrete gets its name from the fact that most formulas use a mixture of water and cement with cellulose fiber. The fiber is usually acquired from recycled newspaper, lottery tickets and phone books. The mixture has the appearance and texture of oatmeal and is poured into forms and dried in the sun, much like the process for making adobe.

"Dried papercrete has very low strength, but fails by slow compression (due to the large air content and hence compressibility) rather than in a brittle manner. Concrete and wood (though dry soft wood can be as high as R-2 per inch, high moisture content reduces this value markedly.) are not known for their insulating qualities; however, papercrete also provides good insulation...

"Unlike concrete or adobe, papercrete blocks are lightweight, less than a third of the weight of a comparably-sized adobe brick. Papercrete is mold resistant and has utility as a sound-proofing material."

[1] - https://en.wikipedia.org/wiki/Papercrete

That's a strange article. Cement-based substances like concrete don't dry, they cure. It's not like adobe.

Also hempcrete [1], an environmentally friendly variation on limecrete which was successfully used in an episode of the recent series Grand Designs: The Street [2].

[1] https://en.wikipedia.org/wiki/Hempcrete

[2] https://www.granddesignsmagazine.com/grand-designs-houses/44...

Cellulose fiber sounds like delicious pest food.

I've made some diy drywall with gypsum,water and toilet paper(in 3:1 paper:gypsum ratio). Its surprisingly strong and dries fast. Is this also papercrete?

> rice husk cinder, limestone crushing waste, and silica sand.

Is this really a new idea? Back in the 90s when I did my civil engineering degree (I changed major later), my professor was big into rice hull ash as an concrete additive. He did tons of research into the properties.

It's probably not a new idea, but it might be newly-relevant seeing as concrete is under the magnifying glass for its emissions as it's curing.

More expensive concrete might have become economically viable if it emits less greenhouse gas or if you need less of it. And if it's not currently economically viable it might still become viable in the future, prompting more research into it by companies hoping to have first-mover advantage.

That said I'm not a concrete expert. I don't know why this sort of concrete isn't currently being used, nor the relative pricing of it relative to ordinary concrete.

If it's cheaper and more resilient, why is it only focused on civil and military structures? What's the trade off?

Compressive strength probably.

It says it seals on its own... suitable for bunkers. if true, regular basements need to be made from this stuff in the future.

My thought exactly.

I suspect it's harder to work with or more finicky about the conditions in which it cures. The trend in the past ~50yr for concrete has been toward stronger concrete at the expense of being more picky about where any when it is poured (gone are the days of pouring whatever into the bottom of a water filled hole on a 33 degree day and expecting a good result) so that would be my knee jerk reaction.

Like everything else in the world this will probably take 10+yr to go from academic paper to being actually used in industry (if it pans out).

Why is there beside civil and military? I thought the two terms were antonyms so isn't that everything, by definition?

"civil defense" not "civil".

https://en.wikipedia.org/wiki/Civil_defense

Probably because (among other reasons) structural reinforced concrete depends on cracking, both to develop internal strength and to prevent abrupt catastrophic failure. ACI building code (or a derivative) applies in most US jurisdictions, and it relies on heavily on the premise of concrete showing cracks before reaching the failure point of the internal steel. It ensures a failure mode that illicits a warning.

(The internal strength development probably wouldn't be as much of an issue with the "rubbery" concrete, assuming the compressive strength is equivalent, but I'm sure there are other considerations I haven't thought of. You're changing fundamental properties of the material that is expected by most designers. Existing brittleness is accounted for and expected.)

Civil Defense and Military applications don't necessarily have the same design requirements, or need to be as compliant with a particular building code, as they're typically exempt from local building regulations and/or have their own separate building standards.

On the other hand, asphalt pavement design is based on principles that could benefit from such a material without having to completely re-invent the design code.

There just isn't enough information in the article to judge the material.

My guess is by lowering the amount of cement they're reducing overall compressive strength, but by including fibrous materials they're resisting cracking. The reported "rubbery" behaviour means the material is overall less stiff and I'm not sure that does good things for development lengths or reinforcing required.

I don't know what to make of the statement that it's "impact proof". Steel yields and concrete crushes, but I guess this is a high strain material.

My initial thought was that it sounded like a good paving material if its sufficiently stiff...

Great explanation, thank you. A cogent answer to a question I would have never thought to ask.

Maybe that visual inspection requirement will change as we develop non-destructive testing options.

Non destructive testing exists and is fairly mature for reinforced concrete. It's just more expensive. But it's not so much about testing, since once a structure is built, you're not going to get the owner to pay for any more testing, until signs of potential failure arise. You need an obvious reason to test in the first place.

Testing also somewhat implies that the design or material is defective; but that's only two paths to failure out of many. More likely, the structure is overloaded, or supplemental supports are removed prematurely, as is what seems to be the case for the recent hard-rock hotel collapse in New Orleans.

This isn't too say that new materials don't have a beneficial use. We would probably need to develop a new and separate sub-discipline, the same way pre-stressed and post-stressed concrete structures are designed, which have since been included into ACI code.

It doesn't say its more resilient, it says its more resistant to cracking. If its more rubbery it might be less stiff and then require different design - i notice they're not recommending this for high rises.

The bottom line is the article doesn't include enough information about this concrete formulation and its price to really know what its good for.

My bet is that by replacing cement with other materials, it decreases its overall compressive strength.

How does this bond with existing concrete? Could it be used for repairs/renovations of existing structures.

Also - reinforced concrete works as the steel rods that give the concrete strength, expand and contract at exactly the same rate as concrete. Is that still the same with this version?

>steel rods that give the concrete strength, expand and contract at exactly the same rate as concrete.

How cool, didn't know that. Makes so much sense.

They're close, but not exact. I think concrete on usually given as 13.5 (0.0000135 in/inR), and steel as 11 (0.0000110).

It's this difference that reduces RC life expectancy from 100's of years (as advertised by the concrete industry in the early 1900's) to the neighborhood of 10-50 years that we typically see.

Whereas glass and platinum, for instance, are generally considered to be exact, and are used for precision measuring and calibration.

I doubt about the mainstream sustainability of it, if considered with mega structures.

Currently, more high-rise building are built then past. The base of building requires high-rigidness and compressible strength which is fulfilled by traditional concrete. But if we replace it with some flexible substance[ideally only at higher loads], It will start bending when traditional concrete would perform easily. moreover it will also affect all the application which are based on rigidness of concrete, eg, Floor tile/stone will crack open, furniture will break, your plumbing will bend etc.

so, much more research is needed. and possible whole other way of construction process has to be created to sustain new challenges.

I don't know the numbers but it doesn't sound like it makes concrete wobbly-wiggly.

And ther are always shearing forces, especially with high-rises (wind), and probably this added plastic helps with that. (Less creeping cracks, better handling of repetitive stress / cyclic elastic deformation - eg bridges, roads, floors.)

> it makes concrete wobbly-wiggly.

That is why i wrote "some flexible substance[ideally only at higher loads],"

yes, it can make positive impact on many use-cases. But I think we should focus more on the production of cement with negative or neutral CO2 yield. Cement is one of the least blamed cause of CO2 emission, but It really should be blamed.

Interesting how we use "more environmentally friendly" now instead of "less environmentally hostile". Language skewed towards marketability.

When has "less environmentally hostile" ever been used in the first place? Hostile itself would be the wrong term anyway - it is usually apathy not some deranged hatred of nature that drives pollution in building materials.

How about this idea: Mix ping-pong balls with concrete. It becomes much lighter then. Because it is lighter it can much more easily support the weight of the (similar) concrete structures above it. Just a thought has anyone tried such a thing?

Two issues: 1) unequal dispersion of the balls could create super weak spots that are mostly empty space. I'm not sure how engineers could use a material where the structural integrity isn't consistent. 2) If water ever penetrated the swiss-cheesyness of the concrete in freezing weather, you'd be in big trouble.

Yeah, this is already a nightmare with rebar in reinforced concrete. Just imagine actual ping pong ball sized voids filling with moisture. Swiss cheese, indeed.

But it wouldn't be holes, it would be water-tight ping-pong balls.

OK, what if you carefully place the balls in a regular pattern?

Imagine placing ping pong balls in a regular pattern in the bottom of an empty swimming pool, then filling it up with water.

You'd have to secure them in place. Perhaps with a metal grid.

Sure it's doable, it just makes the task that much more difficult. Plus you need to ensure there are no unintentional voids from the balls blocking the pour. Code requires that they can't be within 1-2 inches of any steel or the surface of the concrete.

Also, most designs assume a uniform cross section, and changing that greatly complicates the design method.

And remember that the laborers doing this don't always understand (or care) about these sort of restrictions.

It's usually cheaper and less risky to just use a lightweight mix, with injected air, if needed.

Mike Reynolds [0] of "Garbage Warrior" and "Earthship" fame has been reusing empty plastic waste bottles in a similar fashion for decades. The cement forms a matrix around vacancies created by the bottles which become a permanent part of the structure.

He's also used aluminum cans and glass bottles in a similar fashion. Colored glass bottles can produce visual results resembling stained glass, it's interesting.

But these are hand laid like brick laying, so not quite what you're thinking with the ping-pong balls.

[0] https://en.wikipedia.org/wiki/Mike_Reynolds_(architect)

They already do, with mixed results. This[1] is a coverage of a collaps of a parking structure in the city of Eindhoven, the Netherlands. Although it appears the plastic-ball filled concrete was not the cause, but they way they incorporated it into the building was. 1. https://www.newcivilengineer.com/archive/technical-cause-of-...

Thinking bit more generically, you might be really thinking about concrete with air pockets (though ensuring they're spherical might make for excellent load distribution through the side walls). There are already concrete variants called Aerated Concrete and Foam Concrete where bubbles are formed inside the concrete, resulting in a lighter product, though with different structural properties.

https://en.wikipedia.org/wiki/Autoclaved_aerated_concrete https://en.wikipedia.org/wiki/Foam_concrete

It is rather common for slabs to be made lighter by embedding in the concrete pipes (usually either plastic or metal/tin) or actual "pockets" (think of large - usually plastic - largish and squarish containers). Here is a photo of a commercial solution:

https://www.geoplastglobal.com/en/products/slabs/new-nautilu...

There is also an as well already available commercial solution using "balls":

https://www.cobiax.com/intl/produkte/cobiax-el/

similar to the "bubbledeck" technology used in Eindhoven:

https://en.wikipedia.org/wiki/Voided_biaxial_slab

Anyway these are basically an evolution (involution?) of "waffle slabs":

https://en.wikipedia.org/wiki/Waffle_slab

What’s the dry time? And can it be expedited with an industrial “blow dryer” ?

concrete doesn't dry, it cures. it's beneficial to spray curing concrete with water.

Would it flex too much where it shouldn’t?

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