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/
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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.

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u/ImFamousOnImgur Nov 03 '19

I did a paper in undergrad about Roman concrete. Their recipe was no joke. It’s a big reason why their stuff is still standing to this day.

Coliseum? Yup. Roman concrete. Oh and you know how some of the walls collapsed after an earthquake in 1500 something? Yeah those were the sections that were built by a different architect and he didn’t use the same materials.

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u/noelcowardspeaksout Nov 03 '19 edited Nov 03 '19

For the Pantheon they used different grades of concrete made with different additives depending on the qualities they required. The dome has pumice included to make it light for example. It has stood for around 2000 years without being rebuilt.

Edit: Pantheon

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u/ImFamousOnImgur Nov 03 '19

Yup. It’s quite amazing the amount of knowledge they had. A lot of that knowledge was lost when the empire fell.

They think the secret to the quality was the volcanic rock used, and if I recall, it was especially good at setting underwater even.

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u/Opeewan Nov 03 '19

There's a bit more to it than that, salt plays a big part in it:

https://www.nature.com/news/seawater-is-the-secret-to-long-lasting-roman-concrete-1.22231

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u/[deleted] Nov 03 '19 edited Jan 24 '21

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u/Opeewan Nov 03 '19

Obviously they didn't and either came up with their recipe through trial and error or it was a lucky coincidence.

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u/[deleted] Nov 03 '19 edited Jan 24 '21

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u/[deleted] Nov 03 '19

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u/BarkingWilder Nov 03 '19

This probably isn't a million miles from the truth to be honest.

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u/greenwrayth Nov 03 '19

We often fail to remember that the human brain hasn’t changed at all in the last, say, 5,000 years. They were just as smart as we are, we just have more available knowledge, easy calories, technology, and leisure time to use ours.

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u/BarkingWilder Nov 03 '19

Always thought Tim Minchin put it best. We're just monkeys with shoes.

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u/James_n_mcgraw Nov 05 '19

I always think its dumb when people are like people couldnt have built the pyramids or insert great work here. People werent dumb, they had more free time than us and labor was cheap. The pyramids were built by skilled architects and hired farmers in the off season. we may not know exactly how they did it but just because the method was lost to history doesnt mean it wasnt possible. Construction equipment doesnt last 6000 years, stone blocks do. Hell a good example is mount rushmore, a giant statue carved out of a mountainside without making any mistakes all before computers or advanced surveying equipment, or the sphynx is another good example. Very big things that are difficult to imagine how they even accomplished it, but they still did even if you domt understand how.

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u/[deleted] Nov 13 '19

And.... Lots and lots and lots and LOTS of slaves. Same with Roman roads. Technology met raw human labor on a massive scale.

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u/supbrother Nov 03 '19

I do work as a construction materials tech and I can assure you that its basically the same sort of methods we use today for some tests (just with fancier tools).

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u/sambar101 Nov 03 '19

Hey Hoplite come stab this rock right quick

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u/ChzGoddess Nov 03 '19

And I probably should have put the drink down before reading this...

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u/currytacos Nov 04 '19

Not to rain on your parade but Rome didn't have hoplites.

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u/[deleted] Nov 03 '19

It also isn't very different from how we would measure it today.

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u/Nollhypotes Nov 03 '19

Still, we'll need some concrete evidence.

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u/mia_elora Nov 04 '19

Of coarse you do! I think it's a good enough article that you can take it for granite, this time. :)

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u/CptOblivion Nov 04 '19

Well sure, you'd have to leave the planet and go well past the moon to be that far from the truth.

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u/Mattzocrazy Nov 03 '19

To be fair, that does seem like a pretty reliable way to measure the tensile strength of a material over time, just get a burly fella to whack it with a pickaxe once a day and see how much each whack takes off and then measure based on the size of the fragments over time

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u/Cthulhu2016 Nov 03 '19

 lex parsimoniae

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u/ScorpioLaw Nov 03 '19

The pick method was used by the Greeks. The romans liked to use their slaves, and would test the strength of the concrete on them by ramming their heads.

That is until they captured the first slave from Ireland. IT took at least 100 iterations before they succeeded against the thick Irish skulls. There is an old saying in Latin. "Cum bonis capite eius qui residui insulanos vesana"

Source - Www.crazyhistoryfax.com

PS - fun fact!

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u/Casehead Nov 04 '19

What does the Latin say?

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u/_brainfog Nov 04 '19

I was gonna say they chucked rocks at it. You don't need new technology you just need some rocks and force

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u/[deleted] Nov 04 '19

I'm not sure what you mean, Is a pickaxe new technology?

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