Sand and gravel mining “greatly exceeds natural renewal rates” | Hacker News Reader

Sand and gravel mining “greatly exceeds natural renewal rates”

newyorker.com

82 pointssergeant328 comments

Nature is not crushing rock into gravel and sand as quickly as humans are using it. But it is straightforward for humans to crush bulk rock. The New Yorker article actually mentions crushing quarried material toward the middle of the piece. Here is a study from 2008 about replacing sand with crushed stone in concrete (from India, where natural sand shortages are acute), "Experimental Study of Artificial Sand Concrete":

http://ieeexplore.ieee.org/document/4580058/

EDIT: probably shouldn't link directly to sci-hub copy.

The short version: crushed stone is a fine substitute for natural sand in concrete. It actually improves strength modestly compared to concrete made with natural sand. ("Concrete with stone crusher dust was reported to show 17%, 7%, 20% higher compressive, tensile, flexural strengths respectively than those of conventional concrete.")

Of course it takes energy to quarry and crush bulk rock. But the energy input is manageable. The Bond Work Index for granite is 10-15 kWh/ton; for quartz/quartzite it's also up to 15 kWh/ton. That means energy cost up to $1.50/ton at 10 cents/kWh for an electrically driven crusher.

https://www.911metallurgist.com/blog/table-of-bond-work-inde...

For comparison, current concrete sand seems to run about $45/ton:

http://www.earthmaterials.com/1_concrete.htm

You can also crush used concrete to replace aggregate:

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

That doesn't help in countries like India which are growing rapidly, but it can make a big difference in most parts of the US.

I've driven by two large concrete and asphalt recyclers in two different states within the last week. Definitely a big thing!

The rock crusher industry is ready to sell you all the machinery for making sand from larger rocks.[1] Cone crushers break the rocks down, and screens and cyclones sort the result by size. The best sand seems to come from "rock to rock crushing", where most of the cracking forces are applied by other rock. There are big crushers, small crushers, and mobile crushers. There's a whole category on Alibaba for sand-making machines.[2] While this seems to be a problem in India, the rest of the developed world is busily crushing big rocks into little ones.

[1] http://www.metso.com/showroom/construction/new-type-of-crush... [2] https://www.alibaba.com/trade/search?fsb=y&IndexArea=product...

So why can’t we convert the useless ‘round’, ‘smooth’ desert sand into useful angular sand?

E.g. use concentrated sunlight to fuse sand grains together [1], then crush to the desired grain size.

It’s got to be a better solution than shipping sand halfway around the world.

[1] http://www.markuskayser.com/work/solarsinter/

Making bigger rocks from smooth sand to crush into pointy sand would only make sense once we've run out of bigger rocks.

A building under construction near me has a large sign around it advertising a local alcohol company: it provides sand via recycled bottles (for the concrete, I assume). I'm curious how efficient this is in relation to finding new mining exploits nearby, or if this is just marketing.

Could just be marketing or for Aesthetics. Glass and concrete don't always mix that well. My hobby is concrete countertops with glass fibers, and these are specifically alkali resistant. Concrete and glass don't mix well without additives, which may or may not matter for eco friendliness. You will find some fly ash in some concrete mixes, which is a byproduct of power plants more common.

It does seem that using glass aggregate is effective, perhaps not as a primary building material but an ancillary one. This wikipedia article is not amazing but seems to give a passable overview: https://en.wikipedia.org/wiki/Glass_recycling. Having said that, the company in question has run similar environmental programs in the past so it's probably mostly marketing.

Obviously it'll become more expensive until we no longer need the resource, find an alternative, or recycle. Next.

Concrete is a very good material so I don't see "no longer needing it" happening any time soon. Finding an alternative and recycling both sound like hard to tackle and expensive, I wouldn't say this scarcity can be so easily dismissed.

Crushing rocks to make sand is a fine alternative. It's just a matter of additional cost, which will become viable as shortages drive up the cost of natural sand.

The parent's point is that as something becomes more and more scarce, the price will increase. As the price increases, fewer and fewer projects will be able to justify its cost, leading to many to have to find alternatives or not be built at all. To take it to the extreme, as price continues to rise further, at some point there will be no project that creates enough value to justify the cost of concrete, at which point it will "no longer be needed".

He is not dismissing anything, just pointing out a simplified rule of economics.

Luckily, the planet is obviously designed to sustain very well a fully-market-based approach to using its resources.

In this case it really is.

The planet will be fine.

Heck, the Universe will be fine.

Would be funny if this is the second wind for the Middle East after peak oil. Not that shipping sand sounds profitable.

Edit: Apparently, desert sand is too smooth/fine for most construction use.

http://www.nytimes.com/1995/07/29/us/alabama-to-make-prisone... (I support prisoners having good job training, choices and wages.)

I wonder: if Mr Musk's will ever succeed with The Boring Company, would it significantly help with the shortage? By succeed I mean doing tunnels right and left.

Not likely as drilling and boring takes an inordinate amount of time with current alloys and tech.

Not really. You can't use just any soil for construction, it has to be a sandy/grainy variety.

granite or other rock can be crushed and sieved to the right mixture. There is lots of granite and sandstone etc

[disregard this: I jumped the gun]

That's not what this article is about.

Similarly the sun won't last forever and is not renewable.

So what?

Latest is that the expansion rate of the universe is slowing. So, one might predict a big crunch and the end of everything. So what?

Looks like someone wants to get eyeballs for ad revenue. No thanks, not with that story.

Stories of the form the sky is falling no longer get my eyeballs. People who write such stories need to find other, more useful work to do.

Did you even read the story... it's not a "sky is falling" story. (A Miami is falling story, maybe :-P)

It's really more of an interesting look at a resource that few in our part of the tech world even think about, and some of the challenges they face, if you can look past the headline.

No it's not: Wake up. You've been taken in. It's just "the sky is falling", or "Oh we've got trouble, right here in River City. Trouble starts with a T and that rhymes with a G and that stands for gravel." It's just a scare headline and story to get eyeballs for ad revenue.

The good news about such nonsense grabbing people by the heart, the gut, below the belt, always below the shoulders, never between the ears, is that it really is the most scary story they can find. So, all other stories they can find are less scary than their story which is not scary at all which means that all is well. Good.

Maybe if there is some serious problem, then they will write about that, too.

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