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Is the world really running out of sand?

practical.engineering

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Re: Is the world really running out of sand?

#201

Post by dyauspitr »

NeoTar wrote: post #165
dyauspitr wrote: post #154

I didn’t exactly understand the take away from this video. In the first test he does, the river sand concrete is three times stronger than the desert sand concrete, but in the second test, the desert sand concrete is 10% stronger than the river sand concrete. What exactly is going on?

It's normalising for different things. If you normalise for the the same ratio of cement / water / gravel / sand then sharp-sand (crushed rocks) is stronger. If you normalise for workability (i.e. the concrete flows and can be worked easily) you need to add additional water to sharp-sand, which means that the smooth-sand (e.g. river-rocks) end up stronger.

That’s what I mean, he doesn’t really test for absolute strength. Which one is stronger if the right amount of water for the corresponding concrete is added?

Re: Is the world really running out of sand?

#202

Post by dyauspitr »

kilna wrote: post #171
dyauspitr wrote: post #154

I didn’t exactly understand the take away from this video. In the first test he does, the river sand concrete is three times stronger than the desert sand concrete, but in the second test, the desert sand concrete is 10% stronger than the river sand concrete. What exactly is going on?

He explained it in the video. The amount of water was adjusted so the viscosity (well, workability) was identical between the samples in the second test. Less water in concrete has a huge positive influence on strength, and rough sand needs more water to be workable. Thus, for comparably workable samples, rounded sand concrete with less water was actually stronger.

But given the right amount of water, which one has the higher absolute strength?

Re: Is the world really running out of sand?

#203

Post by lazide »

WillAdams wrote: post #189
lazide wrote: post #180

Earlier quoted context omitted.

Since neither the general economy nor agriculture has gotten anywhere near getting off fossil fuels yet, that is assuming a lot isn’t it? Even if electrical grid needs are 100% renewable, that is just a couple percent of most economies energy usage.

For some places that is happening: https://www.smithsonianmag.com/sponsored/more-than-98-percen... 2020 had the UK reaching 43%: https://www.nationalgrid.com/stories/energy-explained/how-mu... Interesting point about electric being only a small part of overall usage --- I guess direct heating and things such as smelting/refining metals makes up the bulk of energy usage?

If we’re being honest, I think we should probably also include raw chemicals that would otherwise be used for things like direct heating. So for example, crude oil used for making asphalt, plastic, etc. or natural gas used for fertilizer.

Since replacing them would consume energy too.

That is a less obvious piece of math, but if we’re talking carbon neutral it would matter doesn’t it?

Re: Is the world really running out of sand?

#204

Post by cochne »

caust1c wrote: post #35

Grady is a hero in engineering reporting and documentaries. I've learned so much about how the world works in other engineering disciplines from Practical Engineering, and often in neglected fields that are losing talent faster than it can be replaced. It gives me hope that teenagers are watching his videos and becoming inspired to go into infrastructure. More than anything, I appreciate his calm and reasoned perspec…

>It gives me hope that teenagers are watching his videos and becoming inspired to go into infrastructure.

Sadly, that was me ~10 years ago, but the lure of FAANG money was too strong and I went into EE/CS after 1 year as a civil engineering major. I wonder if one day we will really start feeling the affects of this talent reallocation, and civil engineering will become a higher paying profession.

Re: Is the world really running out of sand?

#205

Post by mrguyorama »

dyauspitr wrote: post #202
kilna wrote: post #171

Earlier quoted context omitted.

He explained it in the video. The amount of water was adjusted so the viscosity (well, workability) was identical between the samples in the second test. Less water in concrete has a huge positive influence on strength, and rough sand needs more water to be workable. Thus, for comparably workable samples, rounded sand concrete with less water was actually stronger.

But given the right amount of water, which one has the higher absolute strength?

Define "right" amount of water. There is no singular correct amount of water in a concrete mix. It is dependent on the properties you want, the materials you have available, how things are going that day, etc.

Re: Is the world really running out of sand?

#206

Post by ianburrell »

wiz21c wrote: post #163

FTA > And we have engineered machines that can transform big rocks into small ones. OK, so you solve a problem of decreasing resources by using additional energy, so more CO2 emissions...

Funny thing is that crushing rocks could be solution to CO2. Olivine rock chemically fabsorbs CO2 when dumped in seawater. Crushing the rock increases the surface area.

Mining, crushing, and dumping rock are all something that we can do, and should be doable when electricity is cheap and green. It should be more efficient than pulling CO2 out of the air.

Re: Is the world really running out of sand?

#207

Post by JoeAltmaier »

ChuckMcM wrote: post #96
JoeAltmaier wrote: post #89

The whole idea of making your own sand is not sound. It will cost more, perhaps many times more. Seems clear when you think about it: hard to beat the cost of 'natural' sand because you just drive over and load it up. Add any more to that process, it's gonna go up in price. Including crushing rock etc - energy-intensive, then sieving. All add cost over and above, well, just hauling. And vague comments about 'couldn't…

Did you watch the entire video? I ask because Grady discusses EXACTLY this point. He explains that the whole 'more expensive' thing is really just noting the actual cost of sand versus ignoring the externalized costs of mining it. When you dig up a river bed there is a cost there that isn't necessarily reflected in the cost of the sand you mined from there, sometimes because that cost is passed on to someone else who…

Sand is often a byproduct of other operations. So the cost is complex, to be sure.

I was annoyed that he dropped the idea that smooth sand is not necessarily worse, because he couldn't find the paper on that. Not much of an argument.

Then he proceeded to make sand, and came out with what, 50%? stronger cement. Because, of course, it was new sand.

All sand is made by cracking larger stones. The moment it is made, it is as rough as it will ever be. All subsequent natural processes are smoothing, rounding, knocking the rough off the sand. His garage experiment supported exactly that point: 'old' weather-and-water smoothed sand is an inferior product as far as the resulting cement strength is concerned. When compared to virgin sand.

And yes, cracking your own sand is always going to be more expensive than just driving to where good sand is already lying and loading it up. The mining argument is subject to economies of scale, larger diggers and dredges make the cost of mining per pound negligible.

Where the energy cost of cracking your own totally doesn't scale. Every pound you make requires exactly the same exhorbitant energy cost, no matter a pound or a million pounds.

Definitely the cost structure of sand is changing, in future it will only be more expensive. The days of 'big cement' are changing forever. We may never see these days again.

Re: Is the world really running out of sand?

#208

Post by ChuckMcM »

JoeAltmaier wrote: post #207
ChuckMcM wrote: post #96

Earlier quoted context omitted.

Did you watch the entire video? I ask because Grady discusses EXACTLY this point. He explains that the whole 'more expensive' thing is really just noting the actual cost of sand versus ignoring the externalized costs of mining it. When you dig up a river bed there is a cost there that isn't necessarily reflected in the cost of the sand you mined from there, sometimes because that cost is passed on to someone else who…

Sand is often a byproduct of other operations. So the cost is complex, to be sure. I was annoyed that he dropped the idea that smooth sand is not necessarily worse, because he couldn't find the paper on that. Not much of an argument. Then he proceeded to make sand, and came out with what, 50%? stronger cement. Because, of course, it was new sand. All sand is made by cracking larger stones. The moment it is made, it i…

I look forward to wind powered stamping mills.

I heard his comments on smooth sand differently; As I heard it he was saying "People say smooth sand is worse but I can't find any research that would back that up, and even the paper cited in support of that argument doesn't say smooth sand is worse." He then goes on to reason why people might think that (the slump test) but the slump test is really about ratio of water to cement and not the texture of the sand. When he adjusted his water for smooth vs non-smooth sand to achieve equivalent slump tests, he found that the smooth sand concrete was stronger in his experiments.

My summer job as the 'mud man' for the masons building walls in Las Vegas certainly didn't go into this aspect of cement but my brother-in-law who is a civil engineer has a similar reverence / amazement that Grady does for concrete and seemed to agree with Grady's points. He pointed out the 'problem' was getting folks using concrete to change their mix recipes depending on the type of sand, that was, in his opinion, the big stumbling block. He felt any concrete that was mixed with the wrong ratios would under perform and the guys doing the mixing would never admit to screwing it up. They would always blame the ingredients.

Re: Is the world really running out of sand?

#209

Post by westurner »

Someone wrote: post #102
larsrc wrote: post #81

We fools here in Germany sometimes _pay_ to get rid of excess electricity when it's very sunny and windy. How about having some rock crushing machines that instead use that cheap electricity to make more sand? Thanks for the puns, too.

Free power doesn’t mean free production. There’s also labor, wear on the machines and the lost opportunity of using your money to do something else. Building such crushing machines and only use them x% of the time (for, for now, fairly small values of x) may not be a good investment.

So, energy storage should be lucrative and incentivized for us to solve the Duck Curve, and Alligator Curve, and overcharging the grid forces the price to zero or unlucratively below problems.

For firms with depreciating datacenter assets that are underutilized, a Research Coin like Grid Coin or an @home distributed computation project can offset costs

Datacenters scrap old compute - that there's hardly electronics recycling for - rather than keep it online due to relative cost in FLOPS/kWhr and the cost of conditioned space.

Doesn't electronics recycling recover the silica?

Can we make CPUs out of graphene made out of recycled plastic?

Can we make superconductive carbon computers that waste less electricity as heat?

Hopefully, Proof of Work miners that aren't operating on grants have an incentive to maximize energy efficiency with graphene ASICs and FPGAs and now TPUs

Re: Is the world really running out of sand?

#210

Post by mcculley »

eru wrote: post #149
mcculley wrote: post #79

One thing that surprised me when I started running a tugboat business: A country can be both an exporter and importer of sand. Sand of one type goes from the U.S. to The Bahamas to be used in concrete. Sand of another type goes from The Bahamas to the U.S. to be used in aquariums. Specialty sands go to make regulation volleyball courts.

> A country can be both an exporter and importer of sand. That's pretty normal in general. Eg Germany both imports and exports a lot of cars.

It is not surprising to me that products which have lots of differentiation are both imported and exported. It was surprising to me that something I thought of as a commodity goes in both directions.
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