[aurizon]

This is all economics. Ship carried sand is the cheapest freight and from one ocean spot to another (tidewater to tidewater) is the lowest cost. So these ocean based dredges suck up sediment and do some initial water/screen segregartion to get rid of the large lumps and dust(which are dumped and contribute to coral deaths in the dust plume -see Australia.) They then send the ships to where it is needed - usually by the next cheapest way = unit railcars. There is not real sand shortage, there is a shortage of cheap sand. Dictatorships willingly ruin sea coasts, deomcracies less so. There is a huge amount of sand on land = costs you extra to dig sort and move. There needs to be as legally restricted way to do this, so assorted sea shores and sand banks are not sucked up = which BTW, leads to further shore losses as these protective barriers are removes. The USA/Canada and most countries do have these restrictions - varies by country. So pay more for sand by law. Silicon sand for the chip industry is a millionth or less than what is needed for construction - who would never use chip sand anyway = costs a lot more.

[foolmeonce]

Yes, though the relatively small amount of sand that companies suck up with permission from i.e. EU countries in the mediterranean acts as a fig leaf for cheap ocean sand.

There's no real justification for letting all the ocean resource projects continue given the long standing tragedy of the commons and how it aggravates naval turf wars. If we outlaw all of it we will be better off. We can move towards manufacturing sand-like construction filler from our normal glass system, which is able to consume land sand, and such a filler would be visually distinct from raw ocean sand.

[aurizon]

Sand varies a lot - it depends on the rock it weathered from originally. As detailed here, sand dunes create rounded grains that do not interlock in the cement hydrate matrix = weak concrete. Lots more about it here. https://en.wikipedia.org/wiki/Sand

And a curious side note, sand collectors... https://en.wikipedia.org/wiki/Arenophile

[foolmeonce]

Yes, land sand is no good for building directly due to grain shape, but I think it is fine as input to the glass stream. Most manufactured sand is from stone quarries today, but I think a process of making manufactured sand from recycled glass should be able to make something more consistent.

[aurizon]

Recycled soda glass might have too little silica to make durable cement, but high silica glass (90%+) is a good way. recycled bottle glass - being mainly soda glass. A google finds this which shows that up to 15% of waste glass is OK, above that and properties decline. I believe they do use as much as they can as it is a disposal problem. Glass factories recycle their own waste into new glass. Used glass is removed from some recycling facilities, but with so many plastic bottles these days, separation is a labor cost problem. Some references here in the bibliography. https://iopscience.iop.org/article/10.1088/1757-899X/585/1/0... Many are paywalled, so use https://sci-hub.se/ to get access for some of them.

[foolmeonce]

Thanks, that article and it citations look very promising. I'm a little discouraged to see a first data point where clear is correlating with strength though since mixed color recycling waste was my first thought on sourcing. Still it gives me some ideas of areas to learn about with some specific goals in mind.

[aurizon]

Well, clarity = lack of scattering centers, which are also points of stress concentration = dislocations start here and propagate. Now glass with color from metal ions, like gold = ruby red, does not produce weakness. This mean colored glass from dissolved ions is OK, colored with particulates(pigmented) carry weakness. There is a whole gamut of the ways pigments induce weakness.