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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 arti
by philipkglass 9y ago
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/ 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-index-by-minerals 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 http://www.earthmaterials.com/1_concrete.htm
- greglindahl 9y agoYou can also crush used concrete to replace aggregate: https://en.wikipedia.org/wiki/Concrete_recycling 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.
- monknomo 9y agoI've driven by two large concrete and asphalt recyclers in two different states within the last week. Definitely a big thing!
- deleted 9y ago[deleted]
- Animats 9y agoThe 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-crushed-sand-to-replace-natural-sand-in-concrete-production/ http://www.metso.com/showroom/construction/new-type-of-crush... [2] https://www.alibaba.com/trade/search?fsb=y&IndexArea=product_en&CatId=431406&SearchText=sand+maker https://www.alibaba.com/trade/search?fsb=y&IndexArea=product...