alt Hacker NewsDid 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 has to remediate the site after you mined it (like taxpayers). He empirically points out that different sands need a different water/cement ratio and also points out that the papers on sand use in concrete understand that. The 'bug' seems to be that people just add 'x' water to the mix and if the sand changes they might get different results.
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.