alt Hacker NewsSand 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.
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.