I'm not a concrete mix design expert by any means, but I disagree with this post on a few levels. Concrete strength is derived from multiple sources, and grain interlocking is just one of them. I think recent research has shown that grain interlocking does not play a large role in concrete strength. It's unclear to me if your post is talking about grain interlocking or cement/aggregate bonding. I'm not up to speed on research in this area, but I do not believe that you can have a rounded sand that is so smooth that bonding doesn't occur and the idea that the concrete "turns to dust" under any serious load is something that I personally have never heard of.
In fact, the more angular the aggregate is the less workable the concrete becomes. There is a sweet spot of angularity that is desired. I believe the main advantage to increased angularity is in durability (which is due to interlocking, I think, as well as increased void ratio leading to better air entrainment).
Also - the size of the grains is more important than angularity, so I also disagree with the statement that sand "as fine as possible" can be useful for construction work in the context of concrete. While tautologically true because anything too fine (passing #200) would be classified as a silt instead of a sand, the way that it's written is deceptive.
"Also - the size of the grains is more important than angularity, so I also disagree with the statement that sand "as fine as possible" can be useful for construction work in the context of concrete."
Disagree all you want but that doesn't change the fact I've done building construction, including laying foundation, and finer sand is far superior to coarser sand. In fact, coarser sand is rather horrible for construction.
I still don't understand what exactly you're talking about. Are you talking about sand used for concrete or sand in general (e.g. - for subgrade soils).
Sand used in concrete needs to meet a gradation requirement. The gradation requirement uses all sizes of sand as aggregate.
And if we are comparing credentials (which I assume is what your building construction story and youtube link is for?), then I've done nothing but put holes in the ground and fill them up with concrete for almost a decade. Here's what I was doing in 2014: https://www.youtube.com/watch?v=E4Ixw69woSA
I did the construction globally, from USA to UK to Saudi Arabia.
I'm talking about both sand in construction and in general (like for glassblowing, etc.) Portland cement uses the finest sands possible for holding concrete aggregate, which you only really tend to find in desert areas (if you're lucky enough to find a spot that hasn't been above water for more than a million years, that's one reason construction-grade stuff is so hard to find.)
Now days, I do very similar to your link, except it's through mountains, and terminates inside the mountain. Minerals extraction is fun!
In fact, the more angular the aggregate is the less workable the concrete becomes. There is a sweet spot of angularity that is desired. I believe the main advantage to increased angularity is in durability (which is due to interlocking, I think, as well as increased void ratio leading to better air entrainment).
Also - the size of the grains is more important than angularity, so I also disagree with the statement that sand "as fine as possible" can be useful for construction work in the context of concrete. While tautologically true because anything too fine (passing #200) would be classified as a silt instead of a sand, the way that it's written is deceptive.