There are not many slicker things in the world than polished glass. But I'm wondering if you've put crushed glass to the test or if you're just guessing with some physics that is meant for a perfect slippery glass surface. When glass is scored, it can become more "sticky" than most anything. It is hard to thoroughly clean etched glass or scored glass, which is why some photographers keep an extra ground glass for their large format view camera because it takes a long time to get a replacement, and because when they get saturated with dust or marked up with pencil to denote a particular area of the view, it can be impossible to clean. The best ground glass these days is made using the etching process rather than the grit process. So with that as my counter-physics, I am thinking maybe a quick dip in some acid that will etch glass would do the trick! Finding the right acid and how to procure it may be 20 clicks away on Google.
Crushing the glass to sand consistency would produce 2 disadvantages.
1. Bear in mind that there is almost no bonding from papercrete to glass. Now, crushing glass more increases its surface area, and thus the amount of debonding within the mix, which would weaken its tensile strength more.
(I had expected the oposite, that the cement content would bond well ot the glass, and hoped the low level of cement might mean at the higher ph than concrete the cement and glass would not react over time and debond.)
2. It requires more work/time/energy
NT
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