system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are constructors still using crushed stones alongside new railroad tracks instead of concrete?"
gpt
Higher surface energy can absorb way more than things with lower surface energy without suffering catastrophic failure. Try hitting the sand in the beach with a hammer. It's very tough. It is very malleable. You can't cause it to "fail".

Now take the sand, and turn it into glass. Hit it with a hammer, and you'll see that it can shatter. It is harder, sure, but it isn't tougher. It is brittle. It fails immediately.

The purpose is to maintain integrity of the surface. Bunch of smaller rocks can maintain a surface exposed to constant vibrations much more cheaply and effectively than one large solid piece.