How to break a sand block without touching it in Minecraft?

Frits34000 and a couple other redditors for a good while worked on 'sand quarry' machines - you can find the assorted designs on r/redstone.

The gist of it is to lift the sand block using a sticky piston, and while it is still falling, insert a non-full block like a trapdoor into the space it's trying to land in. Unable to solidify into a regular block, sand drops as item - the machine to do just this is fairly trivial, but there are numerous caveats about making it practical.

Frits34000 published a pretty in-depth tutorial on his designs and ways of dealing with the caveats.

So your trying to make a “bulldozer” vehicle. If sand falls on slabs or anything with a height of less than a block. BUT the only one that is pushable is a slab. So you can simply put slabs in front of the vehicle and move it. Note that any sand NOT above the slabs will not break.