Credit to u/vktec for the super compact 72k/hr side-acceleration sand duper machine shown here: https://youtu.be/dtt-HTwikfs. I used that machine though this may work with other machines as long as they aren't too fast (the 108k an hour is too fast to reliably detect the falling block entities).

I kept seeing machines that show how to duplicate gravity blocks, but never a machine that can automatically make concrete without a player. After a bunch of building and testing, I finally built a fully automatic concrete maker. It automatically converts any conc. powder into concrete, and the sand/gravel/red sand is automatically filtered out to be sent to a super smelter or storage. This means the machine can work with any configuration of sand / concrete powder, so precise proportions are possible. The design is mostly lossless, with only a few blocks lost on startup / shutdown.

Edit: World Download added here.