My days of slipping and falling in the mud on my poor big fat butt is over. I am not bouncy anymore. The law of gravity tells me that what falls down, now, needs a crane to get up.
It's called "chat" or "screening"
It is a combination of finely crushed gravels, sand, and limestone, but no, it does not set up hard like concrete. It has "give" to it. I've used it here for years and I like it. It stays soft but used correctly it's durable. It keeps the mud at bay and forms a barrier so that the mud can't really get through it and rise to the top, only if you use enough of it and make it thick. It will not work for you right now. You're too late; you already have too much mud. You have to do this in the dry season. If you just pour it all around your muddy area now, it will do no good and just make you a much deeper mess than what you already have there. It will just churn under and it's not made for spreading all over the place. It simply will not work like you are planning to do.
What you have to do is wait for your dry season. Then I would suggest you only make a path with it, where you walk, where you need it, and a thick one at that. And you have to make it very thick to make it work. One foot of it say for instance will crush and compact down to 1 or 2 inches. But for something to just throw all over on top your mud area, no, waste of money. It will not work used like that and it will not last. Also, if you choose to make paths for yourself, they do have to be refurbished about once a year.
Now I use gravel and made gravel roads all over the place here where I walk or have to drive to unload feed and hay etc. The horses do not have to be on it at all. They can get to wherever they are going on the dirt/grassy areas, but it's never hurt them or their feet. I couldn't be without it, and yes, my horses go out of their way too to roll in the gravel! I have two different sizes that I use but mostly I use 1 inch. I use 2 1/2 inch for where I park my trailer so it doesn't sink in the mud on that side of the barn.
So I say to you, first, in your dry season, do what you have to do first by ditching to solve a lot of your problem. Drainage is important. Ditch, ditch, ditch. Then, think in terms of "paths" instead of covering an entire area.
Good luck and happy muddin!
These are some of my gravel path ways