Fire Clay to set oven floor?

[Xene]

I recently laid and cut old street brick around the foundation of the oven I'm building. I was interrupted by rain, covered my saw with a tarp and upon uncovering it to cut the fire brick, I have found I've left the tray full of wet brick clay. I cleaned the tray and saved the clay that had collected (probably 3 lbs worth!) and now I'm wondering if I could use that under my fire brick as I set the oven floor to level? Would I mix it with sand, or could I use it as-is? I'm going to cut a good portion of the fire brick in half too, so what collects from those cuts I could mix in with this red clay I already have too.

The street brick are the old bricks, I would guess 80-100 years old (back when we made brick with the good stuff!) I hate to dump it out if I could be using it. What do you recommend?