I just got a call from a guy in texas asking what is the max rock size for a 2 1/2" hose.

Todd,not sure.I have used 1" minus with 3" but the mix had to be creamy.Every time Dan (my pumper) gets an order for that he always changes it.It would also look into man or natural sand.Why not go with a stronger 3/8 mix and avoid the grief?

22mm in 2.5" hose, no problems.
What kind of stone and how much is the big question.

3/4" not a problem. 1" is just to big if you ask me. I have got it through, but it's a hard push. you can almost see the rock moving through hose like a worm under the dirt. imo, no bigger than 3/4".

Todd anyrock passing 1/2 screen is perfect and depending on the type of pump if its a ball valve 1,300 lbs max, saying 1/2 minus leaves to much open could be larger rock the best way to figure is 4x the rock size for the size of hose 3/4 x 4 = 3 inch hose, on my line pump 2 1/2 inch is all I use.

3/4 minus for our mix

 Depends on the type of rock also. Crushed or angular rock 3/8" to 1/2" with a good mix. Glacial material or 'river rock' (rounded) 3/4" will go through 2.5" hose.  7/8" minus will too with a high sand ratio 6sac+.

 But Texas?... I'd say 1/2" max. for standard mix designs.

All rocks are not created equal 1/2 round could be 3 inchs long a plug waiting to happen there will be some mixed in that will go threw a 3/4 grate on your hopper what I  get is 7,8,9, size chip limestone , some plant around here can get river rock easy our sand is barged in, fly ash is easy to get with our coal fired steam plants.

3/8 pee gravel wouldnt go in vegas,hahaha.

I did stairs at a hockey arena #1150 1/2 inch river rock #580 cement.never had a problem. I also at times had 350 feet of system 

I always go by the rule of max size of aggregate to be no more than 1/3 of pipe diameter. ie 3inch pipe 1 inch rock.

need to use my telbelt on that job.

Here in So Cal we pump 1" with a 50/50 blend of 3/8" 780 lbs of each and 517lbs cement. With no problem do every day.