First time to do shotcrete job here using transcrete concrete pump(p60), first truck works fine, 2nd truck we didn't make it, three hours of"hose party", next day same thing happen.First truck finished hopper full, pump 1 stroke every 3 minutes. Blockage occurs when we start for the second truck but its only 10 minutes of waiting.2"slump using 3"to 2" hose 60'line downhill job.I admit that we've made a lot of mistakes, such as waiting too long to clear the hose thats why we have a hose party(blow out valve didn't work either),in experienced line hand,slump i think every 2m3 of 4m3 concrete from the truck must be re-checked (add water,re mix etc.),Is pumping in reverse on shotcrete good idea? Seems this is one factor where in it sucks air??.

I know that this is simple problem for most of you doing this job,i really need suggestions or comments as we will continue the job next week, and more shotcrete jobs coming. Thank you in advance

We do shotcrete eveyday with a p 60. we always wet up the last 0.4 m3 in the mixer so its nice and wet in the hoses when where waiting for the next truck And reverse the pump while we wait.

Agree, one thing with shotcrete is relieve the push on the heads, it creates a dry pack then plugs in reducers. The larger more powerfull the machine the worse it gets. Mixes are hard to read at 2' slumps, I always grab a hand full of mud squeeze it throw it against a vertal rock, to see how much of it sticks, then adjust slumps. Just little tricks to check on powder and water content. I hate shotcrete only because they made us put it through a 42 m3 boom pump. It was done allot, but things had to be perfect and not slow waits. Always pull back constantly.

Thank you guys for the input, appreciate it much.

What is the mix design? Could be wrong for pumping. Too much rock?

one other thing to try is just before you start pumping the next truck is take 2-3 strokes in reverse it usually helps

Knowing the mixes where you are, I suggest you check out the fine sand. Also, see if they are adding fly ash or silica.

The most important sand is the fine sand passing the 100 screen (100 holes per sq inch) you need 3% to 5% of your fine sand to be 100. Cement is 200 screen. Fly ash is a round modular, cement flat like a snow flake. So a combination of 25% flyash and 75% cement will reduce bleeding. The 100 sand is the good stuff.