I have one project just finished yesterday. 17 pours i believe 3 times i had trouble with ending up with so-much gravel ending up in hopper without cream, the pump would suck air on one or both cylinders. 

   Only happens on this job. rocky mix, the plants only 10 minutes away, anybody else experience this? I've seen it few times before.  3000 slump usualy 4-5 or tighter.

same thing happen to me. i was having a hard time pumping it . so i told the contractor to fix design or i would stop pumping . its not worth pumping mixes like that.

concrete animal, crazypumpers right. the contractor can add 10% more flyash to make it more pump freindly its cheap and does not affect the strength. what mpa mix is this.

here in PR contractors dont use flyash, its too expensive for them 3000 psi with flyash  $100 per yard and $68 without it.

the contracters up here in alberta actually get urged to use it, by the government. so much to the point where it becomes a problem with the quality of the finishing. the contractors have tried to use as much as 60%. flyash is okay for finishfing as long as its no more than 25% after that it has a tendancey to role and peel. sorry got carried away there. thats to bad about the prices down south. it sure makes the mixes nicer to pump. another possability is to use more natural sand, not so much the river or wasd kind, these type have a tendancy to segragate whereas the quarry sand seems to allow the cement particles ta adhere to the granes thus providing a more pumpable mix.

sounds to me like concrete truck was not proprly mixed due to closeness of plant probably same truck same driver either truck or driver isn't doing job.

I too have had a problem with a mix that whould segregate in that manner, i found that brand x did not have any sand in it and way to much cement in the mix!

this mud not olny flashed quickly but it was hell to pump, i had to back pump 2 or3 strokes and push hard to mud to the outher end,