I've been line pumping concrete for about 4 years now; mostly shotcrete.  So, I've pumped some crazy mixes with a TK50 Putzmeister.

Got an 8 yrd pea gravel job the other day that I thought would be pretty simple. I thought I could pump through 2" line: reducing from 5" to 4" to 3" at the  pump. Turns out I clogged every line I had including the 4". The mix seemed it had a little too much rock from my experience. The blame game went on, so on and so forth for the whole 4 hours of the job. Couldn't even pump a yard and ended up buying the truck.

Got a job with the same mix next week for 80 yards, 200 feet of line going down vertically.

I've never pumped a job that far vertically down before. I've heard it is a little more complicated to pump down than up. My inexperience brings me to your website. Any advice would be very much appreciated.

I sent you an email and I am quite certain you will recieve more tips go with what you know and what makes you comfortable. We all have our little tricks of the trade and everyone here is glad to share their experiences good and bad. Good Luck

would be good to have a section where people could post problem mixes and solutions. we just got done pumping a 10,000 psi mix that had 5 sack cement, 5 sack slag, 1000 lbs sand, 1600lbs 3/4 rock with some add mixtures. viscosity modifier and plastic ides. very difficult to pump. took third try to get mix right to pump.

I had that exact same problem last month from the same RM plant I pumped for all summer. The thing is, there are two types of Pee rock mixes. One is for tail gating and one is for pumping. After calling other RM plants I found out. Because of course they like to blame the pump.. The PUMPABLE mix has !200 rock and 1800 sand. The tail gate mix has 1800 rock 1200 sand. I had 8yds I couldn't even pump threw the first hose. I sent the mud back they added two yds of sand and 10 bags cement, to make a total of ten yds.(the contractor decided he need the extra mud anyway). It pumped great.

Why on earth would you pay for the concrete? Cold day in hell before that happened around here, they can find someone else. I pump pea gravel with 2.5" hose, 2" is too small for mixes around here, too many jams.

WTF

You had to buy what?

So next week if the same mix doesn't pump you gonna buy 80 yards.

Glad I live in Norway where all concrete is measured withing +- 5 kg or there about.
But we get funny mixes from time to time.
Counting out the obvious stuff like putting the recycled rock in the sand and other stupid things, I would say it's a whole lot of things to consider.
You can get 2 batches of the same mix, but one is not pumpable. Why?

Because the RM company don't do their job, got a bad batch of something or just the odd screwup.

If the chem like retarders, plasticizers... are old they don't work as supposed to, if they have sat to long and not been stirred, they can separate and don't work, if they are in an open container they can loose their effect or just a bad batch from the producer and so on.
Much to consider.

And then you have the rocks and sand, if you don't control the moist in the aggregate or get it wrong the concrete can be bad, and if you get aggregate with the wrong grading curve? (Is that the right word? My technical dictionary only goes english -> norwegian...) your in for some fun, is there is to little fine stuff or too much coarse stuff you get something that looks like a rock plug, the opposite you will get ball like plugs of fine silt. Also a propblem with recycled aggregate. And the rock don't have to be 22mm just because it passed through a 22mm mesh...

And if the plant has been producing other mixes there can be leftovers from that.

And then you have the drivers, don't know elsewhere, but here in Norway you are supposed to only rotate the drum 2-3 times pr minute when driving, then mix it up 2 min before unloading. Worst case, you get 'false air' (to fast) or nothing (no remix), either is a bitch with lines. And when unloading a small load all the fine stuff tend to stick and all you get out is rock. Same with high slump, too fast when start to empty = rocks.

And high slump doesn't necessary good plasticity or viscocity or pumpable mud and the other way round.

There is no real good answer to this question, just a lot of if's and maybe.
It is only through years of experience you can say a batch has good pumpability or something you have to hammer through, just by looking at it.
But it's NEVER the pumpers fault, YOU DON'T MAKE THE CONCRETE, or deliver it...
But I guess thats why I love this job, you never know what you are gonna get or what the next brings.
Always learning new stuff and seeing new things is fun, although it can be hard from time to time.

Do you guys use PP-fibre?(glassfibre) The stuff that look like feathers...
If I get a rocky miz I usually throw a couple of bags and some plasticzicer in and mix it up, it makes a nice plastic pumpable mix.

Your well maintained concrete pump will always tell you if it is the wrong mix.

No opinion - just fact.

sometimes the stone may be to sharp or there are not enough fines in the mix. If you grab a handful of concrete and squeeeze it tight in your hand and no slurry comes out between your knuckles. Thats a good sign that it wont be real good to pump. Hows your cuting ring and wearplate look? if you keep them up to date most putzmeisters would pump just about anything.

when you are pumping down hill, you could try puting a small soft sponge in front of your slurry to hold it all back a bit as you push it through. It works well and I have done it heaps of times in the past. It was taught to me by an older guy that had beeen on the pumps for around 23 years.

Had a bad 14mm, 28 Mpa mix the other day. Sorry, I don't know Psi.  About 25 meters.  I went low Rpm and high volume and this worked until I had rock build up in the hopper. 

I then went the other side with max Rpm and low volume.  This worked better but still not great. 

I stayed with the high Rpm and added in a 4" hose and this made a lot of difference.  Now I go 5>4, 4" hose (12 feet long) 4>3, 3" hose, 3>2 1/2 and then 2 1/2" hoses.  It seems that reducing in stages works better for me than all at once.  It also cuts down on the hose kicking around so much. 

I don't know if the machine would make a lot of difference. I have a Schwing wp1000, I think it is a bit more powerfull than yours but not a lot.  I am sure some of the others could tell you how much difference pump type would make.  I have only ever owned this one pump and it is great.  10 years old and going great. 

I've lost hose because of a bad mix. 300 over sandy 6sack pea gravel mix works great for 2". 50/50 will be fine in 3". As long as the customer is told up front what mix you require. You should never pay for mud. It is our policy to make sure the customer understands what we require. These pumps make great lie detectors. Trust your pump.

What makes a mix pumpable, rule of thumb is that it is in your rental terms and conditions, and as such you never pay for unpumpable concrete. For a mix to go thru your system it has to be cohesive, meaning it has to have the proper segragation of aggregates, as well as the correct amount of fines ( being sand, flyash or what ever the mix designer for the ready mixer with his knowledge) decides that it will be able to make it thru all your 90 degree bends, not counting the added friction of going thru what ever amount of hose you are pumping thru ( because we all know the added friction). Just be glad you were not going thru a boom first.

For your next pour do what was said in the previous post as far as priming and make sure that the ready mixer knows the specifics of the project, pump on, and never get back charged for a load of mud, unless your machine is not capable due to your inability to maintain it to it's specs.

If it wont pump add water? (in most cases) Sounds like you got an exposed mix. Pretty common in these parts. 10% over-rocked pea-mix for exposed agg.finish.

 Look at it like traffic on the freeway. The cars are the rocks, the space in between them is sand & fines. If there's too many cars (rocks) when there's a lane reduction...>traffic jam< (plug)

And always remember that if you were pumping the day before and all was good then nothing changes over night in your pump!!!! You still have the same pump and gear. why should anything be diferant the next day??? Its a fact that pumps dont lie, pumps cant change over night but concrete mixes always vary and thats the issue 99% of the time. You cant pay for crete cause it wont pump especially if you keep up withh your serviceing>