1

Crane and hopper are still standard for many big or high jobs; these things get the small and intermediate jobs. And yes, it's a screw pump. 

Mechanical/construction engineering just facinates me, what with how so much experience and science goes into it.  I remain amazed that we can build 80-story towers in the gumbo soil here in Houston, with no bedrock, and they don't sink.

2 Don't they use a similar type of rig for that new-fangled concrete "printing" they've been playing with?

3

Those things come in different sizes. I watched a 7 story building going up in Cambridge when I worked there, and they used a really big one of those to pump concrete up to the top of it.

Which they pretty much had to do because they didn't use a tower crane for that project. The whole thing got built using a derrick crawler crane. Seeing them lifting stuff that high with a crane like that scared the heck out of me, but they knew what they were doing, and construction went without a hitch.

4 Mythbusters did an episode on removing cement from a cement mixer (well, really, concrete from a concrete mixer) that had (hypothetically) got stuck in traffic and had the concrete set inside it.

After failing to make much of an impression on it with a chisel or a jackhammer, they eventually tried half a ton of high explosive.  The truck went away.

There was a girl at my last job, working part time in the call centre while she studied civil engineering.  Smart and cute...  And way too young for me, unfortunately.

5 I think that if you're going to use that much explosive, it's probably a good idea to do it out in the middle of nowhere in Nevada, and to stand back about 10 miles.

6 IIRC, having seen this episode, that's exactly what they did, use a desert.  They backed up over two miles, and had to get special permissions, plus clear the airspace.  They did find most of the truck frame afterwards...

7

But note that that was presented as an atypical case, as they pointed out that concrete trucks DO over time develop a thinnish layer spread over the inside of the hopper, but they aren't usually allowed to set up like that.

Of course I don't actually know what's done, but if I were in charge of things and one of my trucks was about to set up like that, I'd probably tell the driver to get it out of traffic any legimite way possible and dump the load somewhere so as to not ruin the truck.  A truckload of 'crete would probably take long enough to set fully that you'd have time to get it emptied out with moderate effort.

8 Mike Rowe from Dirty Jobs cleaned out a "normal" operational deposit in a concrete truck (it looked to be about 1/10 of the volume) on one of his shows, and yes, it was set.  They used these mini-jackhammer thingies and lots of sweat.  I would not want that job. 
The company that did it was exclusively in that business.  Mostly they do regular maintenance cleaning but they also cleaned up "accidents" as well, up to about 1/4 of volume, if I remember correctly. 
The Mythbusters definitely had more fun.

9

RickC:

Ready-mix truck drivers try to do exactly that.  The father of a college buddy of mine owned a ready-mix plant, and told us about a time that he got stuck in traffic, then had to hurredly pull over, dump his load, and wash out.  By the time he finished, he couldn't even put a heel print in the pile of concrete.  Another trick that the drivers will use is to carry a bottle of pop with them.  If they dump soda into the truck while the concrete is still plastic and mix it up, it'll keep it from setting.

Referring to the OP,  concrete w/o reinforcement weighs about 144 pounds per cubic foot (IIRC--I know the weight with reinforcement is 150 pcf).  So the pressure required to pump concrete 10 ft into the air is:

10 ft *144 pcf * ft^2/(144 in^2) = 10 psi

10

144 lb/ft^3? Is that dry or wet? The stuff about reinforcement makes me think you're talking dry, unless they've somehow managed to make concrete that generates rebar as it sets (though given some of the things I've seen, I would hesitate to put past some clever engineer... especially one that somehow made a compressor pump that wouldn't be damaged beyond repair by pumping something with gravel in it).

11 I don't think I want to get into this. CatCube, I'm sure your number is way, way low, but I'm going to close this thread now.