Had some trouble pumping lightweight today. Small line pump... about 625 psi on material. Agg. looked like lava rocks. 6sk. looked pumpable. Was told I needed to pump it wet. 7" out of the truck was coming out my hose about  4" slump. I was also told that the agg. needed to be under a vacume so water would be sucked into the rock. Some sprinkle the rock with water and some store it underwater? This is all new to me. Would like to hear some stories about pumping lightweight... anybody?

Can go either good or bad. If it dries up real bad through the pump you have dry rook. Concrete companies dont bring in new loads unless it is a big pour. So you will get the left over so it will be dry. You will have to wet concrete up with water. the pump will push water into the rock thats why you are going from a 7 to a 4

The stuff you are on about is called LYTAG over here (uk) can catch ou out if you ain't carefull. It's supposed to be soaked overnight but that never happens so when you start pumping it sucks up the moisture and makes it harder to pump. The problem is that it is batched by weight and not volume so if it is not soaked over night you get even more of the damned stuff to suck up the moisture in the load.When ever I start pumping the next load I always give it a couple of pumps in reverse to break up the plug that sometimes forms when waiting between loads.It would be intresting to here comments from others.

Happy Pumping

soaking is very important. pumped 120m yesterday, with lightweight. was supposed to pour on saturday, but r/m supplier recieved the agg. on friday. needed 48hrs to soak. 6" slump no probs. but 4" slump a lil harder.

If it is not soaked really good, it will dry up on you quickly. One thing is do not stop pumping. If you have to stop, make sure you back pump a few times before you try going forward.

Well done.Light weight concrete a night mare to pump.they are small poly balls it has to be very wet like pure water by pumping you press the water out of it. they are normaly soaked over night.there is an adative that coates the balls. if you ever have to move suck the boom back with a sponge ball.

Everyone here has offered some good information.  I learned many years ago about light weight concrete and small line pumps.  I can put it in one word: DON'T.

Light weight aggrigate is very pourous, usually burnt or cooked rock.  If not saturated properly and when you put it under pressure (which is what a pump does), it pushes the moisture from the mix into the rock and then you don't have any "fat" to carry the mix through the pipe or hoses.  No matter, you will still receive the blame from the concrete company.  Trust me, been there and done that.

I would never attempt to put it through anything less than 4" system.  The less hose the better.  Never try to force it through, but just pump it hard enough to ease it through.  If a block forms in the system, don't try to force it through.  This just makes it worse.  Find the blockage and break the system as close as possible to that and then try to shake it out.

There are a few ways to saturate the rock.  Yes, one is a vacume chamber where they introduce the water at a certain point and the rock absorbs it.  This isn't possible in most states, and to be honest, I have never seen it done this way.  The second way is to heat the rock and then hit it with cold water.  This will also allow the rock to absorb the water.  Most of the time they will pile it up and spray water on it for a day or two.  Not as effective, but given enough time it certainly helps.  The last method is some of the companies will batch the rock in a mixer drum the day before and then fill the mixer with water and let it sit over night.  This is good, but not on large pours.  It would take too many trucks.  And finally, some companies have large pits where they dump the rock in and then fill the pit with water and let it sit for a period of time.  I would still take the time to make a call to the plant and ask a few questions on how they are preparing the mix.

everyone here has great advice no doubt.there are 2 ways to prove your point and take the blame off of u,all u need is a cup of water or a hammer.i have put light weight through 2 inch too 5 inch sum days great sum days a total nightmare,but one thing is for sure i NEVER tell a customer that it cant be done.theres always a way.here in wy i guess we got it better than most places we got a great relationship with the batch plants,we do for them and they do for us so u might try talking to the reps of the plant to asst u also before the day goes wrong and educate them in what the pump needs instead of placing blame. then the batch looks good u look good and the customer is happy with a job that is done.  

72 hrs soaking minimum and it cuts your problems out tremendously,one trick get a 5 gallon bucket fill with water get a handful of the lightweight concrete throw it in the bucket if you have more than 5 rocks floating get ready for a long day,planning is the key we will not attempt if it isnt soaked for 72 hrs not that it cant be done but usually you have regulations about water to cement ratio on such jobs so it needs to be presoaked are you can make a costly mistake by not being able to get the pour finished due to unpumpable concrete unless you get it like water not good for anyone because the strongest lightweight mix is 4000 psi and your water to cement ratio to high along with floating aggregate is not good for anyone soak your aggregate 72 hrs

also this method used i have pumped through lines from 5" to 2" i have mix designs for all the way down to 2" if anyone needs them just send me a message but the key is preplanning the pour so the rock is soaked and taking moisture tests the day before the pour and i have cut our lightweght problems virtually out