Placing wall concrete

[MTDENG]

We are pouring 8" thick, #5@15 EW, 14' tall walls with a 4000psi 3/4" mix. The pumper can't go below 4" hose for the 3/4" aggregate size and the design engineer wants to keep the 3/4" rock for strength and shrinkage. The 4.25" stinger the pumper has will not fit down inside the wall. A very informed shotcrete friend says he can design a 5000psi mix that he can pump through a 2-1/2" hose. I also considered building an oval steel chute 3"X12" that would attach to the boom pump's 4" hose. This would be placed inside the wall to within a few feet of the bottom. I always prefer to buy a tool if I can rather than make it, anyone seen anything like this? Or maybe just modify the mix and go with a 2-1/2" pump.
Tremieing into a wall with 3" or so clearance must have been done before thousands of times. Any help greatly appreciated.
On the one pour we did discharging from the top (dumb, dumb, dumb), the rebar did a fairly brilliant job of separating the coarse agg from the mix and depositing it on the bottom foot or so of the wall. Dumping a foot of gravel in the bottom of the forms before the pour would have achieved about the same result. Yes, we vibrated the wall well.

Thanks,

Michael

 

[boffintech]

Why not use a leave-out in the wall form about midway up. Pump the mix up to the bottom of the leave-out, close it up, then pump into the top.

 

[Speedycrete]

The oval tremie pipe is a common solution. There is no 'manufactured' one that I am aware of. Brundage Bone has developed a 'mud snake' tremie hose for applications such as this, but if it happens to fill up and expand, jamming in the rebar, then it's a detriment. The tremmie pipe along with a shortened hose so as not to exceed the boom manufacturer's tip load specifications is the best way to go, IMHO.

Pose this question at:

http://www.concretepumping.com

Lots of professionals with experience in situations as this.

 

[MTDENG]

Thank you very much for the responses. Since I posted, we have done 2 more pours. The first, we used a 3/8 shotcrete mix with 2" slump and added a gallon of Glenium per truck to bring the slump to 6-7" or so and we pumped it through a 2" hose. Pumped fine, but the 5 minute spin in the mixer on a 10 yard truck was not enough to mix the Glenium throughout so the slump started high and after 20 minutes it dropped to 3".
The next day we noted shrinkage cracks at the top of the wall at each rebar dowel (15" oc) and in the 2 weeks since, have seen some cracks propigate.
The second pour, we changed from crushed to river run rock and dropped the 3/4 rock from 1700 to 1600 pounds and were able to pump it through a 3" hose. Started with 3" slump and did the same with the Glenium. The shrinkage seems much less.
The wall is 8", 13' high and 115' long with control joints each 20' or so. I tried to talk the design engineer into expansion joints, but was assured that control joints would do it. It does seem that to really address the issue of cracks, one should create a gap in the foundation as well.

Cheers,

Michael