Pouring concrete on a steep slope?

[arh13p]

What is the best method to pour concrete on slopes up to a 2:1 that is reinforced. This appliation would be for a liquid tight lagoon. Some as large as an acre in size. The concrete is reinforced with steel for crack control. Has anyone heard of "glacial" pouring? I have done it and Contractors like it because you just let the concrete flow down the side slope while workers are striking it off and leveling it. it keeps labor costs down. What is your opinion of this method? Thanks.

 

[cntw1953]

Depends on the concrete travel distance down the slope. I would utilize chute or conveying hose to gain better control to avoid aggregate seperation, which may lower the quality of the concrete and cause honeycombs, if not vibrate properly.

 

[arh13p]

We pour sometimes up to a 60' length. No vibration on the slope. strike it flat and roller buggy it. Some areas we may encounter honeycombing because the roller buggy won't get it smooth. Do believe this method is acceptable for the intended use of a liner? It will not have any equipment loading. We currently have not had any problems with this method but it kind of goes against ACI for placement methods. This is a unique application however so I am not sure how to specify the placement.

 

[diggerman]

Get about 3 or 4 buggies and create a chain of filling and dumping. Screed and finish. Its about the only way to do it. Very gruesome. Keep slump about a 5 inch max.

 

[PEinc]

For a big pour, I'd try a creter-crane (a conveyor mounted on a hydraulic rough terrain crane) or a pump truck.

http://www.PeirceEngineering.com

 

[arh13p]

We have done it with a conveyor and a pump also as "PEinc" stated. using buggies is out of the question. these are several hundred yard pours. the glacial pouring method consists of approx. 5' strips down the slope. The concrete truck continues to dump the concrete from the top of the slope as the concrete flows down the 5' wide strip to the bottom. workers stike it and roller bugger it. We have not found much evidence of segregation doing it this method. Contractors like it because is keeps the cost down. I was wondering what your opinions are on this method.

 

[Ltwine]

Not on my watch. Good luck.

 

[JedClampett]

We do this quite often for reservoir bottoms. We require the contractor to pour upward (start at the bottom) and push the concrete up the slope with a rotating screed. I'm not sure if a rotating screed is something that can be purchased but the contractors that work our projects rig one up. It has a chain driven drum and is supported by guides of some kind. Make sure there are plenty of laborers available. We usually limit the pours to 30 ft. wide between construction joints and I've seen about 20 workers there to finish the concrete, fill in low spots, etc.
We've had poor experiences with anything done from the top down.

 

[arh13p]

could you share what poor experiences you have had? I would be curious to see if these problems would be related with our concerns. I would appreciate it.

 

[Ltwine]

arh13p:

The contractor is paid to do the work sticking to the standard practices, which have been used for years with proven track record. You may have succeed in using your method in the past many times, however, the owner, and potentially you/your employer, likely to bear higher chances to suffer from the poor result, because so many things could go wrong have indeed went wrong.

 

[arh13p]

Ltwine:
I agree with you 100%. I am on a team to change a construction specification for concrete. We currently only allow the placement from the bottom up, consistent with current industry practice. However, we are getting overwhelming request to consider this method(glacial pouring) with possible additional precautions. The main concern was the chance of having void space on the downstream end of the steel. However after testing cores from this method and methods that were pumped from the bottom up, we didn't find any substantial evidence supporting one method was better then the other. On a 2.5:1 slope, gravity will slump the concrete after placement anyways therefore having the same chance of a void. Many responded they wouldn't do it this method. Why?

What would the main concerns be with the glacial pour method vs. pouring from the bottom up?

 

[Ltwine]

Without special treatment, which I have no clue, 3 ingredients are likely to lost/stick to the bottom after free rolling down a long slope - water, cement, fine sand.
Maybe you can verify it by taking samples at the toe, waist (mid height), and one at the point of concrete discharge (no rolling). I would be surprised that there is not much difference among the samples.

 

[JedClampett]

Our company designs a lot of hopper bottom reservoirs. I can't say exactly why we pour from the bottom up, but it was emphasized in such a way that I didn't want to be the one who changed it. I suspect the concrete is more susceptable to horizontal cracks due the tension forces created when the gravity pulls the concrete down the slope.
There might be more than one or ten ways to skin a cat, but we don't have problems with the sloped walls leaking.

 

[diggerman]

Cranes are quite expensive.

 

[PEinc]

So is screwing up a large concrete pour.

http://www.PeirceEngineering.com

 

[Drumchaser]

Have seen quite a bit of 4 sack/reinforced concrete placed on 2:1 slopes. No lagoon, just scour control under bridge slopes. -NON STRUCTURAL-
Always started at the top (1"-2" slump) and placed coming down the slope. I would hate to see folks having to work it from the bottom up. Gravity would not be your friend.

Usually set temp. 1" by 1" headers at grade up and down the slope to screed board (mag.stright edge) off of and control grade.

 

[Ltwine]

Riprap will do the same if not better.

 

[Drumchaser]

This is Rip Rap.

 

[Ltwine]

Reinforced concrete riprap? I think riprap consists of stone only.

 

[Drumchaser]

I beg to differ sir.
Rip Rap can be either stone or concrete. Most of the bridges I have been involved with have been constructed with the 4"-5" concrete with either #3's on 18" c-c or WWF.

I hate the rock Rip Rap.... simply because its really tough and dangerous to walk on.