Sand Aggregate Mix

[XR250]

I have a job where a residential foundation wall is pushing in significantly. It is in a room with a formed-in-place porch slab above and a slab-on-grade below. The height of the foundation wall is 6 ft. A driveway is adjacent to this area that they do not want to disturb at this time. The wall is too far gone for soldier beams to be effective IMHO.
The contractor has suggested created a one-sided form on the inside face of the CMU creating a reinforced concrete wall. The rebar would be doweled into the upper and lower slabs. He would core holes in the slab above to fill the wall with a 2" pump. The contractor only has a 2" pump that he uses for slab-jacking and it can only pump sand mix concrete. Is there a mix design that will work for this situation? Is there a reason we cant use ASTMC476 Fine Grout Mix with some shrinkage reducing admixtures or something like that. Shrinkage cracks will be acceptable from an aesthetic standpoint.
I supposes he could also rent a pump that can handle pea gravel but we are trying to keep the costs down.

Thanks!

 

[r13]

While the proposed retrofit is doable, I don't think it can be considered a durable solution, especially sandy or pea mix is competent in compression, but can be not so strong in bending. For a half basement (6' underground), I prefer to work from outside, first to figure out the cause, then find better solutions.

 

[oldestguy]

If you have the time, I'd do some testing of mixes making up test cylinders and breaking after same days curing. With that, you can evaluate the problems of injecting via a small size hose also. As you know (seeing your history) the more water in the mix the more shrinkage later and that may give some question to this procedure. Can you hit the form with vibration to help consolidate the "fluid"?

Any chance of forming only some inches short of full height and pump in normal mix via that opening? Later dry pack the top opening with damp mix.

 

[STrctPono]

With a 2" line, I would expect them to be able to get 3/8" pea gravel in the mix but not much else. I would be hesitant to use only a sand-cement mix. But more importantly, I am trying to understand your problem but can't picture it based on the description. Do you have a quick sketch? How thick is this new wall?

 

[JAE]

I’d see if you might still be able to pump the concrete if it had some 3/8” sized pea gravel added - at least to get some semblance of a coarse aggregate in the mix.

I’d also second oldestguy’s suggestion to pre-verify the compressive strength.

Placing a reinforced wall on the inside could at least stabilize the existing outer wall. It may not succeed in helping to waterproof the space but since you didn’t say that was a problem it may not matter.

 

[JAE]

Ha! You beat me to it!

 

[XR250]

Just talked to a friend of mine who has a Mayco pump with a 2" line. Says his will pump 3/4" rock all day long and does not see this as being a problem as long as we core a hole in the upper slab every 5 ft. to do the filling. He suggested a 4000psi pump mix with superplasticizers. So it seems the contractor can just rent one of those.
Some backstory... This wall is going in an unfinished basement that is never intended to be built-out. The owner just wants to make the house safe for another 10 years or so until it will likely be torn down due to the crazy high lot value.

 

[Ingenuity]

I have used Mayco pump that could not pump any course aggregate - it was a ball-valve type Mayco pump. Where-as a Mayco swing-tube type pump can pump course aggregate.

So good idea for your contractor to check on the pump type and aggregate angularity/roundness to be used.

 

[XR250]

I have used Mayco pump that could not pump any course aggregate - it was a ball-valve type Mayco pump. Where-as a Mayco swing-tube type pump can pump course aggregate.

So good idea for your contractor to check on the pump type and aggregate angularity/roundness to be used.

Thanks for the tip