Concrete pour w/ bad honeycombing

[TehMightyEngineer]

Thankfully not our pour but we were asked to help consult on what the best way to repair is and whether it is even salvageable. The intended use is a foundation wall that extends up 8 feet from grade to support an arching wood structure for a salt/sand storage building.

Pictures: [URL unfurl="true"]http://files.engineering.com/getfile.aspx?folder=d7cae854-16d4-41f3-aa76-d221586db5dd&file=Concrete_Pour.pdf[/url]

Reportedly the inspector wouldn't allow the contractor to add additional water despite the slump being really low. Thus, I would guess that the contractor had to vibrate like crazy just to get each lift to flow around the fairly heavy reinforcement (#7 vert. @ 12" o.c., #4 horizontal at 18" o.c.) and they couldn't get a probe vibrator all the way down to properly mix the stiff concrete for the first lift to the second, causing the lift lines seen in the pictures. Yet, because of the assumed large amount of vibrating it appears that over-consolidation occurred at many places.

We're working on find out how bad the voided depth extends into the concrete but I suspect it's fairly bad. So, my question is do you guys and gals think this is repairable? I'm leaning towards "no", mainly because this is going to be a wall with high flexural loads in direct contact with salt, earth, and weather. I suspect that even with the best attempt at an epoxy cement or a repair grout over the voided areas that it's going to crack pretty heavily at those lift lines and the rebar is going to rust right through after a few years.

Thoughts?

Professional and Structural Engineer (ME, NH)
American Concrete Industries
www.americanconcrete.com

 

[Ron]

I agree you need to find out the extent of the lack of consolidation below the surface. If you have good encapsulation of the rebar, then surface repair might be an option; however, it would be better to remove the areas of poor consolidation back to sound concrete, go behind the rebar and make sure the repair locks in behind the rebar.

This is not a repair for a local slab contractor. This requires some expertise in concrete restoration. Check with the International Concrete Restoration Institute (ICRI)to see if they have any qualified contractors in your area.

Considering the exposure conditions, you might want to put an overlay of shotcrete on the wall after the repairs.

 

[dicksewerrat]

Quake wrap?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[TehMightyEngineer]

So, I performed a site visit and it's a lot better than the pictures made it out to be. The honeycombing is only 1-2" deep at the worst spots and typically only the thickness of the coarse aggregate at the other spots. The aggregate is well bonded and it doesn't appear there is anything wrong with the mix as they've hit their target 7-day strength. I think we really just have to be concerned with the corrosion issues.

I don't think the owner or EOR are going to go for just wrapping this given the corrosive service environment combined with the issues of impacts these walls will receive from the bulldozer drivers.

Having gathered more facts it appears that the concrete was 1.5 to 2+ hours from batch to placement. There was retarder and super in the mix but I suspect when I dive into this more that the long delivery time is going to be the major cause. It appears that the mix was just so stiff that it couldn't flow through the rebar or form ties enough and the course aggregate dammed up the cement and fines at the outer surface of the pour and at each lift.

We're going to core it at a few spots to see what the cross-section tells us and what those cores break at. I think we're going to go the way of a well-packed cementous filler of some sort. The site is remote so we're going to have trouble getting anyone to do any shotcrete, otherwise that would be my first choice. I have the ACI/ICRI Concrete Repair Manual and will be using that as my main reference moving forward. The contractor is bringing in an experienced sub-contractor to do the repairs and I'm relatively confident in his abilities. Accepting the sub is really up to the EOR anyway.

Thanks for the advice folks, any more options or suggestions are much appreciated.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Ron]

TME...you got it!