Concrete pour w/ bad honeycombing
Concrete pour w/ bad honeycombing
(OP)
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: http://files.engineering.com/getfile.aspx?folder=d7cae854-16d4-41f3-aa76-d221586db5dd&file=Concrete_Pour.pdf
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?
Pictures: http://files.engineering.com/getfile.aspx?folder=d7cae854-16d4-41f3-aa76-d221586db5dd&file=Concrete_Pour.pdf
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





RE: Concrete pour w/ bad honeycombing
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.
RE: Concrete pour w/ bad honeycombing
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Concrete pour w/ bad honeycombing
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
www.americanconcrete.com
RE: Concrete pour w/ bad honeycombing