Concrete problem - Tall wall pour - Honeycomb

[ATSE]

Attached is a photo of honeycomb (“rock pockets”) in a 24 inch thick concrete wall. The wall height is about 30 feet tall. This is one location of several, where the voids extend well into the wall, passed the outer layer of horizontal and vertical reinforcing. Some places the void is more than 6 inches deep. The project is in California.

I have no experience with this kind of consolidation (lack of). Our specifications require SikaTop 123 for relatively shallow (and typical) honeycomb repairs – up to 1.5 inches deep.

Question #1: Do any ACI documents address “extreme” honeycombing?

Question #2: What kind of poor quality would justify the engineer of record to require corrective action (not sure what) and/or non-destructive testing to confirm the wall are “sound”. My concern is voids in the middle of the wall with no surface manifestation.

Question #3: What constitutes gross incompetence in concrete practice? Not a legal question, a practical question. What code do I have on my side to site this?

Question #4: Will a "repaired" location be expected to perform the same as "original" concrete. I realize that's the point, but is this the reality (i.e. bar lap stresses, permeability...)

For the record, we had a pre-construction meeting and warned the rather overconfident contractor of the challenges and risks associated with tall wall pours. And there were 2 special inspectors present for the 8 hour pour.

My intent is to require repair in 1 inch layers with SikaTop123. Anything else?

 

[ron9876]

Is that what it looked like when they removed the forms?

 

[HSIII]

...was the vibrator non-existent?

 

[ToadJones]

looks like they poured too high before vibrating, or didn't shove the vibrator down deep enough into the forms.

 

[HSIII]

In all seriousness, how did this happen? It looks to me like they didn't vibrate it down sufficiently enough (maybe should have used backup vibrators on the forms, rather than just relying on the main vibrator to reach full depth.

You are right in worrying about internal voids.

1. You could try looking in ACI 301. May be a better bet to try CRSI (

http://www.crsi.org).

2. In my opinion, at any point where reinforcing is even partially exposed, a full corrective action plan is required. As far as NDE methods to determine internal voids, you could use GPR to map the concrete in this area to detect for voids. Another option for NDE is to use sonic/ultrasonic pulse velocity methods to get an "estimated" compressive strength. Still, nothing really tells compressive strength quite like removing a core and testing it for compressive strength.

3. Review the special inspector's reports. Was the concrete ever considered "hot" (beyond mixing time). Was there ever an extensive pause between trucks? Did they ever "drag" the concrete with the vibrator? What did the slumps look like? How did the test results compare to the approved mix design? You can try to reference ASTM C94 "Standard Specification for Ready-Mixed Concrete". You could also try ACI 301 and ACI 318.

4. I would think that the patch should try to mimic the in-situ concrete. I know on a project recently that my firm got involved in (honeycombing, although not nearly as severe as yours) the owner's rep and the EOR both wanted adhesion/cohesion pull tests done on the patch material to prove adequate bonding to the original concrete, as well as a series of compressive strengths on cubes of the patch material to prove the patch material exceeded the in-situ concrete strengths.

Hope this helps.

 

[Gumpmaster]

I don't think repairing with SikaTop 123 in 1 inch layers is a good idea.

Call Sika or BASF up and ask them for a recommendation. You want the product to be something they'll stand behind for that particular usage.

The best documents to help in identifying what needs repair and how to repair it will likely come from the International Concrete Repair Institute (ICRI). They probably have something that covers your situation.

Did you specify a super plasticizer? Walls this tall scream for one.

Is this a water holding structure?

 

[HSIII]

Gump,


Thank you so much!!! I knew I forgot one (ICRI), but I was having a slight brain fart.

Sitting there going "ACI...CRSI...um....darn."

Thanks for clearing my cobwebs.

 

[ron9876]

I have never seen this kind of void in a concrete pour. My guess is that there was both no vibration and a problem with the mix (or old concrete). If this is a significant element I would be concerned about internal voids. Don't know if you can sound it with a hammer since it is so thick.

 

[JedClampett]

I'd start doing a search on hydro-demolition. Obviously, the bottom of a wall is critical is terms of shears and moments. If you direct the contractor to patch the holes, you're providing engineering cover to a poor installation. Plus, every once in a while you need to get a contractor's attention and nothing does that better than ripping out work they already have completed.
Using hydrodemolition they can take out the concrete and not damage the reinforcing.

 

[ATSE]

Thanks for the replies.

Toad: You're likely correct. Plenty of vibrators on site - not sure what else to do to make the contractor behave and try a little harder.

ron: Actually, I just sounded a wall with a framing hammer with similar problems 2 months ago with very helpful results. I was able to identify a workers glove left in the wall during the pour, just below the surface. See photo attached. Marginally scientific, but cheap and provides a relative measure.

JedC: Regarding hydro-demo, can you provide a little more info? We require waterblasting at all construction joints, which is typically done with a generic 2,800 psi light commercial pressure washer. This removes laitance + a smidge more. What equipment would be used, and what would be the progression of work? And how do you keep the waterstop from being damaged?

We will not permit the general contractor to repair; a Sika-trained repair professional will be required.

 

[JedClampett]

I'm talking about removing the whole wall using hydrodemolition (

http://rampart-hydro.com/)

which uses pressures up to 40,000 psi. It's a localized process, so you can, if you're careful, stay away from the waterstop. With concrete that is relatively green, it's not real tough.
Then repour it. As I hinted before, I'll bet the next wall doesn't have any rock pockets.

 

[jorton]

Why not make the contractor provide repair plans stamped by an engineer? You can reject them them until you are convinced that they will provide the same capacity of the original design. It seems this would keep the liability where it belongs - on the contractor.

 

[cvg]

agree with jorton, once you direct the contractor on how to make a repair, you take on the liability. reject the wall and ask the contractor to submit his plan to rectify the poor work by either remove and replace or repair. approve his plan when he comes up with a good one...

 

[DWHA]

Go with the hydro-demo repair.

I have seen where they have used a hydro machine to remove a large hole (about 20'x20') in a wall of a nuke power plant to get replacement equipment in. The wall was on the order of 3' think. The hydro machine took the concrete out with out damaging the bars (they had to remove the bars to get the equipment in and then splice on to new bars when the wall was repoured.

I have also seen where they use them to remove the top 3" or so of a concrete bridge deck to remove the wearing surface down to sound concrete and the pour a micro silica overlay on it.

In my opinion it is the best way to actually fix the problem (not just patch it).

 

[DTGT2002]

Assuming you invoked ACI 301, or used it to create your own specs, the execution section of 5.3 directs to vibrate the concrete to acheive consolidation and so on. So calling this concrete out of spec is certainly a start point. Further, the discountinuous concrete is certainly a structural concern as the wall cannot perform as designed.

As such, this is not the typical repair most contractors would commonly repair.

Was a concrete placement plan submitted for the pour?

With a 24" Wide wall, lowering vibrators down to the concrete is certainly possible, but I would have expected to have vibrators staged within the forms prior to placing the concrete. Reading the impressions left by the forms, I would say these forms, like many good products on the market, are no intended for use with form mounted external vibrators, so proper use of immersion vibrators is key.

How many feet of wall were placed at once? 30 ft in height by what width?


Any idea what the planned placement pattern was? Place successive 2' depths of concrete while vibrating no more than 4' into the fresh concrete?


The picture shows bars of different depth being spliced together. How many mats of rebar are in the wall? Does each mat have the same splice condition? Does substantial rebar congestion exist or are embedded items (planned embedded items) in the areas where the honeycomb was found?


Is the concrete mix/aggregate compatible with the rebar size and spacing?



How was the concrete placed into the form?



No fun for anyone (except maybe the repair contractor). I would expect the suspect concrete (that which is not well consolidated) to be removed (scabblers, light chipping hammers, hydro demolition) to provide a workable surface for repair per ACI recommendations (546 and others). With a proper bonding agent, you might be able to pour concrete back to the repair area but pouring methods can be challenged to fill all the way to the top of the repair opening. It might be reasonable to pour 90% of the void, and pack or inject the final space. Or it might be reasonable to "scrub" in a repair mortar in several stages to install the repair.



Are you willing to say what type of structure?

A good repair plan with good materials and good workers should be able to provide a repair that is as serviceable at the adjacent concrete and hopefully even acheive a matching finish.




As far as calling this a patch, I'd reserve patching for surface blemishes and other non-structural cosmetic work.

Daniel

 

[jheidt2543]

Sorry I'm late to this party, but your first photo looks like a formed corner for either a boxout in the wall or a bulkhead?

I don't recall ever pouring a 30' tall wall in one lift, although we did some pretty tall walls. We always used a hopper and an "elephant trunk" to get the concrete down to the bottom of the wall. Dropping concrete more than 4'-5', especially through conjested rebar, can end up looking like what you've got. Also, mix design plays an important part. Your aggregate size looks OK, but it also looks like it could have been a pretty dry mix.