Defects in a concrete Column 2

[clarke1973]

Hello all, hoping someone can provide some advice with an issue I have.
The contractor cast the column in question, removed the formwork after only 8 hours and in a couple of areas there is some severe honeycombing - reinforcement exposed and voids through the section (see attached pics).
My first reaction was that it should be demolished and start again, as even if those areas could be repaired i'm worried about the rest of the column as clearly they have not compacted the concrete properly.
The contractor is naturally resisting and wants to repair the affected areas and do tests to verify the integrity of the section, which the client is siding with. Ultimately it is my call so I want to be sure my conviction is justified.

Assuming the voids can be repaired with a high strength grout, what tests should be carried out on the remaining areas:

- NDT's to check for voids
- Compressive strength on a core sample
- Permeability test for durability?

Any others? Does anyone have any thoughts, experienced this before?

Thanks

 

[clarke1973]

Another pic...

 

[TehMightyEngineer]

Very similar to a job I just did on a foundation wall with bad honeycoming and unbonded lift-lines. Even repairing with a high-strength topping material like SikaTop 123 PLUS you're going to likely have a lot of voids left in the interior of the column below the honeycombing. When we took cores of our wall we found that the compressive strength was about 60 to 80% of the cylinders cast during the wall pour (this was usually due to internal voids in the concrete). In addition there were significant voids present around the bars where cement failed to fill in the gaps left by coarse aggregate up against the bars. These gaps are likely present in your column and will give you increased development lengths.

That second picture is very scary and I suspect that being able to fill that successfully will be next to impossible without a lot of careful work to ensure the repair concrete was well bonded and filled that space fully. Probably building up a small form and injecting a repair mortar under pressure and watching some witness holes to see if it filled the space fully.

I don't see you getting much comparable info from the cores as I don't see how you can get a big enough core to test and not have it also core through rebar. In these cases of voided concrete a Schmidt hammer is even more useless than normal so I doubt you can get a NDT test of the actual compressive strength.

We did a permeability test on our concrete and found it to be susceptible to corrosion, though it was green concrete so we took it with a grain of salt. Overall I suspect you'll have corrosion issues if this column is in an environment conducive to corrosion.

Overall I suspect you'll come to the conclusion we did that this should be demolished and rebuilt. In my case I had a special circumstance (getting concrete to the site was very expensive) and we had a very large amount of concrete that was still good so it was cheaper and easier to prove that the wall worked with the defects and provide a waterproofing membrane and other protection of the concrete. As you have a much smaller amount of concrete I suspect you'll find that demolishing is the way to go.

I'd go with them for a bit and take some cores of the concrete and see if you can get a rough idea of how the concrete looks on the inside and around the bars. After these come back you'll at least have some info to backup your suspicions and get them to rip it out.

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

http://www.americanconcrete.com

 

[JAE]

Agree with TME. Some other thoughts:
1. The cost of injecting grout, witness holes, delay in the project will be higher than removal/replacement. Your challenge will be to convince the contractor that it would be cheaper to remove/replace.
2. Columns are typically non-redundant elements. No wiggle room to allow a diminished capacity.
3. NDT's, compressive strength, etc. would most likely only prove what you already know in your heart.
4. Not sure how you'd get cores into that column with the size/spacing of the reinforcement shown.



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[TehMightyEngineer]

Here's my post on eng-tips about my wall project: [URL unfurl="true"]http://www.eng-tips.com/viewthread.cfm?qid=395068[/url]. The pictures look very similar to yours.

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

http://www.americanconcrete.com

 

[MrHershey]

Would doubt the honeycombing has anything to do with removing forms at 8 hours. That's shorter than the recommended removal time in ACI 347, but concrete should have long since ceased to be plastic by then. Leaving the forms on for four more hours isn't filling those holes. This looks like it was doomed from the start.

I hear you with the contractor wanting to fix it and client pushing for the same. I get that all the time. I tend to be one who will bend over backwards trying to help contractors fix stuff, but this is an easy teardown to me and would think contractor would think so too once you explain to them the general steps of what they'd need to do. If this were my job, I'd be wasting a lot of their time coming up with testing and repairs that I'm comfortable with. Then there's wasted time actually doing the testing and repairs. And there's no guarantee that your testing is going to come out like you like and the repairs are going to turn out well. It's entirely possible (perhaps even likely, given the photos) they go through with all of that and *still* have to tear it down and do it again. Meanwhile, they could have this column chipped out tomorrow and formed up and poured the day after if they really wanted to. Given the 'looseness' of the material in the pictures, it should be a relatively easy chip job. They'd have to pay for concrete and labor again but it's not like you're not going to have to pay either of those for the repair, plus whatever outlandish fee the overbooked testing agencies are charging currently and waiting for said overbooked testing agencies to get back to you on the results.

Once you convince them to tear it down, there's some coaching to do so you're not doing this again in a week. When they pour back they need to do a lot better on the vibrator. Get it all the way down into the form, try and hit the bottom. Wouldn't be a bad idea to bang the forms with rubber mallets especially near the bottom where it's tough to get the vibrator through. Get some super P in the mix if you don't have it already, perhaps even go self-consolidating if the forms can handle it (and if you do this, stop vibrating so you don't swing your issue too far in the other direction). If concrete has to travel a long way from truck to form, figure out if there's a way to get that down. Doublecheck max aggregate size. Can't tell from pictures but if this is a super high pour maybe consider doing it in multiple lifts like a CMU wall given the amount of reinforcing present.

 

[hokie66]

This is ridiculous. Reject the column, and if the contractor can't do a better job of compaction than that, reject him. Why mollycoddle an incompetent contractor?

 

[Ron]

Just crappy concrete work. Agree with hokie66. You are the engineer of record. Reject it or you'll be pushed into accepting their substandard construction for the rest of the job. Get their attention.

 

[clarke1973]

Thank you for all the replies, some good advice there.

 

[JedClampett]

Something I found out from another contractor mistake. A contractor can Hydro-Demolish concrete and leave the reinforcing intact. The newer the concrete, the easier it is. Basically, I don't know all the details, but they get very high pressure spray, and wear away the concrete. Apparently the reinforcing stays.
They might have to hire a sub to do this, but it has to make the pill a little easier to swallow.