Bridge deck underside repairs 1

[OLDSOUL22]

Dear Fellow Engineers,
I work with a construction management company and one of our clients (private) hired us to design-repair structural deficiencies on one of their bridges (private property in an industrial environment). However their budget is coming short this year and they want to band-aid one of the most occurring findings on the bridge (the exposed highly corroded reinforcement rebars on the deck underside and the spalled concrete). My opinion was that this needs to be addressed immediately with full depth repairs procedure from the deck top side. They agree but they want to postpone the full depth repairs for 2 years where they will most likely fully reconstruct the deck and they want to stop the progression of corrosion into the steel rebars for now. (possibly sand blast the rebars and coat it with one or two coats of epoxy or One coat of a water-based barrier/corrosion inhibitor/passive protection system and leave it exposed till they reconstruct the deck).
My concern is that no coating will be able to fully cover the rebars all around and the corrosion rate might increase in the areas that didn't receive any coating.
Does any one here have experience with similar half-ass repairs? I would be interested if anyone ever done something similar.

Thanks in advance!

Sr. Project Engineer
MSc in Civil Engineering

 

[le99]

Do you know the cause for spalling - humidity or exposure to chemicals? Does the concrete in the non-spalling areas been affected? I suggest to perform a thorough investigation then finding solutions based on the results.

 

[Ingenuity]

Consider the use of galvanic (sacrificial) anodes to provide protection around the repair perimeter (reduce incipient-anode (halo) effect) for the non-repaired areas. Check out Vector Corrosion.

I am not affiliated with Vector, but I do specify and use their technology.

 

[HTURKAK]

Apparently, ( the spallings ), the clear cover is not enough and the deck has drainage problems..Moreover, ( the second picture implies) the steel beams also need repair paint...

Suggest you to speak with repair mortar suppliers ( SIKA etc..) and consider C.P.

 

[bridgebuster]

MAMRO - here in the northeast, coating exposed rebars is not an uncommon half-ass repair. The repair in the photo probably doesn't even qualify as a 1/4-ass repair. I agree full-depth repair is the better way but if the owner intends to replace the deck in the near future epoxy coating may buy them some time. However, the concrete - top & bottom surfaces - needs to be carefully inspected. If the remaining concrete sounds OK and if it's only the cover concrete that's gone it's not too bad. If the rebar has lost a bit of section you could weld a splice bar but an overhead V-groove weld is not easy. You could chip the concrete and tie splice bars but you may be doing more harm than good.

If the remaining concrete isn't solid, you run the risk of a blow out. Here in the northeast, freeze-thaw blowouts in late winter /early spring are typical.

A common temporary fix is to put a plate on the roadway surface and some planking or netting below the spall. Galvanic anodes will prevent corrosion but if the concrete isn't sound there's no point to them. If the owner does intend to replace the deck in the near future the anodes may be an unnecessary expense. I attached a drawing and spec for reference.

 

[OLDSOUL22]

le99- The main issue is the owner ignored the regular maintenance and kept doing cold patches every other year to cover pot holes, deck literally dripping water at numerous locations and the expansion joints(finger plates) has no seal what so ever.

Ingenuity- Thanks for the suggestion I'll check them out.

HTURKAK - That's correct, cover is inadequate at some locations and water infiltrate's from the top deck due to the poor condition of the deck/overlay layer, the bridge will be painted among other repairs for the girders/rockers and concrete repairs for the Piers.

bridgebuster- Thanks for the insight! I don't particularly know much about galvanic anodes but I assume the rebar surface would need to be free from corrosion product (sand blasted), both top and bottom concrete cover are in bad shape and in some instances the remaining thickness is deteriorated too.

I am attaching more concerning pics from yesterday inspection.

Sr. Project Engineer
MSc in Civil Engineering

 

[le99]

If the owner asks for two years extension, unless there are other structural defects, for the bottom side, I might consider 1) sandblasting, 2) forming and injecting grout, 3) providing protective falsework below the deck, 4) if possible posting loading limit.

 

[IRstuff]

The big question would seem to me to be whether anything you do will survive at least 4 years with ZERO maintenance and ZERO inspections, since the owner didn't give a hoot about maintenance before and is unlikely to change their ways, I put in 4 years because the owner has likewise shown a propensity to delay the required replacement and is likely to come up with excuses to delay replacements two years hence. Lastly, do you want to take the risk that something will fail in the next two years, regardless of what you do?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

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[bridgebuster]

Nice pictures. The fourth one would be considered a red-flag condition in NY. The fascia bay looks pretty bad; then again, they're usually the worst locations. A thoughts come to mind:

If the owner asks if the deck will last two years, tell them no. Don't take on that liability. Deteriorated bridge decks are tricky. Maybe the owner will get two years more; maybe 10 years more; or maybe one more week. If you're in a cold climate, you have to be aware of freeze-thaw cycles particularly if it's not air-entrained concrete.

Has anyone performed a hands-on inspection of the deck surfaces? Granted, you'll need a manlift to hammer the underside. If that's not an option you could drag a heavy chain on the top surface to locate hollow areas. At least you can correlate the hollows and spalls on the top with the defects on the underside.

What sort of traffic does the bridge carry in terms of the number of vehicles and vehicle weights? If you have frequent, heavy trucks you might want to put out cones or drums to keep them away from the fascia.

Lay in a big supply of roadway plates.

 

[OLDSOUL22]

le99 - They are making us choose between repairing 3 piers (steel girders, bracing, diaphragms and concrete) and a proper deck repair. Otherwise they only have money for some type of coating. We are working on securing more to the project budget.

IRstuff- I 100% agree. Most likely it is just a line to make us do it. I'm not signing anything with my name on it.

bridgebuster- we did drone inspection for the whole bridge, and we are doing hands-on inspections for piers/spans as we progress in repairs. so far we did the most critical deficiencies in the substructure, steel girders and bearings(some of the bearings were completely out of plumb). It is a 45 span bridge though and it sucks money like a vacuum cleaner. It is the only entrance to an industrial location with heavier than normal truck loads. Right now the load rating is reduced to 80ton. I did hammer the underside at some locations and it appears that every spalled area is surrounded by almost equivalent area of hollow concrete. I raised concerns again today to shake the tree and I'm waiting to see what falls.


Sr. Project Engineer
MSc in Civil Engineering

 

[le99]

I do understand that we often need to prioritize repairs in the industry setting. I think the majority of the available funds should be spent on the deck, which contains way too many defects, and could lead to immediate danger. I don't think they can afford the loss of bridge (by shut down) for a prolonged period. They usually have a budget for cosmetic repair, so the top deck is not as urgent as the defective bearing and main girders. Though everything structural is important, something can be corrected/remediated down the road at an "as need" base, some are not. Good luck.

 

[OLDSOUL22]

Hey Guys!
I have been able to convince our client of the necessity of adequate repairs for the deck! Thank you all for the help!
Now we need to thoroughly inspect the 1 Mile 48ft deck, the deck as shown in the pictures exhibit major spalling, concrete delamination and reinforcement corrosion. What would be the best way to perform the inspection (in terms of quality and cost) in your opinion?
I was trying to convince my company owner to invest in a GPR, but since I never worked one it is not easy to convince someone to throw 20k-40k or God know how much a good one costs, without being able to guarantee that I will be able to use it within the inspection time frame.
My other option would be hammering chain drag test the deck throughout, in this case the top of the deck although lengthy would be relatively easy compared to the bottom face of the deck. Man hours would easily exceed the price of a GPR if extensive inspection to be done the old way. What are your thoughts regarding the inspection procedure?
Thanks in Advance!


Sr. Project Engineer
MSc in Civil Engineering

 

[IRstuff]

Seems to me there are lots of commercial companies that provide GPR services that you can rent by the day, and that would, at least, show some plausible results, or not.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[dik]

Reminds me of Champlain Towers in Florida... the structure is in serious need for remediation; if your outfit doesn't have the skills, you should seek out someone specialised in concrete restoration. As everyone notes there are lots of 'stopgap' fixes, but you should be looking at long term and judging from the condition, it will be expensive. First thing to do is to quickly determine the extent of the damage. Then it's a matter of determining the repair... replacement as req'd, cathodic protection, and new coating and concrete.

You might consider reducing the load rating of the bridge in the short term. As noted, don't even imply an expected life for the structure.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Enable]

When I used to work at a testing company we rather frequently used half-cell testing to assess condition of the reinforcing steel from one side only. It's kind of finicky but experienced techs can generally achieve good results. That said, there are many bridge inspection manuals available to guide your testing regime. I would at least give them a quick read. Here are ones for Alberta, and Wisconsin.

These days I would even think drones might be a good option for assessing the underside. BTW i'm not sure about GPR in this context. It'll pickup voids but it won't tell you if that's from corrosion or something else. I've never used it to assess a concrete structure myself. When I previously worked at a firm assessing structures we relied on the half-cell (corrosion extent) + chain-drag (topside delam) + chloride samples (to corroborate half-cell) + visual.

Also, you don't have to inspect the entire deck necessarily. You can perform some sort of random sampling protocol to asses probabilities of deterioration extent and use that to either decide on further testing (if deviation is too large) or fashion an expected count for the area to be repaired (if standard deviation is low). But if you get paid to test the entire surface definitely do it! It'll be better for firming up estimates, and hey, more cash.

 

[dik]

My dealings with Vector have also been extremely good.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Carbonation testing is also very important... just to see what the effects on the concrete have been.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

I wonder what it's been replaced with... it was an invaluable standard.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[EcoGen]

There have been some experimental work done using GPR to identify defects but almost never used in practice because it does not seem to effectively detect locations of concrete delaminations (i.e. actually hollow upon sounding with a hammer). Since you have a huge area to cover and review, it's definitely worth adding chloride content testing, carbonation testing, and petrographic analysis of cores to your materials testing plan for this bridge in addition to the half cell testing proposed above. The petrographic analysis can determine other defects contributing to the damage such as ASR, inadequate air content, and other issues with the cement matrix.

Some of those soffit photos you shared are very concerning to be honest. I don't think the typical chain-dragging from above (then assuming somethings similar is going on below) is sufficient. I think you really need to get in close to a lot of the soffit areas even if it is time consuming and expensive to gan access. I would also pick a number of the worst spots where you have a Contractor fully remove the corrosion from the bottom bars in the short direction using sand blasting or wire brushing. If you have multiple adjacent flexural bars with over 25% section loss at mid span, you probably have a compromised slab structure at those locations. At which point, I think you should raise a lot more red flags with the governing agency.

It appears from the one close up photo that the delaminations continue beyond the bottom mat and the concrete beyond looks weak/crumbly. I would be very careful accepting to do any sort of field exploration less than the stuff I and others have stated above. If you find a lot of structurally compromised portions, the discussion you're having with them shouldn't be "how do we do half ass repairs in the best way now to reduce costs?", it should be "how soon can we do structural repairs to avoid shutting portions of the bridge down next month or next year?".

I'm also assuming that you have a solid background in concrete deterioration and repair. If not, you should definitely have someone come on board that does. Concrete deterioration and investigation is very finicky. I would love to see the day when we can have a laser scanner device that scans the whole thing in half a day and tells us exactly what's wrong with it and where to do repairs in the most optimized way. Until then, when you are designing and consulting on partial repairs/restoration instead of full complete repairs, you are essentially taking on some of the risk of the unrepaired areas. Areas which may be in much worse condition than you know because it may not have been included in your survey sampling of the deck.

 

[dik]

Just a 'heads up'... my experience with GPR is that it is very dependent on the tekkie doing the work.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik