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

 

[dik]

What drone were you using, if you know?

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

-Dik

 

[bridgebuster]

I disagree. GPR is used regularly to investigate defects in bridge decks. Infrared thermography is another method. In the late 80's I was resident engineer for a mile long structure on I-95 in New Have CT. During design the deck was inspected with IR. The defect map in our plans was >90% accurate.

MAMRO - don't try doing GPR yourself; it's specialized work. In addition to the scan, the data has to be processed - this is one of the drawbacks because the analysis is time-consuming. A mile long structure might take two days to scan the top but upwards of two months for data processing. It's also good to take some cores during the scanning to make sure things are properly calibrated. In late 2019, we looked into GPR & IR inspection of about 175,000 SF of bridge deck; the price was $0.45/sf, which included travel time for the crew, scanning, report etc. Coring was a separate cost. However, the DOT put the project on hold. If you're interested, I can give you the contact information for the company we used. Coincidentally, it's the same guy who scanned the bridge I worked on in the 80's.

Personally, if the photos are a typical representation of conditions, replace the entire deck. I sense it's not possible with your client. Although if you're repairing 40 to 50% of the deck, replacement is a viable option. Earlier, you mentioned that the underside of the deck was being inspected & sounded. You may not need to do GPR/IR. You could supplement that work with limited chain-dragging and coring; focus more time on the areas that don't appear to be distressed.

 

[dik]

That was the reason for the 'heads up'. His experience may have been based on poor tekkie skills and not the methodology. I've not used IR; you've found it to be very effective? Have you encountered any issues with it?

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

-Dik

 

[Compositepro]

One option you can consider is epoxy coating the degraded bars and concrete, spray applied polymer concrete (epoxy/aggregate) to replace spalled concrete, and carbon fiber/epoxy sheets.

 

[dik]

I can just see the letter:

Enclosed please find documents for the partial remediation of your bridge. We would, however, like to inform you that the remediations undertaken, may not improve the general safety of said structure.

YVT
Engineer...

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

-Dik

 

[dik]

Compositepro... someone earlier mentioned the 'corona effect'... painting and patching may not be a panacea...

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

-Dik

 

[EcoGen]

bridgebuster:
It's interesting that you used to use infrared for surveys back in the 80's despite the fact that since then the technology doesn't seem to have improved much. Or at least the cost of NDT methods of surveying don't seem to have reduced far enough for it to be used through out the US's infrastructure which is a shame.

GPR is used regularly to investigate defects in bridge decks.

I'm sure GPR is useful for investigations but not sure how useful it would be for detecting delaminations and internal cracking specifically. Most of the more recent studies I've read on specifically GPR scanning to detect delaminations had much lower accuracy than 90% when compared to chain-dragging and sounding by hand.

Infrared thermography is another method. In the late 80's I was resident engineer for a mile long structure on I-95 in New Have CT. During design the deck was inspected with IR. The defect map in our plans was >90% accurate.

Now IR is a different story and I do think has higher accuracy than GPR specifically for detecting delaminations. Still not sure if it is often as high as 90% when compared to manual sounding. I'm still curious about a few things about your surveying work in the 80's.
[ol 1]
[li]Did you have to wait till sunrise or sunset for when the bridge deck is cooling or heating to do the IR?[/li]
[li]How did you derive the 90% accuracy? Did you also chain-drag and sound the entire top surface or at least some parts of it to compare?[/li]
[li]Were you able to complete the IR survey without shutting down any lanes?[/li]
[li]Was the IR sensor mounted on a vehicle or moved around manually by hand?[/li]
[/ol]

 

[dik]

EcoGen... GPR is great if used properly... and it sometimes takes a little practice to read the output, too... but, great, nonetheless.

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

-Dik

 

[dik]

What sort of sensitivity in IR imaging is needed. There are IR imaging attachments for Smartphones... would they be sensitive enough for a 'quick peek'?

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

-Dik

 

[bridgebuster]

1. Did you have to wait till sunrise or sunset for when the bridge deck is cooling or heating to do the IR? - IR needs sunlight to heat up the deck.
How did you derive the 90% accuracy? We had to prepare as-built drawings. Did you also chain-drag and sound the entire top surface or at least some parts of it to compare? Each night when the contractor went out the inspectors would chain drag the deck and mark out the repairs.
Were you able to complete the IR survey without shutting down any lanes? I wasn't involved with the design; that's when the IR survey was done. One of the designers told me the van drove slowly with a crash truck behind it. Today, the van can travel at 55 mph without a shadow vehicle.
Was the IR sensor mounted on a vehicle or moved around manually by hand?the scanner was mounted to the van

I'll look through my notes for additional info about both methods. Unfortunately, I have to get to work right now.