Rebars Sever Corrosion Effects 5

[ALK2415]

What's your opinions on following lack of QC/QA control of major highway bridge ?
can you estimate actual reduction percentage of bearing capacity of these curved box girder ?
Is there a reliable testing method that could investigate the propagated corrosions among rebars ?
Can loading test (actual loaded trucks HS20-44) prevail "corrosion" and its effects on short terms structural performance

 

[dik]

IRS... in addition to the high passification from the high pH. Over time, the concrete loses this passification from exposure to CO[sub]2[/sub]

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[WesternJeb]

Agree with Littleinch, I don't see any issue based off the pictures. Looks like normal, unharmful rebar corrosion to me.

 

[bugbus]

I've seen much rustier reinforcement than this on job sites before. Unless it's beginning to flake, I don't think it's a problem.

The following is a good guide I think:

https://www.sria.com.au/pdfs/tn-1.pdf

A few snapshots from that guide below...

 

[ALK2415]

For bridge engineering, we all aware of stresses fluctuating nature (reversal or cyclic), especially in continuous box girder !!
Like there will be tensile cracks (0.1 to 0.5 mm) in top and bottom face of given above structure.
So, rainwater penetration and weather moisture accumulation (due to temperature variation between exterior and box interior).
These cracks will grow gradually (knowing that most axel wheel loading are increasing every year) until it surpasses the top surface of these rebars. Where they already have severe damages.
Viewing the problem here, in order to get your engineering perspective and correct solutions to prevent such problems in other sites.
Water jet or Sandblasting devices won’t cost a nickel compared to these structures total COST. If you have new techniques (which have less impact on formwork surfaces) ?
I read many research articles form US and CAN they specifically talk about top cover cracking and salts pentation in bridge structures (which led to invention of FRP rebars i think).
The intension here, to learn from you all and not imposing any false or misleading information and would like to here hear for your side the correct judgment.
and i repeat my sincere respect and gratitude to you all

 

[Lomarandil]

The correct judgement is that surface corrosion on the magnitude of Bugbus' figure #1 is not detrimental, even in bridge structures and bridge decks. Only if it compares to Figure 4 should you consider cleaning.

Since the rebar has already been placed, there is no economical silver bullet to remove rust. Anything powerful enough to clean bars will tear right through your forms. So you're either looking to strip and replace the forms (somehow shoring and bracing the rebar cage to allow that to stay in place during cleaning), or taking down the bar for processing at ground level. And if you're going to take down the bar to clean it, you had might as well just scrap the bar and replace it all with new rebar.

Alternatively, take measurements of some representative bar weights to determine section loss to date, extrapolate with section loss projections over time (using dik's data until concrete will be placed, then a reduced rate after that), and evaluate how much rebar section will be left at the end of the bridge service life. Run analysis using reduced bar section properties, and determine whether the section loss over time will be acceptable.

 

[dik]

If not loose rust, then just leave it as it is...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleWheels]

Depending on the code, many cracks ><0.2-0.3mm can be considered watertight and not really subject to corrosion worse than uncracked concrete. Active (short-term live load) cracks are generally less of a durability issue than long-term dead load cracks. When existing cracks are closed, there isn't much of an access path to the reinforcement for chlorides and oxygen.

Carbonation and chloride penetration are the major reasons that concrete cover increases as intended service life increases.

https://www.concrete.org.uk/fingertips-document.asp?id=736

I would remove flaking rust and suchlike by wire brushing and be less concerned about the rest.

 

[dik]

I've never understood that... due to capillary action and the hydrophilic nature of concrete, I'd have never guessed that... but it seems to be common knowledge.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[IRstuff]

what noticed that moisture could easily penetrate through microcracks, either due to excessive stresses, wrong design, bad utilities (drainage), or underground water seepage. that why concern about there structure.

Presumably, that had nothing to do with the rebar itself, so any rusting or corrosion, given cracks in the concrete, would have occurred regardless of how pristine the rebar was originally.

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

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[LittleWheels]

My apologies, typographical error, < not >.

Regardless, rebar corrosion in most cases is predominately driven by access to oxygen. Reo at the base of narrow cracks, particularly saturated narrow cracks, has limited oxygen availability/ diffusion, hence a very limited corrosion rate. It is the same concept as buried or submerged reinforced concrete having a lower corrosion rate than when exposed to atmosphere.

 

[3DDave]

I have seen a few laser cleaning videos of removing rust using hand-held emitters. OSHA would be so happy to see those in use on the job site.

 

[dik]

3DD... as noted... removal of the rust, if it's tight, may not be beneficial...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[3DDave]

dik - as noted, if rust is flaking, it should be removed.

 

[dik]

...laser cleaning only for loose stuff, then. concur

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[3DDave]

Can imagine rejecting rebar for being insufficiently rusted then.

 

[enginesrus]

If the rust was converted it would be a good thing, then paint over the phosphate converted rust, won't rust under the paint.

 

[Enable]

We build things outside in time periods measured in more than milliseconds so of course steel rusts. It has rusted ever since we started using reinforcing steel in concrete. It will continue to rust just as it always has. This is a non-problem.

 

[Lomarandil]

Wait... Y'all are getting construction schedules that aren't measured in seconds?

 

[TigerGuy]

Maybe somebody already asked this, if so apologies. Why didn't they use "green" iron (epoxy coated rebar)? I've never seen a bridge constructed with regular uncoated rebar in climates with winter weather.

 

[Lomarandil]

Epoxy coated bar is falling out of favor in a lot of locales. My understanding is the coating is liable to get nicked during install. That can be patched, but it's time and labor intensive. And if a location goes unpatched, the corrosion is worse than uncoated bar.