I was involved with some experimental acoustic emission detection of corrosion within reinforced concrete structures back in 2005. https://www.sciencedirect.com/science/article/abs/... suggests things may have progressed somewhat since then.

A little rust can assist with the bond and is not all that bad. If there is a lot of loose rust, that's different. The rebar inspector should have determined that.

It depends on the environment, mix design, concrete cover, admixtures, and the use of de-icing salts.

Reinforcing can be tested for corrosion.

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

-Dik

These projects are of disasterous type. they mostly started in 2021, when COVID spread. so they stopped and continued works
but as you see some ice and continuous rain (and even bad storage at warehouse of steel rebars).
Just thickening when it will fail ?

@ Dik is there a scintific paper support that ?

we usually apply a sand-blasting for large scale reinforcement and mechanical wire-brushing for small corroded area.

@ LittleWheels
can you elaborate if you have the time ?
techniques ---> assessment ----> cost percentage relative to project cost ?
how long did your corporation took to asses the damages ?

You might take samples and measure for diameter and weight loss.

https://www.concreteconstruction.net/how-to/accept...

thanks @ TugboatEng
is there a deterministic method by ASTM for such tests?

https://www.dwreinforcing.com/blog/is-rust-a-probl....

So, is it real rust or mill-scale?

TTFN (ta ta for now)
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As I said, when I was involved, acoustic emission assessment of reinforcement corrosion of reinforced concrete was experimental only. It involved 'listening' for the sound of concrete cracking from expansive rust (difficult to correlate with effective structural damage) or from detecting the phase change in the absence of concrete cracking (highly experimental). Locations were accurately mapped and magnitudes recorded. The same monitoring technique would detect ongoing cracking caused by changes in loading. Even if the technique has progressed to the extent that you are hoping, I am so far out of date that I cannot provide any useful information now. All of this was within decades-old concrete structures. It looks like you are concerned about reo being exposed for long periods prior to pouring, which is quite a different situation.

As dik says, surface rust can actually improve the bond between rebar and concrete https://www.concrete.org.uk/fingertips-nuggets.asp... as long as rust flaking or severe pitting is avoided. This is because the surface texture is increased (similar to but on a smaller scale than rebar ribs) and the surface area is similarly increased. https://precast.org/blog/bond-reinforcement-bond/

I am a fan of high pressure water blasting to remove easily-dislodged rust and contamination from reinforcement prior to pouring. Hydro-demolition is the ideal concrete removal method as steel is simultaneously thoroughly cleaned but remains undamaged and ready for pouring repair concrete.

@ IRstuff
its accumulated for at least three years and started by some miner corrosions "due to bad storage conditions."
additionally, i could say for sure (from similar CON sites) that the fine aggregate has higher percentage of salts and chlorides, which will be a major concern due to propagating of corrosion from top rebar surface to inside layers
i have junior engineers who reported these pictures to me. so its serious and quite harmful.
still they paid some weak "officials" to bypass its poor construction conditions and went on to finish it as shown in first picture
some where south of ***** regions

@ LittleWheels
thanks my bro, for the useful information. you should be experienced in this field don't you ?
I mean, could you recommend some devices that simulate your experimental approach? or at least knowing someone who followed your research?

Quote (Dik is there a scintific paper support that ?)

Not that I'm aware of... The CRSI used to comment that a light, tight rust was beneficial... from another source.

"Q. All of the foundation specs we build on require rebar to be free of rust and mill scale. For years this hasn’t been an issue, until recently when a project manager called us on it. All we can think to do is wire brush the entire lot of rebar. Is this really necessary?
A.Tim Fisher responds: Fortunately, there are a couple of standards you can cite in your defense. The ASTM standard for deformed steel reinforcement (A706) and the Concrete Reinforcement Steel Institute (CRSI) Manual of Standard Practice both give the same recommendation: Reinforcing bar with rust, mill scale, or a combination of both is satisfactory, provided the minimum dimensions, weight, and height of the deformations (the formed protrusions on the bar) of a hand-wire-brushed test sample are not less than the values specified in the standard. In other words, if the rust or mill scale is light, it will not affect the bond to the concrete. In fact, studies have shown that mill scale and light rust enhance the bond between concrete and steel.

Tim Fisher is the field engineering editor for Aberdeen’s Concrete Construction magazine."

but I don't know what studies...

and another source:

"An experimental investigation on the relationship between corrosion of reinforcement and bond strength in pull-out test specimen has been conducted to establish the allowable limit of rust of reinforcement in the construction field. The reinforcing bars used in this study were rusted before embedded in pull-out test specimen. The first component of this experiment is to make reinforcing bar rust electrically based on Faraday's theory to be 2, 4, 6, 8 and 10% of reinforcing bar weight. For estimation of the amount of rust by weight, Clarke's solution and shot blasting were adopted and compared. Parameters also include 24 and 45 MPa of concrete compressive strengths and diameter of reinforcing bar (16, 19 and 25 mm). Pull-out tests were carried out according to KSF 2441 and ASTM C234 to investigate the effect of the degree of rust on bond strength. It is found from the test results that the test techniques for corrosion of bar used in this study is relatively effective and correct. Results show that up to 2% of rust increases the bond strength regardless of concrete strength and diameter of reinforcing bar like the existing data. It might result from the roughness due to rust. As expected, the bond strength increases as compressive strength of concrete increases and the diameter of bar decreases."

https://link.springer.com/article/10.1007/BF028290...

and

"Reinforcing steel samples of six different sizes, each of three varying compositions, were exposed to the atmosphere for periods up to 16 months. The effect of rusting on the yield strength, ultimate tensile strength, and bond strength was investigated. Results indicate that rusting of reinforcement due to atmospheric exposure for periods up to 16 months does not affect the strength properties. The bond stress values for the rusted reinforcing steels after 16 months of atmospheric exposure were greater than the allowable ACI 318-63 and BS CP 110 values. The maximum weight loss after 16 months of atmospheric exposure was 16 mg/cmý, which corresponded to an average reduction in diameter of 0.53 percent."

https://www.concrete.org/publications/internationa...

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

-Dik

@ALK2415 I was not undertaking the research myself, rather I was commissioning and undertaking investigation of some potentially degraded structures, including some then bleeding edge techniques. https://www.ndt.net/article/jae/papers/26-172.pdf

A quick search suggests that acoustic emission condition assessment of RC bridges has progressed in the last two decades and that at least some codification has occurred.

From the above, can it be said that the effect of rust on the integrity of the concrete structure is minimal to non-existent?

Or should immediate tests and the installation of long-term health monitoring system be conducted to ensure the structural safety of the concrete bridge?
Note:
The aggregate materials used in construction were most likely to contain high levels of salts and sulfates. In other words, because of the initial damage to the galvanized surface layer of the reinforcing steel rebars.
and based on this assumption, will this lead to a further accelerated reaction of the rusting process, thus reducing the designed life of the structure or causing a possible collapse?

I would agree that the effect of non-flaking and minor rust is generally minimal to non-existent. Flaking rust reduces bond and severe pitting can change the behaviour and durability.

Aggregates with excessive sulphates and chlorides can certainly be a durability issue, given high enough levels. A percentage of chlorides will probably be locked up as part of the hydration process but the remainder will be free chlorides and able to disrupt the passivated layer formed on the surface of steel within an alkaline environment like non-carbonated concrete. A disrupted passivated layer will allow rebar corrosion to occur. https://www.concrete.org.uk/fingertips-nuggets.asp...

Excessive sulphates have other effects, on the concrete, rather than directly on the reinforcement. https://www.concrete.org.uk/fingertips-nuggets.asp...

I would start assessing the severity of your problem by finding out about the installed concrete's composition e.g. petrography and lab analysis, assessing the mix design (including any cementitious replacement), etc.

Thank you all for your kind answers.

Don't know why you requested my view on this, but I looked at the pictures and thought what's your problem?

Any rebar left outside will create some surface rust but there's nothing shown here that would give me any cause for serious concern, but I'm not a SE or even a civil engineer.
Construction techniques / concrete quality and finishing will have a much bigger impact on longevity that a speck of rust on a bit of rebar. IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Many thanks for your clear opinion. Iam just not convinced that such corrosion for long period of time (3-4 yrs) will not degrade the rebar strength quality or its yielding strength, of such an important structure. my question is that high levels of salts (beyond the allowable ASTM percentage) will combine with the above state of corrosion and further increase this level of risk.

Concrete ostensibly cures by locking up its water content with cement; therefore, there should neither free water nor free oxygen to cause much further rusting.

TTFN (ta ta for now)
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@ IRstuff
May add some info to widen the picture, did surveyed multiple old RC building (from 20 to 60 yrs), 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.
Nothing "TIGHT" in our CONCRETE BIBLE !!! {time, conditions and some bad luck will prove this hypnosis hypothesis}
Though this kind of malfunctioning practice has been addressed, and certain assessments / procedures were developed by others ?

IRS... in addition to the high passification from the high pH. Over time, the concrete loses this passification from exposure to CO₂

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

-Dik

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

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...

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

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.

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

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.as...

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

Quote (many cracks >0.2-0.3mm can be considered watertight and not really subject to corrosion worse than uncracked concrete)

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

Quote:

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! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

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.

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.

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

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

...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

Can imagine rejecting rebar for being insufficiently rusted then.

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

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.

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

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.

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.

Absolutely true. We do not allow the use of epoxy-coated rebar on our projects due to highly concentrated/ intensive corrosion at coating defects.

...the accelerated corrosion at the damaged area causes more epoxy to fail. Concrete cover or HDG (depending on the cause of corrosion) is usually better.

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

-Dik

Zinc will react with caustic cement like aluminum will.

Yes a little... not anything like aluminum, though... not even close. HDG, along with the passivity provided by the high pH of the concrete, and increased concrete cover is often used for corrosion resistance.

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

-Dik

Chrome rebar Link

Cathodic protection of rebar in concrete seems to be falling into favor. Link
Some approaches install passive anodes, others use active systems with external power supplies. Use of cathodic protection with painted rebar should be possible, but ensuring the electrical connectivity of the rebar and anodes would be a challenge.

https://www.wesavestructures.info/cathodic-protect...

Sacrificial anodes are the preferred option amongst our clients, mostly in ports and harbours. Few want to carry out the regular monitoring and maintenance necessary with impressed current systems, though I was involved with some extensive schemes with a highway authority years ago. Comprehensive cathodic protection of epoxy-coated rebar doesn't seem very easy to achieve/ practical.

As a Developer and VP of a GC I have installed nothing but hot dipped galvanized on exposed areas in coastal construction in South Florida, maintaining coatings goes a long way to prevent costly mediation. I have had subcontractors try to spray paint it with cold once or twice, they never did it more than once.

Most of these things are so simple to prevent it frustrates me, Millenium Tower was different, the GC, Foundation Co, Engineer and Architect should all lose their licenses, they bragged about saving a few million and a month of time, that is just someone that should not have a stamp or a license. At that level everyone should know what the appropriate Geotech work looks like.