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Rebars Sever Corrosion Effects 5

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ALK2415

ALK2415

Structural
Sep 15, 2014
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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

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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
 
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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.

 
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@ 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 ?
 
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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 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.
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.
 
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@ 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
 
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@ 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?
 
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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."


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."


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

-Dik
 
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@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.
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.
 
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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?
 
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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.
Excessive sulphates have other effects, on the concrete, rather than directly on the reinforcement.
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.
 
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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.
 
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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.
 
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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 ?
 
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