Using old and corroded reinforcing 1

[atrizzy]

I have a remote client who's asking if they can use some old rebar they have on site for one of my designs. Based on the pictures and tags they sent over, it appears that the rebar has been sitting at their site for nearly a decade. I haven't had a chance to inspect it closely, but as you would expect, the photos appear to show pretty rusty surface conditions.

Any opinions on the use of rebar this old? Assume (conservatively) 10% material loss and increase the As (liberally) by... 20%? Any concerns regarding development and lap lengths due to corroded deformations?

As always, any and all opinions are appreciated.

 

[KootK]

Is there not a way to have some sampling done with respect to section loss? I'd want that. A little bit of rust takes up a ton of space so I suspect that you're fine here and 10% would be plenty conservative. That said, depending on the environment, a lot can happen in a decade. Especially if nobody's been paying any attention.

 

[r13]

Unless for non-structural elements, do not use a decade old rebars. The loss of cross section might not be substantial, but likely uneven from bar to bar, and the locations of weakness are unpredictable. Will the steel supplier re-issue certification for the stock? Likely not.

 

[BridgeSmith]

I read some research recently showing bond was actually slightly better for bars with surface rust.

Section loss is a different matter. Depending on how it's been stored, the section loss could be negligible or substantial. I would want some representative samples wire-brushed to bright metal and measured for remaining diameter.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[robyengIT]

my personal (very personal) opinion :
1 - tell them to clean from rust
2 - cut 5 pieces 1 m long and weight them (all together)
3 - you can calculate the average weight of 1 meter
4 - with weight as per point 3 you can have the cross area of the rebar
5 - assume a safety factor, let's say, 20%

 

[r13]

Since the prevalent sentiment is sampling the bars, I think it is prudent at least to talk to a steel supplier, or testing lab, to come up an extent (%) of sampling in order to re-classify the stock. From that point, you should be more comfortable and confident in making the decision, as to what extent the reduction should be, or none.

BridgeSmith is correct, slight rusty rebars perform better in bonding with concrete, a knowledge based on test results.

 

[atrizzy]

Great ideas folks, I think I'll propose some type of material cleaning/testing plan in order to justify using this material and allow the client to decide if the benefit is worth the cost involved with sourcing new rebar.

Thanks again.

 

[canwesteng]

I'd only be concerned if you lost deformations to rust and as a result concrete bond. If you had actually lost 10% of the section the rust would look so bad the client would have just thrown them out, but if you have lost 10% I can't see any way you can use these as surely the deformations are long gone. I've seen bar rust (real rust not mill scale), and they become round or square-ish before they corrode away to nothing.

 

[atrizzy]

Very good point canwesteng, if the corrosion is such that the deformations are effectively lost, the material will not be accepted.

 

[Tomfh]

It’s not rocket science.

clean the rust and measure the bars.

 

[atrizzy]

Thanks Tomfh, that's helpful.

Unless of course I'm compelled to consider the presence of statistical variation, heavy localized corrosion, anchorage reduction due to deterioration of the deformations, etc.

 

[Tomfh]

Measure the narrowest sections, apply additional reduction factor if you’re still worried.

Increase lap lengths (double Normal length) if you feel the deformations are too small.

 

[oldestguy]

If you really have to use them, why not two or three where one would do?

 

[r13]

If the bars were kept in a warehouse, the problems should be minimal. But if left at ambience, anything can happen, especially in a industry setting, where accumulation of dirt, spill/dumping of oil/grease, attacking by corrosive air, are common. The efforts required to clean up the bars to return to usable state, could be substantial. By the way, how many bars are in question? A few bars, or a few tons?

If congestion is not a problem, oldesguy's suggestion maybe applicable to an extent.

 

[SlideRuleEra]

Rebar size is not stated (it makes a difference) and it takes very little reduction in rebar radius to result in 20% material loss.
I ran the calcs on two rebar sizes,#4 and #8, assuming uniform reduction in radius:

#4 with 20% material loss: Radius reduction of 0.024" ( 0.6 mm )

#8 with 20% material loss: Radius reduction of 0.052" ( 1.3 mm )

From the rebar description I expect a lot more steel has been compromised by rust than 20%... and what has been lost is the most important part, the deformations, as noted by canwesteng.

http://www.SlideRuleEra.net

 

[r13]

Other than a few bars, consider economy and owner/installer's mentality, I really doubt the inspection and cleaning can be done comprehensively and thoroughly. I'll offer any statement only after assessed myself on site.

 

[Brad805]

What do they want to use the rebar for? If something critical, I would be inclined to say no just because. If for something like a slab on grade, then I might be more inclined to talk about this. Unless we are talking about a large tonnage of materials, I doubt re-use of the materials will be cost effective if they need to clean and test each piece. They can re-sell for scrap and buy new.

 

[Agent666]

A word of warning, any localised pitting would be like accepting someone taking to your new reinforcement with a grinder to take out a little nick and saying it was OK, are you fine with that?

The point is if there is localised pitting then you're also affecting the ductility you'll get out of the bar. You'll concentrate any inelastic strain at the localised loss of area. At your ultimate capacity of a member if you look at the bar strains they could be 20 times the yield strain.

I'd say no, too many unknowns.

 

[Tomfh]

Unless we are talking about a large tonnage of materials, I doubt re-use of the materials will be cost effective if they need to clean and test each piece

Beats getting rid if it and buying new steel.

A watering can full of acid would clean it up quick. Then inspect it and measure the narrowest point with a set of calipers.

 

[Brad805]

Tom, I am not suggesting it would be difficult to clean and if it were my personal project I would think about it. That said, there is a cost for the owner/contractor and a cost for the EOR to do this measuring and undoubtedly write some sort of report justifying the decision. If the site is so remote one needs to fly in materials, that would change things. If not, it could easily turn into an exercise to save pennies. Getting rid of scrap steel is not difficult either.