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.

 

[atrizzy]

Brad, that's exactly the issue. The site either requires flying in new materials, or waiting for an ice road to form, months from now.

 

[dhengr]

Atrizzy:
Was the rebar stored in the mud, or up on blocking and out of the mud? What sizes and lengths? Have them sand blast some of it and measure the dia. and the size and height of the deformations, a good representative sampling. Have them take some photos of the cleaned rebars. Then, talk with the right engineers at ACI and CRSI, and see what advice and ideas they have to offer. I suspect this isn’t the first time they have had that question.

 

[r13]

Just somethings to think about in decision making.

- Rebars is very expensive in some countries, or under developed areas, in which the labors are relatively cheap. Every bar needs to be utilized to its last means.
- This condition is reversed in the North America. Also, it is not rare in using helicopter to transport building materials to minimize headaches on transportation through congest areas, shorten wait time, and on roof works for hi-rise and large scale industrial buildings.

 

[miningman]

Having spent a lot of time at remote fly in minesites perhaps my perspective is relevant. The OP has an opportunity here to use engineering judgement rather than strictly following procedures. What is the normal F of S applied to rebar ??? 4 to 1 perhaps??? By simply giving the owner some recommendations to allow usage of this material he will earn some brownie points with the owner.

I have buried hundreds of tons of scrap steel at minesites....... it has zero value as scrap after shipping costs.

I would be a lot more concerned with what steps the owner intends to take when pouring the concrete in minus 20 or 30 centigrade. What would be the effects of localized failure??? Only the owner can speak to this but I suspect it would be minimal.

Is the mineste in permafrost ??? I suspect yes, and how to effectively deal with this is likely more critical than minor russting.

 

[r13]

miningman,

Just curios, will you allow the use of decade old dynamite, that was left unattended without shield, and possess risk of un-timely setoff (explode too early or too late)? Don't you need a method to support your judgement call? Ignore my question if that would never occur.

ACI does have specification for concreting in cold regions. But I don't know if it covers up to the temperature range as you stated.

 

[RayGon]

Concrete and steel chemical reactions with a bit of rust results in a very good adhesion between the two materials. So a slight surface rust is not a problem. Pitted surface however is a concern only if it deep enough that the chemical reaction does not reach the steel. The rust can further develop if the structure is exposed to water that can reach the reinforcement and promote further corrosion.

In regards to strength, I’ve been involved in rectification a of old buildings that suffered from neglect resulting to spalled RC sections due to corrosion of the reinforcements.

You’d find that if the reinforcement loss is less than 10% the design strength is not too much affected considering that in the design you already used an additional 50% of the Live Load and at least 25% Dead Load. Also a 10% loss of cross-sectional area corresponds to slight to heavy surface rust that can be power brushed off the steel in my experience.

My advise would include to power wire brush all rusted reinforcement to expose steel surface and assess the Cross-section loss of areas. Design the section using bar area 10% reduction (e.g. Bar Area N12=100mm2). However, your client should weigh in the cost of materials with the cost of labour. By providing them an acceptance parameter you put the ball in their court.

You should set the parameter of acceptance to say 10% loss in cross-section. Do your design using 10% less bar area. If there is a chance to have new bars in the project don’t mix them and try to place those cleaned reinforcements to areas that are not too structurally sensitive area - such as secondary reinforcements or the middle-strip of the slab if you really have to use them. Your FEA run would be of help to identify those areas In the structure. YOU MUST DO THE INSPECTION YOURSELF AS THEY ARE ASKING YOU TO TAKE ON A RESPONSIBILITY THAT IS OUTSIDE THE NORM. Usually the steel supplier should take these calls. But we are ENGINEERS we can do such things WE MAKE THINGS HAPPEN!!!!

Or you can take the conservative road and just tell the client that he should send them to be recycled. Nothing wrong with that, but I sense that you want to keep your client with you. He can always go and ask another engineer and he may give them an answer your client want to hear.

 

[r13]

YOU MUST DO THE INSPECTION YOURSELF AS THEY ARE ASKING YOU TO TAKE ON A RESPONSIBILITY THAT IS OUTSIDE THE NORM. Usually the steel supplier should take these calls.

Hitting the head right on. Agreed.

 

[SKJ25POL]

atrizzy (Structural)(OP),
I apologize if you have answered this question, were the rebars stored indoor or outside? and could you please share some pictures?
If we see we can help better.

Thank you