Author Topic: Phospmoric acid.  (Read 3016 times)

Offline mattinker

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Phospmoric acid.
« on: November 25, 2019, 10:09:47 AM »
Hi,

Coming out of lurk mode! I am in the process of re-enforcing the steel structure of the building I live and work in. It's an industrial building that is fifty years old, steel frame that wasn't galvanised. I've welded in patches and bolted on re-enforcing plates on the bottom four inches of the pillars. My plan is to cast concrete around the bases as  protection against rust and to fill in the masonry that I had to break out to get access.  I have treated the steel with Phosphoric acid, after as much de-rusting/de-scaling as possible, my problem is, will the concrete react with the Phosphoric acid or should I paint before pouring the concrete?

Your thoughts would be most welcome! Regards, Matthew

Offline awemawson

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Re: Phospmoric acid.
« Reply #1 on: November 25, 2019, 10:57:38 AM »
Well the concrete is very alkaline and (obviously) the acid is very acidic, so they will tend to neutralise each other.

However steel in concrete shouldn't rust if covered  by at least 40 mm - or at least that's the rule for re-inforcing bars in concrete - minimum 40 mm over cover - (to exclude the oxygen).



Andrew Mawson
East Sussex

Offline mattinker

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Re: Phosphoric acid.
« Reply #2 on: November 25, 2019, 01:31:43 PM »
Thanks Andrew,

The rest proofing from burying in concrete was the aim, I suppose I'm a bit belt and braces, as I really don't want it to rust! I will probably paint over the phosphoric acid to separate it from the concrete.

No other suggestions? I'm not very good at Chemistry!

Regards, Matthew

Offline chipenter

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Re: Phospmoric acid.
« Reply #3 on: November 25, 2019, 01:44:19 PM »
Phosphoric acid leaves a hard glittery surface ideal for primer , red oxide will do both seal and stop rust .
Jeff

Offline mattinker

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Re: Phospmoric acid.
« Reply #4 on: November 25, 2019, 02:20:50 PM »
Phosphoric acid leaves a hard glittery surface ideal for primer , red oxide will do both seal and stop rust .

Thanks, I've been using phosphoric acid for a very long time, I've always had very good results with it. My problem is what reaction it might have with concrete. Lead oxide is no longer available here in France as a primer (house painters here used to mix phosphoric acid into metal primer here!).

Regards, Matthew

Offline Will_D

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Re: Phospmoric acid.
« Reply #5 on: November 25, 2019, 06:16:38 PM »
Reinforced concrete uses a twisted steel (rusted) steel bar hat may or may not be high tensile. The rust and the twist improve the tensile strength of the rebar in the concrete.

Steel rusts in conjunction with water and oxygen. Concrete is an oxygen deprived environment so as long as the steel is below a critical depth then it cannot rust any more.

Crtical depth is about 27 to 50 mm or so, see here:

https://www.concreteconstruction.net/how-to/construction/placing-reinforcing-steel_o

HTH Will

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Offline mattinker

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Re: Phospmoric acid.
« Reply #6 on: November 26, 2019, 09:15:52 AM »
Thanks Will.

If this was a rebar problem, that would apply, but, this is the base of a steel "I" beam pillar, so it's more difficult. I have reinforced with welded and bolted plates and I intend to protect the feet with concrete, but, this will only be the first 5or6 inches, so above, there's nothing and a potential damp penetration. I have found out that Phosphoric acid is used as a concrete cleaner/etcher, so I'll need to do something to separate the phosphoric acid from the concrete. I am thinking either of neutralising the acidity or simply painting to  protect the concrete.

Regards, Matthew

Offline awemawson

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Re: Phospmoric acid.
« Reply #7 on: November 26, 2019, 12:36:41 PM »
Matthew I very much doubt that the phosphoric acid, once it has reacted  with the rust and dried out, will adversely affect the concrete to any significant degree.

Andrew Mawson
East Sussex

Offline PekkaNF

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Re: Phospmoric acid.
« Reply #8 on: November 26, 2019, 01:13:26 PM »
This is interesting problem. I am aware remotely only three different structures that might be applicable to this on to a limited degree.

1. In very harsh conditions epoxy coated rebar is used. There are some paints to be used with structures that stick out of concrete. I have heard that there are different types of concrete and some of them (and partly reinfoce materials or expanders or such) can cause incompability problems.  Maybe local shop sells something like this and you can contact someone.
https://www.rustoleum.com/product-catalog/industrial-brands/industrial-choice/spray-paint/rb1600-system-rebar-epoxy-spray-paint

Once I had some problems with a testpiece and one particular one-mix two component epoxy and after a day the chemist on their development department called me and told that he thinks he knows what the problem was and told me how to avoid it.

2: Here in building industry hot galvanized mounts are used when something is attached onto concrete. hardware sores sell J-bolts and pilar brackets that the other end is stuck into concrete and then cast. There is screw that is used to level the pilar bracket.

4: machine building in industrial buildings inside: Long bolts are welded into bottom rebars and stays added. These bolts are covered with elastic material to prevent them from sticking into concrete 8that would be bad for tenssioning (torquing bolt), concrete is cast, then end of the bolt is painted and grouting is cast to level. Then baseplates are leveled and injection epoxy layer is injected between grouting and base plates. Finally bolts are torqued and then concrete will shrink 400 years and after that starts eroding.

* Typos due not using glasses
« Last Edit: November 27, 2019, 03:44:36 AM by PekkaNF »

Offline mattinker

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Re: Phospmoric acid.
« Reply #9 on: November 26, 2019, 03:49:54 PM »
Matthew I very much doubt that the phosphoric acid, once it has reacted  with the rust and dried out, will adversely affect the concrete to any significant degree.
Thanks Andrew
I think your right! I just don't want to take a risk!!

Offline mattinker

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Re: Phospmoric acid.
« Reply #10 on: November 26, 2019, 03:52:24 PM »
This is ineresting problem. I am aware remotely only three different sructures that might be aplicable to this on to a limited degree.

1. In very harsh conditions epoxy coated rebar is used. There are some paints to be used with structures that stick out of concrete. I have heard that there are different types of concrete and some of them (and partly reinfoce materials or expanders or such) can cause incompabilyt probles.  Maybe local shop sells something like this and you can contact someone.
https://www.rustoleum.com/product-catalog/industrial-brands/industrial-choice/spray-paint/rb1600-system-rebar-epoxy-spray-paint

Once I had some problems with a testpiece and one particular one-mix two componenet epoxy and after a day the chemist on their development department called me and told that he thinks he knows what the problem was and told me how to avoid it.

2: Here in building indusry hot galvanized mounts are used when something is attached onto concrete. hardware sores sell J-bolts and pilar brackets that the other end is stuck into concrete and then cast. There is screw that is used to level the pilar bracket.

4: machine building in industrial buildingis inside: Long bolts are welded into bottom rebars and stas added. These bolts are covered with elastic material to prevent them from sticling into concrete 8that would be bad for tensioning (torquing bolt), cocrete is cast, then end of the bolt is painted and grouting is cast to level. Then basepaltes are leveled and injection epoxy layer is injected between grouting and base plates. Finally bolts are torgued and then cocrete will shrink 400 years and after that starts eroding.

Pekka,
This is a fifty year old industrial building that I'm repairing for what I hope is the last time! Thank you for your thoughts!! Regards, Matthew

Offline awemawson

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Re: Phospmoric acid.
« Reply #11 on: November 26, 2019, 04:13:15 PM »
The steel boat repairers having grit blasted and welded up any horrors  spray phosphoric acid on to remove flash rusting then apply epoxy primer. Can you not use something similar as a barrier coat if only to quell your concerns ?


("Project Brupeg", and "SV Seeker" on Youtube are examples)
Andrew Mawson
East Sussex

Offline JerryNotts

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Re: Phospmoric acid.
« Reply #12 on: November 27, 2019, 03:36:03 AM »
When jobs were done by professionals on the basis of many years experience the correct process for steel sections was shotblast totally clean and dry then zinc rich primer. NB Primers of any type always need another coat of paint on top. All allowed to dry thoroughly, 5 days plus. Many structures in the British Isles are still standing over 50 years later.

Jerry

Offline mattinker

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Re: Phospmoric acid.
« Reply #13 on: November 27, 2019, 05:50:08 AM »
Jerry,

Thank you for your comment! This job is in a hole in a wall where nobody could shot blast anything! It is less accessible than the other three pillars that I've done, it is below ground level on the outside, below the floor behind the soil pipe, grey water pipe, gas supply and the water pipe! Curiously, I have been metal working my entire life, most of that professionally! I want to get as much rust protection as possible as I can't get into all of the nooks and crannies!

Regards, Matthew

Offline mattinker

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Re: Phospmoric acid.
« Reply #14 on: November 27, 2019, 07:41:39 AM »
The steel boat repairers having grit blasted and welded up any horrors  spray phosphoric acid on to remove flash rusting then apply epoxy primer. Can you not use something similar as a barrier coat if only to quell your concerns ?


("Project Brupeg", and "SV Seeker" on Youtube are examples)

That's the sort of thing Andrew. The biggest problem for me is rust removal. It's realy hard to get to!