Help!! Rusting concrete!!

[DepDavid]

Home build in Buriram was completed last year. There is a one meter wide sidewalk around the perimeter of the house. The concrete was dyed and stamped.

 

It was poured from two trucks, purchased from the same place the other 15 truck loads I have used over the last 5 years have come from.

 

6x6 mesh was used for strength. No vapor barrier.

 

Now I have a lot of surface rust spots and several areas where it appears it is rusting from the inside out and is causing 1cm holes surrounded by much larger rust stains.

 

The first load has no rust spots. The second truck load is where the problem is.

 

We used a lot of terra-cotta tile in other areas and put a shiny sealer on all of it. My builder asked if I wanted the walkway shiny too. I said I prefer the natural look. He never said the cement needed to be sealed and we could use something not shiny.

 

I have looked around the village, no one used sealer and no one has rusted pitting concrete.

 

I contacted the retailer and suggested the problem lies with a bad batch of concrete. The salesman’s first response was that it happens all the time here due to poor quality of sand. They sent out their expert who determined it was a sand issue. He said he contacted my builder who told the sales rep that I refused to have it sealed! Well the builder left before finishing sealing the terra-cotta so I can’t imagine he would have done the sidewalk!!

 

I contacted the owner of the shop who said he is going to contact the supplier of the concrete to come see if he can determine what is causing the issue. He is indeed trying to help.

 

At this same meeting the salesman said the concrete should have been sealed and sealers are used all the time like in the big warehouse stores. Ok so if used all the time you have in stock, right? NO. Ok so if used all the time you can order? Sure let me get the PC and we will pick the best product. 5 minutes of thumbing through catalogs and brochures neither even found the page listing any sealer. Quite obvious they had not sold any as if they had it would be on the shelf or they would know exactly where to look. <deleted>.

 

SO, now, awaiting second expert. Builder drops off bag of the coloring agent said drill out the rust spots fill and use sealer. Wait, why is this now my responsibility to repair??

 

However my biggest issue is if I do as described will that prevent further rust and pitting, or will the sealer trap moisture in the concrete making it worse??

 

I look forward to and appreciate any information that those experienced in these matters may share!

 

 

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[Lacessit]

Rust is like a leak, it never gets better of its own accord. Drilling out the rust spots won't improve matters, unless you can get a corrosion inhibitor in there somehow.

The cause of the rust is most probably excess chloride ( salt ) in the sand or the water used to make the concrete. Normally the high pH of concrete tends to inhibit corrosion; however, too much chloride defeats pH.

The cheap and nasty solution is to drill out the rust spots and pour sodium nitrite solution ( 5% ) into the holes. If you don't have more rust spots after a month, it's worked. IMHO your chances are not good, because the whole load has chloride evenly distributed against the steel, and you would only be tackling what is visible.

The most effective solution is to rip the whole lot up and start over. Or learn to live with rust spots.

Sorry I can't be more positive in my response.

Edit: i suppose you could always ask the builder why inhibitor was not specified in the concrete mix, but you'd probably just get a blank look.

Edited July 6, 2019 by Lacessit

[expatfromwyoming]

Your problem will likely be a combination of iron rich sand and the use of salty water. You can look forward to having to replace it.

[Lacessit]

7 minutes ago, expatfromwyoming said:

Your problem will likely be a combination of iron rich sand and the use of salty water. You can look forward to having to replace it.

Must admit, I didn't think of iron rich sand.

[Puchaiyank]

I wish I had your problems...????

 

Amway...sold a good concrete sealer years ago...I know they are big in Thailand...maybe you can try them...

[DepDavid]

I thank you all for your responses!


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[AndyCherry]

The rust is obviously from the reinforcing. As a corrosion engineer this is a common occurrence. As 'Lacessit said it is a chemical reaction caused by high chlorides either by unwashed sea sand or saline water. Unfortunately there is no cure as concrete is slightly porous and the salts will leech each time it gets wet. This will cause the reinforcing to corrode. I doubt if sealants would have helped. The best sealant would have been a small amount of washing up liquid in with the mix ( an old trick from when I wanted to be a civil engineer light years ago). On major construction a sample of the mix is site tested before pour and rejected of too many chlorides or ph too high. 

So as others have said the only real solution is to rip it up and start again or live with rust spots and eventual cracking and failure as the reinforcing corrodes.

Sorry I can't suggest an easy solution.

P.S currently the new terminal at Cebu Airport Philippines is one of my current projects and as you can imagine the concrete on the plane stands is 1 1/2 to 2 M thick so a real problem if the mix is bad.

[Artisi]

4 hours ago, AndyCherry said:

The rust is obviously from the reinforcing. As a corrosion engineer this is a common occurrence. As 'Lacessit said it is a chemical reaction caused by high chlorides either by unwashed sea sand or saline water. Unfortunately there is no cure as concrete is slightly porous and the salts will leech each time it gets wet. This will cause the reinforcing to corrode. I doubt if sealants would have helped. The best sealant would have been a small amount of washing up liquid in with the mix ( an old trick from when I wanted to be a civil engineer light years ago). On major construction a sample of the mix is site tested before pour and rejected of too many chlorides or ph too high. 

So as others have said the only real solution is to rip it up and start again or live with rust spots and eventual cracking and failure as the reinforcing corrodes.

Sorry I can't suggest an easy solution.

P.S currently the new terminal at Cebu Airport Philippines is one of my current projects and as you can imagine the concrete on the plane stands is 1 1/2 to 2 M thick so a real problem if the mix is bad.

Cebu, but you probably have good control on QA and the supplier/s, not the near enough - good enough - who cares approach of Thailand. 

[Kwasaki]

7 hours ago, DepDavid said:

I thank you all for your responses!

https://theconstructor.org/practical-guide/how-to-control-rebar-corrosion-in-concrete/12148/