Potential corrosion of the steel rebars within retaining wall 4

[dan00]

Is there any way to estimate the effective life span of steel reinforcement in a wet environment?
Here is the problem:
The rebars are grouted and located approx 3" or less from the face of the wall.
Where the seepage through retaining wall is occurring, the seepage is through hairline cracks and through grout between blocks. The worst case scenario is to assume that the rebars are in constantly wet condition.
Soil samples of on-site soils adjacent to the wall indicate:
- pH of 8.01
- soluble sulfate content range of 210 to 270 ppm
- chloride content range of 1029 to 1437 ppm
- minimum electrical resistivity range of 4452 to 5936 ohm-cm.
Thanks a lot

 

[stanweld]

I can only state that in a similar instance, concrete spallation was noted in less than 18 mos.

 

[EdStainless]

You need to have some corrosion potential measurements made.
My hunch is that you have a serious issue.
Top coating and sealing may be your only options.

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Rust never sleeps
Neither should your protection

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[kenvlach]

Is the block wall fully grouted, or just where the rebar is?

I suggest adding Zn anode rods against both sides of the wall (& within the wall if not fully grouted), wired to the rebar. From plots of corrosion vs. time where cathodic protection was retrofitted to already-corroding well casings, in Practical Handbook of Corrosion Control in Soils, CASTI (2000), this may add 2 years to the life of the steel.

 

[unclesyd]

You may want to look at the thermal spraying of zinc on concrete for anodic protection of the steel. I don't have any experience with the process but saw it being done not long ago.

http://www.corrosionsource.com/events/intercorr/techsess/papers/session4/abstracts/bullard.htm

http://www.matscieng.sunysb.edu/tsl/infra/sum-pap1.html

 

[EdStainless]

Good point Syd. The older method would be to use a Zn mesh to cover the surface of the wall. This would then be topped with a sealer.
As an alternate to these sacrifical systems you could look inot having an impressed current system installed.
Either way you need to have a system in place to measure the corrosion currents so that you can check on the condition.

As long as the pH stays high you woun't have much damage. Back in the crevices the pH will begin to drop and pretty soon the wall will be bleading rust and the surface will start to spall as corrosion swells the bars.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[kenvlach]

A lot depends upon the history of the wall & how much damage, visible & hidden has occurred.
If the wall is too wet for flame spraying zinc, maybe can pressure grout with a cement-lime slurry -- gives some sealing to allow subsequent spraying & raises the pH. Ideal pH for steel is 11.9.

But, the best solution may be to tear down the wall, install better drainage, then build a proper one with coated steel and anodes and well sealed on the soil side.

 

[epoxybot]

I'm not sure but if the rebar are grouted in epoxy the problem might be exascerbated. In the old days we use to promote the benefit of epoxy injection as a corrosion encapsulant. Now we know that it either projects the problem elsewhere or magnifies the problem where corrosion was less active. Epoxies make very good electrical insulation so that portion of the bar may be dead to the corrosion potential.

Any comments on this are definetly welcome. Think of it like epoxy coated rebar with big chips in the coating.

I think Electrochemical chloride extraction and Re-alkalization are more aggressive approaches to remedial corrosion work. Cathodic protection is more for sustained prevention and long term durability.