Rebar Corrosion Protection in Paused Construction

[KootK]

I've inherited an RC condominium structure for which the construction proceeded to grade and then was put on hold due to economic issues. There is exposed rebar all over the place at lap splice locations. Is has been exposed for a couple of years to date and may be exposed for a couple more. When construction stopped initially, the contractor "greased" the rebar of their own accord.

What are the appropriate measures to take in such a scenario? Apply some kind of epoxy coating to the rebar? Cast the rebar in low strength concrete to be chipped away later? Can I simply do nothing and have the bars sandblasted clean when construction resumes? I'm uncertain as to how long unprotected rebar can be left exposed before section loss becomes an issue. The environment is not especially corrosive.

Does anyone know of any published recommendations (ACI/CRSI)?

Thanks,

KootK

 

[SlideRuleEra]

KootK - There is a product advertised for protection of exposed rebar; I have not used it and don't know anyone who has. Here is a link to the spec sheet:

http://www.cortecvci.com/Publications/PDS/MCI_Coating_for_Rebar.pdf

My experience with temporary preservation of exposed rebar was for construction of an electric utility generating station. On the first unit we needed to preserve exposed foundation rebar until the next unit would be built - expected to be four years. Turned out that there was a 10 year delay. This exposed rebar had been protected with heavy grease, wrapped in several layers of polyethylene. It was too corroded to use. What did work, and worked well, was method you mentioned. Underground electrical ductbanks that would need extension had the exposed rebar encased in lean concrete. As could be expected, that rebar was in excellent condition when the lean concrete was removed. Overall there does not seem to be much, if any, literature on this subject.

How much corrosion is acceptable is a little easier to answer. According to CRSI, not much - no loss of weight or reduction in height / shape of the rebar's deformations. See the last question on this CRSI FAQ:

http://www.crsi.org/index.cfm/steel/faq

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[kingnero]

couldn't you (epoxy)paint it? Grit blasting afterwards would still be easyer/cheaper than removing lean concrete...
and how comes that rebar with grease, covered in polyethylene was "too corroded to use"? In my (inexperienced) opinion, that does sound like a good solution for this problem? unless vandalism was involved ?

 

[TomDOT]

Polyethylene sheeting and the (random, on-hand) grease are very likely to weather away to ineffectiveness well before 10 years elapses in many climates.

I've found that a single layer of 4 mil poly sheeting tends to last about 6 months outdoors here in Texas before significant embrittlement has set in.

 

[SlideRuleEra]

Kingnero - Perhaps you are right, epoxy paint with blasting later MAY be good... just not much published research in this area.

As TomDOT mentioned, polyethylene sheeting exposed to sunlight (ultraviolet) will literally "flake away" in a short period of time. That happened, but the multiple layers did take a few years to disintegrate. Vandalism was not a problem, the first unit of the generating station went into use immediately and operated essentially 24/7 (it still is, 30 years later ).

The problem with grease was the normal "wear & tear" anything experiences outdoors in a hot, humid, dusty, heavy industrial environment that is bustling with activity.

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[TomDOT]

Epoxy paint works well on structural steel (often pigmented heavily with metallic zinc) and it is routinely blasted off at EOL - should work for exposed rebar as well.

 

[KootK]

Excellent advice. Thanks for you help guys.

 

[TXStructural]

Any method that inhibits corrosion and allows for cleaning late should be fine. Attend to the area where the concrete and air meet, since corrosion can focus there, where water can puddle and corrosion protection is often difficult to apply. Epoxy is tenacious, but it is not resistant to sunlight, so an acrylic or other zinc-rich coating intended to be exposed would be better. Even a conventional rattle can of red oxide primer will probably be better than epoxy for this purpose. Grease works fine for short periods, but will tend to create problems with the concrete as it will migrate into the concrete surfaces.

Placing "temporary" concrete around the bars protects it by excluding air and moisture, but primarily it creates a very alkaline environment which reduces corrosion significantly. If you choose this method and there could be a cold joint where moisture accumulates, consider coating the bars at the interface area where bars exit existing concrete with something like Sika Armatec.

I would not leave it exposed unless the climate is consistently dry.