Early on-set of chloride corrosion in precast units
Early on-set of chloride corrosion in precast units
(OP)
Hello guys.
These slabs they are externally exposed in a soffit of a loading dock in a chopping centre, around 3km (approx 2 miles) from the Indian Ocean.
They have been in place since approx 2004 (8 Years).
Several, but not all of the units exhibit similar staining. It runs in line with direction of rebar. However no spalling is noted.
I have only visually inspected from ground level 5m (16ft)
Have a look at the image - I have a felling the rust staining is a sign of the beginning of chloride corrosion of rebar, however there is no rust staining.
These slabs they are externally exposed in a soffit of a loading dock in a chopping centre, around 3km (approx 2 miles) from the Indian Ocean.
They have been in place since approx 2004 (8 Years).
Several, but not all of the units exhibit similar staining. It runs in line with direction of rebar. However no spalling is noted.
I have only visually inspected from ground level 5m (16ft)
Have a look at the image - I have a felling the rust staining is a sign of the beginning of chloride corrosion of rebar, however there is no rust staining.






RE: Early on-set of chloride corrosion in precast units
RE: Early on-set of chloride corrosion in precast units
Dik
RE: Early on-set of chloride corrosion in precast units
RE: Early on-set of chloride corrosion in precast units
It's most strange that, given the location and proximity to the ocean, all external concrete was not specified with some kind of coating. I remember once reading, or hearing in a lecture, about different types of sealant to reduce porosity/permeability of concrete.
Am i correct in saying that whilst it will not eliminate corrosion, applying a sealant will reduce transport of water - and chloride ions dissolved within - to the rebar?
Do you have any suggestions as to what an appropriate sealant may be (either chemical class or a proprietary/trade name).
Many Thanks for all your help guys
RE: Early on-set of chloride corrosion in precast units
i need more investigation than a photo from 5m's away. I would check the cover to the steel before starting with any works, maybe even expose a bar? I have viewed similar staining on freshly pour concrete when the form work has reflected some rust from rebar left in the rain. Not suggesting this is the cause in this case, just suggesting that I would want more information.
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RE: Early on-set of chloride corrosion in precast units
Unfortunately the survey we have been commissioned to undertake allows for only walk-through and overview style reporting for this centre to prepare a technical due diligence report for an investment company.
I will simply suggest further investigation is necessary with a cover-meter or electrical resistivity meter to determine cover to rebar.
A profile of the transport characteristics [sorptivity, absorption, permeability, ion transport] to determine the quality of that covering concrete would also be useful.
Im thinking of suggesting the use of Autoclam/Permit (Amphora Non Destructive Testing) or the Germann Apparatus.
I know these are available and used in UK/Ireland - and have inclusion in British/Euro standards. I am currently in Australia.
Does anyone know of any similar apparatus used in USA that they may be more familiar with here in Australia/NZ?