spalling of concrete in saltwater ambients
| spalling | concrete | saltwater |
When the rebar starts to rust inside the concrete, the volume of the rust is 3-4 times bigger than the original steel .
What you get is the effect that the expansion of the rebar tears the concrete apart from the inside.
In the early days of concrete construction at sea this was a big concern.
Will floating concrete structures last ?
What can you do to avoid it ?
What kind of life expectancy do concrete structures have in the high seas ?
Today we can say that those data points are in.
There are floating concrete structures with 30 years at sea and no spalling at all.
Even some of the old ww1 and ww2 concrete ships where reported with rebar so clean that you can still read the mill stamp on the rebar.
So if something spalls in saltwater ambient today it is considered that there are grave errors in the concrete mix in first place - it is not a “property of concrete per se” it is rather a “property of idiots at work” spalling happens in concrete construction when the cement is stolen from the building site or unsuitable aggregates are used in first place, or there is not the concrete cover of 3 cm that the norms require. Only these factors give way to “rebar rusting”.
The critical zone is not underwater but the splash zone.
Ok, so what I take from this is that sticking to the proper well-tried and tested mix and procedure is the key, which ensures low permeability and other desirable properties.
However, when talking about a submarine there will certainly be a splash zone due to diving and surfacing, thus air provided for the cathodic reaction. Might this allow rusting to occur eventually even with adequate concrete cover?
The very possibility of this ‘time bomb’ ticking inside the wall and not being able to see it is disturbing. This makes your suggestion of transferring reinforcement somewhere else very intriguing. It makes me wonder if layers of steel mesh embedded in some water-resistant matrix, using superplasticizer perhaps, could double as reinforcement and coating?
answer | over here |