Reinforced concrete poured under salt water 1

[Settingsun]

Has anyone got data or literature on corrosion of steel reinforcement in concrete poured underwater? The reinforcement is submerged and then concrete poured by tremie. The concrete displaces the water yo give a solid block but presumably some chloride contamination remains on the steel.

If possible, comparison of bare steel to galvanised reinforcement, and whether any concrete admixtures are effective at preventing corrosion.

 

[blacksmith37]

That will result in a significant corrosion with steel . Stainless rebar would be an alternative; although it may have some pitting caused by chlorides. Galvanized and polymer coated steel would have limited corrosion resistance ; They could be of use for a limited planned life.

 

[dik]

With a proper tremie job, there should be little issue... add more concrete cover to the rebar... maybe 6" or 8". I haven't looked into it, but HDG rebar should provide years of service. There may be admixtures the reduce the permeability.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

Ron... you should jump in... it's one of your areas of expertise.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[SSCon]

There's a lot of experience with concrete structures in the North Sea but I've never heard of one being poured subsea. Corrosion of rebar is prevented through the use of cathodic protection - DNVGL-RP-B401 - and having long lifespans subsea bas been shown to be easy to achieve.

I don't imagine corrosion for a subsea-poured structure will be much more of a concern as what oxygen is trapped will be used up fairly quickly.

 

[dik]

SSC... active or passive CP?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

link, from SSC:

https://www.engr.mun.ca/~sbruneau/teaching/8751ocean/DNV cathode design.pdf

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[SSCon]

In CP active is the anode and passive is the cathode. It can be done electrically or with a sacrificial anodes (aluminium or Zinc).

It's done with sacrificial anodes subsea. There's a ton of literature on this if you search google scholar.

The DNV doc' is the industry standard for CP design subsea and I don't think the fact that the structure is poured subsea is going to make that much of a difference.

 

[dik]

BPS is for the other post, too...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[EdStainless]

When poured underwater the initial anode consumption will be higher, but then it will taper off.
Though the presence of Cl might also increase the currents (higher conductivity).
Probably should add excess anode material for adequate CP life. I have seen ZnAl alloys used also.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[dik]

I messed up a bit... with my initial reply, I completely forgot about CP... the most reasonable approach.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

The Florida DOT has done several studies on this. The bridges in the Florida Keys have had issues with corrosion. Limiting the initial chloride content of the concrete helps.

Passive systems for CP are usually better for remote applications. Impressed current systems require maintenance, which can easily be neglected.

Agree with dik....make the concrete dense and increase the cover.

 

[Settingsun]

Hi Ron, has the Florida DOT published these studies? I didn't find much from a web search.

 

[horacio Torres]

The following paper could help you, is in spanish

https://produccioncientificaluz.org/index.php/tecnica/article/view/4569/4564

Horacio

 

[FacEngrPE]

This document is not specific to cathodic protection of rebar, but it contains most of the information necessary for roughing out a preliminary design. UFC 3-570-01 Cathodic Protection

The attachment from NY DOT is more specific to rebar in bridges. The vendors of the vendors of these systems are usually helpful with concepts, and often provide the installation engineering with the product.