Salt Environment 4

[dik]

I just got a call from an engineer that is doing a project in a salt environment (not marine). Other than providing a great concrete mix and sufficient concrete cover, are there any other issues that should be addressed? Any recommendations about reinforcing steel? placement? type? grade? Concrete sealants? coatings? anything else? Thanks...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SlideRuleEra]

With the steps you are considering (good concrete & cover), "normal" rebar can work, but if higher performance is needed:

Galvanized, epoxy-coated, or stainless steel reinforcing steel, listed in my order of preference when considering most project goals, including cost.

 

[dik]

Thanks, SRE... I'm not big on epoxy coating; many DOTs are getting away from them, too, but HDG and SS are options. Have you used WWM or WWF?

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EdStainless]

I saw a job at a chemical plant recently and they used a duplex SS rebar (not sure which alloy, 2101 I think).
It has good strength and great ductility, and good corrosion resistance.

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P.E. Metallurgy, consulting work welcomed

 

[dik]

Thanks, Ed... against chloride salts? Any idea of the costs? 2x, 3x?

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SlideRuleEra]

dik - No, we didn't use either WWM or WWF.
The biggest concern with salt (or crushed/pulverized coal or coal ash for that matter) is if it gets wet. Then the chances of rebar corrosion really go up.

 

[dik]

Thanks...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

SRE... have you successfully used any type of surface coating/sealer?

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SlideRuleEra]

dik - We used epoxy based coatings on concrete in water treatment areas and in sumps collecting corrosive liquids at our generating stations. On most slabs, abrasion, from coal dust, would compromise a coating fairly quickly... just went with good concrete and rebar cover.

We did not use galvanized rebar, but should have for (utility sized) cooling tower basins.

 

[EdStainless]

dik, the cost impact depends on how rebar-heavy the project is.
I have heard people tell me numbers from 10% to 30% total project cost increase using SS.
Considering that steel is 0.50-0.75/lb and lean duplex SS (2304 or 2101) is going to be 2.50-3.50/lb, the rebar itself is 4-6x.
But all other costs (excavation, prep, laying bar, cement, pour & finish) will be the same.

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

 

[dik]

Thanks SRE and Ed...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TLHS]

Can you field bend the small SS bars? I wouldn't be worried either way, since it's not that big a deal to get everything pre-done these days unless it's weird field fit geometry. Just curious.

I'm curious how salty you're talking. I'm less worried, personally, about coastal stuff using more traditional methods of corrosion resistance. If it's something like a salt storage facility, though, I think you start getting justified pushing harder, because it's immediately obvious to everyone involved that there are further risks.

 

[dik]

Thanks TLHS... Storage containment for 'solid' salt... hopefully dry, several feet/metres 'deep'. I know pure salt (NaCl) does not absorb moisture, but many impurities make it hygroscopic... I don't know what the condition of this salt is. I think it's dry. I don't know the life expectancy of the structure, or the 'ease of repair'.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JStephen]

Does either the owner or salt supplier have any guidelines for construction?
I recall, years ago, quoting some granular salt storage silos for a salt company, and they were aluminum, which is a combination that wouldn't have occurred to me.
I seem to recall seeing fiberglass rebar, is it useful on something like that?

 

[dik]

Thanks JS... the owner does not have the background and is looking to the engineer. I made a couple of suggestions, to the engineer, this AM and was hoping for added info to help him. I don't know if he's a member, but have given him a link to this thread. The containment is concrete, with a structural roof over.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EdStainless]

The austenitic and duplex rebar can be bent and welded in the field if needed.
You do need shield gas for the welding.
I did some work for a salt plant once.
They had a 316SS dry fire sprinkler system.
One day the air leaked enough to trip the pumps on.
The system went from about 10psi air to being filled with 80psi water.
Hundreds of feet of 2sch10 SS pipe split open and flooded the place.
The piles of salt and dust on the tops of the pipes absorbed enough moisture that they were heavy pitted and SCC cracks everywhere.
Lowest temp that I have ever seen CSCC that wasn't a swimming pool.

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

 

[dik]

It seems, Ed, that everyone seems to get the neat projects...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JoelTXCive]

Dik - here's some good generic background info.

https://ftp.txdot.gov/pub/txdot-info/brg/design/corrosion-protection-guide.pdf

I like this chart & discussion in the document...

 

[dik]

Thanks Joel... good publication...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SlideRuleEra]

Q: We have had a request for our recommendations as to the type of concrete to use in a rock salt storage bin. Can you help us?

A.: If kept completely dry, rock salt (sodium chloride) has little effect on concrete other than abrasion. It is likely, however, that at some time during its service life, a rock salt storage bin would become moist from leakage, condensation, or storage of moist salt. If so, some sodium chloride solution would be absorbed by the concrete. Although there is some slight possibility of expansion cracking from this cause, the more serious possible effect is from magnesium chloride, often found in rock salt as an impurity. This may cause cracking, followed by corrosive attack on the reinforcing steel. The best way to prevent trouble is to use concrete of high strength (hence high abrasion resistance) and low absorption. These properties are enhanced by proportioning concrete to have as low a water-cement ratio as practicable. A hard rock aggregate of low absorptivity would be helpful. Ordinary Type I portland cement can be used. At least 2 inches of cover should be provided over the steel. It might also be well to use air-entrained concrete to prevent salt-scaling in case the concrete ever becomes frozen while wet.

From: Concrete Construction Magazine