Hydrogen sulfide corrosion of concrete

[jojolli]

My firm was recently hired to inspect a sewage diversion structure that had been deteriorated due to exposure to hydrogen sulfide. We inspected the tank and found that about 1" to 2" of concrete could be easily removed and underneath we found a white pasty substance. This seems to be consistant with the research I have done on hydrogen sulfide corrosion. The tank is structurally okay, however I am also trying to find an acceptable method of patching and possibly adding a coating to the concrete. I am thinking of including a silica fume admixture to the patch. I also ran across a product called ConShield and I was curious if anyone had any experience with this. I have found many coatings that seem to be effective with hydrogen sulfide. I guess I am just asking for some advice on the matter from someone with more experience.

Thanks in advance,

Josh Jolliff, E.I.

 

[hacksaw]

You might try NACE. There are a lot of queries about sulfide corrosion, though not specifically regarding concrete.

 

[ischgl99]

Corrosion of concrete in wastewater treatment systems is very common. Sulfide reducing bacteria transform the hydrogen sulfide gas into sulfuric acid, which corrodes the concrete forming gypsum as you have seen.
I have not heard of anyone using Conshield, so I can't comment on how effective it is. There are a couple of other ways of dealing with it, one is to reduce the H2S in the system and the other is crown spraying. Magnesium hydroxide and caustic soda are used to reduce the H2S in the system, which prevents the sulfuric acid from being produced and magnesium hydroxide based crown spraying coatings are used to neutralize the acid that is formed. LA county has been using this on their piping systems, this article mentions a number of places and what they do

http://www.epa.gov/owm/mtb/sewcl.pdf

Mike Bensema

http://www.dutchmenservices.com

 

[BobPE]

mbensema is correct on the poin that you should eliminate the potential to form H2S. I am assuming that your tankage at the WWTP has a lot of force mains entering the influent stream. What is the tankage used for? Is there aeration in the tankage?

If you have had 2 inches of concrete damage, you must assume structural damage. Even if your calcs say that the structure will hold, the 2 inches missing was there for a specific structural reason which was to protect the rebar. The concrete is probqably to badly damaged to use a coating system since it would be too risky to put you PE on a repair that may fail in a few months and not be seen for several years until inspected agian, usually when the tank fails, and it is usually inspected by engineers like me that will look at your repair and attempt to assign blame in your direction.

Raise a big flag now to the client. I dont know much about your situation, but a major repair sounds necessary. Definately, restrictions on tank derainage should be considered. My blind idea of a repair may include a chemical resistive shotcrete system since the damage sounds significant over the entire tank wetted surface.

BobPE