Wastewater treatment tank structural concrete issues 3

[EvanPE]

I'm a PE in a consulting firm brought in on a structural issue at a wastewater treatment facility. After Googling I determined both this site and were sites that could potentially answer my questions. I noticed there are many common usernames between both sites. Are these the same sites, or is one better than the other?

I'm looking for solid pointers from seasoned structural engineers - preferably ones with concrete experience.

Thanks for your input.

Two issues:
1. We have a coating on the inside of the structure that appears to be failing. We believe the coating to be asphaltic.
2. Underneath the coating that has failed, we've noticed the concrete is soft and friable.

Evan
wasteconsultants.com

 

[phamENG]

I'm confused - what's your question?

You're describing a textbook case of hydrogen sulfide attack on (now) unprotected concrete, but I don't know what you're looking for.

 

[dik]

Wastewater treatment facilities are really tough on concrete... from corrosion, cavitation, etc. The acidic products actively react with the basic (pH basic) concrete. There are also corrosion issues. They, invariably, have to be coated with a high quality coating system. Over time, the coating system can fail and it should be replaced with a new one ASAP, else deterioration can be very rapid. If using tar modified epoxies, some of these are carcinogenic... best check.


Dik

 

[EDub24]

What structure are we talking about? Wastewater treatment plants have different processes between the sh*t (literal ) coming in and *cleaner* sh*t coming out (ex. primary and secondary treatment, clarifiers, thickeners, digesters etc) levels and hence different levels of corrosivity for the concrete. It would help to be a little more specific.

 

[hokie66]

And no, the two sites are not the same, but there are some common participants.

 

[r13]

Do you notice someone with link to the other site under his signature?

 

[dik]

retired13... I hang both places...


Dik

 

[msquared48]

You also get hanged both places, dik!

Mike McCann, PE, SE (WA, HI)

 

[dik]

Hehehehehe... somebody once said I was well...


Dik

 

[EvanPE]

Gentlemen,

Thank you for your responses. Sorry, but I’ve been away on another project with limited internet access.

I am really scratching my head on this. I’m concerned that the coating failure has initiated a concrete failure which might lead to a structural failure. Any additional thoughts appreciated.

 

[jayrod12]

It is quite likely the case. They'll need to expose the concrete for further review. No better option.

 

[phamENG]

Just bear in mind that the coating failure isn't what caused the concrete failure - it exposed it to the hazardous, toxic, and corrosive atmosphere and that is what is causing the concrete failure. This may be obvious and what you meant, but I just want to make sure.

In areas where the coating is still intact, it's unlikely that the concrete has been damaged below it. Where there are cuts, blisters, or otherwise damaged coating you're likely to have concrete degradation underneath. Unless you're talking about a really small area or very shallow damage, it's often best to strip the coating, blast the concrete to remove any loose material, patch the concrete, and reapply a more resilient coating.

 

[EvanPE]

I thought to add the main points that Ron shared:

...Asphaltic coatings are sometimes used for concrete structures subjected to aggressive environments such as wastewater treatment plants. Asphaltic materials application onto concrete usually requires good surface preparation and a primer. When both are not present or poorly done, the coating will fail. Once failure of the coating occurs, the concrete beneath the coating will deteriorate in the aggressive environment.


...This is a good example of deterioration of the surface due to either carbonation or chemical attack. Once you have the concrete exposed, you can determine the extent of the issue and take samples for a proper petrographic examination of the concrete...

I hope this helps everyone.

 

[Ron]

@EvanPE.....thank you. When I was doing WWTP design and construction, our motto was "It might be $hit to you but it's bread and butter to me"

Good luck with your issue....interestingly, I just was engaged on a similar project where a municipal utility has very similar problems. It is not an uncommon issue when coatings fail to have underlying damage as a result. I will start my investigation in a couple of weeks....once the litigation is over I will post a "lessons learned" synopsis.

 

[EvanPE]

Do you do much litigation work?

Also, I thought the article SuperSalad recommended was excellent. "The Basics of Deteriorating Concrete at Wastewater Plants: Tips on Causes, Repair, and Resources".

 

[Ron]

@EvanPE....yes. About 80 percent of my work is forensic/litigation related. We have 4 licensed professional engineers with extensive experience in building forensics. Two of us are structural engineers, one has a background in geotechnical and one is a materials engineer. We each do a lot of cross-over into respective areas to assist. I have more experience than the others so I get to work in a lot of different areas. I have worked with each of my colleagues for at least 20 years so we know each other well and work together well. They are a talented group.

 

[EvanPE]

Our firm does around 5% litigation billing, however I am not involved in any part of that business. And, that 5% is most direct involvement with existing clients on projects gone sideways.

What can I do to move into that area? Would you recommend it?

 

[EvanPE]

Thank you. So your litigation is specialized in the Civil Structural Construction. So, there must be all different types of engineers practicing this in different areas.

Thank you again.