Evaluating Deteriorating Concrete Structures

[Hold0Fast]

I'm a new engineer in a petro-chemical facility, and I have been tasked with evaluating the condition of a concrete structure that was built in the mid 70's. The structure and equipment has been untouched since roughly 1985, and it still supports a horizontal drum and 2 heat exchangers.

So there is a large amount of cracking, spalling, and large areas where there is exposed reinforcement. I'm looking for some recommendations on how to evaluate the existing condition of the structure and develope a recommendation for proceeding with demolition or re-use.

Thanks for your help.

 

[JedClampett]

First thing you need to do is survey the damage, determine if there is any imminent danger (assuming not) and analyze the cause of the damage. Common sense is a great guide. If you go out with a clipboard and have a pissed off look on your face, that goes a long way toward credibility.
I've seen a lot of repairs that were not well thought out that ended up failing in short order. Once you've figured out the causes, you can pinpoint the repairs. If the concrete didn't have enough cover, maybe just repouring new concrete may do the trick. Maybe drainage wasn't well implemented and standing water has got to the reinforcing. If it's heat damage, you might have to go beyond the concrete. Actually 25 years is not a long life for concrete structures, so the causes are not likely to be just age.
My advice is to go out, take pictures and go over them with your friendly Sika Representative (

http://usa.sika.com/).

Or bring him or her out there.
As far as replacement vs. repair, there's no easy answer. If the facility can be taken out of service, maybe replacement is the answer. It's basic economics. The cost of repairs vs. the cost of replacement factoring in the fact that repairs are likely to be of a lower quality than new work.

 

[ukengineer58]

most people and by that i mean project managers clients etc will push you into agreeing to an indadequate repair. all they want to do is cover it over. resist. work out the cause and do it properly.

 

[bridgebuster]

ACI has a lot of information

342 - Evaluation of Concrete Bridges and Bridge Elements
345 - Concrete Bridge Construction, Maintenance, and Repair
364 - Rehabilitation
365 - Service Life Prediction
437 - Strength Evaluation of Existing Concrete Structures
546 - Repair of Concrete
562 - Evaluation, Repair, and Rehabilitation of Concrete Buildings

also, look at various DOT sites and FHWA. Many have standard repair details and their bridge inspection manuals will cover concrete deterioration.

 

[JAE]

To add to the good thoughts above:

The damage could be due to a vast array of causes and the cure should respond to the cause. This can be a very obvious issue (exposure to water/chorides for instance) or something more nuanced and difficult to pin down.

This effort of evaluating concrete can be very tricky and if you've never done it before I would caution you on taking this on without someone there who knows what they are doing.

As you see from bridgebuster's list, ACI has a lot of information on this topic and some engineering firms actually have this type of evaluation/repair as their major niche market of work. So it can be highly specialized.

In most cases, documenting all the conditions is a first step:

1. Mapping out all cracks and spalls along with chain-drag or other means to locate delaminations.
2. Thermal imaging to locate moisture migration and patterns.
3. Sampling concrete to test for ASR, chloride content, etc.
4. Measuring section loss on rebar.
5. Investigating sources of concrete damage (rebar rust-expansion, water infiltration, thermal movements, structural stresses)
6. Evaluating repair types and methods along with causes (i.e. you must avoid problems from applying a band-aid to the damage without addressing the root cause).

 

[Ron]

Good info above...I'll add...

ASCE-Guideline for Structural Condition Assessment of Existing Buildings (11-99)

This effort of evaluating concrete can be very tricky and if you've never done it before I would caution you on taking this on without someone there who knows what they are doing.

This is exactly right. It will be a great opportunity for learning, but the potential to miss a critical issue is high without experience.

 

[Hold0Fast]

Ron/JAE,

I do have some additional help on this. So fear not, they aren't trusting a rookie 100% on this. I'm just trying to do as much as I can, and trying to prove myself, if you will.

Thanks for all the references and information. I have a lot of reading to do this weekend it looks like. If anyone else has a recommendation, let me know!

 

[Ron]

H0F....good to know. Learn all you can. Deteriorating structures and failures teach us a lot more than the "perfect" ones.

Good luck and stay active in the forums....we all learn a lot here.

 

[JAE]

Hold0Fast,

Also check this out: International Concrete Repair Institute Link

Probably some good source references there.

Specifically the Concrete Repair Bulletin Magazine:
Magazine link