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Longevity of concrete material

Longevity of concrete material

Longevity of concrete material

I’ve got a good question for everyone. How long does concrete last?

The context of the question is long-term mine opening closures. We’re contracted to close mine openings for a governmental regulator. We’re currently designing them to last a LONG time with stainless steel. They’re not back-filled and everything is available for inspection.

Some openings have an existing vertical concrete collar and a horizontal cover. Wall thickness is around 10” (250mm). Cover thickness is greater. Vertical concrete was back-filled. It currently looks brand new. The collar was constructed in the early 1960’s so its 50+ years old today. Typically the vertical concrete is heavily reinforced 4% range.

I seek to remove the horizontal concrete cover, foam fill the collar and replace the cover with a stainless steel cover. The reason for foam fill is to make the walls free of normal stress from bending moment induced from soil pressure.

So now the concrete is used for vertical support on the cover (for which it’s grossly oversized) and is not subject to typical environmental exposure. The environment does have freeze-thaw exposure.

Two questions.

1) what’s your prediction on how much longevity we have before the concrete collar would require replacement? Recall that it’s now 50+ years old and looks great. Also, we need approximately 1/2” of concrete for structural purposes.

2) is there any research to back up any predictions? For this client we’re going to need it for them to believe us. Without this “backup”, the client will be spending much more than I think they should be on vertical skirting, long columns and landscaping to prevent the backfill.

Thank you in advance.

RE: Longevity of concrete material

Just speaking off the cuff here, I'd need to research a bit more to make sure I'm not missing or overstating anything.

10" down to 1/2"? From what you described I'd suspect carbonation of the concrete causing a loss of passivization of the reinforcement and the subsequent rust jacking and freeze-thaw action spalling the concrete to be the most detrimental effect. That said, I've seen some pretty poor mass concrete last over 110 years; albeit with major spalling and failure of the cement (exposed to deicing salts and heavy freeze-thaw cycles).

Eventually the cement paste breaks down due to acids and other environmental wear and tear, and that's hard to prevent.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

RE: Longevity of concrete material

Forgot to fully answer your questions:

1) At least another 50 years and probably a lot more if you can suffer heavy spalling.

2) I'm sure I can dig up something. My first stop would be the concrete repair manual and see where that led me.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

RE: Longevity of concrete material

For most mine closures. the most relevant concrete related question is " how much acid mine drainage will the concrete have to withstand??" ie pH and sulphate levels.

I am aware of one hydraulic plug , partialy installed in british columbia that was designed for a 1000 year life but did not contain concrete because concrete could not withstand the low pH that existed.

RE: Longevity of concrete material

If it looks new after 50 years, I would expect at least another 50 years of service.

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