your hard metal rod

"OPPOsaurus WRX" (opposaurus) 09/27/2019 at 09:36 • Filed to: None

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is it supposed to be exposed like that?

and you crack is showing, that i s not supposed to happen either

facw > OPPOsaurus WRX 09/27/2019 at 09:49

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Second shot makes it look like it’s been repaired before too.

In any event, I’ve got this feeling like we really should be using some sort of non-corroding FRP rebar instead of steel. It doesn’t even seem to be that much more expensive.

Self-healing concrete seems neat as well, though IIRC, they are still working out the kinks with that.

Nibby > OPPOsaurus WRX 09/27/2019 at 09:54

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speaking of metal

Ash78, voting early and often > facw 09/27/2019 at 09:59

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I guess the theory is that’s the concrete protects it from corrosion, but I see exposed rebar under almost every 30+ year-old bridge I pass under.

facw > Ash78, voting early and often 09/27/2019 at 10:09

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It’s been a while since I read up about this, but my understanding is that a big part of the problem is that steel rebar is insufficiently protected from corrosion before the concrete is poured, so it’s already rusting when it goes in, allowing things to start going downhill almost immediately (though it may take a long time for cracks large enough to be noticeable to show up on the outside).

Ash78, voting early and often > facw 09/27/2019 at 10:14

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Yeah, kind of funny how so much rebar and metal lath (re-mesh?) seem to be rusted from day 1. I was doing concrete research when I was building my own climbing holds and most sources insisted that it was just superficial, and that any rust coating would be too expensive or would just come right off during handling, so they didn’t bother. I opted against any mesh in my holds because if a chunk were to break off, I don’t want a climber’s hand to hit rusty metal. That’s just bad for business. So I just limited my sizes instead, no reinforcement needed (it was just DIY, I never actually sold them)

merged-5876237249235911857-hrw8uc > Ash78, voting early and often 09/27/2019 at 10:28

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If the cover is sufficient it stays protected, but if the resteel is set too close to the outside of the concrete, it can corrode and spall.  

merged-5876237249235911857-hrw8uc > facw 09/27/2019 at 10:29

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I’ve actually heard that the surface rust actually increases the bonding between the resteel and the concrete, but I haven’t dug into find research to support that.  Looks like I have something to do now.

OPPOsaurus WRX > Nibby 09/27/2019 at 10:47

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wow, that was fucking terrible.

Nibby > OPPOsaurus WRX 09/27/2019 at 10:51

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no u

shop-teacher > OPPOsaurus WRX 09/27/2019 at 11:56

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You should see some of th e underpasses in the City of Chicago.

Highlander-Datsuns are Forever > facw 09/27/2019 at 13:12

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SOP for Caltrans now is epoxy coated rebar so you don’t get spalling when the bar rusts and expands. It’s expensive but it works. FRP probably doesn’t have a high enough modulus to replace steel .

facw > Highlander-Datsuns are Forever 09/27/2019 at 13:39

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Hmm, I’m obviously well outside my depth here, but some quick reading seems to suggest that while FRP does have a much lower modulus, that is sometimes a benefit, depending on the types of stresses the concrete is subject to. Also seems that in general they have higher tensile strength than steel, but lower shear strength, which again probably means it’s not something that you’d consider as a drop in replacement for an existing design, but could enable new designs.