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dik (Structural) (OP)
2 Apr 12 16:28
Does anyone have any information on the use of HDG reinforcing in contact with non-coated bars?

This is related to bridge deck bottom reinforcing.

Dik
hokie66 (Structural)
2 Apr 12 17:14
dik,

This reference is applicable.  Read what it says in about the 8th paragraph.

http://www.gaa.com.au/index.php?page=corrosion-of-reinforcement
dik (Structural) (OP)
2 Apr 12 17:29
Thanks, Hokie...

The issue is non galv bars in a precast girder having galvanised bottom rfg in contact... lots of concrete cover and the bridge deck would likely work in the event the bottom rfg disappeared at the support.

Dik
hokie66 (Structural)
2 Apr 12 17:46
In the event of loss of protection by the alkaline concrete, the situation as described would tend to make the zinc corrode faster.  The zinc would still be effective, just not for as long.  With galvanizing, loss of the zinc does not cause a local corrosion acceleration of the steel similar to that which occurs with damage to epoxy coated bars.  
TXStructural (Structural)
3 Apr 12 0:30
I have not read the link provided by Hokie, but it is correct to say that the galvanizing will work to protect not only the coated bars, but also the uncoated bars in some cases.

It is generally preferred to use the same materials throughout to reduce corrosion where there may be differential alkalinity and chloride ion concentrations between the top and bottom bar locations.  One of the reasons top bars can corrode faster is the grounding of electrons through the bottom bars, allowing the top bars to corrode by way of a macrocell.  NEVER use epoxy bars in combination with uncoated bars for this reason.
DST148 (Structural)
3 Apr 12 9:26
@dik: Not directly related to your OP.
ACI Chapter 12 gives coating factor for uncoated reinforcement and epoxy-coated bars. What coating factor would you use to determine the development and splice lengths of HDG bars?
hokie66 (Structural)
3 Apr 12 18:16
1.0...HDG doesn't affect the development.
DST148 (Structural)
4 Apr 12 22:09
@hokie66: Thank you.
dik (Structural) (OP)
5 Apr 12 13:55
It's not an issue with the coating factor... it's the discontinuity that causes the concern.  The application is bottom slab bars over a girder support... the girder shear connectors are not HDG and the slab steel is... it's the point of contact of the two items.

The rebar located on the bottom is less likely to experience carbonation and the chloride intrusion will be minimal. I wasn't concerned about it, but some others were.

Dik

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