Painting rebars 2

[acerians]

Hello to all,

We will soon be constructing a foundation on a deep area with suspected acidic soil, One member of the team suggested painting with local enamel primer paint, any comment or suggestion on this matter.Thanks


Ace

 

[bridgebuster]

Why not buy epoxy coated rebar and save yourself the trouble of painting?

 

[Ron]

That won't work. Besides, the acidic soil will attack the concrete first.

Consider using higher density concrete (adding silica fume for instance) and increasing the cover on the rebar. Find out the level of acidity. You might be able to use stainless steel rebar or epoxy coated rebar to help, but painting the rebar with an epoxy primer would result in concentrated areas of corrosion due to "holidays" in the coating, porosity in the coating or lack of bond between the coating and the steel.

Further, painting will compromise the bond between the steel and the concrete. Epoxy coated rebar doesn't have that issue.

 

[cvg]

since the soil is "suspected acidic", I would test and confirm first and then you might consider getting a corrosion engineer to give you a recommended plan to mitigate any corrosion issues with your structure

 

[RHTPE]

Ron - you state that:

Further, painting will compromise the bond between the steel and the concrete. Epoxy coated rebar doesn't have that issue.

If the epoxy coating on the bars did not affect bond, then why do epoxy coated bars require longer development lengths?

A bit misleading perhaps?

Ralph
Structures Consulting
Northeast USA

 

[bridgebuster]

Ralph,

I think the point Ron was making is that applying an epoxy based paint to rebar could be problematic if the bars don't have proper surface preparation. The epoxy applied to rebar is by fusion bonding. Epoxy coated rebar is not the same as painted rebar.

 

[Ron]

BB...that was my point. Thank you.
Ralph...yes, but didn't mean to be misleading, just trying to be brief! Painting, as BB noted, is not the same as the bonding process used in epoxy coating the rebar. One of my concerns is the inconsistency you would get in attempting to field paint or even shop paint rebar. Paintable epoxies would not have the same shear transfer capability as coated rebar would have. The indirectness of shear strain transfer in epoxy coated rebar is one of the reasons for longer development lengths.

 

[RHTPE]

I just wanted to be sure that the OP knows that development length for epoxy coated bars is NOT the same as for uncoated bars.

I knew what Ron meant, but the OP might not have.

Ralph
Structures Consulting
Northeast USA

 

[Ron]

Ralph...good point!

 

[bridgebuster]

no problem Ralph

 

[acerians]

Thanks to all input, i have learned much points. We will check the acidity of the ground and check factories for any availlable local materials for that purpose. Thank you verry much.

 

[boo1]

consider reviewing:

http://www.concreteconstruction.net/images/Choices in Corrosion-Resistant Rebar_tcm45-347334.pdf

CRR steel bars to ASTM A1035/A1035M or ASTM A955/A955M see attached

 

[TomDOT]

The FBE coating on rebar should have an adhesive pull-off strength of at least 5,000 PSI. General industrial epoxy paints (liquid applied, solventborne) are more typically in the 1,000-2,000 PSI range.