Paint and Embedded Steel

[LSPSCAT]

I am writing to inquire for you thoughts on paint on embedded steel. I currently have two particular situations the first is a wide flange that is completely embedded in concrete. I have called for this item to not be painted. Consulting Engineer has questioned this item and has made reference to epoxy coated rebar and so similiarly the wide flange should be painted. Do has anyone have any references for the preferred practice?

The second situation is for a wide flange that will be fastened to a concrete wall in the vertical position. A grout pad will be placed behind the wide flange to provide for even bearing and to act as a waterstop. I have called for the wide flange to be completely coated with an epoxy paint. As this will be exposed to the elements I feel the complete section should be painted to prevent corrosion, particulary at the edges. A Consulting Engineer is concerned about the adhesion between the grout and epoxy paint and states the grouted surface should not be painted. I can see the concern about adhesion, however, I have similiar concerns even with the bare steel and grout - "mortar and steel no deal". Any preferences or thoughts?

 

[BridgeSmith]

I think you are on the right track on both counts. We use epoxy coated rebar only for bridge slabs and other components that will be exposed to weather and deicing chemicals that lower the the normally high Ph value found in concrete to a point where corrosion of the steel can begin. I would say that unless your embedded beam is exposed to a marine environment or has less than 2" of concrete cover, it should not have a problem.

I'm not sure how adhesion, or a lack thereof, between the grout and the steel column creates a problem, but in the situation you describe, I wouldn't count on the grout to inhibit rust even on the surface facing it. If enough moisture gets between the steel and the grout, the grout will not protect it. If adhesion is required, I suggest applying an adhesive over the paint, and if the concern is the grout sticking to the paint, a properly cured epoxy paint should have less adhesion than the bare steel.

 

[Ron]

LSPSCAT...fully embedded items in concrete are better protected by the passivity created by the alkalinity. If you coat the embedded item, any breach in the coating (and there will be some) will become a corrosion concentration cell, exacerbating the corrosion of the item at that location. That can result in a significant loss of section that can locally weaken the member.

If you don't coat the item, the corrosion is general and slow. It will last for many years, just as rebar.

 

[msquared48]

That's why Ron has been around here so long - there's no need of a coat in Florida!

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Ron]

Mike...exactly, now let me get my flip flops on and get another cup of coffee.

 

[frv]

Ron is exactly right.. I had a materials professor rail against epoxy-coated rebar for that precise reason..

 

[LSPSCAT]

I have seen the epoxy coated rebar in action when I used to work in the field. It is absolutely impossible to protect the epoxy coating during handling and tying the steel. Ineevitably you are always running around trying to cover up rust spots with tough up expoxy before the pour. We had seen some relatively new rebar hollowed out...only left with the thin epoxy shell!

Any additional thoughts on the grout / plate interface where the steel is not completely embedded?