Epoxy or...? 1

[pcnj50a]

Can anyone give me an idea if there are viable alternative materials to epoxy for rebar coating? The CRSI site seems to be epoxy-specific, and while it is no doubt a fine material, I can't imagine that it has no disadvantages and that there's no alternative coating.

 

[civilperson]

Hot Dipped Gaqlvanized

 

[pcnj50a]

Well, for some reason, my browser will not allow me to give you a "thank you" vote. So... thank you. Do you (or anyone else) think that it's worth putting a barrier coating over the Zn, sort of belt and suspenders? And is epoxy really the best barrier coating?

 

[civilperson]

Epoxy causes less bond strength between steel and concrete and thus the development lengths and splices are longer.

 

[pcnj50a]

I've read about polyester and Abcite being viable alternatives to epoxy. Any feedback?

 

[TXStructural]

The bare steel surface is typically passivated by the alkaline concrete, thus protected. It takes a breakdown of that protective interface (cracks, chlorides, carbonation) to get corrosion of the rebar. Coated rebar doesn't get this benefit, so consider that.

Research indicates that epoxy bars are extremely durable, particularly when care is taken to avoid damage during fabrication and placement. The epoxy barrier is very good at resisting chloride attack, and improving the life of the structure. The adhesion of the epoxy to the bar is very important. As long as the coating is intact, the service life is infinite, but where the coating is compromised, corrosion will happen.

Galvanizing is a sacrificial coating, and when used appropriately, galvanized bar is the right choice for some structures. The finite life of the coating lends it to certain structures - it extends the life of the bar, but will not be infinite.

Bars which are coated, or combine coatings, provide good service life, but must be selected for the intended use, since one isn't "better" than the other. For instance, as galvanizing under an epoxy coating gets sacrificed, you can lose adhesion of the epoxy, allowing movement of moisture, chlorides, and oxygen onto adjacent rebar surfaces. In some exposures, this might be the best choice.

Another option is stainless-clad steel bar or solid stainless. Also MMFX shows potential for improved corrosion resistance.

Industry consensus is that the practical answer today for bridges and other salt-exposed structures is epoxy. For other uses, standard rebar is generally a great choice. Between these extremes, choose what fits your use.

 

[jike]

Other options are corrosion inhibiters, cathodic protection, galvanized bars, stainless bars, etc.

Potential problems with epoxy bars has to do with damage to the coating from mishandling or erection. All locations need to be repaired otherwise it is only as good as that one damaged location. Also, field cut bars need to be touched up on the ends. Special ties need to be used.