Rebar in high pH environment

[VaStruct]

I am in the process of designing several bottom ash containment areas for several power plants that burn wood pulp. I have been told that the bottom ash has a high pH (~12) and will be fed by a conveyor belt out onto the concrete slab on grade for the containment area which has either concrete walls or concrete curbs around all four sides. The bottom ash will be allowed to dewater while sitting on the concrete (there is a trench drain at the low end). As concrete has a naturally high pH and the high pH of concrete helps to form an oxide layer on the rebar that reduces the rate of corrosion of the rebar, I'm thinking that epoxy coated rebar would not be necessary for this application. Anyone have any experience/thoughts about this?

 

[hokie66]

No experience with ash containment, but I agree with your logic. High pH is what protects the reinforcement. But I would want to confirm for myself what you "have been told", because I am guessing the ash could be highly variable. Not a fan of epoxy coated bar, but that is a topic we have discussed many times before in these forums.

 

[dik]

The surrounding concrete has a pH of approx 12 or so... the high pH increases corrosion resistance with the concrete. I'm not sure about ash, but a dense, high strength concrete should suffice.

Dik

 

[Ron]

Agree with above. Should not be an issue unless the bottom ash attacks the concrete. A high pH typically creates a passivating condition that protects rebar.

 

[TXStructural]

A high pH generally protects carbon steel against corrosion in concrete, however I would be concerned that other chemicals in the ash (i.e., potassium salts and other residuals), and the constantly wet environment, could result in corrosion. Epoxy-coated bar should perform well, if you observe precautions against macrocell corrosion.