How does water make rebar corrode?
How does water make rebar corrode?
(OP)
I'm working on a Home Inspection book and I'd like to know (in laymen's terms more or less) why water corrodes steel. What is the chemical process? Oxidation?
-Kent
-Kent





RE: How does water make rebar corrode?
Rusting of reinforcing steel in concrete is a slightly more complicated matter involving a loss of protection afforded by the concrete. The loss of protection is two fold; the concrete protects the iron from the environment by covering it. In addition, the concrete, due to its alkalinity protects the steel from corrosion (It's a little more involved than that). The problem with corrosion of steel in concrete is that the rust products have a greater volume and cause the concrete to spall off exposing more steel. As briefly touched on, for the steel to rust in the first place, the alkaline protection must have been compromised.
It's possible to write pages about this issue and I hope the above brief outline will help you.
Dik
RE: How does water make rebar corrode?
Water can also reduce the pH of concrete thus taking away the protective passivation it provides to the rebar when the high pH is maintained.
The corrosion of rebar can be on a microscopic or macroscopic level, usually with both occurring simultaneously. In the "micro" sense, small corrosion cells or batteries are set up on the surface of the rebar where variations in the steel occur and where certain constituents in the concrete (aluminum compounds for instance) create galvanic cells that remove material from the rebar. In the macro sense, oxidation caused by the dissolved oxygen in water or by the electrolysis of water releasing oxygen allows the premise that dik laid out.
As dik said, the corrosion of rebar can be rather complex and we've attempted to simplify and summarize it in a layman's nutshell.
RE: How does water make rebar corrode?
Kent