Rebar Corrosion - how to distinguish active or not
Rebar Corrosion - how to distinguish active or not
(OP)
We recently did a large number of half-cell tests on the top of a parking garage floor (the traffic topping and membrane and underlying concrete topping had been removed), and got a large number of measurements more negative than minus 350 mV, even though there were no top bars in the midpanel region of the flat slab (midpanel is the area common to mutually perpendicular middle strips). We felt then that it must be the corrosion activity of the bottom bars in the 7.5" thick slab. So we broke out the entire midpanel in one of the bays so that we could inspect the rebar for corrosion. The attached photo is representative of the rebar condition. The bottom of the slab was hammer tapped before breaking it out and no hollow sound was found that would indicate concrete delamination due to corrosion.
Question:
Some of the bars had the sort of surface rust as shown in the attached photo. How can we distinguish whether it is due to active corrosion due to corrosive chlorides, or whether it was just rust that was on the rebar in the original construction before the concrete was placed?] It was built 55 years ago, but has been protected by a waterproofing membrane and mastic wearing course which we believe was placed not too many years after the garage was built.






RE: Rebar Corrosion - how to distinguish active or not
RE: Rebar Corrosion - how to distinguish active or not
RE: Rebar Corrosion - how to distinguish active or not
RE: Rebar Corrosion - how to distinguish active or not
Half cell potentials readings below -0.35 indicate there is a 90% probability of corrosion occurring, but that doesn't tell you anything about how long it has been in that state or the progress of the corrosion.
RE: Rebar Corrosion - how to distinguish active or not
I do not see the observed corrosion as an issue.
How long has the concrete been in place?
RE: Rebar Corrosion - how to distinguish active or not
What Hokie66, Yaschief and Ron say was my judgement too. Nice to have some confirmation. Thanks. Much appreciated.
Andy
RE: Rebar Corrosion - how to distinguish active or not