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| === Cathodic protection of rebar === | I would love to see a review by a concrete engineer - this seemed a little "selective". [[ ConcretePlanet | Book notes here ]] ----- === Cathodic protection of rebar === Rebar iron won't oxidize nearly as fast if it is biased cathodically. Too much voltage, and the electrode will emit hydrogen, which can embrittle the iron. Without knowing the voltage drop through the concrete, it is difficult to bias the iron properly. ==== A proposed invention ==== I'm releasing this idea into the public domain. If it makes sense, please use it to protect America's aging reinforced concrete, saving lives and tax dollars. Perhaps a joint project between the CE and ME departments at Duke could get some papers out of it. I can imagine this turning into a little circuit board with a solar cell, a battery, and a small integrated circuit with a simple bluetooth radio transceiver for status logging and bias calibration, mass produced and added to thousands of reinforced concrete structures. ---- If you live in a place like Oregon with lots of rain and humidity, and have cheap telephone jacks with inadequate gold plating, you've listened to anodic oxidation of copper - it makes a hissing noise, which I presume are the little electrochemical events of copper ions oxidizing, adding up to electrical noise. I presume the current drawn from a cathodic bias circuit at too low a voltage will make a similar noise. If the current is detected with a "virtual ground" amplifier, the capacitance of a few hundred feet of rebar can be nulled, and the wideband noise measured. I also presume that hydrogen generation is a higher energy phenomena, and has a different noise spectrum. So proper bias on a rebar electrode will be between the "copper oxidation hiss" and the "hydrogen hiss". It would be instructive to digitize the electronic spectrum of a piece of rebar in concrete as a function of voltage, and see if these hisses can indeed be distinguished, and a bias point chosen for the optimum tradeoff between hydrogen and oxidation, perhaps even slowly varying the voltage to alternate between the phenomena, reducing the briefly oxidized iron. I do not know how well this would work for really large expanses of tied rebar - chances are there will be DC voltage gradients across the structure, so some portions of the electrode will be oxidizing while others will be reducing. While this technique might still help prolong the lifetime of existing reinforced concrete, it will probably work best on rebar electrodes carefully designed to match areas of similar ambient electrical potential and long term water infiltration and pH changes. |
Petroski Notes
Not ready yet!
Random bits about the book "To Forgive Design" 2012 by Henry Petroski, and related ideas.
Book Notes
More Later
=== Reliability and failure in chip design ===
More Later
Abusing statistical distributions
More Later
Vintage Tektronix oscilloscopes
More Later
Robert Courland's "Concrete Planet"
I would love to see a review by a concrete engineer - this seemed a little "selective". Book notes here
Cathodic protection of rebar
Rebar iron won't oxidize nearly as fast if it is biased cathodically. Too much voltage, and the electrode will emit hydrogen, which can embrittle the iron. Without knowing the voltage drop through the concrete, it is difficult to bias the iron properly.
A proposed invention
I'm releasing this idea into the public domain. If it makes sense, please use it to protect America's aging reinforced concrete, saving lives and tax dollars. Perhaps a joint project between the CE and ME departments at Duke could get some papers out of it. I can imagine this turning into a little circuit board with a solar cell, a battery, and a small integrated circuit with a simple bluetooth radio transceiver for status logging and bias calibration, mass produced and added to thousands of reinforced concrete structures.
If you live in a place like Oregon with lots of rain and humidity, and have cheap telephone jacks with inadequate gold plating, you've listened to anodic oxidation of copper - it makes a hissing noise, which I presume are the little electrochemical events of copper ions oxidizing, adding up to electrical noise.
I presume the current drawn from a cathodic bias circuit at too low a voltage will make a similar noise. If the current is detected with a "virtual ground" amplifier, the capacitance of a few hundred feet of rebar can be nulled, and the wideband noise measured.
I also presume that hydrogen generation is a higher energy phenomena, and has a different noise spectrum. So proper bias on a rebar electrode will be between the "copper oxidation hiss" and the "hydrogen hiss". It would be instructive to digitize the electronic spectrum of a piece of rebar in concrete as a function of voltage, and see if these hisses can indeed be distinguished, and a bias point chosen for the optimum tradeoff between hydrogen and oxidation, perhaps even slowly varying the voltage to alternate between the phenomena, reducing the briefly oxidized iron.
I do not know how well this would work for really large expanses of tied rebar - chances are there will be DC voltage gradients across the structure, so some portions of the electrode will be oxidizing while others will be reducing. While this technique might still help prolong the lifetime of existing reinforced concrete, it will probably work best on rebar electrodes carefully designed to match areas of similar ambient electrical potential and long term water infiltration and pH changes.