|Abstract or Summary
- Steel corrosion in reinforced concrete is a major concern to
transportation agencies nationwide because of the expenses incurred for
repair and ultimate shortening of bridge life. Cathodic protection (CP), as a
remedy, has been applied to reinforced bridges in the US since 1974.
However, application of this technique is largely empirical, lacking
fundamental understanding. In order to optimize the performance of a CP
system, it is important to monitor the rebar potential with respect to a reliable
reference electrode. Moreover, because of potential variation in the concrete,
reference cell placement is fundamental to ensure effective protection.
The work plan was divided into two parts: laboratory scale
experimentation and computer simulation. In the experimentation section,
the response of graphite probes was compared to that of an Orion silver-silver
chloride electrode. Graphite probes behaved as well as the standard electrode.
Furthermore, the home-made graphite probes behaved the same as the
commercial ones. This will allow much greater experimental latitude since
the home-made probes are much more economical than the commercial
A finite difference code was developed to assess the performance of
cathodic protection. The potential distribution in a two dimensional
geometry of a concrete block with a sprayed zinc anode at one boundary and
an iron cathode at the other side was calculated under cathodic protection.
The equations were solved by means of a Gauss-Seidel iterative method with
the help of an overrelaxation factor. An interval halving method was used to
solve for nonlinear boundary condition at the iron.
The effects of concrete pore saturation, concrete cover, and applied potential were studied to determine the degree of protection and proper placement of the reference electrode in concrete. Furthermore, a sensitivity analysis was performed versus input parameters: concrete conductivity, oxygen mass transfer coefficient, and oxygen reduction polarization parameters. The results of the simulation showed that the center of the rebar is less protected than the other locations. Therefore, the reference electrode should be located as close to the center as possible.