Related studies to cathodic protection of reinforced concrete structures (FHWA-OK-83-06)

Abstract

Cathodic protection of steel in portland cement concrete requires information concerning several different areas. This report describes studies which were pointed toward developing an understanding of several of these. A study of making an asphaltic concrete conductive was accomplished using coke breeze mixed with asphalt and aggregate. Mixes containing 45% coke breeze, 7-11% asphalt and the remainder a standard aggregate were found to be appropriate for conductive layers for cathodic protection. It was found possible to determine corrosion rates electrochemically using linear polarization. This laboratory technique gave corrosion rates similar to values obtained in other laboratories using other techniques. Testing in the laboratory and bridge decks of molybdneum-molybdneum oxide electrodes indicated these would be useful as embeddable reference electrodes in concrete. Silver-silver chloride electrodes were not found to be stable in this application. These electrochemical half-cells, Mo/MoO should prove to be useful for cathodic protection systems which require controlled potentials. Reinforced concrete cylinders were exposed to cathodic protection level currents for five years. Pullout strengths and concentrations of sodium, potassium and chloride ions were determined throughout this time period. These data indicate the cathodic protection currents reduce the bond strength of the steel and concrete after about 3.5 years, due to accumulation of sodium and potassium at the interface between steel and concrete.