Effect of temperature on cathodic protection criterion for reinforced concrete structures

This paper presents the results of the effect of temperature on the cathodic protection (CP) level needed for effective control of chloride corrosion of reinforcing steel in concrete structures. The chloride₃levels in the concrete were 8 and 32 lb/yd³ (4.76 kg/m³ and 19 kg/m³) and chloride gradients were 1.5 and 2.0. Chloride gradient was created by embedding in the concrete specimen a relatively higher chloride-bearing macrocell and thereafter connecting the macrocell steel and the main steel through an external resistor. Current reversal technique was used to establish the protection level needed for effective control of reinforcing steel corrosion. Two sets of specimens were used: specimens of the first set (called reference specimens) were kept at the controlled room temperature of 25 °C (77 °F), and the specimens of the second set (called temperature-treated specimens) were kept in a temperature chamber having a peak value of 60 °C (140 °F). It was found that the corrosion activity of the reinforcing steel mcreases with an increase in the temperature to which concrete is exposed. Increased corrosion activity at a higher temperature exposure of 60 °C (140 °F), required an increased level of cathodic protection as indicated by higher protection current density, higher instant off protection potential and marginally higher at the beginning of the polarization period. The 60 °C (140 F) temperature effect requires about 20 percent higher level of protection in terms of current density and about 20 to 30 mV higher instant off potential/decay potential for an initial polarization period of two months. Thereafter no additional protection is required against the temperature effect. The subsequent reduction in the level of cathodic protection required at higher temperature is indicative of a dominant influence of the electromigration factor in the interactive relationship between increased corrosion activity and the beneficial effect of electromigration of ions caused by the higher temperature.