Criteria for cathodic protection of steel in concrete in the context of Arabian Gulf environment
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Saudi Digital Library
Abstract
This study attempts to formulate and quantify various relevant considerations which influence the effective cathodic protection of corroding reinforcing steel in concrete structures in the Gulf environment. The parameters included in the research program are: chloride content, temperature, reactive aggregates, depth of reinforcement in a two mat system and secondary effects. It was found that the instant off, shift and decay potentials as well as the current density needed for adequate protection of steel are dependent on the chloride gradient as well as the chloride content in concrete. A 60°-C exposure required only about 20 percent higher level of protection in terms of current density/instant off potential/decay potential for an initial polarization period of two months. Enhanced activation in the initial period reduces the corrosion activity subsequently due to the beneficial electromigration of ions requiring a reduced protection on a long term basis. The decay potential criterion was found to be least sensitive to chloride content, chloride gradient and temperature effect, although it does not explicitly indicate the level of protection current which is automatically adjusted to accommodate the various factors influencing corrosion activity.
In a two mat reinforcement system, the top mat was significantly overprotected when the bottom mat was just adequately protected from the anode source located above the top mat. The top mat suffers overprotection to an extent which would cause an unacceptable 30 percent reduction in the steel-concrete bond in a period of about 8 years. However, the bond reduction for a practical cathodic protection current density of 1-3 ma/ft² was found to be negligible. In high alkali-cement concrete containing reacive aggregates, cathodic protection current significantly advances the cracking time and softens the mortar at the steel-concrete interface reducing compressive strength and hardness.