Migration of ions in concrete due to cathodic protection current

Four constant current densities of 32.3, 108, 215 and 538 ma/m2 (03, 10, 20 and 50 ma/ft2) at the steel surface area were used in the test program which also included chloride content of concrete as the second variable. These four current densities were maintained in steel of reinforced concrete specimens for an activation period of 14 months. At the end of the activation period, concrete powder samples were obtained from three locations of a particular specimen; near the steel, near the anode and the midpoint of steel and anode. These samples were then analyzed for Cl-, Na+, K+, Ca++ and Mg++ ion concentrations. It is observed that cathodic protection (CP) current drives away Cl- ions from near the steel to a short distance away. Due to the negative polarity of steel in a cathodically protected reinforced concrete structure, Na+, K+, and Ca++ ions from the concrete pore solutions get accumulated near the steel surface. K+ ions migrate towards the steel surface at a higher percentage when compared with the migrations of other cations. The effect of CP current on the migration of Mg++ ions towards the steel in reinforced concrete specimen is not clear from the results obtained in the test program. © 1991