Effect of the paste–anode interface under impressed current cathodic protection in concrete structures

Journal article, 2018

Impressed current cathodic protection (ICCP) is a powerful method to prevent and stop corrosion of steel in concrete structures. To evaluate the long-term effect of ICCP, accelerated tests have been adopted using high current densities. A carbon fiber reinforced polymer mesh was introduced as anode. The presented research focused on the changes at the paste-anode interface as a consequence of applying current. The treated samples were characterized by various techniques.

Calcium dissolution was found with an average thickness of 0.34 mm around the anode after charges of 6*10^6 C/m2 were applied, equivalent to applying 4 mA/m2 of anode surface for 30 years. Calcium dissolution resulted in a white zone around the anode, where the calcium silica ratio was lowered and almost no crystal phase was observed. NMR results show clear Q3 and Q4 peaks in the white zone, which contained extended branched and networked structures of hardened cement paste. An increased resistance caused by the formation of the white zone may eventually make the system fail because of insufficient current densities. CFRP has been proven suitable for ICCP application even at a current density of 4 A/m2 of anode surface.