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Hierachy of Quality for Avoiding Acidification in Cathodic Protection

Paper Number: 63
Author/s: H Fatemi
Organisation: Roads and Maritime Services, Sydney, Australia

Abstract

This paper charaterises the acidified titanium mesh anode backfill mortar in an impressed current cathodic protection (ICCP) system. Testing samples were taken form a bridge structure in which the ICCP system had been in service since 2009. The acidified slots at the bridge piers showed the typical brown stains around the embedded anodes on the surface. However, further investigation showed two distinct acidification products in the backfill mortar adjacent to the anode and about 10mm away from the anode. Scanning electron microscope (SEM) was used for imaging and energy dispersive spectroscopy (EDS) was utilized for undertaking elemental analysis. The product adjacent to anode (greyish color) had higher levels of chlorine, whereas the product farther away from the anode (brownish color) included higher levels of iron and aluminum. On the other hand, both products showed high levels of silicon and oxygen. The results suggest chlorine evolution or migration from the saline sea water at the anode which can form hypochlorite and hydro-chloric acid and in turn results in the anode’s backfill mortar acid attack. Also, observation of higher level of iron and aluminum in the acidification products that were away from the anode could be due to their ion positive charge being repelled from the anodes. Finally, morphology and spot elemental analysis of acidified products showed that it mainly comprises of sand and gypsum particles without much binder. This could be due to dissolution of cement paste as a result of acidification and therefore reducing the binder content and in turn the binding capacity of the acidified mortar.