Investigations into the cause and consequence of incipient anodes in repaired reinforced concrete structures

The incipient anode (or halo) effect often occurs on repaired reinforced concrete structures. The diagnosis of this problem is widely reported in literature to be macrocell activity. It is deemed that the cause of incipient anodes is the loss of the natural cathodic protection provided by the corroding steel to the steel in the parent concrete adjacent to the patch repair. This diagnosis however, is based on very limited data. Indeed recent potential measurements on field structures repaired with cementitious proprietary materials have provided data that suggests that macrocell activity is not a cause of incipient anode formation but is instead a consequence. Alternative mechanisms that may cause incipient anode activity include repair/parent material interface effects, residual chloride contamination within the parent concrete, and/or vibration damage to the steel/parent concrete interface during repair area preparation. The aim of the work presented here was to assess the impact of macrocell activity on the formation of incipient anodes around the perimeter of repairs in patch-repaired reinforced concrete structures. Data was collected from a major multi-storey car park and a bridge structure both located in the UK. The analysis challenges the widespread view that macrocell activity is a cause of incipient anode formation. Indeed this work illustrates that the data supporting the existing diagnosis is not convincing and suggests that macrocell activity is primarily a consequence of incipient anode formation and the cause is more likely to be a result of other factors.