POTENTIAL DEVELOPMENT OF SACRIFICIAL ANODE CATHODIC PROTECTION APPLIED FOR SEVERELY DAMAGED RC BEAMS AGED 44 YEARS

Abstract

Sacrificial zinc anodes, as one of the cathodic protection repair system, are typically embedded in the patch repair section with high resistance mortar to offer corrosion protection on reinforced concrete (RC) structures. Steel bars within the repair area passivate because of alkalinity of the fresh repair material, the absence of chlorides and the abundance of dissolved oxygen in the pore solution of the freshly mixed concrete or repair mortar. As a result, the rebar potential in the repair rises above the passive steel potential, therefore, in the parent concrete a macro-cell corrosion occurs. This study reviews the performance of sacrificial zinc anodes installed in the parent concrete to protect the rebars from re-deterioration and suppress the incipient ring anode or macro-cell corrosion activities around the boundary between parent concrete and patch repair concrete, from a view of potential development.
Two specimens of 44-year-old severely damaged RC beams having a span of 2400 mm and 200x300 mm cross-section, both suffering from chloride-induced corrosion of the reinforcement are prepared as “RC1” and “RC2” marking. The polymer modified mortar as the material of patch repair section is applied to the middle tension area in the dimension of 70x150x800mm. Four cylindrical sacrificial zinc anodes with 30 mm diameter and 130 mm length installed in the parent concrete by LiOH cementitious coating material. Corrosion inhibitor applied to the tension steel bar surface of the patch repair section in RC2, since the natural macro-cell corrosion was naturally occurred before the repair. Half-cell potential test of rebar by silver/silver chloride reference electrode (SSE) in every 5 cm on the side section of specimen’s surface, and the current density of sacrificial zinc anodes are measured regularly on 0, 7, 14, 21, and 32-days presented in this paper.

The results during the early age of zinc anode embedded in damaged RC beams indicate that sacrificial zinc anode had a profound effect on polarizing the potential of rebar in the parent concrete. The high protection concentrates in the surrounding of anodes in parent concrete and no significant protection of the rebar in patch repair section because of the inherent differences in properties between patch repair material and parent concrete. The rust inhibitor applied in the patch repair is not enough to keep the polarization of rebar in noble values, too. The high resistivity of patch repair material reduced the effectiveness of the sacrificial anodes in parent concrete to protect all cross-section of rebar in RC beam structure.