PRE-PACKAGED ZINC SACRIFICIAL ANODE

Conventional patch repair of corroded concrete structures inevitably introduces “incipient anode” effect due to the different electrochemical behavior of the “new” and “old” rebar/cement. The newly patched area has a higher potential than the neighboring area (which may still be contaminated with chloride) and is the cathode in the corrosion process, while the rebars in the neighboring areas become the anode and start to corrode. Conventional patch repair treats only the symptoms not the cause and the incipient anode effect makes this repair a never-ending process.

One innovative product that uses pre-packaged zinc sacrificial anode (commercially known as Galvashield XP - registered trademarks of Fosroc international) can provide solution to the incipient anode induced corrosion (Fig.3). Since zinc is pre-packaged in a specially formulated mortar that maintains the surface reactivity of zinc, electrons released from zinc will be readily transferred to the neighboring steel rebar network. The effective protection distance by such an embedded unit is sufficient to suppress the incipient anode effect. Installation of such an integrated system is easy and flexible. There are no special techniques required. The self-contained wire ties allow attachment to vertical, horizontal and overhead positions (Fig.4). The effectiveness of the pre-packaged zinc sacrificial anode on the preventing rebar corroison is demonstrated in Figure 5.

Fig.3a (left) Zinc encased in special mortar (Photo copyrighted by FOSROC International ) Fig.3b Cross-sectional view of the zinc anode (Photo copyrighted by FOSROC International )

Fig4.(left) Installed zinc anode (Galvashield XP) (Photo copyrighted by FOSROC International )
Fig.5 Effectiveness of pre-packaged zinc sacrificial anode on the corrosion of rebar (Photo copyrighted by FOSROC International )

Laboratory experiments showed that the zinc anode can suppress the formation of incipient anodes around the repair (Fig.5). Field applications include car parks, buildings, bridges and any other reinforced concrete structures where conventional patch repairs can not provide acceptable performance.