What is a 'sacrificial anode'?

A sacrificial anode is a block of active metal (usually zinc) wired to the steel rebar within a concrete repair. Because zinc is more electrochemically active than steel, the corrosive current attacks the zinc *instead* of the rebar. The anode 'sacrifices' itself to protect the steel. We install these in patch repairs to prevent 'incipient anode formation' (the halo effect), where corrosion accelerates in the steel adjacent to the new patch.