Using zinc penny sheets from the mint as the sacrificial anode, the salt water acts as an electrolyte. Concrete is porous and ions will flow through it - connect the zinc sheet that is mounted at the splash zone of the piling with a wire to the rebars which are exposed at the top of the pile (the concrete piles that hold bridges above water) and the steel rebar wont oxidize and cause the concrete piling to crack. Bridge life is improved from 70yrs expectancy to >300 years. It is currently being used on the 7-mile bridge in south florida and being implemented in a lot of other places.