Corrosion of reinforcing steel and other embedded metals is theleading cause of deterioration in concrete. When steel corrodes, theresulting rust occupies a greater volume than the steel. This expansion creates tensile stresses in the concrete, which can eventuallycause cracking, delamination, and spalling (Figs. 1 and 2).Steel corrodes because it is not a naturally occurring material.Rather, iron ore is smelted and refined to produce steel. Theproduction steps that transform iron ore into steel add energyto the metal.Steel, like most metals except gold and platinum, is thermodynamically unstable under normal atmospheric conditions andwill release energy and revert back to its natural state—ironoxide, or rust. Thisprocess is calledcorrosion.For corrosion to occur,four elements must bepresent: There must beat least two metals (ortwo locations on asingle metal) at different energy levels,an electrolyte, and ametallic connection