Greetings from Bridging Solutions!

This installment of “A Bridge Moment” provides a summary of the basics on corrosion of reinforcing steel in concrete. Corrosion of reinforcing steel and other embedded metals is the leading cause of deterioration in concrete. Expansion forces are created when embedded steel corrodes because the rust that forms occupies a greater volume than the steel. The expansion forces create tensile stresses in the concrete, which can eventually cause cracking, delamination and spalling.

Steel corrodes because it is not a naturally occurring material. The production steps that transform iron ore into steel add energy to the metal. Steel is thermodynamically unstable under normal atmospheric conditions and will release energy and revert back to its natural state – iron oxide, or rust. This process is called corrosion. For corrosion to occur, there must be at least two metals (or two locations on a single metal) at different energy levels, an electrolyte and a metallic connection.

In reinforced concrete, the rebar may have many separate areas at different energy levels. Concrete acts as the electrolyte, and the metallic connection is provided by wire ties, chair supports, or the rebar itself. Our next installment will tell the rest of the story about corrosion of the embedded steel inside concrete and how to prevent or slow down the process.