Treatment Prevents Corrosion in Steel and Concrete Structures
- Monday, 14 April 2008
NASA’s Kennedy Space Center is located on prime beachfront property along the Atlantic coast of Florida on Cape Canaveral. While beautiful, this region presents several challenges, like temperamental coastal weather, lightning storms, and salty, corrosive, sea breezes assaulting equipment and the Center’s launch pads. The constant barrage of salty water subjects facility structures to a type of weathering called spalling, a common form of corrosion seen in porous building materials such as brick, natural stone, tiles, and concrete. In spalling, water carries dissolved salt through the building material, where it then crystallizes near the surface as the water evaporates. As the salt crystals expand, this creates stresses which break away chips, or spall, from the surface, causing unsightly and structural damage.
The potential for corrosion heightens as concrete structures age, because over time concrete loses its acidity, or pH. When it starts out, poured concrete has a high pH value, between 11 and 13, which helps to inhibit corrosion. Over time, though, this value drops, and when the pH value dips into the 8 to 9 range, there is potential for corrosion of the steel reinforcing bars, or rebar, causing further structural concerns.
In the mid-1990s, to protect the rebar, NASA developed an electromigration technique that sends corrosion- inhibiting ions into rebar to prevent rust, corrosion, and separation from the surrounding concrete. An ounce of prevention is worth a pound of cure, and with the help of Florida’s Technological Research and Development Authority, an independent state agency that partnered with Kennedy on technology transfer initiatives, the Center began working with Surtreat Holding LLC, of Pittsburgh, Pennsylvania, a company that had developed a chemical option to fight structural corrosion in 1997. Surtreat’s method was to apply its anti-corrosive solution product, TPS-II, to the surface of a corroding concrete slab, where it would then seep through to the rebar, coating it and preventing further corrosion.
Combining Surtreat’s TPS-II with electromigration fit well in the Kennedy dual-use program, part of NASA’s technology transfer and commercialization effort. The cooperative effort involved Surtreat providing NASA with the corrosion-inhibiting chemical and concrete test slabs, along with technical support as needed. Kennedy provided testing specifications and procedures, then prepared the concrete with the Surtreat chemical and carried out an environmental evaluation of the treatment. Kennedy’s materials scientists reviewed the applicability of the chemical treatment to the electromigration process and determined that it was an effective and environmentally friendly match, suitable for use at the NASA facility.
Ten years later, NASA is still using this combined approach to fight concrete corrosion, and it has also developed a new technology that it believes will further advance these efforts. The technology is a liquid galvanic coating, applied to the outer surface of reinforced concrete, to protect the embedded rebar from corrosion. The coating contains one of several types of metallic particles—magnesium, zinc, or indium. An electrical current established between metallic particles in the applied coating and the surface of the steel rebar produces cathodic protection of the rebar. The current forces a flow of electrons from the coating (anode) to the rebar along a separate metallic connection. This surplus of electrons at the rebar (cathode) prevents the loss of metal ions that would normally occur as part of the natural corrosion process. The technology, made of inexpensive, commercially available ingredients, can be applied to the outside surface of reinforced concrete (most rebar corrosion prevention must be applied directly to the rebar) and with a conventional brush or spray, eliminating the need for expensive, specialized labor.