Luckett and Farley Structural has been working tirelessly with one of our clients to address certain corrosion issues they've been having at their facility. We all know that concrete cracks; well, carbon steel rusts. But the processes within their 2002 industrial building exposes the structure to the double whammy of extreme heat and steam, occurring in hot-cold cycles throughout the year. This chloride-filled environment has done a number on the wide flange beams and girders above this process area and to the reinforcing steel within adjacent 24" thick concrete walls.
In situations like these, the objective is to restore the structural components to their "pre-rusted" condition (strength and stiffness), as reasonably and feasibly possible. Even more importantly, when you're playing with your client's money, the focus should be on educating and advising them of their options: there is ALWAYS more than one way to address a problem and they all have financial implications.
Here is our procedure/methodology for repairing corroded structural steel:
- Step 1: If there is an imminent hazard as a result of the corrosion, provide temporary shoring.
- Step 2: Prepare a testing program to evaluate the impact on the quality of the material or extent of corrosion; document the damage.
- Step 3: Provide viable repair schemes for a Contractor to estimate and the Owner to review; obtain feedback on feasibility and cost.
- Step 4: Perform the repairs. Give due consideration to the fact that the existing members may already be loaded/stressed prior to repairing. Any new material added to the corroded member may not be as effective if the (gravity) load isn't removed first!
- There are numerous methods to repairing structural steel: most are project-specific and can involve supplemental plating, reinforcement, etc. What's most crucial is Step 5: Either eliminate the corrosive environment or protect against it.
Since eliminating the harsh environment is obvious (if you have the luxury to do so), here's just a couple protection solutions we've employed that you may consider for your own corrosion ailments:
-Cathodic Protection with Galvanic Anodes: Attach zinc anodes to the reinforcing mat in a grid-like pattern to force the corrosion to occur within the less-noble metal...zinc. These galvanic anodes do deteriorate so care and caution into providing the proper quantity should be given.
-Corrosion Inhibitor: Since concrete is porous, this type of product can be spray-applied to coat the surface of the existing concrete.
-Epoxy Coating: If heat is not a factor, this could be a viable option in which the carbon steel is coated with a barrier to protect against chloride attack.
-Cathodic Protection with Inorganic Coating: Not many companies manufacture this type of solution, but it's ideal for our case in point, wherein an inorganic ceramic (zinc) coating is applied to the structural steel and an AC current is connected. This forces the corrosion to occur within the zinc coating, slowing the rate of corrosion on the protected substrate by as much as 1/25 of the pre-coated condition. This technology appears to have proved successful for many years and perfected by one company in particular, Applied Semiconductor. The benefit here: it can withstand temperatures of up to 800 degrees Fahrenheit!
In situ, galvanizing, like painting, is typically not as effective as the aforementioned options in that it's spray-applied since it relies on proper bond with the substrate and is more susceptible to scraping/flaking off with time and exposure.
Like a tooth cavity, the longer you wait to address corrosion of your steel building, the more money you will spend when you eventually decide to take action. Take steps sooner rather than later (or when it's too late) to correct the issue, as it won't fix itself. At least, that's what my dentist says, anyway.