Article: Polymer Concrete For Structural Restoration And Corrosion Protection Of Concrete Support Columns
By David E. Snider and Heather M. Ramsey of Sauereisen Inc.
A large copper mine and refinery in the western United States had a dilemma. Their cell house, which contains over 1,500 cells, each holding more than 20,000 gallons of electrolyte, had experienced severe corrosion and structural degradation of the support columns for the tanks. These columns support the cells in their solvent extraction and electrowinning process. This process entails immersion of a stainless steel cathode or "starter plate" into the electrolyte. Pure copper is deposited onto the starter plate during this 10-day digestion process. The collected copper is then further refined at a separate location. Over time, highly acidic leakage from the cells had corroded the support columns to the point that their ability to adequately withstand the imposed load was in doubt. Additionally, the refinery desired to upgrade the facility's ability to withstand seismic activity.
The leakage, primarily copper sulfate and 25% sulfuric acid at a pH of 1.0 or less, corroded not only the concrete but more significantly the No. 8 reinforcement bar (rebar) encased in the concrete. Corrosion of the rebar resulted in an increase of internal pressure due to expansion of the corrosion products, therefore putting the concrete in high tensile stress. The direct effect of this stress was cracking and spalling of the concrete.