Suffering from severe corrosion related damage, a Washington, DC office building's terra cotta cornice was in need of repair. For this project, it was determined that an impressed current cathodic protection (ICCP) system would be the best method for preserving this landmark building's cornice. The main joint above the modillions, which was cracked and open in areas, had been poorly repaired with a Portland cement mortar. Over many areas, the outrigger system that supports the cornice had lost much of its section through corrosion. The corrosion product was up to ¾-inch thick causing downward stresses and cracking on the terra cotta modillions.
After a thorough investigation and polarization trial, it was concluded that the cornice could be treated with an Impressed Current Cathodic Protection (ICCP) system through a carefully planned and well executed design, even though the installation of an ICCP system on a cornice is atypical. ICCP was the best solution for this project for several reasons including the non-destructive nature of the technology, cost savings associated with ICCP versus terra cotta replacement and the long-term solution to corrosion related damage that ICCP provides. The cathodic protection system was installed as part of an overall exterior restoration scheme. The joints were repointed as the installation was occurring, which masked all signs of the system.
The installation only required one major joint to be chased out, just above the modillions on each elevation. The major components of the system were installed within this joint, with the external wiring being brought into the structure at the brickwork just below the terra cotta cornice. The internal components were installed in the mechanical space within the attic, with all wiring and internal connections terminating at distributed power supplies. These were then connected to a main control unit, which can be remotely accessed via the internet for remote monitoring.
During the restoration, it was discovered that the terra cotta cornice was in far worse condition than previously anticipated. This required additional supports to be added to the cornice and careful planning between the engineers, quality assurance team, structural engineers, installation team and masons. All supports had to be carefully bonded to the cathodic protection system so that the new steel was electrically continuous.
One of the major challenges of this project was the design-build approach. Based on the budget, time-frame for completion and overall contracting schedule, there was not a lot of lead time for the investigation period. Not all buildings are suitable for ICCP, so time needs to be allowed to properly investigate the facility to determine the method's applicability for a project. After Electro Tech CP spent a week on site investigating the building and conducting non-destructive numerous tests, the building was determined to be suitable for this application.
Another challenge was training. Only a handful of contractors in the United States have installed ICCP systems in historic buildings. This requires a strong site presence and specialized training of the installation contractors. For this reason, Structural Preservation Systems (SPS) was chosen to perform the installation.
In the end, the client was very pleased with the outcome of the work from all parties involved. Open communication and teamwork between the conservators, engineers and SPS were crucial to the success of this project. The system has been successfully running since January 2007 and is controlled by specialist power supplies and a main control unit specifically designed for steel frame corrosion in heritage buildings.