Alcatraz Island Cell House Historic Preservation

PULLMAN performed historic concrete repairs to the external façade, windows and pilaster. STRUCTURAL TECHNOLOGIES was brought in to provide cathodic protection solutions to protect the embedded reinforcement within the pilasters of the cell house external face.  Structural Technologies designed the Impressed Current Cathodic protection System and provided detailed installation procedures as well as site supervision and oversight for the critical installation and testing.

Crews installed the ElectroTechCP™ Impressed Current Corrosion Control System designed and manufactured by STRUCTURAL TECHNOLOGIES. The Impressed current system consisted of state of the art power supply and monitoring system specifically designed for cathodic protection that could deliver and monitor protection current with 1mA accuracy and protection levels with 1mV accuracy. The ICCP current is delivered via Mixed Metal Oxide Coated Titanium Anodes installed within the concrete cover and the Pilasters. For monitoring purposes Manganese Dioxide Reference Electrodes were permanently installed across the entire structure to ensure that the ICCP system is functioning as per design and corrosion protection criteria is achieved. The state of the art cathodic protection monitoring system has remote access capability that enables Structural Technologies engineers to monitor and operate the system remotely from our office in Columbia, Maryland.

In terms of quality, a specifically tailored project QA/QC plan was put in place with several tests, inspection and hold points to insure that each component of the ICCP system was tested prior and after installation.   

One of the most important installation tasks that received special attention was the confirmation of the existing steel reinforcement electrical continuity. Given the age of the structure and the resources used during installation as well as the workmanship available to the original builders it was expected that the structure will have a large number of embedded steel elements not electrically continuous with each other. Structural Technologies had to make several continuity tests, GPR scans and meticulous excavation to both test and correct the needed electrical continuity within each zone, all this while preserving the historic nature of the structure . Following the completion of the electrical continuity tests and corrections, a stray current test was conducted to determine the extent of the ICCP system influence during a pilot installation, this test confirmed the system current requirement and established the boundaries of ICCP system effect. The test allowed Structural Technologies design team to further fine tune the design and eliminate the risk associated with stray current by effectively identifying the possible metallic items falling within the ICCP system area of influence.

The next step was repairing the concrete elements and then installation of the ICCP system for the entire structure. The installation of the ICCP system required several checks for the proper installation. A detailed quality assurance and conformity program insured that not only all reinforcement and embedded metallic items were made continuous but each and every system component was installed correctly. The circuit’s performance were verified and recorded at each step of the process insuring that no short circuits exist and anode encapsulation was as per design requirement. Once the installation was completed pre-commissioning tests insured that the system will function as intended and primary current demand was verified. The system was commissioned successfully and protection levels were achieved as per NACE criteria for all Pilasters after the first three months of operation.

Much preplanning went into working on a historically sensitive project with the added challenges of it being a one of the region’s most popular tourist destinations. Accessible only by boat, crews had to board ferries provided by the General Contractor to early morning shifts so that tourism could continue during the day undisturbed. After completion of a shift, the exterior work site had to be limited to the lowest noise level possible as tourists arrived each morning. Safety programs were put in place to ensure that tourists would not be affected by the ongoing construction.

In addition to working around the site access challenges, crews were trained on bird sensitivity to protect the natural wildlife that Alcatraz Island is home to. The island acts as a sanctuary for cormorants, pigeon guillemots, waterfowl such as snowy egrets and black-crowned night herons.

Despite multiple challenges posed, the work was conducted under a tight schedule and was successfully completed on budget and without any safety incidents.