The 3rd Ave Bridge, located in Minneapolis, Minnesota, received a cathodic protection (CP) system in the form of zinc thermal spray coating (TSC) on the underside of the North approach of the bridge to extend the structure's service life.
As part of the work, an area of the TSC application was selected to be monitored for performance verifications. VCS verified that the TSC in this zone was isolated from the reinforcement steel so that the performance of the CP system could be monitored utilizing a junction box. VCS was responsible for inspecting all of the structure connections installed by Vector Construction Inc. to ensure that they were electrically continuous in the directly shorted zones and isolated from the TSC anode system in the monitored zone.
At least two structure connections were installed per 200 square feet.
For the monitored zone, before applying the TSC on the concrete surface, a permanent silver/silver chloride reference electrode was installed to allow for performance verifications. Upon installation, VCS terminated the structure, anode, test, and reference electrode wires inside the junction box. VCS verified that the monitored zone received polarization current from the TSC anode. VCS was also responsible for verifying the bond strength of the TSC to the concrete substrate. Bond testing of the applied TSC was performed following the ASTM D4541 Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers. At a few locations, VCS identified that the bond test was below the project specification requirements and informed the contractor immediately to redo those regions. After the areas were redone, VCS retested those regions and verified that the bond strengths passed the required strength per the project specifications.
As part of the scope of work, VCS was also required to measure the nominal thickness of the applied TSC. VCS measured the thickness of the TSC by placing a small piece of tap in the spray application area and removing the tape along with the TSC sample after spraying in the area was completed. The sample of TSC was then measured with calipers at the rate of 1 measurement per 20 ft2 of a continuous application area and verified that sufficient and equal amounts of TSC were applied throughout the designated structure area.
Overall, VCS verified that the TSC CP system on the 3rd Ave Bridge was installed per the project specifications and confirmed that the system was working as intended to mitigate corrosion of the reinforcing steel in the application areas.