Replacing thermal sprayed zinc anodes on cathodically protected steel reinforced concrete bridges.

Details

• Creators:
  Shi, Xianming ; Cross, Jon Doug ; Liu, Yajun ; Fortune, Keith ; Ewan, Levi
• Corporate Creators:
  Western Transportation Institute
• Corporate Contributors:
  Oregon. Dept. of Transportation. Research Section ; United States. Federal Highway Administration
• Subject/TRT Terms:
  Cathodic Protection Reinforced Concrete Bridges Reinforcing Steel Retrofitting Spray Painting Thermal Sprayed Zinc, Anode Replacement, Cathodic Protection, Reinforced Concrete, Bridge Preservation, Surface Preparation Zinc Coatings
• Publication/ Report Number:
  FHWA-OR-RD-12-02
• Resource Type:
  Tech Report
• Geographical Coverage:
  Oregon
• Corporate Publisher:
  Oregon. Dept. of Transportation. Research Section
• Abstract:
  "This research aimed to address questions underlying the replacement of arc-sprayed zinc anodes on cathodically protected steel reinforced concrete bridges and to develop a protocol to prepare the concrete surface for the new anode, through a combination of literature review, practitioner surveys, laboratory studies, and field investigation (Pier 9 of the Yaquina Bay Bridge, Oregon). Concrete with an equivalent electrochemical age of 5 to 45 years was found to have a reaction layer of ~1 mm. To achieve strong initial bond strength of new zinc to the profiled concrete surface, the current ODOT sandblasting operating configuration (#8 nozzle with high sand volume) is too aggressive and should be changed to #6 nozzle with low sand volume to achieve target RMS macro-roughness of 1.2-2.1 centi-inches and micro-roughness of 3.5-5 μm. It is recommended to adjust the anode removal and surface profiling based on the electrochemical age of the existing concrete. Wherever possible, large aggregates (e.g., diameters ¾ in. and bigger) should be avoided for exposure by surface profiling. For non-electrochemically aged concrete, the surface should be profiled to achieve a RMS macro-roughness of 1.1-1.8 centi-inches and 5-36% exposed aggregates. For existing concrete with relatively high electrochemical age (14 yrs), the surface should be profiled to achieve a RMS macro-roughness of 1.1-1.5 centi-inches and 44-55% exposed aggregates. The following recommendations were made for old anode removal and surface preparation before new anode application: use a reasonably low air pressure and a reasonably hard and dense abrasive material for sandblasting; have a reasonably thin coating per pass during arc-spray operations; and have a slightly thinner overall Zn coating layer (15-17 mils vs. the currently used 17 mils). It is also desirable to have concrete with good surface cohesion strength and a minimum of 150 psi initial bond strength. For existing concrete with an equivalent electrochemical age of more than 8 years, the reaction layer should be completely removed prior to profiling and arc spraying (e.g., 4 mm grinding)."
• Format:
  PDF
• Funding:
  SPR 682
• Collection(s):
  University Transportation Centers US Transportation Collection
• Main Document Checksum:
  urn:sha-512:d2ffc3ebe0edd9926788e5c1938b6dcc8553a7d48231f3917a11f9ee97cf82b9320ddb61aaaddf055a9967a2e4dd21fe1eee73924de01601d53c164d39e761c8
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/23391/dot_23391_DS1.pdf
• File Type:
  [PDF - 6.44 MB ]