Performance of Zinc Anodes for Cathodic Protection of Reinforced Concrete Bridges
Operation of thermal spray zinc (Zn) anodes for cathodic protection (CP) of reinforced concrete structures was investigated in laboratory and field studies conducted by the Albany Research Center (ARC) in collaboration with the Oregon Department of Transportation. The purposes of the research presented in this report were: evaluate the need for preheating concrete to improve the adhesion of the anode; estimate the service life of thermal spray Zn CP anodes; determine the optimum thickness for Zn CP anodes; characterize the anode-concrete interfacial chemistry; and correlate field and laboratory results. Laboratory studies involved accelerated electrochemical aging of thermal sprayed Zn anodes on concrete slabs, some of which were periodically wetted while others were unwetted. Concrete used in the slabs contained either 1.2 or 3 kg NaCl /m3 (2 or 5 lbs NaCl /yd3) as part of the concrete mix design. The Zn anodes were applied to the slabs using the twin wire arc-spray technique. Half of the slabs were preheated to 120-160 C (250-320 F) to improve the initial Zn anode bond strength and the other half were not. Accelerated aging was done at a current density of 0.032 A/m2 (3 mA/ft2), 15 times that used on Oregon DOT Coastal bridges, i.e, . 0.0022 A/m2 (0.2 mA/ft2) Cores from the Cape Creek Bridge (OR), the Richmond San Rafael Bridge (CA), and the East Camino Underpass (CA) were used to study the anode-concrete interfacial chemistry, to relate the chemistry to electrochemical age at the time of sampling, and to compare the chemistry of the field anodes to the chemistry of anodes from the laboratory studies. Cores from a CALTRANS study of a silane sealant used prior to the application of the Zn anodes and cores with galvanized rebar from the Longbird Bridge (Bermuda) were also studied. Aged laboratory and field anodes were characterized by measuring some or all of the following parameters: thickness, bond strength, anode-concrete interfacial chemistry, bulk chemistry, anode resistance, circuit resistance, electrochemical age, and air and water permeability. Models are presented for the operation of periodically-wetted and unwetted thermal spray Zn anodes from the initial energizing of the anode to the end of its service life. The models were developed in terms of bond strength, circuit resistance, anode-concrete interfacial chemistry, electrochemical age, and anode condition. The most significant results of the research are: (1) preheating concrete surfaces prior to coating with Zn is unnecessary; (2) anodes generally fail due to loss of bond strength rather than Zn consumption; (3) Unwetted anodes fail more quickly than periodically-wetted anodes; (4) 0.47-0.60 mm (12-15 mil) anode thickness is adequate for most Oregon DOT coastal impressed current CP (ICCP) installations; (5) based on bond strength, thermal spray Zn ICCP anode service life is approximately 27 years at 0.0022 A/m2 (0.2 mA/ft2); (6) anode reaction products alter the anode-concrete interface by rejecting Ca from the cement paste, by replacing it with Zn, and by the accumulation of a Zn mineral layer that includes chloride and sulfur compounds; (7) CP system circuit resistance provides an effective means for monitoring the condition of Zn ICCP anodes as they age.
- Research Organization:
- Albany Research Center, Albany, OR (US)
- Sponsoring Organization:
- Oregon Dept. of Transportation; Federal Highway Administration (US)
- DOE Contract Number:
- none (FWHA contract/grant no. SPR 364)
- OSTI ID:
- 804079
- Report Number(s):
- DOE/ARC-TR-02-011; FHWA-OR-RD-02-10; SPR 364; TRN: US200305%%819
- Resource Relation:
- Other Information: Also available at ODOT; PBD: 1 Mar 2002
- Country of Publication:
- United States
- Language:
- English
Similar Records
Alternate anode materials for cathodic protection of steel reinforced concrete
Anodes for cathodic protection of reinforced concrete
Related Subjects
ANODES
CATHODIC PROTECTION
CONCRETES
CURRENT DENSITY
HEAT TREATMENTS
PERFORMANCE
REINFORCED CONCRETE
SERVICE LIFE
SULFUR COMPOUNDS
US DOT
ZINC
SCANNING ELECTRON MICROSCOPY
ANODE
THERMAL SPRAY
TWIN-WIRE ARC SPRAY
REBAR
REINFORCING BAR
REINFORCED CONCRETE BRIDGES
CONCRETE
IMPRESSED CURRENT CATHODIC PROTECTION
SACRIFICIAL ANODE CATHODIC PROTECTION
CIRCUIT RESISTANCE
ELECTROCHEMICAL AGE
BOND STRENGTH
ZINC MINERALS
CHLORIDE
SALT
LIFE CYCLE COST
PH