TRIMM is supported by funding from the 7th Framework Programme Call: SST.2011.5.2-2. Theme: Advanced and cost effective road infrastructure construction, management and maintenance
Corrosion monitoring
Dr. Mirjam Bajt Leban ZAG and IGH [email protected] The main aim of the research work within this project was: 1. To select appropriate measurement techniques and parameters for direct assessment of corrosion activity, 2. To „translate“ the output of this corrosion monitoring system into values which can be implemented in the maintenance and asset management for cost-effective operation.
Presentation: Principle of monitoring techniques Summary of laboratory and in-situ investigation Corrosion criteria definition Proposed corrosion monitoring system Methods/techniques used during TRIMM project
Inspection Monitoring (continuous) Direct assessment of Half-cell potential Embedded reference corrosion activity (potential mapping) electrode Galvanostatic pulse EIS technique Macrocell current Electrical resistance probe (ER)
Determination of Resistivity of fiber optical sensors influencing parameters concrete (pH, Cl-) Humidity resistivity sensors pH, Cl-, T (concrete resistivity, humidity) Macro-cell current measured by Principle: multi-depth sensors (IGH): electrochemical method •Macro-cell current between cathode and anodes, icorr •Steel-stainless steel potential, Vcorr •Electrical resistivity of concrete between neighbour anodes by AC method, ρconcrete
Electrical resistance probes (ZAG): Principle: physical method • Wheatston breadge – change of resistance because of thickness reduction is measured. • Measured resistance is proportional to thickness u h h reduction and via that 0 1 u proportional to corrosion rate of U U U out u ER sensor made from metal. Uin U
h h0 h Multi depth macro-current and electrical resistance sensors sensitive for detection of changes of corrosion processes and corrosion rate regardless to the corrosion activator Multi depth sensors Electrical resistance sensors
•Corrosion and chloride content increasing near reinforcement time dependent processes
0,45 0,4 0,35 0,3 0,25 0,2
Cl- content (% 0,15 0,1 0,06% Cl, carbon steel corrosion initiation 0,05 0 0 5 10 15 20 25 30 CR (um/Y) Koper harbour test site Since December 2013
Goals: long-term behaviour, compare different zones of exposure, compare different measuring techniques
Data avaliable on WEB page: www.corrosion- kp.zag.si IGH: Maslenica, Cetina and Krka bridge (Croatia)
Maslenica Cetina Krka (over river) No. of sensors: 21 No. of sensors: 6 No. of sensors: 6 Installed: 1996 - 1997 (during bridge Installed: March 2006 - 2007 Installed: July 2003 - March 2004 construction) Measurements: May 17th 2007, January Measurements: May 8th 2004, Type of measurements: 29.01.2014. 19th 2014 September 12th 2004, February 3rd (initial measurements not available). Type of measurements: anode Ladder 2005, January 19th 2014 Type of measurement: Anode Ladder (macro cell current), concrete resistivity, Type of measurements: Anode Ladder (macro cell current), concrete resistivity, Half cell potentials, temperature (macro cell current), concrete resistivity, Half cell potentials, temperature, Half cell potentials, temperature chloride levels and concrete properties IGH: Maslenica, Cetina and Krka bridge (Croatia)
Maslenica Cetina Krka (over river)
Corrosion at the top and Initiation of arch foot after No corrosion in 10 years foot of arch – 5 cm under 7 years concrete cover layer, after 18 years 0,6 2007 0,5 2012
0,4
0,3 % Cl-
0,2
0,1 0,06% Cl, carbon steel corrosion initiation
0 0123456
Chloride depth (cm)
Chloride content (% on concrete weight) measured on Maslenica bridge Chritical corrosion sites – pavaments, carriageway Water Spray zone, construction, water droplets, high moderate drainage corrosion risk corrosion risk
Splash, tidal zone, high Moderate corrosion risk, corrosion risk mostly due to carbonatization SEA • Macro-cell currents transformation to corrosion rates (CR):
2 • Icorr = 0,1 μA/cm – CR = 1.1 μm/Y - corrosion initiation (Condition category=1)
2 • Icorr=3 μA/cm – CR = 34 um/Y - first cracks apperance (Condition category=5)
CR = icorr*11.46
No corrosion Depassivation Cracking Delamination Loss of bond
ER PROBE MACRO-CELL CURRENT SENSOR PROS CONS PROS CONS Measuring 1 sensor per Nothing noted Measurements at Galvanic interactions depths chosen depth different depths between anodes
Measuring Good for Not appropriate High sensitivity to Breaks down at severe range early stages for long term corrosion initiation corrosion (stage 5) 1-3 monitoring (stage 1) during stages Good for stages 1- 4-5 4 and some time in stage 5 Cost Not costly Nothing noted Not costly sensors Expensive and sensors and and instruments for complicated automatic automatic manual data data acquisition system data reading acquisition system Results User-friendly Nothing noted Nothing noted Strong: needs expert to interpretation simple data interpret the results analysis (extensive and complicated data analysis and interpretation) December 2013 Spring 2014 Krk bridge Koper harbor
Multidepth
Location of sensors
MnO2 electrode
Macrocell current
Sections repaired 2013 •Multi depth sensors (December 2013), •ER probes (July 2014) ER probes, EN system Combined with other conventional inspection methods Good correlation between both methods during the investigation (verified in lab) Both techniques can be used for chloride as well as carbonation induced corrosion Macro-cell sensor is sensitive for detection of anodic/cathodic changes at different depth of „corroded concrete“, however, results need interpretation Electrical resistance (ER) sensors are sensitive method to detect initiation and monitor changes in damaged concrete in earlier stages Installation of sensors on critical corrosion sites of construction – necessary inter-collaboration between designer-projectant and corrosion specialist