Durability of Reinforced Concrete under Impressed Current Cathodic Protection
Doktorsavhandling, 2018

Impressed current cathodic protection (ICCP) and prevention (ICCPre) are reliable and efficient techniques to stop, control and postpone corrosion in reinforced concrete structures. However, the wide application of this technique has been limited by the high cost of the anode system. Moreover, the long-term electrochemical effects on the anode-concrete interface and the steel reinforcement are still not completely clear. These effects can be beneficial or unfavorable, which will influence the performance and service life of the structure. Therefore, the long-term electrochemical effects greatly need to be quantified and taken into consideration in durability design.

The present thesis has been devoted to gaining more solid scientific understanding into this issue through experimental work. A novel and affordable carbon fiber reinforced polymer (CFRP) mesh was used as anode material instead of traditional metallic anode. Accelerated tests, using relatively high current densities, were adopted to evaluate the long-term electrochemical effects. The impact of the accelerated tests was studied and modeled. Varied characterization and monitoring techniques were employed to analyze the anode-concrete interface and the steel condition as well as chloride content.

The results show that the CFRP meshes are suitable as anode material for cathodic prevention applications, with a service life of more than 100 years.
Calcium leaching at the anode-concrete interface was inevitable as a consequence of chemical reactions and mass transport under current exchange. The chemical changes can cause material loss and increase the resistance of the concrete and eventually make the system fail. With low current densities, the chemical changes can be significantly reduced. A nonlinear conversion model was proposed to estimate the performance under low current densities from the results of the accelerated tests. The difference between the nonlinear model and the linear model can be 30% to 40%. When the current density is less than 2 mA/m2, the service life regarding the anode-concrete interface can be longer than 70 years. For the critical chloride content, under a current density of 2 mA/m2, the critical value can be increased nearly by a factor of two and the service life against chloride ingress can be increased by a factor of seven according to the DuraCrete model under the specific modeling condition.

Considering both the anode-concrete interface and the chloride content at the steel surface, it has been successfully proven that by applying low current densities, the service life of reinforced concrete structures can be significantly extended, to the range of 100 years or more. The cost of such ICCPre applications can be further reduced by using CFRP mesh anodes without compromising the performance of the system.

durability

cathodic protection and prevention

anode system

service life

critical chloride content

Chloride initiated corrosion

SB-H4, Sven Hultins gata 6
Opponent: Dr. Véronique Bouteiller, The French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR), University of Paris-Est, France

Författare

Emma Zhang

Chalmers, Arkitektur och samhällsbyggnadsteknik, Byggnadsteknologi

Carbon fiber as anode material for cathodic prevention in cementitious materials

5th International Conference on Durability of Concrete Structures,; (2016)p. 300-308

Paper i proceeding

Effect of the paste–anode interface under impressed current cathodic protection in concrete structures

Materials and Corrosion - Werkstoffe und Korrosion,; (2018)

Artikel i vetenskaplig tidskrift

Zhang, E.Q., Z. Abbas, L. Tang, Predicting service life of cathodic protection and prevention system in reinforced concrete using accelerated tests

Zhang, E.Q. and L. Tang, Effect of cathodic prevention on chloride threshold content for as-received steel in concrete

Kloridinducerad korrosion av armeringsstål är en av de främsta orsakerna till skador på betongkonstruktioner, såsom motorvägsbroar, tunnlar och hamnar. Katodiskt skydd med påtryckt ström (ICCP) och förebyggande (ICCPre) är tillförlitliga och effektiva tekniker för att stoppa, kontrollera och fördröja korrosion i armerade betongkonstruktioner. Den breda tillämpningen av denna teknik har dock begränsats av den höga kostnaden för anodsystemet. Dessutom kan systemets prestationsförmåga och livslängd påverkas av anod--betong--gränssnittet och stål-betong-gränssnittet, av vilket mekanismerna ännu inte är helt klara.

Denna avhandling har ägnats åt att få mer grundlig vetenskaplig förståelse i fråga genom experimentellt arbete. Ett nytt och kostnads effektivt kolfiberförstärkt polymer (CFRP)-nät användes som anodmaterial istället för traditionell metallanod. En accelererad testmetod användes. Varierad karakteriserings- och övervakningsteknik användes för att analysera de kemiska och mikrostrukturella förändringarna av anodbetong-stålsystemet.

Resultaten visar att CFRP-näten är lämpliga som anodmaterial för katodiska förebyggande applikationer, med en livslängd på mer än 100 år. Genom att lägga till en mycket liten strömdensitet i de armerade betongkonstruktionerna kan stålet stå för högre kloridhalt i betongen utan korrosion och livslängden mot kloridinträgning kan förlängas från 20 år upp till 140 år. Beträffande anod-betong-gränssnittet kan livslängden vara längre än 70 år under en strömdensitet mindre än 2 mA/m2.

Med hänsyn tagen till både anod-betong-gränssnittet och stålets tillstånd har det framgångsrikt visat sig att vid användning av låga strömdensitet kan livslängden hos armerade betongkonstruktioner förlängas betydligt, upp till 100 år eller mer. Kostnaden för sådana ICCPre-applikationer kan minskas ytterligare genom att använda CFRP-nätanoder utan att äventyra systemets prestationsförmåga.

Chloride induced corrosion of steel reinforcement is one of the major causes of damage of concrete structures, such as high-way bridges, tunnels and harbors. Impressed current cathodic protection (ICCP) and prevention (ICCPre) are reliable and efficient techniques to stop, control and postpone corrosion in reinforced concrete structures. However, the wide application of this technique has been limited by the high cost of the anode system. Moreover, the performance and service life of the system can be affected by the anode–concrete interface and the steel–concrete interface, of which the mechanisms are yet not completely clear.

The present thesis has been devoted to gaining more insight into this issue through experimental work and more a solid scientific understanding. A novel and affordable carbon fiber reinforced polymer (CFRP) mesh was used as anode material instead of traditional metallic anode. An accelerated testing method was adopted. Varied characterization and monitoring techniques were employed to analyze the chemical and microstructural changes of the anode–concrete–steel system.

The results show that the CFRP meshes are suitable as anode material for cathodic prevention applications, with a service life of more than 100 years. By imposing even a very small current density to the reinforced concrete structures, the steel can stand higher concentration of chloride without corroding, and the service life against chloride ingress can be extended from 20 years to 140 years. Regarding the anode–concrete interface, the service life can be longer than 70 years under a current density less than 2 mA/m2.

Considering both the anode–concrete interface and the steel condition, it has been successfully proven that by applying low current densities, the service life of reinforced concrete structures can be significantly extended, to the range of 100 years or more. The cost of such ICCPre applications can be further reduced by using CFRP mesh anodes without compromising the performance of the system.

Ämneskategorier

Infrastrukturteknik

Kompositmaterial och -teknik

Korrosionsteknik

ISBN

978-91-7597-711-9

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4392

Utgivare

Chalmers tekniska högskola

SB-H4, Sven Hultins gata 6

Opponent: Dr. Véronique Bouteiller, The French Institute of Science and Technology for Transport, Development and Networks (IFSTTAR), University of Paris-Est, France