Characterization of black corrosion in reinforced concrete structures: analyses of field samples from southern Sweden
(2019) In Dissertations in Geology at Lund University GEOR02 20172Department of Geology
- Abstract (Swedish)
- I den här studien karakteriseras fenomenet anaerob korrosion utifrån både litteraturstudier om korrosionsprocesser och korrosionsprodukter samt genom undersökning av fältprover från betongkonstruktioner i salthaltiga undervattensmiljöer i södra Sverige. Anaerob korrosion av armering i vattenmättad betong är ett omfattande men hittills relativt ouppmärksammat problem. Detta fenomen kan leda till allvarliga skador som försämrar betongkonstruktionens bärighet om dessa skador förblir oupptäckta. Svartrost har korrelerats med den anaeroba korrosionsprocessen och utgör en av de korrosionsprodukter som bildas under processen. Vid undersökning av cementproverna observerades främst rödrost som ett resultat av den ökade syretillgången, i de översta... (More)
- I den här studien karakteriseras fenomenet anaerob korrosion utifrån både litteraturstudier om korrosionsprocesser och korrosionsprodukter samt genom undersökning av fältprover från betongkonstruktioner i salthaltiga undervattensmiljöer i södra Sverige. Anaerob korrosion av armering i vattenmättad betong är ett omfattande men hittills relativt ouppmärksammat problem. Detta fenomen kan leda till allvarliga skador som försämrar betongkonstruktionens bärighet om dessa skador förblir oupptäckta. Svartrost har korrelerats med den anaeroba korrosionsprocessen och utgör en av de korrosionsprodukter som bildas under processen. Vid undersökning av cementproverna observerades främst rödrost som ett resultat av den ökade syretillgången, i de översta millimetrarna av täckskiktet. Svartrost var mer frekvent förekommande med ökande djup i betongproverna. De svarta korrosionsprodukterna är fördelade i sprickor och hålrum i betongen samt tenderar att visa ett internt cykliskt mönster med alternerande tvåvärt och trevärt järn. Både svartrost och potentiellt en kloridvariant av grönrost (GR(Cl–)) har observerats i anslutning till armeringsjärnet. De fältprover som har undersökts med hjälp av polariserad optisk mikroskopering och svepelektronmikroskoperning (SEM) visar även på nedbrytning av den omgivande cementpastan. Urlakning av grundämnena Ca, Al och Si är ett tydligt återkommande fenomen i betongens täckskikt, runt armeringsjärnet och i de hålrum där korrosionsprodukter återfinns. Ettringit, portlandit och gips har observerats i sprickor och hålrum i betongen och troligtvis bildats till följd av urlakningen. Utfällningar av korrosionsprodukter, kallade noduler, på betongväggarna tyder på en utåtgående transport av de lösta järnjoner som diffunderar i betongens porvatten. Dessa utfällningar består främst av svartrost med en yttre skorpa av rödrost, vilken verkar som ett skyddande hölje för de inre skikten av korrosionsprodukter. Detta gynnar i sin tur den anaeroba korrosionsprocessen som kan fortgå tills armeringsjärnet är helt urholkat. (Less)
- Abstract
- In this study, the phenomenon of black corrosion is characterized by both literature studies on corrosion processes and corrosion products, and by analyzing field samples from saline subaqueous concrete structures in southern Sweden. Anaerobic corrosion of reinforcement in water-saturated concrete is an extensive but yet relatively unnoticed problem. This phenomenon can lead to serious damages that, if undetected, weaken the load-bearing capacity of the concrete structure. Black rust has been correlated with the anaerobic corrosion process and is one of the corrosion products formed during this process. When studying the concrete samples, mainly red rust was found in the superficial layer (i.e. millimeters in depth) as a result of the... (More)
- In this study, the phenomenon of black corrosion is characterized by both literature studies on corrosion processes and corrosion products, and by analyzing field samples from saline subaqueous concrete structures in southern Sweden. Anaerobic corrosion of reinforcement in water-saturated concrete is an extensive but yet relatively unnoticed problem. This phenomenon can lead to serious damages that, if undetected, weaken the load-bearing capacity of the concrete structure. Black rust has been correlated with the anaerobic corrosion process and is one of the corrosion products formed during this process. When studying the concrete samples, mainly red rust was found in the superficial layer (i.e. millimeters in depth) as a result of the increased oxygen supply. Black rust was more frequently observed with increasing depth in the concrete. The black rust is usually distributed in cracks and cavities and tends to show an internal cyclic pattern with alternating ferrous and ferric iron. Both black rust and potentially a chloride variety of green rust (GR(Cl–)) have been observed in connection with the reinforcement bar. The field samples that have been examined using polarized optical microscopy and scanning electron microscopy (SEM) do also show signs of degradation of the surrounding cement paste. Leaching of cementitious elements (Ca, Al and Si) is a recurring phenomenon in the concrete cover, around the reinforcing iron, and around cavities where corrosion products have been detected. Ettringite, portlandite and gypsum, were observed in cracks and cavities in the concrete and have probably formed as a result of the leaching. Precipitations of corrosion products, called nodules, on the concrete walls indicate an outward transport of the dissolved iron ions that diffuse into the pore water of the concrete. These deposits mainly constitutes of black rust products with an outer crust of red rust which act as a protective casing for the inner layers of corrosion products. This, in turn, favors the anaerobic corrosion process which can continue until the reinforcing iron is completely eroded. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/8974829
- author
- Halling, Jenny LU
- supervisor
- organization
- course
- GEOR02 20172
- year
- 2019
- type
- H2 - Master's Degree (Two Years)
- subject
- keywords
- black rust, anaerobic corrosion, reinforced concrete, corrosion products, green rust, microbial corrosion
- publication/series
- Dissertations in Geology at Lund University
- report number
- 554
- language
- English
- additional info
- External supervisor: Jan Erik Lindqvist, RISE CBI
- id
- 8974829
- date added to LUP
- 2019-04-29 22:30:28
- date last changed
- 2019-04-29 22:30:28
@misc{8974829,
abstract = {{In this study, the phenomenon of black corrosion is characterized by both literature studies on corrosion processes and corrosion products, and by analyzing field samples from saline subaqueous concrete structures in southern Sweden. Anaerobic corrosion of reinforcement in water-saturated concrete is an extensive but yet relatively unnoticed problem. This phenomenon can lead to serious damages that, if undetected, weaken the load-bearing capacity of the concrete structure. Black rust has been correlated with the anaerobic corrosion process and is one of the corrosion products formed during this process. When studying the concrete samples, mainly red rust was found in the superficial layer (i.e. millimeters in depth) as a result of the increased oxygen supply. Black rust was more frequently observed with increasing depth in the concrete. The black rust is usually distributed in cracks and cavities and tends to show an internal cyclic pattern with alternating ferrous and ferric iron. Both black rust and potentially a chloride variety of green rust (GR(Cl–)) have been observed in connection with the reinforcement bar. The field samples that have been examined using polarized optical microscopy and scanning electron microscopy (SEM) do also show signs of degradation of the surrounding cement paste. Leaching of cementitious elements (Ca, Al and Si) is a recurring phenomenon in the concrete cover, around the reinforcing iron, and around cavities where corrosion products have been detected. Ettringite, portlandite and gypsum, were observed in cracks and cavities in the concrete and have probably formed as a result of the leaching. Precipitations of corrosion products, called nodules, on the concrete walls indicate an outward transport of the dissolved iron ions that diffuse into the pore water of the concrete. These deposits mainly constitutes of black rust products with an outer crust of red rust which act as a protective casing for the inner layers of corrosion products. This, in turn, favors the anaerobic corrosion process which can continue until the reinforcing iron is completely eroded.}},
author = {{Halling, Jenny}},
language = {{eng}},
note = {{Student Paper}},
series = {{Dissertations in Geology at Lund University}},
title = {{Characterization of black corrosion in reinforced concrete structures: analyses of field samples from southern Sweden}},
year = {{2019}},
}