Chloride Induced Corrosion of Reinforcement Steel in Concrete - Threshold Values and Ion Distributions at the Concrete-Steel Interface
Doktorsavhandling, 2013

The chloride threshold value (Cth), or critical chloride content, is defined as the chloride concentration at the depth of the reinforcement, which initiates the depassivation of steel in concrete. However, very limited information is available regarding the chloride distributions at the interface with the steel. The main objective of this work is to improve the knowledge and understanding about the mechanisms leading to depassivation of steel in concrete, by studying the influence of the steel surface condition and the concrete-steel interface on the corrosion initiation and the chloride distributions along the concrete-steel interface at the time of depassivation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used for spatial resolved chloride profiling in cementitious materials. A range of materials with increasing degree of heterogeneity (i.e. cement paste, mortar and concrete) and exposed to chlorides under different conditions (i.e. mixed-in, diffused and migrated) was studied. The system was optimized for maximum chloride sensitivity, while allowing for the detection of other elements such as calcium and iron. At a scan speed of 100 µm/s, a spatial resolution of 300-400 µm and limits of detection of 0.05 wt% of cement were determined. The chloride distributions along the concrete-steel interface and possible differences between passive and active regions were studied, for different steel surface conditions under free corrosion conditions as well as under potentiostatic control. The results have shown that along the interface, a range of chloride concentrations can be expected, with higher values around the corroding active sites. It was suggested that chlorides preferentially accumulate at the anodic regions even prior to depassivation, leading to pitting corrosion. A local migration mechanism was proposed to account for the chloride build-up around the anode regions, due to the formation of local potential gradients on the passive layer of the steel as a result of differences in the moisture content and oxygen availability, concentration of aggressive species and metallurgical properties, such as inclusions or mill-scale along the steel. In particular the steel surface condition and the presence of air voids at the concrete-steel interface were recognized as major factors influencing the development of potential gradients along the steel surface.

LA-ICP-MS

pitting corrosion

chloride threshold values

concrete-steel interface

Hall VK, Sven Hultins gata 6, Chalmers University of Technology, Gothenburg
Opponent: Prof. Mette Rica Geiker, Department of Structural Engineering, NTNU, Trondheim, Norway

Författare

Nelson Dias Ferreira Da Silva

Chalmers, Bygg- och miljöteknik, Byggnadsteknologi

Critical Conditions for Depassivation of Steel in Concrete: Interface Chloride Profiles and Steel Surface Condition

Nordic Concrete Research,; Vol. 45(2012)p. 111-123

Artikel i övriga tidskrifter

Application of LA-ICP-MS for meso-scale chloride profiling in concrete

Materials and Structures/Materiaux et Constructions,; (2012)p. 1369-1381

Artikel i vetenskaplig tidskrift

Betongkonstruktioner har stor betydelse för en hållbar samhällstillväxt på grund av sin stora andel av använda resurser och krav på bärande funktion samt behov av lång livslängd. Armeringskorrosion är en av de vanligaste orsakerna till skador på armerade betongkonstruktioner. Stora resurser går varje år till reparation av dylika skadade konstruktioner. Bristande beständighet hos betongen i infrastrukturen kan orsaka katastrofer med allvarliga ekonomiska följder, miljöbetingade och sociala konsekvenser, etc. Avsikten med detta projekt är att förbättra kunskapen och förståelsen av kritiska förhållanden för armeringsjärnskorrosion i betong genom meso-nivåanalysering på betong-stålskontaktytan. En metod baserad på LA-LCP-MS (Laserablation induktivt kopplad plasma masspektrometri) har utvecklat för meso-nivåanalyser. Resultaten visar att kloridinträngning var relativt homogen och kloridjoner jämnt distribuerades på betong-stålskontaktytan om det fanns ingen detekterbar korrosion på stålet. Men efter korrosionsinledandet har högre kloridhalter uppmätts runt korrosionsaktiva områden. Resultaten visar också att kloridackumulering vid korrosionsområdet var icke-proportionell mot korrosionstiden. Det framgår från resultaten att stålets yttillståndet starkt påverkar metallkänslighet mot gropkorrosion och armeringsjärnen med fabrikationsrepor var mer känsliga för korrosionsinitiering. Lokalmigrationsmekanismen föreslås för att ta hänsyn till kloriduppbyggnaden kring anodiska områden.

Concrete has great significance for the sustainable growth of society due to its large share of the resources used and requirements for load-bearing function and long service life. Corrosion of steel is one of the most common causes of damage to concrete structures. Large resources go every year to repair such damaged structures. Lack of durability in concrete infrastructure can cause disasters with serious economic consequences, environmental and social impacts. The purpose of this project is to improve the knowledge and understanding of the critical conditions for rebar corrosion in concrete by meso-level analysis of the concrete-steel interface. A method based on LA-LCP-MS (Laser ablation inductively coupled plasma mass spectrometry) has been developed for meso-level analyses. The results show that chloride penetration was relatively homogeneous and chloride ions are uniformly distributed in concrete-steel interface if no detectable corrosion of the steel. However, after corrosion initiation higher chloride content has been measured around the corrosion active areas. Results also show that chloride accumulation at the corroding area was not proportional to the corrosion time. It appears from the results that the steel surface state strongly influences its sensitivity to pitting corrosion and the reinforcement steel with mill-scale was more sensitive to corrosion initiation. Local migration mechanism is proposed to account to chloride build-up around the anodic areas.

Drivkrafter

Hållbar utveckling

Styrkeområden

Building Futures

Materialvetenskap

Fundament

Grundläggande vetenskaper

Ämneskategorier

Husbyggnad

ISBN

978-91-7385-808-3

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie

Hall VK, Sven Hultins gata 6, Chalmers University of Technology, Gothenburg

Opponent: Prof. Mette Rica Geiker, Department of Structural Engineering, NTNU, Trondheim, Norway

Mer information

Skapat

2017-10-07