Bernhard Elsener

Corrosion of steel in concrete : prevention, diagnosis, repair

Reinforced concrete has been developed and applied extensively in the 20th century. It combines the good compressive strength of concrete with the high tensile strength of steel and has proven to be successful in terms of structural performance and durability. However, there are instances of premature failure of reinforced concrete and prestressed concrete components due to corrosion of the reinforcing steel with very high economic implications of such damage. This book focuses on the chloride and carbonation induced corrosion of steel in concrete, presenting transport mechanisms and electrochemical concepts. Other types of corrosion of steel and degradation of concrete are also treated. The main emphasis lies on design and execution aspects related to durability of new and existing structures. New methods and materials for preventative measures, condition assessment and repair techniques are discussed. This makes this book an invaluable reference for any engineer and materials scientist involved in research and practice of corrosion protection, rehabilitation and maintenance of reinforced concrete structures and components. Owners, designers and contractors will profit by this updated state of the art.

Quantitative evaluation of oxidative stress, chronic inflammatory indices and leptin in cancer patients: correlation with stage and performance status.

In advanced cancer patients, the oxidative stress could take place either at the onset of disease or as a function of disease progression. To test this hypothesis, the following parameters were investigated: the erythrocyte activity of the enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx), the serum activity of glutathione reductase (GR) and the serum total antioxidant status (TAS). The total antioxidant capacity of plasma LMWA was evaluated by the cyclic voltammetry methodology. We further determined the serum levels of proinflammatory cytokines (IL‐6 and TNFα), IL‐2, leptin and C‐reactive protein (CRP). All of these parameters have been correlated with the most important clinical indices of patients such as Stage of disease, ECOG PS and clinical response. Eighty‐two advanced stage cancer patients and 36 healthy individuals used as controls were included in the study. Our findings show that SOD activity was significantly higher in cancer patients than in controls and GPx activity was significantly lower in cancer patients than in controls. Serum values of IL‐6, TNFα and CRP were significantly higher in patients than in controls. Serum leptin values of cancer patients were significantly lower than controls. SOD activity increased significantly from Stage II/ECOG 0‐1 to Stage IV/ECOG 0–1, whereas it decreased significantly in Stage IV/ECOG 3. GPx activity decreased significantly in Stage IV/ECOG 2–3. An inverse correlation between ECOG PS and serum leptin levels was found. Serum levels of IL‐2 decreased from Stage II/ECOG 0–1 to Stage IV/ECOG 2–3. A direct correlation between Stage/ECOG PS and serum levels of both IL‐6 and CRP was observed. Cisplatin administration induced a significant increase of GPx after 24 hr. In conclusion, this is the first study that shows that several “biological” parameters of cancer patients such as antioxidant enzyme activity, cytokines, leptin and CRP strictly correlate with the most important clinical parameters of disease such as Stage and ECOG PS.

Macrocell corrosion of steel in concrete – implications for corrosion monitoring

Macrocell corrosion with a local anode and a large cathode frequently occurs in chloride induced corrosion of rebars in concrete and is responsible for very high local corrosion attacks and reduction in cross-section found e.g., in bridge decks or substructures. In model-macrocells in electrolytes and in mortar the influence of the conductivity and cover depth on potential and macrocell current distribution have been studied both in open circuit conditions and under external anodic polarisation. The results have shown that low electrolyte conductivity and low cover facilitate the location of the anode of the macrocell by potential measurements due to a concentration of the spreadout of the macrocell action. Under anodic polarisation the imposed current is concentrated on the local anode. The consequences for corrosion monitoring by half-cell potential mapping and by polarisation resistance measurements on locally corroding rebars are discussed.

HALF-CELL POTENTIAL MAPPING TO ASSESS REPAIR WORK ON RC STRUCTURES

Abstract Rational, cost effective strategies for the repair and rehabilitation of bridge components have to be based on reliable information on the level and rate of deterioration. Rapid, non-destructive techniques such as half-cell potential mapping can detect and locate the main cause of deterioration, the localized chloride-induced corrosion of the rebars, and thus, greatly improve the quality of condition assessment and repair works. After completing restoration suitable monitoring techniques should be made available to control its effectiveness and durability. This paper reports on the successful use and limitations of half-cell potential mapping as an assessment technique after completion of repair work. The examples presented and discussed include traditional repair (replacement of chloride contaminated concrete), electrochemical chloride removal (ECR), electrochemical realkalization (ER) and the application of surface applied corrosion inhibitors. It is shown that due to possible changes in resistivity and pH of the concrete pore solution induced by the repair work, a correct interpretation of half-cell potential readings after repair work requires precise knowledge on the mechanism of corrosion protection of the repair strategy, and a sound experience in half-cell potential mapping on RC structures.

The electrochemical removal of chlorides from reinforced concrete

Abstract Results of a 2-year field study performed in Switzerland to evaluate the process and to obtain information on the efficiency of electrochemical chloride removal as a restoration technique for chloride contaminated concrete are presented. It is shown that about 50% of the initial chloride content is removed within 8 weeks (ca 5 × 106 C m−2). In the treated zones of the structure the half-cell potentials became more positive by about 80–100 mV. A comparison with the theoretical efficiency for chloride removal, calculated from the transference number of chloride ions, show that mainly the free chlorides in the pore solution of the concrete are removed. Due to the slow chemical equilibrium between bound and free chlorides, a second treatment after several months also removes originally bound chlorides. For severe and inhomogeneous chloride contamination local zones with active rebars and high chloride content may remain after the treatment.

Migrating Corrosion Inhibitor Blend for Reinforced Concrete: Part 1—Prevention of Corrosion

Abstract The efficiency of a migrating corrosion inhibitor in preventing corrosion of mild steel was investigated in saturated calcium hydroxide (Ca[OH]2) solutions and in mortar. The protective ef...

Migrating Corrosion Inhibitor Blend for Reinforced Concrete: Part 2— Inhibitor as Repair Strategy

Abstract The efficiency of a migrating corrosion inhibitor in stopping or reducing corrosion of steel has been investigated in saturated (sat.) calcium hydroxide (Ca[OH]2) solutions and mortar. In solution, a slight decrease of the corrosion rate was found when the inhibitor blend (10%) was added after the onset of pitting corrosion. Investigation of the diffusion rate in mortar demonstrated the high mobility of the hydroxyalkylamine molecule in porous cement paste. Thus, it was assumed that it is, in principle, possible to obtain high inhibitor concentrations at the rebar to influence corrosion rate. However, on reinforced mortar samples showing chloride-induced pitting corrosion, no reduction of the corrosion rate could be detected after inhibitor application. The discrepancy between the observed high diffusion rate and the lack of corrosion mitigation was rationalized by the fact that only the diffusion of the volatile component of the inhibitor was measured. Migration of the nonvolatile component (car...

XPS, AES and ToF‐SIMS investigation of surface films and the role of inclusions on pitting corrosion in austenitic stainless steels

Chemical inhomogeneities (inclusions) present in the alloy are known to affect the stability of the passive film on stainless steels in the presence of chloride ions. In this work, three surface analytical techniques—XPS, AES and time-of-flight SIMS (ToF-SIMS)—have been used to characterize the surface films formed on stainless steels following mechanical polishing and immersion in an aggressive 6% FeCl 3 solution, which is utilized for testing the pitting corrosion resistance of stainless steels. Two 18Cr8Ni stainless steels were investigated: one with a low sulphur content, DIN 1.4301 (0.003% S), and one with a high sulphur content, DIN 1.4305 (0.29% S). The XPS results show that the surface films on both steels are composed of mixed iron‐chromium oxyhydroxides with a higher chromium content compared to the bulk composition. The average passive film composition and the film thickness remained unchanged despite increasing sulphur content in the steel after mechanical polishing. Angle-resolved XPS results suggest the presence of hydroxides in the outer layer of the passive film, which is confirmed by ToF-SIMS its high surface sensitivity. Auger and ToF-SIMS imaging with high lateral resolution allow the inclusions to be characterized: sulphur and manganese maps show the power of imaging SIMS for studying the distribution of elements that are present in very low concentrations. It is shown that on the MnS part of the inclusions no (protective) oxide or hydroxide film is formed after mechanical polishing. This might be the reason for the well-documented role of these inclusions as pit initiation sites. Copyright ” 2000 John Wiley & Sons, Ltd.

Electrochemical characterization of TiN coatings

The corrosion behaviour of titanium nitride (TiN) CVD coatings on AISI 316L stainless steel and on inert Si3N4in hydrochloric acid is studied with a.c. and d.c. electrochemical methods. The electrochemical behaviour of TiN on stainless steel can be divided into active and passive behaviour according to the state of the substrate. The measurements indicate that there is an oxide layer on TiN that is responsible for its noble electrochemical behaviour. A model that describes the formation of the oxide layer on TiN in an electrolyte is proposed. In this paper the corrosion resistance of TiN-coated stainless steel is studied with both a.c. and d.c. electroThe beneficial combination of electrical, chemical, opti- chemical methods. cal and tribological properties of titanium nitride (TiN) makes it a suitable material for various thin film applications. TiN coatings obtained by chemical vapour deposition (CVD) and physical vapour deposition (PVD) are 2. Experimentaldetails electrochemically noble compared with most structural materials and their corrosion is negligible in most of the CVD TiN coatings 7 I.tmthick on AISI 316L stainless ordinarily used electrolytes. The electrochemical behavi- steel and on inert silicon nitride (Si3N4) were used as our of the coated materials is characterized by defects materials. The substrates were polished to 1 j.tm prior to and pores that reach through the coating and expose the the deposition. Titanium oxide layers were found on the less-corrosion-resistant substrate material to an aggres- as-received coatings using X-ray photoelectron spectrosive environment. The corrosion resistance is determined scopy (XPS). The electrolytes were prepared from conby the porosity, the passivation ability of the substrate centrated hydrochloric acid (HC1) and deionized water. and the magnitude of cathodic current of the coating. They were deaerated prior and during the experiments The corrosion resistance of TiN is usually reported to with nitrogen gas flushing. The measurements were be excellent, but different explanations for the phenome- performed in room temperature. The electrochemical non have been given. Thermodynamic studies indicate cell has been described in ref. 8. that TiN itself is not very stable in water solutions but Open-circuit potentials were measured with a Keithley it can be oxidized to a more stable compound Ti(OH)3 197 digital multimeter. Electrochemical impedance and further to Ti02 H~O at pH higher than 2 by the spectroscopy (EIS) measurements were performed with hydrogen evolution reaction [1]. Ti02 and its suboxides a Zahner 1M5 impedance measurement system in the [2] and an oxynitride with Ti in an oxidation state frequency range from 100 kHz to 0.2 mHz with a perturbetween TiN and Ti02 [3] have been detected on TiN bation amplitude of 10mV. The impedance spectrum of with surface analysis methods. Titanium oxide has been each specimen was measured several times during the found to cover partially the surface when TiN is polar- immersion time at the open-circuit potential. The EIS ized at +1.3 V with respect to a standard hydrogen results were interpreted with a three-dimensional electrode in 1 N HC1 [4, 5]. The noble electrochemical transmission-line-based model introduced in refs. 9 and behaviour at potentials below this passivation potential 10. Potentiodynamic polarization curves (scan rate, 5 has been explained to be caused by the presence of a mY per 25 s) were measured with a Solatron 1286 monolayer of elemental nitrogen [6] or by a nitrogen- electrochemical interface that was operated by a personal enriched layer [7]. The layer shields the underlying computer. Electrochemical experiments were started titanium ions from the external potential and prevents when the corrosion potential did not change by more their oxidation as well as that of N3 ions [7]. than 1 mY min’ usually within 4h.

Exploiting XPS for the identification of sulfides and polysulfides

The identification of surface sulfide and polysulfide species based on the curve fitting of S2p photoelectron spectra and, for the first time, of X-ray excited S KLL Auger spectra has been performed. The different sulfur chemical states present on the surface (sulfide S2−, central S and terminal S in polysulfide chains) could be unambiguously assigned in the chemical state plot. Sulfur atoms in the central or terminal position, respectively, are found on a line with slope ca. −3 irrespective of the cation indicating similar initial state effects. On the other hand, for a given polysulfide, e.g. K2Sn, sulfur atoms both in central or terminal positions are found on the same line with slope −1 indicating similar final state effects. This behavior can be rationalized with the fact that the negative charge in polysulfide chains is located mainly on sulfur atoms in the terminal position; indeed, sulfur present as central S shows a binding energy shift of −0.6 eV with respect to elemental sulfur (S8), and sulfur in terminal S a shift of −2.4 eV. An application of this approach tested on commercial alkali polysulfides is provided for the curve fitting of SKLL signals and sulfur speciation of three different sulfide minerals enargite (Cu3AsS4), chalcopyrite (CuFeS2) and arsenopyrite (FeAsS). Also for the surface of mineral sulfides, terminal S atoms and central S atoms in the polysulfide chains can successfully be identified.