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• Techniques electrochimiques qualitatives et quantitatives pour mesurer les effets des additions sur la corrosion des armatures

  C. Andrade, J. González

  Silicates Industriels (1982). Vol. 47, pp. 289-295

  
  

  Abstract

  Les auteurs resument une serie de considerations theoriques sur l'incidence que les additions actives peuvent avoir dans la corrosion des armatures. Ensuite, ils attirent l'attention sur le manque de normes ou recommandations de travail, qui s'appuient sur des essais suffisants, et qui pourraient permettre de delimiter les causes et conditions qui influent sur la duree des armatures ; finalement ils exposent une systematique d'essais qu'ils ont realisee pour etudier cette incidence au moyen de techniques electrochimiques, et les differences de comportement trouvees entre les differents ciments.

  Abstract
  Les auteurs resument une serie de considerations theoriques sur l'incidence que les additions actives peuvent avoir dans la corrosion des armatures. Ensuite, ils attirent [...]

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• Les effets des cycles d’humidité sur la corrosion des armatures galvanisées dans les mortiers carbonatés et non carbonatés

  J. González, A. Vazquez, C. Andrade

  Matériaux et Construction (1982). Vol. 15, pp. 271-278

  
  

  Abstract

  Galvanisation of steel reinforcement has been usual practice for the last decades as a protection against certain types of aggressive agents. However, recent results, mostly European, have thrown doubts on the usefulness of galvanisation. The results presented here contribute to explain this controversy. We have identified three factors that may influence the corrosion kinetics of galvanized steel bars embedded in concrete, although they usually go unheeded: type of galvanized coating, type of cement and humidity during curing and hardening. From these factors, this report deals mostly with ambient humidity. Corrosion rate was basically estimated from the Polarisation Resistance in reinforced mortar specimens that were cyclically subjected during curing and hardening to different ambient humidities. The influence on the corrosion kinetics of the structure of the galvanized coating which, in turn, depends on the chemical composition of the steel, is also discussed. Finally, the behaviour of bare and galvanized steel are compared, and criteria are given on the usefulness of galvanized coatings.

  Abstract
  Galvanisation of steel reinforcement has been usual practice for the last decades as a protection against certain types of aggressive agents. However, recent results, mostly [...]

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• Corrosion Rate of Galvanized Steel Immersed in Saturated Solutions of Ca(OH)2 in the pH Range 12–13 8

  A. Macías, C. Andrade

  British Corrosion Journal (1983). Vol. 18 (2), pp. 82-87

  
  

  Abstract

  The influence of the alkaline content of cement on the corrosion kinetics of galvanized reinforcements has been studied, by means of the polarisation resistance method, in saturated solutions of Ca(OH)2 with additions of NaOH, KOH and SO2 4, thus simulating the liquid phase of concrete.It has been established that below a threshold pH the coating protects the surface; above this pH the coating is attacked, disappearing in a few days. Cements with low alkali contents and proper concrete dosage must therefore be used to ensure that the pH remains below the threshold value.

  Abstract
  The influence of the alkaline content of cement on the corrosion kinetics of galvanized reinforcements has been studied, by means of the polarisation resistance method, in [...]

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• Corrosion rate of galvanized steel immersed in saturated solutions of Ca(OH)2 in the pH Range 12-13.8

  A. Macías, C. Andrade

  British Corrosion Journal (1983). Vol. 18 (2), pp. 82-87

  
  

  Abstract

  The influence of the alkaline content of cement on the corrosion kinetics of galvanized reinforcements has been studied, by means of the polarisation resistance method, in saturated solutions of Ca(OH)2 with additions of NaOH, KOH and SO²4, thus simulating the liquid phase of concrete. It has been established that below a threshold pH the coating protects the surface; above this pH the coating is attacked, disappearing in a few days. Cements with low alkali contents and proper concrete dosage must therefore be used to ensure that the pH remains below the threshold value.

  Abstract
  The influence of the alkaline content of cement on the corrosion kinetics of galvanized reinforcements has been studied, by means of the polarisation resistance method, in [...]

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• SEM Study of the Corrosion Products of Galvanized Reinforcements Immersed in Solutions in the pH Range 12·6 to 13·6

  M. Blanco-Varela, C. Andrade, A. Macías

  British Corrosion Journal (1984). Vol. 19 (1), pp. 41-48

  
  

  Abstract

  In previous work on galvanized reinforcements in contact with Ca-containing highly alkaline media the authors have reported the existence of a threshold pH below which the Zn in contact with such a medium is passivated, but at pH values above this it corrodes continuously until it totally disappears. In this paper, after a brief literature review concerning the identification of the corrosion products in these media, they report that the passivation detectedfrom the data of the polarisation technique agreed with the results of an SEM study. This showed that below the threshold pH value the surface is covered with a continuous layer of calcium hydr.oxyzinccite, Ca (Zn(OH)3)2.2H2O, and above this pH this layer is increasingly composed ofnon-passivating ZnO, to the detriment of the calcium hydroxyzincate content. They have also established that it is the (Ca2+) ions that control the amount of calcium hydroxyzincate formed, and therefore the likelihood of the formation of a continuous passivating layer. Finally, they report that if the calcium hydroxyzincate isperfectly developed, a later increase of thepH does not affect the stability.

  Abstract
  In previous work on galvanized reinforcements in contact with Ca-containing highly alkaline media the authors have reported the existence of a threshold pH below which the [...]

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• Corrosion rate of three different types of galvanized coatings of steel reinforcements in contact with mortar

  A. Molina, M. Blanco, C. Andrade

  International Congress on Metallic Corrosion (1984). Vol. 1, pp. 412-417

  
  

  Abstract

  Corrosion of galvanized reinforcements in concrete is controlled by three factors: the type of the cement, the type of metallographic structure and the humidity of conservation of the concrete. The behaviour of three different types of galvanized coating embedded in mortars made with three different Portland cements: low, medium and high alkali content, was studied. The corrosion rate was measured by means of the linear polarization (Polarization Resistance) technique. The results show that the thicker the pure zinc layer is, the greater the resistance against the corrosion of the chlorides.

  Abstract
  Corrosion of galvanized reinforcements in concrete is controlled by three factors: the type of the cement, the type of metallographic structure and the humidity of conservation [...]

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• Effect of four coating structures on corrosion kinetic of galvanized reinforcement in concrete

  J. González, A. Vazquez, G. Jauregui, C. Andrade

  Materials and Structures (1984). Vol. 17 (6), pp. 409-414

  
  

  Abstract

  In the present work is described the effect of the characteristics of the galvanized coating on corrosion rate of reinforcing bars embedded in a concrete without additives and in another with 2% CaCl2 in terms of cement weight. To this end, the following materials were subjected to the action of a moisture saturated atmosphere for a period of400 days: an annealed-galvanized coating; another one obtained by dipping in a molten Zn bath with0.025% Al and some others produced at450 and430°C in an ordinary bath. The attack evolution vs time was controlled by measuring the polarization resistance. The electrochemical determinations were gravimetrically verified and supplemented by a metallographic examination of tests coatings. In the absence of chlorides, the attack is fully tolerated. Chlorides radically change the corrosion behaviour of galvanized steel and increase the attack by a factor of2.8 in the most favourable case, but in these conditions, coatings with thick, homogeneous η layer outperform the usual ones, and specially the annealed ones.

  Abstract
  In the present work is described the effect of the characteristics of the galvanized coating on corrosion rate of reinforcing bars embedded in a concrete without additives [...]

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• Corrosion of galvanized steel reinforcements in alkaline solutions: Part 2: SEM study and identification of corrosion products

  A. Macías, C. Andrade

  British Corrosion Journal (1987). Vol. 22 (2), pp. 119-130

  
  

  Abstract

  A report is presented of the morphology and composition of the corrosion products formed on galvanized corrugated steel reinforcing bars immersed in 0·05–1·5M KOH solutions designed to simulate concrete pore environments. The morphology was studied by SEM of the in situ corrosion products and optical examination of transverse sections of the bar; phase identification was performed by X-ray diffraction and IR absorption analyses. Passivation events on the corrosion potential and corrosion intensity curves can be related to precipitation of prismatic Zn (OH)2 crystals which form a compact layer on the surface. Active corrosion is associated with formation of porous ZnO layers or precipitation of Zn(OH)2 in the solution rather than on the galvanized surface. A solution-precipitation mechanism involving ZnO and Zn(OH)2− 4 intermediate species is proposed for formation of the passivating Zn(OH)2 coating, although this scheme must be complemented to take account of the localized corrosion observed at pH < 12 in the first part of this study

  Abstract
  A report is presented of the morphology and composition of the corrosion products formed on galvanized corrugated steel reinforcing bars immersed in 0·05–1·5M [...]

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• Corrosion of galvanized steel in dilute Ca(OH) 2 solutions (pH 11·1–12·6)

  A. Macías, C. Andrade

  British Corrosion Journal (1987). Vol. 22 (3), pp. 162-171

  
  

  Abstract

  The corrosion behaviour of. galvanized bars was studied in 0·1–3 g Ca(OH)2 (pH 11·1–12·6) solutions designed to simulate the aqueous phase found in concrete pores. Corrosion potential and current density were monitored over the course of the 33 day tests and the corrosion products were examined by light and electron microscopy, X-ray diffraction, and IR absorption spectroscopy. Most specimens showed high initial corrosion rates which fell to a lower, nearly constant level after ∼6 days. The corrosion kinetics were found to depend only on solution pH. Ca2+ concentration had no effect other than on the nature of the corrosion products: Ca(Zn(OH)3)2.2H2O is the passivation product in the presence of calcium ions, Zn(OH)2 in their absence. Localized corrosion was observed at pH <11·5.

  Abstract
  The corrosion behaviour of. galvanized bars was studied in 0·1–3 g Ca(OH)2 (pH 11·1–12·6) solutions designed to simulate the aqueous phase [...]

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• Corrosion of galvanized steel reinforcements in alkaline solutions: Part 1: Electrochemical results

  A. Macías, C. Andrade

  British Corrosion Journal (1987). Vol. 22 (2), pp. 113-118

  
  

  Abstract

  The behaviour of galvanized corrugated reinforcing bars has been studied in 0·001–1·5M solutions of KOH and NaOH designed to simulate aqueous environments found in concrete pores. Specimens were immersed for 33 days in polyethylene cells, corrosion potential, corrosion intensity, and pH being monitored throughout. Polarization curves were also obtained after 50 min and ∼ 33 days' immersion. It was possible to establish pH ranges in which localized corrosion (< 12), stability (12–13·4), and complete dissolution of the galvanic coating (> 13·4) occurred. A white, dusty corrosion product was observed on most specimens at the conclusion of the tests. Hydrogen dissolution on the galvanized bars occurred at pH values higher than the threshold level of 12·8±0·1.

  Abstract
  The behaviour of galvanized corrugated reinforcing bars has been studied in 0·001–1·5M solutions of KOH and NaOH designed to simulate aqueous environments [...]

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