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• Corrosión de armaduras galvanizadas y sin proteger embebidas en cemento aluminoso estabilizado

  M. Pérez, F. Triviño, C. Andrade

  Materiales de Construcción (2012). Vol. 31 (182), pp. 49-68

  
  

  Abstract

  El cemento aluminoso, cuya obtención se basa en la fusión de bauxita y caliza, ha demostrado desde que fue patentado en Francia, en 1908 por Cementos Lafarge, unas propiedades excepcionales que lo hacen idóneo para ciertas aplicaciones. Tales propiedades son fundamentalmente el desarrollo de elevadas resistencias mecánicas en las primeras edades de hidratación, posibilidad de hormigonar en tiempo frío, una gran resistencia química al agua de mar y a los sulfatos, propiedades refractarias, etc. Todo ello hizo que el cemento aluminoso del tipo fundido, con un 40 % de Al₂O₃, se utilizara ampliamente en la construcción. Sin embargo, a partir de un determinado momento empezaron a observarse alteraciones en algunas obras construidas con hormigón de este tipo, manifestándose importantes pérdidas de sus resistencias mecánicas (1). Las causas de tales deterioros han sido ampliamente estudiadas (2)-(13), atribuyéndose la principal a la "conversión" de los aluminatos cálcicos hidratados hexagonales en hidratos cúbicos, según reacción [1]

  Abstract
  El cemento aluminoso, cuya obtención se basa en la fusión de bauxita y caliza, ha demostrado desde que fue patentado en Francia, en 1908 por Cementos Lafarge, [...]

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• Estudio por SEM de los productos de corrosión de armaduras galvanizadas sumergidas en disoluciones de pH comprendido entre 12,6 y 13,6

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

  Materiales de Construcción (2012). Vol. 34 (195), pp. 55-66

  
  

  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 whith 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 detected from the data of the polarisation technique agreed with the results of an SEM study. They show that below the threshold pH value the surface is covered with a continuous layer of calcium hydroxyzincate, Ca[Zn(0II)j2-^ HjO, and above this pH, the layer increase its proportion of non-passivating ZnO, to the detriment of the calcium hydroxyzincate contents. They have also established that it is the (Ca^'^) ions that control the amount of calcium hydroxizincate formed, and therefore the likelihood of the formation of a continuous passivating layer. Finally, they report that if the calcium hydroxyzincate is perfectly developed, a later increase of the pH 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 whith such [...]

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• Durabilidad de las armaduras en el sistema Dragados-Plastbau

  C. Andrade, J. Rodríguez

  Informes de la Construcción (2012). Vol. 38 (383), pp. 49-53

  
  

  Abstract

  En un sistema de las características del presente, los elementos metálicos que pueden sufrir corrosión son principalmente la malla y los conectores que atraviesan el poliestireno. La porosidad del microhormigón y el no siempre suficiente espesor de recubrimiento pueden permitir una carbonatación del microhormigón que alcance la malla durante el período de vida útil previsto para la estructura. Este riesgo de corrosión por carbonatación viene acrecentado en este sistema particular por una posible aparición de fisuras (retracción, movimientos de dilatación y asentamientos diferenciales, etc.).

  Abstract
  En un sistema de las características del presente, los elementos metálicos que pueden sufrir corrosión son principalmente la malla y los conectores que [...]

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• La importancia del curado en el comportamiento posterior frente a la corrosión de las estructuras de hormigón armado

  W. López, S. Feliu, J. González, C. Andrade

  Materiales de Construcción (2012). Vol. 41 (223), pp. 5-17

  
  

  Abstract

  Steel in contact with fresh concrete is covered by a layer of passivating oxydes due to the alkaline nature of the pore solution. The presence of oxygen plays an important role in this passivation process as well as in the corrosión one when is developped due to the ingress of aggressives, such as, chioride ions. In the present paper, results are commented on the behaviour found when oxygen is limited due to the concrete curing conditions, in a completely saturated chamber Surprisely, the results indícate that the oxygen availability during the curing has a marked influence on the future corrosión beabieviour This allows to deduce that the mechanisms involved are not so simple as was currently accepted and that new specific tests are needed to clarify the controversial points.  

  Abstract
  Steel in contact with fresh concrete is covered by a layer of passivating oxydes due to the alkaline nature of the pore solution. The presence of oxygen plays an important [...]

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• Study of corrosion rate variability in indoor and outdoor specimens

  F. Pedrosa, C. Andrade

  (2011). Advances in Modeling Concrete Service Life. RILEM Bookseries, vol 3, pp. 33-42. Springer, Dordrecht

  
  

  Abstract

  Behavior, time evolution and variability of the corrosion process in reinforced concrete structures is an important factor to have in mind if structural service life is to be determined. Corrosion development and its consequences over time are often empirically deduced. It would be significant to improve as much as possible the prediction accuracy of corrosion process behavior. In the present paper, a series of hygrothermal and corrosion data obtained for indoor and outdoor reinforced concrete specimens are summarized by means of descriptive statistics. For a T-beam exposed to continental weather conditions, temperature, relative humidity, corrosion potential and corrosion current density measurements were taken since the year of 1993. The same measurements were made for an outdoor pile exposed to the same conditions. The indoor studied specimens are two small slabs exposed to lab conditions for which corrosion measurements were taken in the first 96 days period. Chloride was added to the concrete mixture of one specimen in order to accelerate the corrosion process. Electrochemical corrosion rate measurements using modulated confinement of the current were taken by means of Gecor 8 system device. Temperature and relative humidity were measured both inside and outside of the outdoor specimen using a probe. Hygrothermal and corrosion results were plotted on time scale in order to visualize possible correlations. A first approach to a statistical analysis is made by describing the raw data obtained by means of average value and standard deviation for different variables. Results show that the accumulated corrosion progress linearly in time. In the outdoor exposed specimen two corrosion rates Icorr were noticed, being the highest for the first period where no cracks were yet produced. After cracking occurs corrosion rate decreases. No direct relation between RH and Icorr was observed.

  Abstract
  Behavior, time evolution and variability of the corrosion process in reinforced concrete structures is an important factor to have in mind if structural service life is to [...]

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• Ruptures of prestressing cables

  J. Balayssac, C. Andrade, J. Sánchez, H. Scheel

  (2011). Non-Destructive Assessment of Concrete Structures: Reliability and Limits of Single and Combined Techniques. RILEM State of the Art Reports, Vol 1, pp. 305-334, Springer, Dordrecht

  
  

  Abstract

  The structures involved are prestressed concrete structures. The aim is to detect either failures of prestressing cables (or strands) or as a preventive measure to detect corrosion or damages before failure.

  Abstract
  The structures involved are prestressed concrete structures. The aim is to detect either failures of prestressing cables (or strands) or as a preventive [...]

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• Corrosión del acero desnudo y galvanizado en yeso

  M. Gómez, C. Andrade

  Materiales de Construcción (2012). Vol. 38 (212), pp. 5-20

  
  

  Abstract

  Gypsum is a relatively lovi/-cost building material much abounding in our country. When it is put in contact with steel, it may produce high corrosion rates due to its pH value (close to 7). This work reports the results obtained in studying the corrosion rates of bare and galvanized steel in contact with gypsum and plaster, as well as the influence curing thermal treatment applied to gypsum, enviromental relative humidity and addition of compounds with different natures and purposes may have in such process. In-situ observations, as well as the measurement of the Polarization Resistance and the weight loss have been used as measurement technics. From the results obtained it has been possible to deduce that galvanized steel has better behaviour in dry enviroments than bare steel in the same conditions and moist atmosphere induces proportionally more corrosion in galvanized steel than in bare one. Additions to gypsum do not modified these conclusions, though it may be pointed out that addition of nitrites or lime improves the behaviour of bare steel, while galvanized behaviour is not modified. The addition of lime is not recommended because phenomena of dilated along time expansion may take place. 

  Abstract
  Gypsum is a relatively lovi/-cost building material much abounding in our country. When it is put in contact with steel, it may produce high corrosion rates due to its pH [...]

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• Influencia del contenido en álcalis de los cementos sobre la corrosión de armaduras galvanizadas

  C. Andrade, A. Macías

  Materiales de Construcción (2012). Vol. 31 (184), pp. 83-93

  
  

  Abstract

  Las armaduras galvanizadas han mostrado un comportamiento errático en los ensayos llevados a cabo hasta ahora, encontrándose en la literatura datos muy contradictorios. Los autores han encontrado que las siguientes tres variables tienen una decisiva importancia: a) pH del mortero u hormigón, que depende básicamente de la cantidad de álcalis del cemento, b) tipo de estructura metalográfica del recubrimiento galvanizado, que depende principalmente del tipo de acero y su contenido en Si y C, y c) la humedad contenida en los poros del hormigón. En este trabajo se presentan resultados relacionados sólo con el punto a). Se ha podido comprobar que existe un valor de pH umbral o crítico por encima del cual el recubrimiento galvanizado se corroe severamente, debido a la formación de capas no-protectoras de productos de corrosión. La evolución de la velocidad de corrosión se ha seguido mediante la Resistencia de Polarización, y las pérdidas de peso se han determinado también, gravimétricamente

  Abstract
  Las armaduras galvanizadas han mostrado un comportamiento errático en los ensayos llevados a cabo hasta ahora, encontrándose en la literatura datos muy contradictorios. [...]

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• Estabilidad de la capa de hidroxizincato cálcico formada en las armaduras galvanizadas ante un posterior aumento del valor del pH

  A. Macías, C. Andrade

  Materiales de Construcción (2012). Vol. 36 (204), pp. 19-28

  
  

  Abstract

  In previous works on galvanized reinforcements in contact with Ca- containing highly alkaline media, the authors have reported the existence of a threshold pH of 13,3 ± 0,1, below which the Zn in contact with such a medium is passivated by formation of a continuous layer of calcium hydroxyzincate, but at pH values above this it corrodes continuously until it totally disappears. The investigation on the stability of the calcium hydroxyzincate layer after an increase of the pH to very high alkaline values, is the aim of the present paper. It has been establised that if the calcium hydroxyzincate is perfectly developed, a later increase of the pH does not affect the stability.

  Abstract
  In previous works on galvanized reinforcements in contact with Ca- containing highly alkaline media, the authors have reported the existence of a threshold pH of 13,3 ± [...]

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• Corrosión de armaduras y su inspección en hormigones de cemento aluminoso

  C. Andrade

  Informes de la Construcción (2012). Vol. 44 (422), pp. 39-48

  
  

  Abstract

  Until recently has not become evident the magnitude of the problem that the corrosion of the reinforcement supposes for concrete technology. That is why, when aluminous cement preliminary degradations appeared it was not foreseen the dimension of future consequences..Now, the long term difficulty that aluminous cement presents is, in addition to the loss in mechanical strength, the possible corrosion of reinforcement. In present work are described aspects related to the processes which may originate the corrosion and given are some practical indications on how evaluate it.

  Abstract
  Until recently has not become evident the magnitude of the problem that the corrosion of the reinforcement supposes for concrete technology. That is why, when aluminous cement [...]

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