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• Identificación de presencia de cemento aluminoso en hormigones mediante el uso del pachómetro

  C. Andrade, J. Lozano, V. Seguí, E. Hernández

  Informes de la Construcción (1992). Vol. 44 (419), pp. 65-70

  
  

  Abstract

  The observation of the premature degradations detected in High Alumina concretes due to the transformation and carbonation of this kind of cement has promoted the interest to develop in-situ testing methods for the fast Identification of HAC presence. In present work, preliminary results are given on the use of magnetic methods (pachometer), usually employed in the concrete cover verification, to identify the existence of HAC in a concrete. The laboratory results have been verified in practice and show that HAC can be clearly distinguished of an OPC concrete with the pachometer used in present experimentation. The research has also indicated that fly ash cements as aluminous one, have a lower magnetic reluctance. La constatación de los daños que se producen en estructuras de hormigón de cemento aluminoso, debido a su rápida transformación y carbonatación, ha llevado a intentar poner a punto diversos métodos de detección acelerada in situ de la presencia del citado cemento. En el presente trabajo se aportan unos primeros resultados sobre el empleo de métodos magnéticos (pachómetro) habituales en la medida del espesor del recubrimiento de armaduras para identificar si un hormigón está fabricado o no con cemento aluminoso. Los resultados de laboratorio se han contrastado en obra pudiéndose comprobar que el pachómetro utilizado es capaz de detectar perfectamente la presencia de aluminoso previa calibración con un hormigón de portland puro. Esta investigación preliminar también ha permitido comprobar que los hormigones de cenizas volantes presentan, como el aluminoso, una menor reluctancia magnética

  Abstract
  The observation of the premature degradations detected in High Alumina concretes due to the transformation and carbonation of this kind of cement has promoted the interest [...]

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• A reply to the discussion by A. Xu and S. Chandra of the Paper “calculation of chloride diffusion coefficients in concrete from ionic migration measurements”

  C. Andrade

  Cement and Concrete Research (1994). Vol. 24 (2), pp. 380-384

  
  

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• Calculation of chloride diffusion coefficients in concrete from ionic migration measurements

  C. Andrade

  Cement and Concrete Research (1993). Vol. 23 (3), pp. 724-742

  
  

  Abstract

  A critical review is offered on the Rapid Chloride Permeability Test standarized by AASHTO, pointing out its limitations and errors but recognizing its contribution to the developing of a simple and quick test for chloride migration. Then another review is made on the electrochemical fundaments of the processes developped in concrete when an electrical field is applied and on the basic equations of mass transport (Nernst-Plank and Nernst-Einstein) which can be applied to calculate ionic movements. The limitations and assumptions needed for a simplified resolution of these equations, are presented, as well as numerical examples of calculation of the Effective Diffusion Coefficient of chlorides, Deff, in steady state condition. Finally, considerations on the possibility of calculation of Deff from simple resistivity measurements are also offered.

  Abstract
  A critical review is offered on the Rapid Chloride Permeability Test standarized by AASHTO, pointing out its limitations and errors but recognizing its contribution to the [...]

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• Suitability of Assessment Methods for Identifying Active and Passive Zones in Reinforced Concrete

  J. González, P. Rodríguez, C. Andrade, M. Benito

  Corrosion engineering (1995). Vol. 51 (2), pp. 145-152

  
  

  Abstract

  The ability of various electrochemical techniques to differentiate between areas of reinforcing steel (rebar) with high and low corrosion activity and to define the boundary between such areas was studied. These techniques are based on determining the corrosion potential (E[sub corr]), the galvanic current between an external stainless steel (SS) sensor and the bar (I[sub g]), the apparent polarization resistance (R[sub p][sup ap]), or the polarization resistance (R[sub p]) under electric confinement conditions. Values of E[sub corr] and I[sub g] (the current flowing between a SS counter electrode [CE] and the rebars) were shown to distinguish active areas from passive ones very well when the areas were isolated electrically, but with difficulty when the areas were in electric contact, which is usually the case. Values of R[sub p][sup ap] or i[sub corr] (both calculated using the Stern-Geary equation) were shown to define areas of high corrosion rates in a structure where passivity prevailed much better. However, excessive i[sub corr] values were estimated because the polarized area of the rebar (especially with passive rebars) was much greater than the CE area. Finally, the confinement of signal distribution permitted definition of the exact boundary between active and passive areas, regardless of whether they were isolated or interconnected. In addition, i[sub corr] values obtained with this technique were shown to provide a reliable quantitative index of the damage rate in reinforced concrete structures.

  Abstract
  The ability of various electrochemical techniques to differentiate between areas of reinforcing steel (rebar) with high and low corrosion activity and to define the boundary [...]

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• La realcalinización y la extracción electroquímica de los cloruros en las construcciones de hormigón armado

  L. Bertolini, F. Bolzoni, B. Elsener, C. Andrade

  Materiales de Construcción (1996). Vol. 46 (244), pp. 45-55

  
  

  Abstract

  Realkalisation and electrochemical chloride removal techniques, developed for rehabiliting carbonated and chloride-containing structures, are presented. Electrolysis and electromigration mechanisms and consequences as well as electrochemical conditions at the reinforcement surface are discussed and compared with cathodic protection ones. Furthermore, possible side effects are commented. Se presentan técnicas electroquímicas de realcanización y extracción de cloruros, desarrolladas con el fin de rehabilitar estructuras carbonatadas y que contengan cloruros. Se discuten y comparan los mecanismos y consecuencias de la electrólisis y la electromigración, así como las condiciones electroquímicas en la superficie de las armaduras con los de protección catódica. Se comentan, también, los posibles efectos secundarios.

  Abstract
  Realkalisation and electrochemical chloride removal techniques, developed for rehabiliting carbonated and chloride-containing structures, are presented. Electrolysis and electromigration [...]

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• Mathematical modelling of a concrete surface skin effect on diffusion in chloride contaminated media

  C. Andrade, J. Díez, C. Alonso

  Advanced Cement Based Materials (1997). Vol. 6 (2), pp. 39-44

  
  

  Abstract

  Concrete skin is considered the closest zone to the surface of concrete cover of reinforcements. It usually has a different composition than the internal concrete due to phenomena such as contact with molds or segregation of aggregates. In addition, environmental actions induce a gradient of moisture along the cover depth. These circumstances sometimes produce an irregular chloride profile in the cover, which either exhibits a maximum of chloride content some millimeters inside the outer surface or sometimes shows an anomalously high chloride concentration right at the concrete surface. In the present paper, analytical modeling of chloride diffusion is used to study the relative influence of the skin thickness. This theoretical analysis aims to show that there are cases where, if the diffusivity of the skin and the bulk concrete are very different, an error is introduced when the “skin effect” is not accounted for. The clarification of this error may contribute to understanding the differences found between laboratory experiments and the long-term record of chloride profiles in the same concrete.

  Abstract
  Concrete skin is considered the closest zone to the surface of concrete cover of reinforcements. It usually has a different composition than the internal concrete due to phenomena [...]

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• Evolution of pH during in-situ leaching in small concrete cavities

  A. Sagues, E. Moreno, C. Andrade

  Cement and Concrete Research (1997). Vol. 27 (11), pp. 1747-1759

  
  

  Abstract

  Small amounts (0.4 cc) of neutral water placed in small cylindrical cavities (5 mm diameter) in concrete exposed to 100% relative humidity first developed a pH comparable to that of a saturated Ca(OH)2 solution. The pH then increased over a period of days-weeks toward a higher terminal value. A micro pH electrode arrangement was used. This behavior was observed in samples of 12 different concrete mix designs, including some with pozzolanic additions. The average terminal cavity pH closely approached that of expressed pore water from the same concretes. A simplified mathematical model reproduced the experimentally observed behavior. The model assumed inward diffusional transport of the pH-determining species in the surrounding concrete pore solution. The experimental results were consistent with the model predictions when using diffusion parameters on the order of those previously reported for alkali cations in concrete. The cavity size, cavity water content, and exposure to atmospheric CO2 should be minimized when attempting to obtain cavity pH values approaching those of the surrounding pore water.

  Abstract
  Small amounts (0.4 cc) of neutral water placed in small cylindrical cavities (5 mm diameter) in concrete exposed to 100% relative humidity first developed a pH comparable [...]

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• Progress Report 1994-97

  C. Andrade

  Materials and Structures (1998). Vol. 31 (3), pp. 153-157

  
  

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• L Aniversario

  D. Ribé, C. Nombela, C. Andrade, F. Aguirre, M. Fisac, V. Mas, Á. García

  Informes de la Construcción (1998). Vol. 50 (456-457), pp. 3-13

  
  

  Abstract
     

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• Editorial

  C. Andrade

  Informes de la Construcción (1999). Vol. 51 (462), p. 3

  
  

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