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• Structural Assessment of Corroded Beams

  M. Prieto, A. Noval, C. Andrade

  ECS Transactions (2010). Vol. 3 (13), pp. 20-42

  
  

  Abstract

  This paper shows how the corrosion and mechanical actions can be taken into account in a simple model for the assessment of structural elements. This work is framed in the Project Benchmark des Poutres de La Rance in which several partners have participated. The Project tried to characterize the degradation of reinforced and prestressed concrete structures after an aging in marine atmosphere with non-destructive methods and to evaluate different existing models for the structural assessment. For this aim a 4-point bending test was performed on six prestressed concrete beams. The model gives a reasonable approach for the assessment of structural elements. Similar rules can be adopted for other failure modes. It is important to notice the need of reliable input data for the assessment and also the need of integration of deterioration processes in design.

  Abstract
  This paper shows how the corrosion and mechanical actions can be taken into account in a simple model for the assessment of structural elements. This work is framed in the [...]

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• Molecular Dynamics simulations of Hydrogen Embrittlement: preliminary results

  J. Sánchez, P. Andrés, C. Andrade, J. Fullea

  Anales de Mecánica de la Fractura. (2010).

  
  

  Abstract

  Hydrogen embrittlement is believed to be one of the main reasons for cracking of structures under stress. High strength steels in these structures often include a ferritic core made of alpha-iron (body centered cubic lattice). Previous work [1] was concerned with the interaction of atomic hydrogen with iron using first principles calculations. We studied the effect of interstitial hydrogen in the iron lattice and the stress induced by the interstitial hydrogen in the host lattice. In this paper we study the dynamical behaviour of hydrogen inside the iron lattice. Using ab-initio Molecular Dynamics we obtain hydrogen diffusion paths and by taking statistical averages we extract diffusion coefficients from Einstein’s equation. Depending on temperature, the diffusion path involve going through tetrahedral or octahedral sites. Simulations where a number of hydrogens occasionally coincide in one unit cell have been performed to elucidate the effect of interactions between hydrogens

  Abstract
  Hydrogen embrittlement is believed to be one of the main reasons for cracking of structures under stress. High strength steels in these structures often include a ferritic [...]

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• Estudio del efecto sumidero de CO2 de los materiales de base cemento

  I. Galan, C. Andrade, M. Prieto, P. Mora, J. López, M. Sanjuan-Barbudo

  Cemento y Hormigón (2010). Vol. 939, pp. 70-83

  
  

  Abstract

  Uno de los principales problemas relacionados con el cambio climático es el efecto invernadero, producido por la absorción parcial de la radiación infrarroja emitida por la Tierra por parte de los gases denominados "de efecto invernadero", entre los que se incluye el dióxido de carbono. El trabajo aquí planteado se enmarca dentro de las iniciativas acometidas por la industria del cemento para contribuir a la reducción del efecto invernadero y los estudios realizados para estimar la contribución de los materiales de base cemento en la lucha contra el cambio climático. Para ello se estudia el alcance del efecto sumidero de CO2 que supone la carbonatación del hormigón. La Convención Marco de las Naciones Unidas sobre el Cambio Climático de 1992 recoge en su artículo 1 la definición de sumidero: "Por sumidero se entiende cualquier proceso, actividad o mecanismo que absorbe un gas de efecto invernadero, un aerosol o un precursor de un gas de efecto invernadero de la atmósfera".

  Abstract
  Uno de los principales problemas relacionados con el cambio climático es el efecto invernadero, producido por la absorción parcial de la radiación infrarroja [...]

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• CO 2 sink effect of concrete carbonation

  I. Galan, C. Andrade, P. Mora, J. López, M. Sanjuán, M. Prieto

  Proceedings of Special Technical Sessions. Second International Conference on Sustainable Construction Material s and Technologies (2010).

  
  

  Abstract

  Although carbonation of cement phases is well known, the amount of carbon dioxide combined during the process has been much less investigated. Related to the greenhouse effect much more attention is being paid to the sinks for C02 in order to correctly compute the gases emission during production of materials. In the case of cement a strict calculation should discount the C02 emitted from that fixed by the concrete. This is the aim of present work which is a study of the cement based materials ability to combine C02. Using Thermogravimetry and Differential Thermal Analysis as well as phenolphthalein indicator, quantities of C02 combined and carbonation depth in several cement pastes and concretes exposed to different environments have been measured. A calculation to estimate the contribution of cement based materials carbonation to the partial re-absorption of the C02 emitted in cement production is proposed.

  Abstract
  Although carbonation of cement phases is well known, the amount of carbon dioxide combined during the process has been much less investigated. Related to the greenhouse effect [...]

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• The use of electrical resistivity as a NDT for the specification of concrete durability

  C. Andrade

  Proceedings of 6th international conference on concrete under severe conditions (CONSEC '10) (2010).

  
  

  Abstract

  The calculation of the time to reinforcement corrosion and service life dura-tion is a subject of increasing interest. In present communication is explained how to use the electrical resistivity to calculate both the initiation and propagation periods in the case of carbonation and chloride penetration, although only the case of chlorides is illustrated here. The main advantage is that resistivity is an inexpensive non destructive measurement that can be used for routine quality control. The resistivity is an indication of the porosity and pore connectivity. It increases with time as hydration proceeds which is an indication of aging or pore refinement. In addition to the measurement of the resistivity it is necessary to calculate a "reaction factor" for accounting of the binding with cement phases. Concerning the propagation period, the electrical resistivity is an indication of the moisture content of concrete and therefore, it has a relationship with the corrosion cement. A model is proposed in which the resistivity is introduced in the square root of time law.

  Abstract
  The calculation of the time to reinforcement corrosion and service life dura-tion is a subject of increasing interest. In present communication is explained how to use the [...]

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• Correlación entre ancho de grieta del recubrimiento del concreto y corrosión del refuerzo en elementos expuestos a un ambiente natural contaminado por cloruros

  C. Andrade, A. Muñoz, A. Torres-Acosto

  Concreto y cemento (2010). Vol. 1 (2), pp. 30-41

  
  

  Abstract

  La corrosión del refuerzo genera daños variados a estructuras de concreto que influyen en la capacidad de carga; entre estos daños se puede mencionar el agrietamiento del recubrimiento del concreto. Este trabajo proporciona resultados de campo en el tema de propagación de grietas del recubrimiento del concreto por corrosión del refuerzo después de una exposición natural por varios años. Los elementos estructurales evaluados fueron una viga T y una columna cuadrada expuestos al ambiente atmosférico de Madrid, España. Dos formulas empíricas fueron usadas para correlacionar los valores obtenidos del agrietamiento del recubrimiento por corrosión: w=k Px/(C/φ), y w=k Px/Ro, en donde w es el ancho de la grieta por corrosión, k es una constante de proporcionalidad, Px es la penetración por la corrosión en el tiempo, C/φ es la relación recubrimiento de concreto/diámetro del refuerzo, y Ro es el radio original del refuerzo.

  Abstract
  La corrosión del refuerzo genera daños variados a estructuras de concreto que influyen en la capacidad de carga; entre estos daños se puede mencionar [...]

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• Determination of chloride diffusivity through partially saturated Portland cement concrete by a simplified procedure

  A. Guimarães, M. Climent, G. Vera, F. Vicente, C. Andrade

  Control and Building Materials (2011). Vol. 25 (2), pp. 785-790

  
  

  Abstract

  A recently proposed methodology for measuring the diffusion coefficient of chloride ions through concrete partially saturated with water, has been applied to five high-early-strength Portland cement mortars. The method is based on putting solid NaCl in contact with the concrete surface during the diffusion test. The results obtained indicate a strong dependence of the diffusion coefficient on the water saturation degree. The ionic diffusivities through these mortars are higher than those obtained with the same approach for five pozzolanic cement mortars of similar compositions. It has been also shown that the proposed test methodology and a different one based on the interaction of HCl(g) with the tested concrete surface, can yield comparable results. The D values obtained are of similar magnitude, and the same type of dependence on the water saturation degree is found through both methods, when applied to similar Portland cement concrete mixes with cement content of about 350 kg/m3 and water/cement ratios between 0.5 and 0.6.

  Abstract
  A recently proposed methodology for measuring the diffusion coefficient of chloride ions through concrete partially saturated with water, has been applied to five high-early-strength [...]

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• Observations on the Morphology of Oxide Formation due to Reinforcement Corrosion

  C. Andrade, F. Tavares, L. Toro, J. Fullea

  (2011). Modelling of Corroding Concrete Structures. RILEM Bookseries, vol. 5, pp. 179-193. Springer, Dordrecht.

  
  

  Abstract

  The oxide formed during corrosion has an expansive character which induces the cracking of concrete cover. The properties of this oxide layer are focussing the interest due the need to introduce its mechanical characteristics in the models to calculate crack width. In a previous paper it was suggested that the oxide behave as “water” and in consequence it has to be modelled so, which fitted very well in the experiments and model associated an that time. The attribution to the water was based in the observation that the rust has not mechanical consistency and was like a suspension. However, much recent papers insist in attributing other much higher young modulus to the rust. Present paper tries to insist in the original concept by illustrating the formation of the rust in solution and in mortar. The oxides are of mixed colours evolving in function of the time to contact to open air and they have not mechanical consistency, being apparently hydrophilic by retaining large amount of water.

  Abstract
  The oxide formed during corrosion has an expansive character which induces the cracking of concrete cover. The properties of this oxide layer are focussing the interest due [...]

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• High Strength Steels Fracture Toughness Variation by the Media

  J. Sánchez, J. Fullea, C. Andrade

  (2011). Modelling of Corroding Concrete Structures. RILEM Bookseries, vol. 5, pp. 137-146. Springer, Dordrecht

  
  

  Abstract

  The stress corrosion cracking process is at this moment an unknown mechanism of deterioration. It is a process that implies the joint action of the media, the presence of corrosion or a surface defect and of stress in the metal. Prestressing tendons can suffer SCC jointly with hydrogen embrittlement which dramatically changes not only the type of fracture (from ductile to brittle) but also the kinetics of the process leading to unexpected collapses. The metal should be resistant to this type of process which can be characterized by its toughness and therefore by its damage tolerance. This research shows that the Fracture Toughness change when the steel corrodes, questioning the idea that is an intrinsic characteristic of the material. The reduction in the fracture toughness of steel wires when they are in contact to aggressive media involve that the material fractures with a lower crack depth for the same stress level. That means that the material becomes less damage tolerant, which implies that it is necessary to detect defects of smaller size, as for example, small notch, pits or superficial cracks. In the paper some results of the percentage of decrease of the toughness of prestressing wires suffering corrosion are presented

  Abstract
  The stress corrosion cracking process is at this moment an unknown mechanism of deterioration. It is a process that implies the joint action of the media, the presence of [...]

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• Bond Response in Structural Concrete with Corroded Steel Bars. Experimental Results

  M. Prieto, P. Tanner, C. Andrade

  (2011). Modelling of Corroding Concrete Structures. RILEM Bookseries, vol 5, pp.231-241. Springer, Dordrecht

  
  

  Abstract

  The growing interest in upgrading existing reinforced concrete structures or extending their service life, and in ensuring greater durability in new designs, has led to a need for resistance models that take deterioration processes into account to verify structural safety. Bond activation between reinforcing steel and concrete is of cardinal importance in this context. A number of experimental studies have been conducted in recent years on bond failure, which normally leads to brittle behaviour. The findings have diverged rather widely, however, due primarily to differing test conditions. The present paper presents an experimental programme for eccentric pull-out tests in which specimens were subjected to both accelerated and natural corrosion in an attempt to surmount these inconsistencies. It also introduces an embedded fibre-optic sensing system with corrosion-resistant fibre Bragg grating sensors and discusses some of the findings.

  Abstract
  The growing interest in upgrading existing reinforced concrete structures or extending their service life, and in ensuring greater durability in new designs, has led to a [...]

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