COLLECTIONS

Documents published in Scipedia

• An accelerated leaching test to evaluate the long term behaviour of concrete in waste disposal

  A. Hidalgo, C. Andrade, C. Alonso

  L'industria Italiana del Cemento (2001). Vol. 766, pp. 498-507

  
  

  Abstract

  The present work describes an accelerated leaching method that with a rapid process allows to develop and evaluate cements for use in a nuclear disposal, and the understanding of the long term effects. The method has been developed to study the stability of cementitious materials in contact with bentonite, to be used in high level radioactivity waste repositories, assuming that granitic water will be the leachant agent. Nitric and carbonic acids have been selected to induce the accelerated acid attack on pastes. Results have indicated the more aggressive character of carbonic acid and the suitability of the acid neutralisation to find out the alkaline reserve of the different tested pastes.

  Abstract
  The present work describes an accelerated leaching method that with a rapid process allows to develop and evaluate cements for use in a nuclear disposal, and the understanding [...]

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• Towards excellence

  S. Shah, C. Andrade

  Materials and Structures (2002). Vol. 35 (8), p.446

  
  

  Abstract

  Progress has been made in American public education in the last 20 years, and the pending American Defense Education Act, inspired by the National Defense Education Act, would enable school districts to address many of the current problems of public schools. (MSE)

  Abstract
  Progress has been made in American public education in the last 20 years, and the pending American Defense Education Act, inspired by the National Defense Education Act, would [...]

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• Statements and Conclusions

  L. Amleh, C. Andrade, N. Buenfeld, B. Buhr

  (2003). Life-Cycle Cost Analysis and Design of Civil Infrastructures Systems, pp. 432-439

  
  

  Abstract

  Engineers have been dealing with deterioration in concrete structures since shortly after their initial use. Before 1980 deterioration was taken into consideration predominantly using rules of thumb developed through experience. After 1980 simple engineering models, such as Fick's law, the Hetek's model and time dependent models, were developed and became more widely used. With time these models, both deterministic and stochastic, are becoming increasingly more sophisticated and are increasingly based on "physical" parameters. This trend will continue and future models will be based even more so on the physical, chemical and mechanical laws and principles that govern material and structural behaviour.

  Abstract
  Engineers have been dealing with deterioration in concrete structures since shortly after their initial use. Before 1980 deterioration was taken into consideration predominantly [...]

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• Calculation of initiation and propagation periods of service life of reinforcements by using the electrical resistivity

  C. Andrade

  (2004). International RILEM Symposium on Concrete Science and Engineering: A Tribute to Arnon Bentur Editor(s): J. Weiss, K. Kovler, J. Marchand, and S. Mindess

  
  

  Abstract

  Reinforcement corrosion is attracting research interest in many areas due to the economic consequences of the damage generated by the process. Several proposals can be found on prediction of the time to reinforcement corrosion and service life duration. In the present communication a proposal is made on using the electrical resistivity to calculate both the initiation and propagation periods. For the time period to corrosion onset, the electrical resistivity serves to model the porosity and its connectivity and therefore can be used to calculate transport processes. Due to the reaction of chlorides and carbon dioxide with cement phases, the resistivity has to be factored by a “reaction factor”, r, to account for this. 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 current. The service life can be expressed with the following equation: t_l = t_i + t_p = x^2 rho_es r_CICO2 / k_CI,CO2 + P_x . rho_ef / k_corr Based on this, minimum resistivity values can be established according to cover thickness and as a function of exposure classes.

  Abstract
  Reinforcement corrosion is attracting research interest in many areas due to the economic consequences of the damage generated by the process. Several proposals can be found [...]

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• Evaluacion del comportamiento a largo plazo de hormigones en almacenamientos de residuos radiactivos de alta actividad

  A. Hidalgo, L. Fernández, S. Petit, C. Alonso, C. Andrade

  Boletin de la Sociedad Española de Cerámica y Vidrio (2004). Vol. 43 (2), pp. 548-586

  
  

  Abstract

  The present work describes an accelerated leaching method that with a rapid process allows to develop and evaluate cements for use in a nuclear disposal, and the understanding of the long term effects. The method has been developed to study the stability of cementitious materials in contact with bentonite, to be used in high level radioactivity waste repositories. Nitric acid has been selected to simulate in an accelerated way the pH decreasing produced when concrete is in contact with groundwaters. Evaluacion del comportamiento a largo plazo de hormigones en almacenamientos de residuos radiactivos de alta actividad El presente trabajo describe un ensayo acelerado de lixiviación, que mediante un proceso rápido, permite desarrollar y evaluar cementos para su uso en instalaciones nucleares, y la comprensión de su comportamiento a largo plazo. El método se ha desarrollado para estudiar la estabilidad de materiales de base cemento, en contacto con bentonita, que serán utilizados en almacenamientos de resíduos radiactivos de alta actividad. Como agente lixiviante se seleccionó el ácido nítrico, con objeto de simular de forma acelerada, la disminución del pH que se produce cuando el hormigón entra en contacto con aguas subterráneas.

  Abstract
  The present work describes an accelerated leaching method that with a rapid process allows to develop and evaluate cements for use in a nuclear disposal, and the understanding [...]

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• Are service life models appropriate for use in design of reinforced concrete structures for exposure to chloride salts?

  C. Andrade

  (2004). Third International RILEM Workshop on Testing and Modelling Chloride Ingress into Concrete Editor(s): C. Andrade and J. Kropp Print-ISBN: 2-912143-48-9, pp. 93-104

  
  

  Abstract

  Chloride ingress leading to corrosion of embedded steel is the most detrimental process affecting the durability of reinforced concrete structures. Various authors have suggested methods of calculating the time to depassivation of reinforcing steel by modelling chloride penetration on the basis of a solution of Fick's second law of diffusion. This involves several assumptions, including boundary and initial conditions that may be fulfilled in idealised laboratory tests but not in real structures. The situation calls for an explicit recognition of the limited knowledge that exists regarding both detailed mechanisms of chloride ingress and threshold chloride concentrations that cause depassivation of steel in different types of concrete subjected to different conditions of exposure. These uncertainties can result in major inaccuracies when models are used to predict the long-term performance of structures. Despite the admitted lack of detailed understanding of the process of chloride penetration, tentative proposals are outlined for alternative methods of determining performance indices useful in some circumstances for specifying the durability of structures exposed to chloride salts. They depend on measurement of one parameter (steady-state diffusion coefficient or electrical resistivity) to account for the transport process and a separate parameter to account for chloride binding. The values obtained provide a means of ranking different types of concrete in terms of their expected performance when exposed to chloride environments in which diffusion is likely to be the dominant transport mechanism.  

  Abstract
  Chloride ingress leading to corrosion of embedded steel is the most detrimental process affecting the durability of reinforced concrete structures. Various authors have suggested [...]

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• Model for prediction of reinforced concrete service life based on electrical resistivity

  C. Andrade

  IBRACON Mater J. (2005). Vol. 1, pp. 1-5

  
  

  Abstract

  Reinforcement corrosion is attracting research interest in many areas due to the economical consequences of the damage generated by the process. Several proposals can be found on prediction of the time to reinforcement corrosion and service life duration. In present communication a proposals is made on using the electrical resistivity to calculate both the initiation and propagation periods. For the time to corrosion onset, the electrical resistivity represents the porosity and its connectivity and therefore can be used to model transport processes. Due to the reaction of chlorides and carbon dioxide with cement phases, the resistivity has to be factorised by a “reaction factor” accounting for it. Concerning the propagation period, the electrical resistivity is an indication of the moisture content of concrete and therefore, it has a certain relationship with the corrosion cement. The service life can be expressed with the following equation: corr x ef Cl CO es ClCO l i p k P k x r t t t ρ ·ρ 2 2 , 2 = + = + Based in it, minimum resistivity values can be established according to cover thickness and in function of exposure classes.

  Abstract
  Reinforcement corrosion is attracting research interest in many areas due to the economical consequences of the damage generated by the process. Several proposals can be found [...]

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• Reinforced-concrete cover cracking due to the pressure of corrosion products

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

  Proceedings of the 6th International Conference on Fracture Mechanics of Concrete and Concrete Structures (2007). Vol. 3, pp. 1857-1864

  
  

  Abstract

  Reinforcement corrosion is one of the most important phenomena that reduce the service life of the reinforced concrete structures. Steel corrosion reduces the strength and bond of the reinforcement and the oxides formed cause internal stresses that crack the concrete cover. The prediction of the evolution of these effects is a problem that involves chemical and mechanical aspects. The phenomenon is not well known and quantitative descriptions of development and magnitude of stresses produced by a corroding rebar to concrete are scarce and although there are several models in the literature they do not universally reproduce the experimental results. This work presents a summary of the available experimental evidence on the amount of internal expansion needed at the reinforcement level for concrete cover to crack and formulas to estimate the expansion. Also, results are presented on the pressure needed for concrete cover to crack together with the experimental technique used for the verification of the assumptions and crack propagation analysis.

  Abstract
  Reinforcement corrosion is one of the most important phenomena that reduce the service life of the reinforced concrete structures. Steel corrosion reduces the strength and [...]

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• Elasto-plastic model for beams damaged by corrosion

  M. Prieto, A. Muñoz, C. Andrade

  Revue Européene de Génie Civil (2007). Vol. 11 (1-2), pp. 163-178

  
  

  Abstract

  This article describes the elasto-plastic model that has been applied to analyse the beams damaged by corrosion. CONTECVET Manual, which contains the principles of this kind of structural evaluation, has been adopted. This Manual recommends considering the reduced section of the concrete and of the reinforcements as well as the possible reduction of the concrete steel bond. The first part of the article describes the basis of the structural model and, the mechanical behaviour of the materials. In the second part, the results of the experimental tests are presented and compared with the results of the model. The results indicate an enough good accordance, if the typical scatter of this type of experimental tests is taken into account.

  Abstract
  This article describes the elasto-plastic model that has been applied to analyse the beams damaged by corrosion. CONTECVET Manual, which contains the principles of this kind [...]

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• Stress corrosion cracking and fracture toughness variation of High Strength Steels

  J. Sánchez, J. Fullea, C. Andrade

  (2010). Avances en Seguridad y Durabilidad. Ciclo de vida de las estructuras.

  
  

  Abstract

  The stress corrosion cracking (SCC) process is at present a not fully elucidated mechanism of deterioration. It is a surface process that implies a corrosion and stress synergy, but the most practical consequence is that stress corrosion cracking can modify the mechanical characteristics of the metal causing brittle failure. Previously, we present some results about stress corrosion cracking, crack propagation rate or, even, crack arrest conditions in High Strength Steels. This kind of steels is usually used in prestressed and postensioned structures. These wires are of eutectoid composition and cold drawn. It is well established that failures occur when the wires are in contact with electrolytes of specific compositions while under stress. In the case of concrete, the electrolyte is its pore solution and the stress levels result from the different loads applied due to structural requirements. In this work we suggest some improvements of the Mechanism of SCC based in the Surface Mobility of vacancies on the crack surface proposed by Galvele. Improvements consist in incorporating the electrochemical corrosion as one of the sources for the creation of vacancies and some mechanical effects, both produce synergic effect in the crack propagation rate and they are important for a more comprehensive explanation of the process. On the other hand, 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 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.

  Abstract
  The stress corrosion cracking (SCC) process is at present a not fully elucidated mechanism of deterioration. It is a surface process that implies a corrosion and stress synergy, [...]

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