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• Fracto-surface mobility mechanism in high-strength steel wires

  J. Sánchez, J. Fullea, C. Andrade

  Engineering Fracture Mechanics (2017). Vol. 186, pp. 410-422

  
  

  Abstract

  Stress corrosion cracking, a mechanism governing steel deterioration, has yet to be fully understood. This article introduces a supplement to the surface mobility mechanism proposed by Galvele to include fracture mechanics principles. In the model proposed, anodic dissolution is regarded as the source of vacancies that would be driven by a stress gradient to the crack tip under non-stationary conditions. Denominated the fracto-surface mobility mechanism (FSMM), it explains material mechanical failure based on vacancy diffusion across the metal surface.

  Abstract
  Stress corrosion cracking, a mechanism governing steel deterioration, has yet to be fully understood. This article introduces a supplement to the surface mobility mechanism [...]

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• Design and evaluation of service life through concrete electrical resistivity

  C. Andrade

  ALCONPAT (2018). Vol. 8 (3), pp. 264-279

  
  

  Abstract

  This paper describes the use of concrete electrical resistivity as durability performance parameter and the complementary information that resistivity can provide like: setting period, mechanical strength and degree of curing. Also, it is explained how to design the concrete mix to obtain a target resistivity. Current codes have prescriptive requirements for the durability of concrete and reinforcement corrosion. However, modern trends specify the performance rather than the concrete characteristics. This performance approach demands to define a durability controlling parameter, such as the chloride diffusion coefficient, with its corresponding test and the model to predict the time to steel corrosion.

  Abstract
  This paper describes the use of concrete electrical resistivity as durability performance parameter and the complementary information that resistivity can provide like: setting [...]

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• Brief historical notes

  C. Andrade

  ALCONPAT (2018). Vol. 8 (3), pp. I-V

  
  

  Abstract

  Anniversaries are a good excuse to make some summaries of historical events. Very briefly, some advances made from the initial research in the speciality of reinforcement corrosion which started in the 60’s are summarized. The use of electrochemical techniques was a milestone which enabled, from the decade of the 1970, to study the effect of each variable with much more rigour. The studies on service life started in the decade of 1980, although they were not of general interest until the next decade. From 1990 RILEM Committees and the Iberoamerican Program on Corrosion of CYTED extended the knowledge so widely that in the XXI century the subject attracts much research interest.

  Abstract
  Anniversaries are a good excuse to make some summaries of historical events. Very briefly, some advances made from the initial research in the speciality of reinforcement [...]

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• Apparent diffusion coefficient of oxygen and corrosion control of reinforcement rebar coated with primers

  E. Pazini, C. Andrade

  ALCONPAT (2018). Vol. 8 (3), pp. 288-301

  
  

  Abstract

  The present work evaluates the influence of five different types of coatings applied on the rebar on apparent diffusion coefficient of oxygen (Dap (O2)) and on the corrosion intensity (Icorr) in comparison with a reference coating composed of a cement-sand mortar. Oxygen flow (J (O2)) until the rebar was measured by potenciostático method in the steady state and the corrosion intensity (Icorr) was monitored by the Polarization Resistance technique (Rp). Evaluations for porosity of coatings were made through magnifying glasses, optical microscopy and SEM. The primers that represent barrier protection systems were, under the conditions tested, less permeable to oxygen. The apparent diffusion coefficient values (Dap (O2)) ranged from 2.1 x 10-6 cm2/s to 4 x 10-9 cm2/s, causing variations in the corrosion intensity measurements (Icorr), due to the cathodic corrosion process control.

  Abstract
  The present work evaluates the influence of five different types of coatings applied on the rebar on apparent diffusion coefficient of oxygen (Dap (O2)) and on the corrosion [...]

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• Corrigendum to “Threshold concentration of chlorides in concrete for stainless steel reinforcement: Classic austenitic and new duplex stainless steel”

  A. Panchón-Montaño, J. Sánchez, C. Andrade, J. Fullea, E. Moreno, V. Matres

  Construction and Building Materials (2018). Vol. 189, p. 1303

  
  

  Abstract

  The authors regret that Equation 1: 30%w Ni not is correct. Should be changed to 30%w N, so that is; PREn = %w Cr + 3.3%w Mo + 30%w N-%w Mn. Footnote in Fig. 5 is not correct. Should be changed to “Micrographs (4×) of EN 1.4362/2304 duplex rebar; left: after removal from specimen; right: after pickling (4×)”. The authors would like to apologise for any inconvenience caused

  Abstract
  The authors regret that Equation 1: 30%w Ni not is correct. Should be changed to 30%w N, so that is; PREn = %w Cr + 3.3%w Mo + 30%w N-%w Mn. Footnote in [...]

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• Threshold concentration of chlorides in concrete for stainless steel reinforcement: Classic austenitic and new duplex stainless steel

  A. Panchón-Montaño, J. Sánchez, C. Andrade, J. Fullea, E. Moreno, V. Matres

  Construction and Building Materials (2018). Vol. 186, pp. 495-502

  
  

  Abstract

  Stainless steel rebars is used to lengthen the service life of structures in aggressive media. Corrosion resistance was studied in five grades of mortar-embedded stainless steel: EN 1.4307, EN 1.4404, EN 1.4482, EN 1.4362 and EN 1.4462. A modified accelerated chloride attack was applied to prevent steel rebar polarisation and artificial re-passivation. The critical chloride concentration was determined. Based on corrosion rate, service life was calculated for a given exposure at two probability levels.

  Abstract
  Stainless steel rebars is used to lengthen the service life of structures in aggressive media. Corrosion resistance was studied in five grades of mortar-embedded stainless [...]

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• Updating Carbon Storage Capacity of Spanish Cements

  C. Andrade, M. Sanjuán

  Sustainability (2018). Vol. 10 (12), pp. 1-15

  
  

  Abstract

  The fabrication of cement clinker releases CO2 due to the calcination of the limestone used as raw material, which contributes to the greenhouse effect. The industry is involved in a process of reducing this amount liberated to the atmosphere by mainly lowering the amount of clinker in the cements. The cement-based materials, such as concrete and mortars, combine part of this CO2 by a process called “carbonation”. Carbonation has been studied lately mainly due to the fact that it induces the corrosion of steel reinforcement when bringing the CO2 front to the surface of the reinforcing bars. Thus, the “rate of carbonation” of the concrete cover is characterized by and linked to the length of service life of concrete structures. The studies on how much CO2 is fixed by the hydrated phases are scarce and even less has been studied the influence of the type of cement. In present work, 15 cements were used to fabricate paste and concrete specimens withwater/cement (w/c) ratios of 0.6 and 0.45 which reproduce typical concretes for buildings and infrastructures. The amount of carbon dioxide uptake was measured through thermal gravimetry. The degree of carbonation, (DoC) is defined as the CO2 fixed with respect to the total theoretical maximum and the carbon storage capacity (CSC) as the carbonation uptake by a concrete element, a family or the whole inventory of a region or country. The results in the pastes where analyzed with respect to the uptake by concretes and indicated that: (a) the humidity of the pores is a critical parameter that favours the carbonation reaction as higher is the humidity (within the normal atmospheric values), (b) all types of cement uptake CO2 in function of the CaO of the clinker except the binders having slags, which can uptake additional CO2 giving aDoC near or above 100%. The CSC of Spain has been updated with respect to a previous publication resulting in proportions of 10.8–11.2% of the calcination emissions, through considering a ratio of “surface exposed/volume of the element” of 3 as an average of the whole Spanish asset of building and infrastructures.

  Abstract
  The fabrication of cement clinker releases CO2 due to the calcination of the limestone used as raw material, which contributes to the greenhouse effect. The industry [...]

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• Advances in Characterization of Gas Transport in Concrete: Determination of Oxygen Diffusion Coefficient from Permeability Coefficient and Porosity

  P. Linares, C. Andrade, D. Baza

  (2018). Service Life and Durability of Reinforced Concrete Structures. RILEM Bookseries, Vol 17, pp. 87-97. Springer, Cham

  
  

  Abstract

  One of the most relevant mechanisms that influence the life service of concrete (carbonation, compactness, alkaline protection) is gas diffusion through its mass. However, determination of gas diffusion coefficient in concrete is not a simple task. There is not a general standard which determines the test procedure. Other approaches or alternative parameters could be used in order to obtain the gas diffusion coefficient, including the use of permeability coefficient. Both parameters are dependent on material porosity and moisture content. The literature already proposes generic correlations for these parameters, but these correlations do not support the direct derivation of the gas diffusion coefficient. This paper presents the results of research carried out to analyse these generic correlations and to propose specific expressions that support the derivation of a value for the oxygen diffusion coefficient, based on the porosity and permeability coefficients. The research was centred on a experimentation process to obtain these parameters. A diffusion chamber was designed and built for use with two types of concrete mix, two distinct concrete curing processes and three separate values for humidity. Each test case sought to derive values for oxygen diffusion and permeability coefficients.

  Abstract
  One of the most relevant mechanisms that influence the life service of concrete (carbonation, compactness, alkaline protection) is gas diffusion through its mass. However, [...]

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• Propagation of reinforcement corrosion: principles, testing and modelling

  C. Andrade

  Materials and Structures (2018). Vol. 52 (2), pp. 1-26

  
  

  Abstract

  Reinforcement corrosion is the risk most frequently cited to justify concrete durability research. The number of studies specifically devoted to corrosion propagation, once the object of most specialised papers, has declined substantially in recent years, whilst the number addressing initiation, particularly where induced by chlorides, has risen sharply. This article briefly describes the characteristics of steel corrosion in concrete that need to be stressed to dispel certain misconceptions, such as the belief that the corrosion zone is a pure anode. That is in fact seldom the case and as the zone is also affected by microcells, galvanic corrosion accounts for only a fraction of the corrosion rate. The role of oxygen in initiating corrosion, the scant amount required and why corrosion can progress in its absence are also discussed. Another feature addressed is the dependence of the chloride threshold on medium pH and the buffering capacity of the cement, since corrosion begins with acidification. Those general notions are followed by a review of the techniques for measuring corrosion, in particular polarisation resistance, which has proved to be imperative for establishing the processes involved. The inability to ascertain the area affected when an electrical signal is applied to large-scale elements is described, along with the concomitant need to use a guard ring to confine the current or deploy the potential attenuation method. The reason that measurement with contactless inductive techniques is not yet possible (because the area affected cannot be determined) is discussed. The method for integrating corrosion rate over time to find cumulative corrosion, Pcorr, is explained, together with its use to formulate the mathematical expressions for the propagation period. The article concludes with three examples of how to use corrosion rate to assess cathodic protection, new low-clinker cements or determine the chloride threshold with an integral accelerated service life method

  Abstract
  Reinforcement corrosion is the risk most frequently cited to justify concrete durability research. The number of studies specifically devoted to corrosion propagation, once [...]

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• Concrete Structures: On-site electrochemical techniques and concrete resistivity to predict service life Part 1 - Corrosion measurement techniques

  C. Andrade

  Ochrona przed Korozją (2019). Vol. 1 (4)

  
  

  Abstract

  Concrete protects the steel of the reinforcements in a similar manner than do the paints but with the particularity that it is a material chemically active and evolving for decades. Concrete provides a very alkaline electrolyte encapsulated in its pore network. The steel may remain passive indefinitely but chlorides and atmospheric carbon dioxide penetrate the pores and reaching the reinforcement promote corrosion, which impairs the concrete structural properties inducing the cover cracking and the loss in steel-concrete bond. Calculation of service life is becoming an important subject in engineering terms due to the increasing demand to produce buildings and infrastructures with service life beyond 100 years. In the paper focus will be devoted to two main areas: 1) the measurement techniques in concrete and permanent probes, including on site methods for large structures and contactless (inductive) methods 2) the illustration of the corrosion resistance control exerted by concrete resistivity which enables the calculation of the diffusion of ions through the concrete and the prediction of the corrosion rate in function of the climatic conditions

  Abstract
  Concrete protects the steel of the reinforcements in a similar manner than do the paints but with the particularity that it is a material chemically active and evolving for [...]

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