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ABSTRACT Reinforcement corrosion leads to several damage types that influence the structure service lifetime, among which can be mentioned the cracking of concrete cover due to the increase in volume [...]

A brief exercise is made on reporting some achievements in the history of reinforcement corrosion. It is a difficult task to try to summarize because there are numerous protagonists in the history then choices were made from a personal point of view. In the decade 1960–1970, reinforcement corrosion was a subject only of marginal interest because the number of built environment was limited. 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 rigor. The studies on service life started in the decade of 1980, although they were not of general interest until 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.

Calcination of carbonate rocks during the manufacture of cement produced 5% of global CO2emissions from all industrial process and fossil-fuel combustion in 2013. Considerable attention has been paid to quantifying these industrial process emissions from cement production, but the natural reversal of the process—carbonation—has received little attention in carbon cycle studies. Here, we use new and existing data on cement materials during cement service life, demolition, and secondary use of concrete waste to estimate regional and global CO2uptake between 1930 and 2013 using an analytical model describing carbonation chemistry. We find that carbonation of cement materials over their life cycle represents a large and growing net sink of CO2, increasing from 0.10 GtC yr−1in 1998 to 0.25 GtC yr−1in 2013. In total, we estimate that a cumulative amount of 4.5 GtC has been sequestered in carbonating cement materials from 1930 to 2013, offsetting 43% of the CO2emissions from production of cement over the same period, not including emissions associated with fossil use during cement production. We conclude that carbonation of cement products represents a substantial carbon sink that is not currently considered in emissions inventories.

This work is part of the DURACON Ibero-American project, which seeks to characterize concrete durability under environmental conditions, based on reinforced concrete sample exposure in at least two different atmospheres (marine and urban), for each of the 11 countries in the project. Specimens were exposed to the environmental conditions of 13 Mexican sites (8 urban and 5 marine atmospheres). Concrete specimens were 15 x 15 x 30 cm, with 6 rebars each, and three concrete covers (15, 20 and 30 cm). Two concrete mixtures were used with water/cement ratios of 0.45 and 0.65, respectively. Six reinforced and six plain concrete specimens were placed on each exposure site. Environmental data was collected on each exposure site, including rainfall, relative humidity, time of wetness, temperature, wind velocity, and carbon dioxide/chloride concentrations. Corrosion rates and potentials, as well as concrete resistivity were measured in the reinforced samples. Carbonation depths were measured on the plain ones. The present work focused on the measurements of environmental parameters during the first two years of exposure to analyze the potentiality and the probability of carbonation-induced corrosion, and the evaluation of the corrosion initiation period for the reinforcing steel on the 13 Mexican exposure sites.

La durabilidad de los aceros de alta resistencia en medios agresivos está condicionada por la fragilización por hidrógeno. La fragilización por hidrógeno está presente en muchos de los fallos de estructuras o componentes de acero. En estudios anteriores se ha mostrado el efecto del hidrógeno intersticial dentro de la red de hierro a nivel atómico, y se concluía que el hidrógeno no establece enlace químico con el hierro pero introduce tensiones internas que debilitan los enlaces hierro-hierro y disminuyen la tenacidad de fractura. En el presente trabajo se ha simulado la propagación de una fisura en una matriz de hierro en presencia de hidrógeno. Se han acoplado factores como el transporte de hidrógeno, los gradientes de tensiones y la variación de la tenacidad de fractura en un modelo multifísico de elementos finitos. El comportamiento en fractura se ha simulado mediante dos leyes cohesivas, una lineal y otra polinómica. Los resultados muestran que existe una influencia de la ley cohesiva sobre la propia velocidad de propagación de la fisura y el perfil de concentración de hidrógeno.

Los Comités CEN/TC 250/SC2 (Eurocódigo 2) y CEN/TC 104/SC 1 (Hormigón) han creado un “Joint Working Group” JWG TC250/TC104 con el fin de revisar los aspectos relativos a la durabilidad en el Eurocódigo 2 “estructuras de hormigón” y en la norma EN 206-1 “hormigón”.Este JWG ha estudiado la posibilidad de clasificar los hormigones no sólo por resistencia mecánica sino también por durabilidad en función de la clase de exposición. En este JWG se propone realizar esta clasificación en base a un ensayo directo de resistencia a los cloruros y a la carbonatación, lo que obligaría a realizar estos ensayos de una forma más o menos rutinaria en el futuro. Como alternativa, el grupo espejo español ha propuesto que la clasificación se haga primero en base a las dosificaciones como se ha realizado hasta el momento y, con el fin de avanzar en los criterios prestacionales, también mediante ensayos indirectos de durabilidad (indicadores de durabilidad). En el presente artículo se expone la propuesta española en comparación con la propuesta recogida en el JWG. Se discuten las ventajas e inconvenientes de cada una y se presentan las tablas resumen que se han enviado desde el TC140/SC2 de AENOR para la revisión del capítulo 4 del Eurocódigo 2.

La corrosión de la armadura es uno de los problemas de mayor impacto económico en el ciclo de vida de las estructuras de hormigón por lo que es necesario optimizar las estrategias de reparación de estructuras corroídas. Sin embargo, a nivel internacional no hay códigos que permitan una evaluación por lo que se incluirán criterios en la revisión del Eurocódigo 2 para la evaluación de estructuras existentes y deterioradas. En el presente artículo se resumen el trabajo realizado en el proyecto Contecvet, financiado por la Comisión Europea, y los avances realizados desde entonces. En las estructuras existentes, una primera precisión consiste en determinar si el deterioro ha alcanzado a la armadura, y en ese caso, cuánto se ha afectado al comportamiento estructural. Calculada la velocidad de corrosión a partir de los datos tomados en la propia estructura es posible estimar la velocidad de avance del deterioro mediante los modelos desarrollados y la vida residual remanente. Se resumen los modelos y expresiones para estimar la capacidad resistente de estructuras con armaduras corroídas a considerar en la elaboración del nuevo Eurocódigo 2.

Reinforcement corrosion is one of the major durability problems that need to be solved in order to extend the service life of a structure. It is influenced, on one hand, by the concrete itself, sound or polluted (chlorinated or carbonated), and on the other hand, by the environmental conditions (controlled or outdoor). To explore the influence of temperature and humidity, electrochemical characterisations (potential, linear polarisation resistance and corrosion rate) were carried out on reinforced concrete prisms. A database of more than 3000 values has been delivered. The results enabled us to deduce that both parameters have influences on each other. Moreover, considering the four concretes, the corrosion order obtained in controlled conditions may be different from the one obtained in outdoor conditions.La corrosion des armatures est un problème majeur dans la durabilité du béton qui doit être résolu afin d’augmenter la durée de vie des structures. Elle dépend, d’une part, de la nature du béton (sain ou pollué (chloruré ou carbonaté)) et, d’autre part, des conditions environnementales (contrôlées ou naturelles). Afin d’étudier l’influence de la température et de l’humidité, des caractérisations électrochimiques (potentiel, résistance de polarisation linéaire, courant de corrosion) ont été réalisées sur des prismes en béton armé. Une base de données, avec plus de 3 000 valeurs, a été constituée. Les résultats montrent que les deux paramètres interagissent l’un sur l’autre. De plus, l’ordre de corrosion obtenu dans des conditions contrôlées peut être différent de celui observé dans des conditions naturelles.

In this work, different mortars with different degrees of damage brought about by the action of the freeze-thawing cycles are evaluated. Analysis of its state is carried out by different usual evaluation methods. Results obtained through these methods are compared with the electrical impedance spectroscopy. Moreover, this non-destructive technique is employed to evaluate the state of mortars and the amount of internal damage.

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). We compute the interaction of atomic hydrogen with iron using first principles. The interstitial hydrogen can be placed in two high symmetry positions: octahedral and tetrahedral sites. Our calculations provide diffusion barriers between these sites. These barriers have been analyzed to understand the propagation of hydrogen through the iron lattice. We analyze how these barriers can be modified by the hydrogen concentration. The results show the main site for high and low hydrogen density and they show the diffusion coefficient variation by the hydrogen density.

This work presents the three-year results of the project: Effect of the environment on reinforcement durability (DURACON), which is investigating the influence of the meteorochemical parameters of marine and coastal-marine environments on concrete durability performance, by measuring the electrochemical parameters (corrosion rate and corrosion potential) of the embedded reinforcing steel. To that effect, concrete specimens were exposed to the marine environments making a total of 21 test stations distributed among ten countries (Argentina, Bolivia, Chile, Colombia, Costa Rica, Mexico, Spain, Uruguay, Portugal and Venezuela). This paper presents the reinforcement electrochemical evaluation, which allows identifying its corrosion activation. The chloride ions concentration which induces the reinforcement corrosion is also presented, depending on the environment to which the concrete specimens were exposed.

Reinforcement corrosion leads into several damages which influence the structural load-bearing capacity, among which can be mentioned the cracking of concrete cover. This work study formulations to estimate the crack width of structural elements from the data of corrosion rate measured in two structural elements, made in 1990, with chlorides added in the concrete mix. These elements, one T beam and one column, were exposed at the atmosphere of Madrid, Spain. Two expressions have been fitted to the results: w = k Px / (c/f) and w = k Px / Ro, where w is a crack width in the time, k is a proportional factor, Px is the corrosion penetration in the time, c/f is the concrete cover/diameter relation and Ro is the original radius of the bar. The first expression has resulted the most adequate.

ABSTRACTThis 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.

This study aims to analyze the effects of supercritical carbonation (CO2 at 20 MPa and 318 K) on the physicochemical properties of ordinary Portland cement pastes. The evolution of the main crystalline phases of the cement pastes during carbonation was determined by means of X-ray diffraction and thermogravimetric analysis. The pore structure was analyzed by low-temperature N2 adsorption−desorption and mercury intrusion porosimetry techniques. Finally, the microstructure of the samples was observed by using scanning electron microscopy coupled with energy-dispersive X-ray detection for chemical analysis. For a natural carbonation process, diffusion of CO2 into the pores of the cement paste is considered as the rate-controlling step. Instead, the accelerated reaction kinetics of calcium carbonate precipitation in the supercritical process was chemically controlled by the detachment of calcium ions from solid portlandite or CSH gel. The total pore volume of the studied cement pastes decreased with carbonation, which was associated with the deposition of the formed CaCO3. Samples carbonated under the supercritical conditions developed a higher volume of gel pores than those obtained by natural carbonation.

In rat brain, calcification associated with excitotoxicity has been proposed to play a protective role, whereas in human brain, nonartherosclerotic calcification is present in several pathological conditions without any clear significance. To determine if calcification can be viewed as a protective step of calcium homeostasis during chronic and acute neuronal suffering, cerebral cortex and hippocampus of patients with Alzheimer's disease, vascular dementia and neonatal hypoxia-ischemia were investigated. To investigate the human specificity, these two areas were also studied in dogs with established cognitive deficits. In all groups, calcium precipitates were observed in the cerebral parenchyma associated with neuronal damage. The cerebral cortex presented a higher degree of calcification than the hippocampus. The neonatal hypoxia-ischemia group was characterised by a higher degree of calcification, whereas the groups with lowest calcification were the Alzheimer's patients and dogs. As shown by X-ray microanalysis, in the precipitates, calcium is mainly associated with phosphorus in a form that resembles hydroxyapatites. Thus, intracellular calcium concentration associated with neuronal suffering may reduce the energy extrusion. We propose that, to help overcome excitotoxicity, calcium precipitation acts in CNS of vertebrates as a new compartment of the calcium homeostasis in which free cytoplasmic calcium ions are inactivated by phosphate ones.

Concrete pore solutions are concentrated electrolytes in which the activity of the chemical species must be calculated properly to determine the equilibrium state of such solutions. In this work, the chloride‐ion activity coefficients in synthetic concrete pore solutions have been obtained potentiometrically, using different calibrated Cl−ion‐selective electrodes (ISEs); also, a discussion about the performance of the different Cl−ISEs in alkaline media is presented. Experimental results are compared with the calculated results, using Pitzer's specific ionic‐interaction model, and good agreement is observed between them.

The ‘integral’ test method aims at the simultaneous determination of the chloride migration rate and chloride threshold content. This information is required for durability performance design of reinforced concrete structures in the marine environment. Standard tests are generally designed to be applied on saturated samples to improve their repeatability and reproducibility, but this condition differs from the actual conditions of depassivation in structures in service. This paper compares results of the ‘integral’ test method applied on concrete made with ordinary Portland cement and a water-to-cement ratio ranging 0.35–0.50, preconditioned for full saturation and a saturation degree of 77%. Results are contrasted with concrete properties commonly associated with its performance concerning chloride ingress. The variation in the saturation degree in the range 77–100% showed a greater effect on the chloride ingress rate than in the chloride threshold content. The determined chloride threshold decreases with increasing w/c ratio.

Carbon dioxide sequestration by cement-based materials is a chemical process known as carbonation. Carbon dioxide absorption by cement consists of its reaction with calcium hydroxide, among other Portland cement components. This phenomenon should be taken into account in the calculation of the net contribution of cement production to greenhouse gas emissions. Therefore, carbon dioxide uptake should be considered into future life-cycle assessment protocols.

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