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Laboratory and numerical corrosion experiments impose an electric potential on the metal surface, differing from natural corrosion conditions, where corrosion typically occurs in the absence of external current sources. In this work, we present a new computational model that enables predicting corrosion under charge-conservation conditions. The metal potential, an output of the model, is allowed to change, capturing how the corrosion and cathodic reactions must produce/consume electrons at the same rates, as in natural conditions. Finite element simulations are performed over a large range of concentrations and geometric parameters. The results highlight the notable influence of the charge-conservation assumption and pioneeringly quantify corrosion rates under realistic conditions. They further show: (i) the strong coupling between the corrosion rate and the hydrogen and oxygen evolution reactions, (ii) under which circumstances corrosion pits acidify, and (iii) when corrosion is able to become self-sustained lacking oxygen. • A numerical model for corrosion in absence of external current sources is presented. • The model requires corrosion currents to be counteracted by cathodic reactions. • We simulate pencil-electrodes under varying geometric and environmental conditions. • We show strong influence of available oxygen and external surface area on corrosion. • Oxygen is required to develop acidic pits, but pits can sustain corrosion lacking oxygen. [ABSTRACT FROM AUTHOR]

In order to better exploit the chloride migration test on cementitious materials and the movement of ion in the migration cell and to calculate the ion diffusion coefficients from the measured currents, knowledge of the transference numbers is required. In this paper, calculations of transference numbers of the ions involved in the standard migration test are proposed. This has been achieved from a global mass balance of the ion moving in the three zones of the migration test (catholyte, anolyte and sample). The leached ions from the sample and those generated from the electrode processes were considered. The transference numbers obtained in the catholyte are 0.35; 0.25; 0.05; 0.02; 0.33 for Cl−, Na+, K+, Ca++, OH− and 0.23 for H+ in the anolyte. Those in the sample tested are 0.23; 0.11; 0.41; 0.14 and 0.11 for Cl−, Na+, K+, Ca++ and OH−, respectively. Results of ion diffusion coefficients obtained from the transference numbers varied depending on the interpretation method used; possible causes are discussed. [ABSTRACT FROM AUTHOR]

There are few data on corrosion rates of reinforcements in real marine conditions. In present work corrosion rates at long term are presented in the case of small specimens and large reinforced concrete blocks in direct contact to natural sea water. The small specimens had embedded bars at different cover depths and the tests lasted from 10 to 23 years and the corrosion rates have been measured periodically by using the polarization resistance method. The large blocks have been semi-buried around 25 years in the tidal area of a beach in the South of Spain. Their corrosion rates have been measured only four times and the curiosity is that the bars are not corroding in spite of the high contamination at the 3 cm cover depth after so long exposure. Finally, is presented the statistical distribution of corrosion rates found in other structures also in marine environment. [ABSTRACT FROM AUTHOR]

A method to substitute the recognized toxic phenolphthalein in mortars and concretes is proposed. It comprises putting a portland cement sample in contact with an innocuous solution, curcumin-based, which acts as an indicator yielding a red color in areas where there is alkaline reserve (pH ~ 12) and yellow in carbonate zones (pH ≤ 9). Solutions containing curcumin extracted from commercial turmeric powder and from the rhizomes of the turmeric plant were prepared by using ethanol as a solvent. Subsequently it has been experienced with solutions in which curcumin has been used with a purity of over 95%. The dissolution of curcumin can be used with the same reliability as phenolphthalein in the carbonation process with the advantage that it is safe and presents no health risks. [ABSTRACT FROM AUTHOR]

Abstract: Several models have been published to calculate service life of reinforced concrete based on considering diffusion as the main ingress mechanism. However, these models have some limitations and involve destructive and time consuming testing. The authors have developed an alternative model based on electrical resistivity, which is a non-destructive test. When measured in concrete, electrical resistivity is an indication of its pore connectivity and also can be related to the concrete resistance to the penetration of gases and liquids. The main basis of the model has been already published. The present paper describes the calculation of the so-called “reaction or retardation factor” which is necessary for the model to take into account the amount of bound chlorides or carbon dioxide. The resistivity alone only appraises the available porosity which is equivalent to the effective diffusion coefficient. To consider the retardation in the ingress due to the chloride and carbon dioxide binding, it is necessary to include such an effect. In the model this is done by multiplying the resistivity measured at 28days in water saturated concrete by a reaction factor, r b, which will give the “apparent resistivity” equivalent to the apparent diffusion coefficient r Cl. The value of r Cl is calculated from the ratio between effective and apparent diffusion coefficients. This paper gives such values for several cement types. [Copyright &y& Elsevier]

Abstract: In the present the paper, various tests are described using white and ordinary Portland cement blended with fly ash and a slag to assess their effect on reinforcement corrosion. Natural and accelerated chloride diffusion, carbonation and corrosion tests were performed. The results indicate that the most resistant cement against chloride attack is the slag cement which on the other hand, performed as the less resistant to carbonation in the conditions of the test. The most resistant to carbonation is the ordinary Portland cement having the higher portlandite content. As there is the demand to link microstructure and observed performance of the different cementitious materials, an attempt is made. The work emphasizes the effect of mineral additions on the corrosion process in order to collect systematic information about the controlling parameters in the different periods of the service life of reinforced concrete structures. [Copyright &y& Elsevier]

Abstract: Natural carbonation and accelerated carbonation are compared in terms of CO2 combination. Thermogravimetrical analysis, neutron diffraction and weight measurements were used to quantify the amounts of CO2 in samples exposed to different CO2 and relative humidity (RH) conditions. An exponential equation is proposed to describe temporal evolution: combination rates and maximum values are obtained both for natural and accelerated processes. The influence of RH in these parameters is analyzed. At 100% CO2 an increase of RH from 53 to 75% diminishes the combination rate considerably, but increases slightly the maximum CO2 binding. At 0.5% CO2 both the rate and the maximum are higher for intermediate RH, with a linear relation between both variables. Equivalences between the different processes have been calculated: the amount of CO2 combined in 1h at 100% CO2 and 65% RH carbonation is equivalent to approximately 36days of natural exposure outside and 54days inside. [Copyright &y& Elsevier]

Spatial variability of reinforced concrete structures is responsible for part of the uncertainties that are associated with most parameters in structural durability and reliability models. Consequently, its effects should not be overlooked on structural reliability analysis for deteriorating structures. The present study characterized the spatial variability of concrete electrical resistivity and corrosion rate by means of descriptive statistics, estimations of probability density functions and correlation matrices. Data for these two corrosion parameters was obtained by monitoring two 50 cm × 40 cm × 10 cm reinforced concrete slabs on a laboratory environment. Chloride was added to the mix of one of these specimens in order to promote corrosion. The main objective of the test set was to contribute in quantifying and characterizing the spatial variability of these two corrosion parameters in order to improve inspection planning of concrete structures and also probabilistic models that employ these parameters as variables. The variation obtained for corrosion rate and resistivity was considerable taking into account the small size of specimens tested. When compared with concrete resistivity, corrosion rates presented a larger spatial variability, especially when there is active corrosion. Data distribution for resistivity was found to be positively skewed. Correlation between resistivity values obtained in different locations of the slabs was strong, decreasing with distance as expected. As such, the spatial autocorrelation was determined for the concrete resistivity. On the contrary, adjacent measurements of corrosion rate showed no correlation between themselves. A better knowledge of the variables behaviour is fundamental for the quality of any probability based model. • Corrosion rate presented larger spatial variability than concrete resistivity. • Correlation between resistivity values obtained in different locations of the slabs was strong. • Spatial autocorrelation was determined for concrete resistivity. • Measurements of corrosion rate did not show correlation between themselves. [ABSTRACT FROM AUTHOR]

Abstract: This work analyzes the protection capacity of modified Portland cement mortar with polymers: styrene butadiene, acrylic latex with reinforced plastic fibres and acrylic latex with silica fume, using the electrochemical polarization resistance (R p) technique to monitor the behaviour of steel bars embedded in the specimens, when placed in environments with CO2 and chloride. Results indicate that only chemical, physical and mechanical characterizations are not sufficient to classify these materials from the point of view of protection against aggressive agents. There is evidence that material performance depends on workability, chemical composition of squeezed pore solution in addition to the porosity and resistivity which have an important role in the protection against the corrosion of steel bars. [Copyright &y& Elsevier]

Water absorption testing has the attraction of being simple, relatively quick and use water as a fluid which is the key substance in the possible concrete deterioration. However, in spite of the advantages its application has remained empirical, except for the testing of resistance to frost, through the identification of the critical degree of saturation. Rilem TC-116 studied this test, among others, for the characterization of concrete resistance against transport through the concrete pore network. Results indicated a low discriminating ability of the absorbency for qualifying concrete resistance and then, it seemed necessary to try to move forward by making the link between the absorption testing and the concrete pore microstructure. In the present work, thanks to the X-Ray computed tomography, it is described the evolution of the water front in three paste-specimen with different w/c ratios (different pore radius distributions). The observations allowed us to deduce that all the pores start to fill simultaneously, but the bigger ones fill quicker and rise less. The saturation degree is measured along the height of the sample, showing that each pore size has a different rate which becomes constant after the first hour. Washburn's equation was applied to the progressive advance of the water front, resulting in a pore radius much smaller than the one expected. [ABSTRACT FROM AUTHOR]

Abstract: The high strength steels employed as reinforcement in pre-stressed concrete structures are drawn wire steels of eutectoid composition with a pearlitic microstructure. This work is focused on the study, by atomic force microscopy, of the early stages of the corrosion of such steels as a consequence of their exposition to a sodium chloride solution. The obtained images show the pearlitic microstructure of the steel, with a preferential attack of the ferrite phase and the cementite acting as a cathode. The corrosion rate was determined by calculating the amount of material lost from a roughness analysis. The obtained results are in good agreement with the predictions of Galvelel’s theory, according to which the corrosion rate slows down as the pit depth increases. [Copyright &y& Elsevier]

Abstract: Even though the electroosmotic flux through hardened cementitious materials during laboratory realkalisation trials had been previously noticed, it has never been in-situ monitored, analysing at the same time the establishment of the electroosmotic flux and the microstructure changes in the surroundings of the rebar. In this paper, two series of cement pastes, cast with CEM I and CEM I substituted in a 35% by fly ash, previously carbonated at 100% CO2, were submitted to realkalisation treatments followed on line by simultaneous acquisition of neutron diffraction data. As a result, it has been possible to confirm the electroosmosis as the driving force of carbonates towards the rebar and to determine the range of pH in the anolyte in which most of the relevant electroosmotic phenomena takes place. On the other hand, the behaviour of the main crystalline phases involved in the process has been monitored during the treatment, with the precipitation of portlandite as main result. [Copyright &y& Elsevier]

Abstract: Diagnosis of dementia of the Alzheimer''s type depends on clinical criteria and exclusion of other disorders because, at this time, a validated biological marker, aside from histological brain examination, remains to be established. The canine counterpart of senile dementia of the Alzheimer type (ccSDAT) is considered a promising model for examining behavioral, cellular and molecular processes involved in early phases of human brain aging and Alzheimer disease (AD). In order to investigate the first events taking place in canine cognitive dysfunction, in this paper we established a new and rapid behavioral test that finely discriminates the degrees of cognitive impairment. Cerebrospinal fluid (CSF) analysis was performed to determine the relationship between each disease stage and modification of cerebral energy metabolism. Our results demonstrate a parallel increase of lactate, pyruvate and potassium concentrations in the severe cognitive deficit. These differences are discussed in view of the neuroprotective role presently given to lactate. [Copyright &y& Elsevier]

Composition and microstructure changes of cement pastes when heating until 620 °C and cooling afterwards have been monitored on site by neutron diffraction. The parameters involved in the study have been the heating ramp, the state of the sample (in block or ground) and the type of cement. The residual state of the samples has also been studied by mercury intrusion porosimetry (MIP) and thermogravimetry analysis (TGA). As a result, it has been possible to monitor the major features of the experiments, i.e., the phases existence domains and their growing and decaying for portlandite, ettringite, calcite, lime, larnite, and hydrated calcium silicate (CSH gel), as well as the loss of free and bounded water during the experiments. In addition, the different residual phases in the matrix depending on the experimental set up have been established, which might have a significant influence in the durability of a concrete after a fire. [Copyright &y& Elsevier]

Two modified Mg-Al hydrotalcites (MHTs), (MHT-pAB and MHT-NO 2 ) were incorporated into mortar (with different w/c ratios) in two different ways: (1) as one of the mixing components in bulk mortar; (2) as part of cement paste coating of the reinforcing steel. Accelerated chloride migration, cyclic wetting-drying and diffusion tests were performed to investigate their effect on reinforcement corrosion. The results indicated that MHTs could be promising alternatives for preventing chloride-induced corrosion when an appropriate dosage is adopted and applied in a proper way, particularly, replacing 5% mass of cement by MHT-pAB in bulk mortar or as a coating of reinforcing steel (MHT-pAB/MHT-NO 2 to replace 20% mass of cement). The effect of MHT-pAB on time-to-corrosion initiation (TTC) of reinforcing steel was estimated using the DuraCrete model. It was found that the incorporation of 5% MHT-pAB in bulk mortar led to a more than double TTC relative to reference mortar without MHTs. [ABSTRACT FROM AUTHOR]

Stainless steel is a corrosion resistant metal that has now wide record of good performance in several aggressive media, in spite of which is not fully immune to different types of attack. In present work is presented the performance of 304 stainless steel as forming part of the tubes of a tank that has been operating from 1964 for Liquefied Natural Gas storage. The stainless steel tubes are part of a pipeline connecting the Liquefied Natural Gas tanks TK-1200A/B at the Barcelona plant. The pipeline had been continuously operating for more than 40 years, with cooling cycles from ambient temperature down to cryogenic temperatures. The paper shows that the working conditions and the marine environment did not embrittle or modify the properties of the tubes. [ABSTRACT FROM AUTHOR]

Abstract: In the last years many approaches to design SCC have been developed, but it remains a very complex process since it is necessary to manipulate several variables and understand their effects on concrete behaviour (fresh and hardened state). The prediction of concrete or mortar behaviour based on paste properties will be a significant contribution to simplify SCC design. With this purpose, two statistical experimental designs were carried out, one at paste level and the other at mortar level, to mathematically model the influence of mixture parameters on fresh and durability properties. The derived numerical models were used to define an area, labelled by self-compacting zone at paste level (SCZ), where fresh properties of the paste enable the design of SCC mortar. Furthermore, in order to extend this link to durability properties, the effect of including aggregate in cement paste was evaluated by means of the electrical resistivity test. [Copyright &y& Elsevier]

The dog is increasingly considered as a natural animal model for the study of normal and pathological human brain aging, because it exhibits anatomical, biochemical and cognitive changes that parallel those seen in humans. This study presents a novel visual semi-quantitative rating scale of canine cerebral magnetic resonance imaging (MRI). Ninety-eight dogs of both sexes from 27 pure breeds, aged 2-15 years, were used. The results suggest that (like in humans) both hippocampal and progressive global atrophy are characteristic features that correlate with aging. When classified according to head shape, cerebral atrophy was highest in mesaticephalic and brachycephalic dogs. This is the first MRI study to characterise a simple, rapid tool for studying age-related canine brain changes that can even be applied by non-experienced observers. The results confirm the possibility of transferring innovative tools developed for human diagnosis to the veterinary field. [ABSTRACT FROM AUTHOR]

Abstract: A test method is proposed for measuring chloride diffusion coefficients through partially saturated concrete specimens with well characterized water contents. It includes an experimental procedure for supplying a limited amount of Cl− to the tested concrete surface, and two mathematical models for processing the experimental Cl− content profiles obtained at selected diffusion times. The use of the more refined model, taking into account the chloride binding by concrete, allows to increase the reliability of the determined diffusion coefficients. For the two tested Portland cement concretes, (water/cement ratios 0.6 and 0.5), the Cl− diffusion coefficient decreases about two orders of magnitude, from 6·10−12 to 2·10−14 m2/s, when the relative humidity of the atmosphere in equilibrium with concrete is lowered from 95% to 54% approximately. [Copyright &y& Elsevier]

A test method is proposed for measuring chloride diffusion coefficients through nonsaturated concrete specimens with controlled water contents. The experimental setup used allows one to supply an initial limited amount of Cl− to the tested concrete surface. The procedure consists of submitting the surface of concrete specimens to interaction with the products of combustion of PVC, which contain mainly gaseous hydrogen chloride. This interaction yields a limited Cl− contamination of the concrete surface. After returning the specimens to their controlled humidity exposure conditions, the kinetics of Cl− transport from the surface inwards may be studied. The experimental Cl− concentration profiles determined at selected time intervals have been adjusted to a diffusion model of “instantaneous plane source,” which takes into account the particular initial and boundary conditions of the experimental procedure, for obtaining the corresponding diffusion coefficients. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]