Scipedia: Documents published in 2020

Advances in the understanding of the hydraulic behavior of wedge-shape block spillways

María Jesús Samper — Mon, 08 Jun 2020 09:12:48 +0200

The technology of wedge shaped blocks (WSB) for spillways has had a rising development through the last forty years, and has proved its reliability for practical applications with spillways executed during the last decade. Ongoing additional research aims to complete the understanding of the hydraulic behavior, improve current design criteria and make this technology available to practitioners, in order to consider this type of spillway together with the conventional alternatives when designing an embankment dam spillway. A summary is here shown of recent research performed by the consortium formed by the research organizations: Research Group in Dam Safety (SERPA) of the Technical University of Madrid (UPM) and the International Center for Numerical Methods in Engineering (CIMNE) and the company PREHORQUISA. Even though the experimental campaign has not been completed, some preliminary conclusions can be addressed about the developed pressures along the block tread and the leakage flow from the joints among blocks and the drainage holes.

Aula Invertida en la Ingeniería del Terreno Asistida por Ordenador

María Jesús Samper — Fri, 05 Jun 2020 14:20:18 +0200

Para superar las limitaciones de la metodología tradicional en la enseñanza de AutoCAD, la Unidad Docente de Expresión Gráfica de la Universidad Politécnica de Madrid está llevando a cabo un Proyecto de Innovación Educativa para implementar una metodología de Aula Invertida (AI) con el apoyo de vídeos educativos. En este trabajo se presentan los resultados de una primera aplicación práctica de la metodología de AI llevada a cabo durante el curso 2016/2017 sobre el tema “La impresión en AutoCAD”. La aplicación de la metodología ha incluido el empleo de un grupo de control y la realización de una prueba objetiva sobre el uso de AutoCAD, la cual ha supuesto un reto organizativo para la Unidad Docente. Los resultados del estudio muestran un mejor rendimiento de los alumnos que han empleado AI. Sin embargo, esta mejora no parece deberse directamente al AI como técnica de enseñanza sino a su aspecto motivador que incide de manera general en el rendimiento de los alumnos.

Development of a predictive model for rheumatoid arthritis mortality using random survival forest

María Jesús Samper — Fri, 05 Jun 2020 13:51:58 +0200

Different machine learning methods have been used to develop predictive models of high quality and precision [1]. Among them, Random Survival Forests (RSF) has been proposed as an alternative to traditional survival models [2], being able to overcome most of the limitation of traditional survival techniques, such as Cox proportional hazards models. Objectives Our objective was to develop and internally validate a predictive model for rheumatoid arthritis (RA) mortality using Random Survival Forests (RSF). Methods Retrospective longitudinal study involving 1,461 patients diagnosed with RA between January 1994 and August 2011, and followed at the outpatient clinic of the Rheumatology Department of the Hospital Clínico San Carlos (Madrid, Spain) until death or September 2013. Demographic and clinical-related variables collected during the first two years after disease diagnosis were used. RSF models were developed, based on 1,000 trees. 100 iterations of each model were performed to measure the mean and standard deviation (SD) of the predictive error and the integrated Brier score (IBS). Missing values were imputed using the function implemented by the randomForestSRC package [3]. The predictive capacity of the variables was assessed using the “variable importance” (VIMP). Two models were constructed using the log-rank (MLG) or log-rank score (MLGS) splitting rules. The model with the lowest prediction error was selected. Next, those variables with negative VIMP were excluded and a final model developed. Results 148 patients died (10.1%). MLG showed the lowest prediction error. All variables exhibited a positive VIMP. Final model showed a mean (SD) prediction error and IBS of 0.187 (0.002) and 0.150 (0.003) respectively. The most important predictor variables were age at diagnosis, median erythrocyte sedimentation rate and number of hospital admissions in the first 2 years after RA diagnosis. Conclusions We developed an accurate and precise model for RA mortality using RSF. Age and disease activity showed the highest influence in mortality.

Development of a predictive model of radiological damage in patients with rheumatoid arthritis based on artificial intelligence

María Jesús Samper — Fri, 05 Jun 2020 13:19:36 +0200

Background Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with increased mortality and disability. Although different factors associated with prognosis have been identified, it is still difficult to predict the evolution of a specific patient. Objectives Our objective is to train and validate a predictive model of disease severity using radiological damage as a surrogate marker, based on Artificial Intelligence techniques, and using clinical and genetic data. Methods Four independent cohorts were included (892 patients with 1667 hand X-rays). Radiological damage was measured with the Sharp/van-der-Heijde score (SvdH). The variables to be predicted [total value of SvdH, erosion component (ES) and joint narrowing (NS)] were logarithmically transformed. As clinical predictors, age at onset of symptoms, sex, duration of the disease at the time of each radiograph, year of onset of symptoms and presence of rheumatoid factor were used. As genetic variables, the single nucleotide polymorphism data obtained from the Immunochip genotyping platform (Illumina) were used. In addition, an interaction between each polymorphism and the duration of the disease was introduced. Three cohorts were used for the selection of variables, generation of predictive models and internal validation. The fourth cohort was used to perform the external validation of the models. Regression trees with random effects were generated using the R package ‘REEMtree’. The goodness of fit of the models was measured using the root mean squared error (RMSE) and the intraclass correlation coefficient (ICC). Results In the cohorts where the predictive models were developed, the RMSEs for total SvdH, ES and NS were 3.16, 1.02 and 2.29 units of the Sharp/van-der-Heijde score, respectively. The ICCs were 0.96, 0.87 and 0.95, respectively. In the external validation cohort, the RMSEs were 7.13, 3.53 and 4.81 units of the Sharp/van-der-Heijde score, respectively. The ICCs were 0.90, 0.78 and 0.88. For the total SvdH, the best fit model contained the variables ‘age of onset of the symptoms of RA’ and the interaction between duration of the disease and 3 polymorphisms: rs10752907, rs4405161 and rs2501617. For the ES, it contained the variables ‘age of onset of AR symptoms’, the polymorphism rs7769752 and the interaction between disease duration and 6 polymorphisms: rs12410412, rs117029499, rs72925969, rs869186, rs11258464, rs4781952. For the NS, it contained the variables ‘age of onset of AR symptoms’, ‘gender’, and the interaction between disease duration and 9 polymorphisms: rs3814055, rs1020822, rs13157991, rs152294, rs2914190, rs10824537, rs2637229, rs114136906 and rs4958241. Conclusions It is possible to generate predictive models of radiological damage of great precision using Artificial Intelligence techniques. This could allow early stratification of patients according to prognosis. It is necessary to validate these models in other populations

Machine learning based seismic stability assessment of dams with heterogeneous concrete

María Jesús Samper — Fri, 05 Jun 2020 11:31:31 +0200

Nowadays, the probabilistic risk assessment (PRA) is one of the standard tools for safety evaluation of the existing dams. Although many factors are involved in risk-informed condition assessment of infra-structures, a detailed numerical simulation plays the key role. A comprehensive numerical model usually includes the interaction of the dam with foundation and reservoir, nonlinearity of the concrete, and appropriate seismic wave propagation. Often, the concrete is assumed to be a homogenous material which facilitates the transient simulations. However, in reality, the mass concrete has a heterogeneous nature especially in the case of old dams suffering from aging and deterioration. The objective of this joint contribution is to evaluate the seismic response of a typical gravity dam with heterogeneous concrete material. Since the simulations are cast in the context of probabilistic methods, a relatively large number of analyses are required to fully understand the impact of concrete random field on the structural responses (i.e. displacements, and stresses). Therefore, a Random Forest (RF) meta-model is adopted in order to reduce the computational burden of the probabilistic simulations. RF is an effective technique in the regression analyses of the systems with large number of inputs, and can provide a measure of input variables' importance. This technique is useful to identify the critical areas within the dam body which deterioration may affect the seismic stability of the dam and jeopardize its integrity.

Soft Computing and Machine Learning in Dam Engineering

María Jesús Samper — Fri, 05 Jun 2020 11:06:42 +0200

In this Special Issue, we solicit high-quality original research articles focused on state-of-the-art techniques and methods employed in the design and analysis of dams. We welcome both theoretical and application papers of high technical standards across various disciplines, thus facilitating an awareness of techniques and methods in one area that may apply to other areas. We seek high-quality submissions of original research articles as well as review articles on all aspects related to artificial intelligence in dam engineering and appurtenant structures that have the potential for practical application.

Mechanisms of corrosion of steel in concrete

María Jesús Samper — Thu, 04 Jun 2020 16:19:58 +0200

The corrosion of metals in concrete is a multibillion dollar problem which affects the construction, transportation, and many other industries. While much has been written about the problem, and numerous reports have appeared which discuss how this corrosion can be controlled, little has appeared on the mechanism whereby this corrosion occurs.

It is well known that highway structures corrode, for the most part, due to the influence of deicing salts or marine environments. Relatively little has appeared about the equally severe corrosion problems which occur in buildings and other nonhighway structures. Most of these structures are not exposed to the salts present in highway structures, yet they still corrode.

This paper discusses how all forms of concrete and similar cementitious environments protect embedded metals. It discusses the three protection mechanisms—passive film formation, changes in the conductivity of the electrolyte, and mineral scales—that have been used to explain how corrosion in concrete occurs. It also presents evidence to explain how, and why, corrosion occurs in these structures, even in the absence of deicing salts, marine environments, or other salt sources. Examples are discussed including buildings, marine piers, foundations, and highway structures.

Concrete durability of the new Panama Canal: Background and aspects of testing

María Jesús Samper — Thu, 04 Jun 2020 13:20:03 +0200

The Panama Canal, vital to international trade, connects the Pacific Ocean and the Caribbean Sea, through the Gatun inland lake (which is almost entirely freshwater). The canal is now 100 years old. Since 2011, new lanes and locks have been or are being built, which will greatly enhance capacity and accommodate vessels with a much deeper draft. This is being done under the Panama Canal Authority (ACP) by a consortium named Grupo Unidos por el Canal, (GUPC), whose engineering division is headed by the firm Sacyr, S.A. Although the concrete on the earlier existing canal is not reinforced, the design for the new canal structures calls for reinforcing steel as an anti-seismic precaution. In its specifications, the ACP requires a 100-year service life for the concrete in all members, which is defined to mean conformity with the 1000-C electrical charge requirement of ASTM C1202, and an application of a reliable method for calculating service life. This chapter describes the tests performed on cores drilled from the old canal and the working program developed with GUPC for demonstrating the requirements, together with complementary test methods. The main tests were the measurement of concrete resistivity, as well as natural chloride diffusion found by ponding. The model used was the LIFEPRED numerical model, using the natural diffusion coefficients. The ageing of the diffusion coefficient was also measured through the resistivity evolution with time. The relationship between electrical charge and resistivity values is shown, along with the variation in these parameters over time. Also given are the chloride diffusion values obtained in four concrete mixes used as examples and their ‘age factor’, which proved to have an even more critical effect on predictions than the diffusion coefficient itself.

Reinforcement corrosion in chloride environment of different concentrations

María Jesús Samper — Thu, 04 Jun 2020 11:43:50 +0200

Steel reinforcement remains passive until a certain amount of chlorides entry in contact with them. The corrosion develops in local areas and extends around depending on the level of chloride concentration. The further evolution of the corrosion depends on the total amount of chlorides although there is a maximum in the expected values of the corrosion rate. In present paper results are given on several tests that have been performed to establish the corrosion rates in chloride environments of different concentrations. First, the chloride threshold for depassivation will be commented on and its dependence of the Cl- /OH- ratio as well as on the electrical potential exhibited by the reinforcement will be discussed. The depassivation occurs for Cl- amounts between 0.2 and 1 % by cement weight for corrosion potentials more noble positive than -200 mVsce. Concerning the values of the corrosion rate, they increase when increasing the chloride concentration until around 1M NaCl, but above this concentration, the corrosion rate does not increase more likely due the decreasing oxygen content in the pore solution. Certain unexpected results are presented to illustrate that the corrosion rate is the result of some counterbalance phenomena, not always taken into account.

Advances in modeling of RILEM TC 178-TMC "Testing and modelling chloride penetration in concrete"

María Jesús Samper — Thu, 04 Jun 2020 11:13:50 +0200

Reinforced concrete structures may prove to be very durable; however their gradual degradation over time impairing both serviceability and structural safety is still a matter of great practical concern in view of the economical consequences related to assessment, maintenance, and repair. Corrosion of embedded steel reinforcement is considered the most detrimental process responsible for structural deterioration and numerous researches are in progress to try to find a comprehensive engineering approach for the initiation as well as the propagation period.

The importance of concrete permeability for the durability of concrete itself or the steel in reinforced concrete was recognized more than a decade ago by Rilem members. A technical committee TC-116-Permeability of concrete as a criterion for its durability was set up and its results were published (Rilem, 1999). This TC-116 promoted an important amount of research and contributed to the advance of understanding the relation between concrete permeability and durability. At the time of the initiation of the work of TC-116 durability was a dealt with on a broad and comprehensive perspective. At the end of the work, the need to study specifically chloride penetration into concrete in more depth was identified, since chloride attack represents the most severe corrosion damage on reinforced concrete structures with tremendous economical consequences. At the same time gaps in understanding many of the individual mechanisms controlling the attack still existed. This was the justification for the formation of a separate Rilem TC on chloride attack and its objectives in the description of the specific deterioration mechanism.

Types of Models of Service Life of Reinforcement: The Case of the Resistivity

María Jesús Samper — Thu, 04 Jun 2020 10:44:56 +0200

The design of concrete structures is usually made by means of a performance approach based on strength tests carried out following testing conditions agreed by convention. A similar approach should also be followed in the case of durability design regarding reinforcement corrosion. This type of consideration enables the definition of a four level methodology for design against reinforcement corrosion in parallel with that followed for strength design. Levels from I to IV are proposed: a] level I would be the prescriptive method already given in present codes based on "deemed-to-satisfy" rules, b] level I is that where still not quantification of the time to reach a limit state is explicit but the minimum life time is assured through performance based tests, c] level III would be the level in which the calculation of aggressive ingress through models having explicit the time is made and d] level IV includes the verification that the resistance of the cover thickness against the penetration of aggressive substances is higher than the environmental action effect including probabilistic treatments. For level II and III the measurement of the electrical resistivity results a very suitable proposal due to this parameter can be measured in a non destructive test and serves to quality control. It is not only a performance test [level II] but it can be included in models of 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. It also results very suitable for measuring concrete aging and then accounting for the reduction of the diffusion coefficient with time. 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. A model is proposed in which the resistivity is introduced in the square root of time law.

Cost-benefit analysis tools

Julio García-Espinosa — Wed, 03 Jun 2020 18:52:03 +0200

The objective of the present report D8.2 in relation with Task 8.3 in Work Package 8 was to provide cost benefit analysis support to FiBRESHiP partners throughout to entire project in the technical work packages related to the analysis of large-length fibre-based commercial vessels (FRP) such as the three types targeted in the project: container ship, Ro-Pax, and Fishing Research Vessel (FRV) and to benchmark them with conventional steel (BAU) vessels. Technical decision support with cost-benefit analysis included production, operation and dismantling of the above mentioned vessels of the same size by using NPV, RRI and ROI calculations, with the reflection of operational costs in fuel saving due to weight reduction. The deliverable reflects to the needs of industry stakeholders by revealing cost-benefit information and concludes with the financial comparison between conventional (steel) and FRP vessels.

Impact of surface roughness on the debonding mechanism in concrete repairs

María Jesús Samper — Wed, 03 Jun 2020 14:25:33 +0200

Surface roughness of the existing concrete substrate was considered to have the greatest impact on the bond strength in repair systems. However, the influence of this parameter has been subject for debates in recent years. The effect of concrete surface roughness is not quite clear, nor there exist a clear relation between the surface roughness and the adhesion in multilayer systems. In order to understand and explain this relation, simple numerical experimentation is used. Repair systems with different roughness parameters are simulated in order to get load displacement diagrams and crack debonding propagation. The influence of roughness on the composite response in simulated direct tension, shear and three point bending test using a lattice model, is studied. Results indicate that roughness has different influence on tensile and shear bond strength. In addition, although it seems to have negligible influence on load bearing capacity of the composite system in bending, it enables more monolithic response and slower debonding propagation.

Experimental and Numerical Study of Bond Response in Structural Concrete with Corroded Steel Bars

María Jesús Samper — Wed, 03 Jun 2020 13:38:33 +0200

Corrosion can affect the bond between reinforcing bars and concrete and hence the transfer of longitudinal stresses. Although a number of experimental studies on bond failure have been conducted in recent years, the findings have diverged rather widely, due primarily to differing test conditions.The present paper reports on an experimental programme consisting of eccentric pull-out tests run on corroded steel bars in specimens subjected to accelerated or natural corrosion [1]. An axisymmetric bi-dimensional FE model with finite deformations initially developed to study bond mechanics with sound steel bars [2], has been enhanced to consider bond effects in corroded steel bars. The model simulation is compared to some of the experimental results for corroded and sound bars and the findings are analysed.

El Eurocódigo 2 y la evaluación de estructuras de hormigón armado con armaduras corroídas

María Jesús Samper — Wed, 03 Jun 2020 12:41:23 +0200

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.

Mechanical Behavior of Masonry Mortars Made with Recycled Mortar Aggregate

R.S. Mora-Ortiz — Tue, 02 Jun 2020 22:07:02 +0200

Recycling is an important habit to avoid waste. This paper evaluates the performance of masonry mortar, elaborated by replacing natural sand with recycled fine aggregate (RFA) obtained from mortar. Five families of mixtures were prepared with different replacement proportions: 20%, 40%, 60%, and 100%. A 1:4 volumetric cement-to-aggregate ratio was used for all mixtures by experimentally adjusting the amount of water to achieve the same consistency of 175 ± 5 mm. The effects of the following procedures were analyzed: (1) the use of a deconstruction technique to collect the RFA, (2) pre-wetting of the aggregates, and (3) the use of a commercial plasticizer. Experimental results show that it is possible to use this type of recycled fine aggregate as a substitute for natural sand by up to 60% in the manufacture of masonry mortar without significantly affecting its properties.

Combination of an adaptive remeshing technique with a coupled FEM-DEM approach for analysis of crack propagation problems (preprint)

María Jesús Samper — Tue, 02 Jun 2020 15:32:13 +0200

This paper presents an enhanced coupled approach between the Finite Element Method (FEM) and the Discrete Element Method (DEM) in which an adaptative remeshing technique has been implemented. The remeshing technique is based on the computation of the Hessian of a selected nodal variable, i.e. the mesh is refined where the curvature of the variable field is greater. Once the Hessian is known, a metric tensor is defined node-wise that serves as input data for the remesher (MmgTools) that creates a new mesh. After remeshing, the mapping of the internal variables and the nodal values is performed and a regeneration of the discrete elements on the crack faces of the new mesh is carried out. Several examples of fracturing problems using the enhanced FEM-DEM formulation are presented. Accurate results in comparison with analytical and experimental solutions are obtained.

Modelling torque and temperature in Friction Stir Welding of Aluminium Alloys

María Jesús Samper — Tue, 02 Jun 2020 15:02:42 +0200

An analysis of the evolution of the torque and of the temperature with welding conditions, in Friction Stir Welding (FSW) of aluminium alloys, was conducted. More precisely, torque and temperature results from a large number of publications, on FSW of AA2xxx, AA5xxx, AA6xxx and AA7xxx aluminium alloys series, were collected. The literature data was complemented with results from a fully coupled thermomechanical analysis of the FSW welding process. Coupling the experimental data, from the literature, with numerical simulation results, the individual influence of the main process parameters, tools and plates characteristics, on the torque and on the temperatures in FSW was assessed. It was found that the tool rotational speed govern the heat generation, while the tool dimensions have a very important influence, not only on the heat generation but also on the volume of material being stirred during welding, which is another important factor determining the welding torque. The traverse speed and the base material thickness were also found to be important factors governing the torque during welding. However, the influence of the traverse speed on torque evolution is conditioned by the tool dimensions. A parametric analysis enabling to understand the relation between process parameters, heat generation, heat dissipation and base material stirring, was conducted. Analytical relations, which enable calculating the torque and the temperature, in FSW of aluminium alloys, were developed based on numerical results and tested using the data from the literature review.

Defect formation and material flow in Friction Stir Welding

María Jesús Samper — Tue, 02 Jun 2020 14:11:03 +0200

This work addresses the issue of the simulation and prediction of defect formation through the analysis of the material mixing during Friction Stir Welding (FSW). A coupled thermomechanical model is used for the FSW simulation. To follow the flow of the material, a tracing technique of the material particles is incorporated in the numerical model. A fast and accurate two-stage numerical strategy is adopted to analyse the FSW process. The speed-up stage intends to reach the steady state quickly. The material tracing is performed in the periodic stage where the rotation of the tool is modelled. The effect of the process parameters and the pin features on the defect formation is studied. The model is capable of predicting defects such as void, wormhole, flash and joint line remnant, as well as the formation of “onion rings” in a single simulation. The results show that the proposed model has significant capability to explain and predict the post-FSW defects

A pseudo-DNS method for the simulation of incompressible fluid flows with instabilities at different scale

María Jesús Samper — Tue, 02 Jun 2020 14:03:17 +0200

In this work, a new model for the analysis of incompressible fluid flows with massive instabilities at different scales is presented. It relies on resolving all the instabilities at all scales without any additional model, i.e., following the direct numerical simulation style. Nevertheless, the computation is carried out at two levels or scales, termed the coarse and the fine. The fine-scale simulation is performed on representative volume elements providing the homogenized stress tensor as a function of several dimensionless numbers characterizing the flow. Consequently, the effect of the fine-scale instabilities is transferred to the coarse level as a homogenized stress tensor, a procedure inspired by standard multi-scale methods used in solids. The present proposal introduces a new way for the treatment of the flow at the fine scale, simulating not only the coarse scale but also the fine scale with all the necessary detail, but without incurring in the excessive computational cost of the classical DNS. Another interesting aspect of the present proposal is the use of a Lagrangian formulation for convecting the eddies simulated on the fine mesh through the coarse domain. Several examples showing the potentiality of this methodology for the simulation of homogeneous flows are presented.

A particle finite element-based model for droplet spreading analysis

María Jesús Samper — Tue, 02 Jun 2020 13:25:38 +0200

A particle finite element method-based model is proposed to analyze droplet dynamics problems, particularly droplet spreading on solid substrates (wetting). The model uses an updated Lagrangian framework to formulate the governing equations of the liquid. The curvature of the liquid surface is tracked accurately using a deforming boundary mesh. In order to predict the spreading rate of the droplet on the solid substrate and track the corresponding contact angle evolution, dissipative forces at the contact line are included in the formulation in addition to the Navier-slip boundary conditions at the solid–liquid interface. The inclusion of these boundary conditions makes it possible to account for the induced Young’s stress at the contact line and for the viscous dissipation along the solid–liquid interfacial region. These are found to be essential to obtain a mesh-independent physical solution. The temporal evolution of the contact angle and the contact line velocity of the proposed model are compared with spreading droplets and micro-sessile droplet injection experiments and are shown to be in good agreement.

INTERVENCIÓN EDUCATIVA PARA LA PREVENCIÓN DE LA CONDUCTA SUICIDA EN ESTUDIANTES DE MEDICINA DE UNA UNIVERSIDAD DE MANIZALES 2017

Sandra Cañón — Tue, 02 Jun 2020 03:41:02 +0200

El suicidio se define como todo acto por el que un individuo se causa a sí mismo una lesión, o un daño, con un grado variable de intención de morir. En Colombia, la mayor parte de los afectados se concentró en el grupo de edad comprendido entre los 20 y 24 años. Se ha determinado que aproximadamente 1100 estudiantes universitarios, se suicidan cada año. Durante la formación médica, se encuentran unos factores de riesgo específicos para esta población como: la sobrecarga de información y de conocimiento adquirido; la falta de tiempo libre, entre otras. Dado que el suicidio es el prototipo de condiciones que solo pueden ser impactadas desde la prevención, y que el gremio médico es considerado como de alto riesgo para asumir este tipo de conductas, es fundamental intervenir escenarios académicos en donde los estudiantes de medicina puedan ser educados con el fin de que desarrollen la capacidad de reconocer en sí mismos y en sus pares, conductas de riesgo, con el fin de evitar muertes prevenibles en estudiantes y profesionales altamente cualificados. OBJETIVO: Realizar una intervención educativa en los estudiantes de medicina de la Universidad de Manizales, con el propósito de prevenir pensamientos y conductas suicidas. METODOLOGÍA: Estudio cuasiexperimental. La muestra intervenida estuvo conformada por 45 estudiantes de medicina de una Universidad de Manizales, matriculados en segundo y sexto semestre. Se utilizó el estadístico t para analizar las muestras pareadas, evaluando por separado los cuestionarios empleados. RESULTADOS: Fueron intervenidos 45 estudiantes de Medicina de la Universidad de Manizales. El 77,8% (n=35) de los sujetos fueron mujeres y el 22,2% (n= 10) hombres. El 44,4% (n=20) de los participantes pertenecían a segundo semestre y el 55,6% (n=25) restante, a sexto semestre. Los cuestionarios y escalas pre-intervención permitieron detectar que: El 11,2% (n=5) de los estudiantes había tenido algún intento de suicidio en el pasado; según la escala CAGE, el 8,9% (n=4) presentaba un consumo de licor de riesgo y el 2,2% (n=1) un consumo perjudicial; mientras que con el cuestionario ISO 30, se determinó que un 20% (n=9) de los estudiantes evaluado tenían un alto riesgo suicida. Las sesiones desarrolladas favorecieron la desmitificación de elementos frecuentemente asociados con el riesgo suicida y permitieron educar a los estudiantes en estrategias saludables para el manejo adecuado de factores como la ansiedad y el estrés. Después del proceso de intervención, y según información obtenida con la escala ISO 30, la cantidad de estudiantes con alto riesgo suicida disminuyó a 11,1% (n=5), y aumentó el número de estudiantes catalogados como de bajo riesgo (31,2%; n=14)

Bond assessment for corroded steel bars in structural concrete

María Jesús Samper — Thu, 28 May 2020 16:27:10 +0200

Corrosion can affect bond between reinforcing bars and concrete and with it the transfer of longitudinal stresses between both materials. Loss of bond is normally characterized by brittle behaviour thus it should be analysed within the framework of the assessment of damaged structures in order to avoid it. Factors that affect bond strength include the weakening of the steel bar confinement due to cracking of the concrete cover and/or stirrup corrosion, development of corrosion products at the interface, and, in the case of ribbed bars, reduction of the relative rib area due to cross-section loss in the steel. A number of experimental studies have been conducted in recent years on bond failure, the findings have diverged rather widely, however, due primarily to differing test conditions.

In an attempt to surmount the inconsistencies in bond prediction with corroded steel bars, eccentric pull-out tests were carried out with specimens subjected to both accelerated and natural corrosion [1]. In this study a semi-empirical formulation accounting for both pull-out and splitting failures is proposed to assess bond of corroded and non-corroded steel bars. This formulation is obtained by means of multiple linear regression analysis of a database of more than 650 tests of corroded and non-corroded bond tests, including the tests performed in [1]. The database used includes a wide range of influencing variables regarding to bond, such as bar diameter, concrete strength, concrete cover, anchorage length, confinement ratio and cross-section loss due to corrosion. Several statistical criteria have been used to analyse the proposed formulation and the influence of the explanatory variables. Also a comparison with several formulations found in literature, including the proposal of Fib Model Code 2010 for corroded bars is performed. The proposed formulation could be used in the structural assessment of corroded reinforced concrete beams.

Cold Drawn Steel Surface Analysis in Contact with Saline Solution: Analysis Using Electrochemical Atomic Force Microscopy

María Jesús Samper — Thu, 28 May 2020 16:09:10 +0200

High strength steels in concrete structures used as reinforcement are usually passivated due to the physical barrier that concrete provides and by a protective passive film developed on the surface by the high alkaline media. Chloride ions can break the passive film. These ions can be found dissolved in the water or in structures in marine environment.

This work is focused on the study, by Electrochemical Atomic Force Microscopy (EC-AFM), of the early stages of corrosion of such steels during exposure to a sodium chloride solution in order to better understand the evolution of the dissolution of steel phases. Additionally, it is estimated the corrosion rate by topographical images and simultaneously by means of measuring the corrosion rate through the linear polarization technique performed in an electrochemical cell specially developed in the AFM microscope. The results show the evolution of the topographical profiles which are compared during some period of time with the electrochemical results.

Electronic and Electrolytic Conduction of Cement Pastes with Additions of Carbonaceous Materials

María Jesús Samper — Thu, 28 May 2020 15:26:47 +0200

Additions to concrete may change some of its basic properties in several ways depending on the nature of these additions. The addition of fibers, in particular, has enabled new concrete characteristics, making standard concrete a very modern composite material. If the fibers are electrical conductors, the properties that change in addition to the mechanical ones, are the thermal and electrical conductivities. The results indicate that the arrangement of the electrodes and the electrode-material interface are relevant, because the use of sponges between electrode and concrete prevents the contact between the metallic electrode and the carbon material which ends in different values of electrical resistance with and without sponges. Moisture conditions, that critically influence the electrical resistance of concrete without additions, resulted, also very relevant when conductive substances are present in the matrix. If the proportion of the carbonaceous addition, that lowers significantly the resistivity, is to be quantified, the best procedure seems to measure in dry concrete (0 % relative humidity) with sponges or, alternatively, wet concrete (100 % relative humidity) with silver painted electrodes (without sponges).

Application of DIC to monitor reinforced concrete structures

María Jesús Samper — Thu, 28 May 2020 14:47:07 +0200

The reinforced concrete structures need to be monitored to ensure their structural integrity, but sometimes those measurements are very local and the instrument is complex to locate physically in the structure and may interfere on it. Digital Image Correlation, DIC, is a non-contact and non-destructive experimental technique capable to measure the displacement field in a big region of a structure with a great accuracy. This allows extracting valuable information from the fracture processes of reinforced concrete structures. Critical for the evaluation of the structural integrity. The identification of the energy dissipated by the structure is essential for the identification of the strength mechanisms that are failing in the structure, and to identify a proper repair. In this paper the penetration of a prestress rebar in concrete is measured with this technique and the energy dissipated by different fractures is fully observed. Comparison is made with traditional measurement techniques. Also, using Fracture Mechanics other valuable information is extracted from the fracture processes of the reinforced concrete beam, such as the Mode I and Mixed Mode fracture energy released at each loading step, which is essential to evaluate the elastic energy that the structure can accumulate before collapse. The examples enable to anticipate the importance of DIC for future studies at large scale of fracture in concrete and other materials related to construction.

Correction to: Propagation of reinforcement corrosion: principles, testing and modelling

María Jesús Samper — Thu, 28 May 2020 13:25:27 +0200

Técnicas para el estudio de la corrosión de armaduras en el hormigón armado y pretensado

María Jesús Samper — Thu, 28 May 2020 12:16:33 +0200

La velocidad de reacción es la variación (aumento o disminución) de la concentración de una cierta sustancia, con el tiempo. La medida de la velocidad de una reacción, cuando la naturaleza de ésta desde el punto de vista de su aplicación industrial es importante, se considera un factor fundamental. En las construcciones de hormigón el conocimiento de su durabilidad (velocidad de posibles reacciones destructivas) es de capital importancia. El hormigón no es eterno, y los accidentes que se han producido, sobre todo en construcciones de hormigón pretensado, han hecho, desde hace años, volcar en este tema de la durabilidad mucha labor investigadora. La corrosión del acero embebido en el hormigón es una de las causas del deterioro de las construcciones civiles, y por lo tanto conocer la velocidad de esta corrosión es una de las metas a la que se dirige la atención de muchos investigadores. Hay dos grupos de técnicas que permiten llegar a evaluar la corrosión del acero en el hormigón armado y pretensado: las técnicas de tipo gravimétrico y las técnicas de tipo electro-químico

Precisiones sobre la corrosión del acero en contacto con hormigón

María Jesús Samper — Thu, 28 May 2020 09:23:22 +0200

En los presentes comentarios se insiste en que, para evaluar la velocidad de corrosión de los metales, en la actualidad se pueden utilizar técnicas electroquímicas no destructivas que permiten seguir la evolución del proceso diariamente, o bien, en el caso de no contar con los aparatos apropiados, se puede acudir a una determinación gravimétrica de la pérdida de metal. La simple observación visual es una valiosa indicación complementaria de las técnicas antes mencionadas, pero no debe utilizarse como técnica de medida única por la subjetividad que conlleva. Tam.bién se precisan algunos aspectos sobre la corrosión que el acero desnudo y el galvanizado pueden sufrir por estar en contacto con materiales de construcción, como son la influencia de la alcalinidad y de la humedad del medio y,, fundamentalmente, se analiza la influencia que puede ejercer el tipo de cemento en el riesgo de corrosión de ambas clases de metales.

In this paper, we emphasize that now it is possible to use some electrochemical non-destructive techniques for measuring the corrosion rate of the metals. Also, it is possible to use the gravimetric determinations if the appropriate instrumentation is not available. The simpple visual observation is a good complementary technique but it must not be used alone because of its subjectivity. Also, we stress some aspects, such as the influence of the alkalinity and the humidity, about the corrosion, that the bare and galvanized steel, can suffer in contact with construction materials. We analyze mainly, the influence of the type of cement on the risk of corrosion of both kinds of metals.

Ensayos de laboratorio sobre el efecto inhibidor de los NO2 sobre la corrosión de las armaduras

María Jesús Samper — Thu, 28 May 2020 08:49:59 +0200

Se presenta el resumen de varios años de investigación sobre el efecto inhibidor de los NO2 en la corrosión de las armaduras. Se ha estudiado su efecto inhibidor mediante el trazado de curvas potenciodinámicas y galvanostáticas y se han medido velocidades de corrosión intantánea usando el método de Resistencia de Polarización. Se ha podido comprobar mediante esta última técnica que, cuando hay Cl presentes desde el momento del amasado, los NO2 inhiben completamente el ataque si se añaden en cantidad suficiente. Cantidades insuficientes de NO2 nunca han provocado mayores ataques en nuestros ensayos, sino que siempre han reducido el área corroída o la intensidad del ataque. Los NO2 son también efectivos en hormigón carbonatado donde, al menos, siempre reducen el ataque cuando no lo inhiben por completo.

Efecto que el tipo de cemento y la dosificación del mortero ejercen en la velocidad de corrosión de armaduras embebidas en mortero carbonatado

María Jesús Samper — Wed, 27 May 2020 11:24:00 +0200

La inexistencia de datos cuantitativos sobre el comportamiento del acero en morteros y hormigones carbonatados ha llevado a la realización de una serie de ensayos para conocer las cinéticas de corrosión de las armaduras. Como técnica de medida se ha utilizado la determinación de la Resistencia de Polarización. En los presentes ensayos se ha realizado un primer estudio con mortero para conocer la influencia de la naturaleza del cemento, la proporción del mismo y la relación agua/cemento (a/c) en la velocidad de corrosión del acero. Los resultados indican que el tipo de cemento no ha presentado una tendencia sistemática que sea digna de resaltar, por lo que no parece que la naturaleza del mismo influya significativamente en la velocidad de corrosión. En cambio, sí parece afectar más significativamente la dosificación del cemento (cuanto más elevada menos corrosión se detecta) y la porosidad o compacidad del mortero que influye en el sentido lógico de más protector el mortero cuanto más compacto y más impermeable resulte.

Corrosión de las armaduras de acero debida a la carbonatación acelerada de soluciones que simulan la composición de la fase acuosa del hormigón

María Jesús Samper — Wed, 27 May 2020 09:06:09 +0200

A pesar de los numerosos estudios realizados en torno a la carbonatación del hormigón, son muy pocos los datos publicados acerca del mecanismo de despasivación del acero y las velocidades de corrosión implicadas en el proceso de corrosión por carbonatación. Por otra parte, aún no se conoce la composición de la fase acuosa de un hormigón carbonatado. Cierta erraticidad en los cambios registrados en la velocidad de corrosión del acero durante la carbonatación acelerada de morteros de cemento, puso de manifiesto la necesidad del estudio del proceso en un sistema simplificado que permitiera considerar aisladamente cada uno de los distintos parámetros. A este fin se utilizaron como disoluciones de simulación de la fase acuosa intersticial del hormigón, disoluciones saturadas de Ca(0H)2 con distintas adiciones de NaOH o KOH. En el presente trabajo, se han registrado simultáneamente los cambios en el valor del pH de la disolución, potencial de corrosión y velocidad de corrosión (medida a través de la determinación de la Resistencia de Polarización) de redondos de acero, durante la carbonatación acelerada producida por un flujo constante de COp gaseoso y/o aire a través de la disolución.

Aproximación al efecto de la resistividad del hormigón en la corrosión de armaduras embebidas en hormigón

María Jesús Samper — Tue, 26 May 2020 16:13:31 +0200

La resistividad del hormigón se ha venido considerando como uno de los factores que afectan a la velocidad de corrosión de las armaduras, aunque, hasta ahora, la única relación encontrada ha sido la establecida entre los potenciales y la resistividad para acero embebido en hormigón contaminado por cloruros. En este trabajo se establecen comparaciones entre velocidad de corrosión de las armaduras, medida a través del método de determinación de la Resistencia de Polarización, y los datos de resistencia eléctrica medidos a través de la compensación de caída óhmica. Los resultados de i^^^^ y R^^^ se han medido en armaduras embebidas en mortero fabricado con tres tipos de cemento a los que se ha sometido a un proceso de carbonatación acelerada. La relación entri i^^^^ y R^^^^ es muy similar en todos los casos y sugiere que la resistencia del hormigón puede actuar como un factor controlante de la velocidad de corrosión de las armaduras.

Evaluación de la eficacia de una reparación para hormigón contaminado con cloruros

María Jesús Samper — Tue, 26 May 2020 15:46:23 +0200

En el presente trabajo se describen los ensayos que se están efectuando en un viaducto de las cercanías de Madrid y que tía sufrido importantes daños por corrosión de armaduras. Estos Ensayos consisten en la medida de los potenciales de corrosión y en un próximo futuro, de la velocidad de corrosión (método de la Resistencia de Polarización Aparente). También se presenta la metodología de los ensayos de laboratorio efectuados para caracterizar la capacidad protectora hacia las armaduras del sistema de reparación utilizado en el viaducto. Los resultado de estos ensayos han mostrado que los materiales de reparación no resultan idóneos para la función repasivante y protectora que deberán desempeñar. Se destaca, finalmente, la necesidad de desarrollar una normativa de ensayos adecuada que permita caracterizar a estos materiales de reparación cuando van a ser usados en obras dañadas por corrosión de armaduras.

Influencia de la conductividad y fuerza iónica de soluciones sintéticas que simulan la fase acuosa del hormigón en el fenómeno de la corrosión de armaduras

María Jesús Samper — Tue, 26 May 2020 15:13:42 +0200

Este trabajo presenta el estudio cuantitativo, mediante la técnica de Resistencia de Polarización (Rp), de la influencia de los iones Cí y OH' en la corrosión de armaduras de acero, en un medio acuoso sintético de similar composición al contenido en los poros del hormigón. Fuerza iónica, conductividad (resistividad) y sus variaciones en función de la concentración de dichos iones, han sido los parámetros de interés escogidos para la evaluación del proceso, además de las medidas de intensidad y potenciales de corrosión. Los resultados muestran claramente el antagonismo de los iones Cí y OH', cuyo carácter agresivo o protector disminuye a medida que aumenta la fuerza iónica del medio.

Propiedades dieléctricas de pastas de cemento con bajo contenido en agua libre

María Jesús Samper — Tue, 26 May 2020 14:22:46 +0200

El hormigón eléctricamente se comporta como un aislante o como un conductor en función de su contenido de agua. Así, el hormigón saturado de humedad presenta valores de resistividad de 50 W m (a 1 KHz) lo que le sitúa en el rango de los semiconductores. Sin embargo, cunado se seca a 100 ºC, la resistividad alcanza valores del orden de 109 W m (a 1KHz), que corresponde a la de un aislante. Por lo tanto, el contenido en agua de los poros del hormigón tiene un gran efecto en su constante dieléctrica. En el presente trabajo se relaciona la constante dieléctrica de la pasta con su contenido de agua a partir de medidas de Espectroscopia de Impedancia Eléctrica (EIS). Para ello se prepararon probetas con una relación a/c=0, 5 con y sin adición de un 2% de CaCl2 que han sido caracterizadas para diferentes contenidos de humedad. Se presenta la dependencia de la constante dieléctrica de estas muestra con la frecuencia, contenido de agua y de cloruros. Los resultados ponen de manifiesto que la constante dieléctrica aumenta con el contenido de agua, siendo los valores muy dependiente de la frecuencia.

Influencia de la humedad relativa y la temperatura en las velocidades de corrosión de estructuras de hormigón

María Jesús Samper — Tue, 26 May 2020 13:43:19 +0200

Cuando el acero se despasiva, la corrosión se empieza a desarrollar a una velocidad que depende principalmente de la cantidad de humedad contenida en los poros del hormigón. En estructuras expuestas a la atmósfera, este contenido de humedad dependerá, no sólo de la humedad relativa del ambiente, sino también de las variaciones de temperatura que se producen con los ciclos día-noche. Para avanzar en el conocimiento de la influencia de las variables climáticas en la velocidad de corrosión de estructuras reales, se han llevado a cabo diversos experimentos. Primero se han realizado medidas de corrosión de barras de acero sumergidas en soluciones que simulan la solución de los poros del hormigón sometidas a varias temperaturas y se han registrado sus variaciones de contenido en oxígeno, de la relación Cl/OH y de su conductividad. También se han efectuado medidas en probetas de hormigón sometidas a una exposición a la atmósfera no protegidas de la lluvia. Los resultados han permitido deducir que las variaciones de temperatura tienen un efecto múltiple en los diversos parámetros, que se contrapesan unos a otros. Así, el oxígeno y el pH disminuyen al elevarse la temperatura pero la proporción de Cl aumenta. La resistividad es el parámetro que mejor se ajusta a las variaciones de la velocidad de corrosión.

Nuevas técnicas avanzadas para la medida in situ de la corrosión en hormigón armado

María Jesús Samper — Tue, 26 May 2020 13:07:00 +0200

Las técnicas de medida de la corrosión en hormigón armado se investigan muy poco en comparación con el creciente número de publicaciones sobre este tema. Sin embargo, existen muchas posibilidades y retos que todavía no han sido exploradas. En el presente artículo se descubren algunas de las presentes posibilidades de las técnicas electroquímicas, tanto in-situ como en laboratorio. En cuanto a las técnicas insitu se refiere, se comentan las posibilidades y limitaciones de los métodos actuales de medida de la Resistencia de Polarización, Rp. Se presta particular atención ante la necesidad de utilizar un anillo de guarda modulado con sensores que controlen esta modulación para obtener valores adecuados de velocidad de corrosión. Después se describen las bases de la nueva técnica relacionada con la medida del estado pasivo en estructuras protegidas catódicamente. También se presentan las bases de un nuevo método de medida de la corrosión sin necesidad de tocar el metal. En cuanto al uso de sensores embebidos, la experiencia, hasta el momento, muestra la difícil interpretación de los datos obtenidos, debido a la importante influencia del efecto de la temperatura. Finalmente, se presentan algunos comentarios sobre la necesidad de trabajar conjuntamente los especialistas en materiales y en estructuras.

Late Holocene evolution of the lower Tagus alluvial plain and heavy metals content : preliminary results

María Jesús Samper — Tue, 26 May 2020 12:15:03 +0200

This paper aims to contribute to the fluvial dynamic knowledge of the Lower Tagus during the late Holocene. Two cores were done in selected geomorphological positions at the alluvial plain. Each ten centimeters of sediments were submitted to sedimentological and geochemical analyses in order to identify human contamination by heavy metals, sedimentation rates and environmental changes in the main channel position The main conclusions are: (1) The witness of the lateral migration of the fluvial channel; (2) The very irregular sedimentation rate, from 3mm per year to 0.1mm per year; (3) The diversified contamination of fluvial sediments and fluvial channels by heavy metals, namely Cu due to cooper sulphate vineyards and Pb due to petrol and Cr from the tanning industries

Determination of the OH content in the aqueous phase of hardened cementitious materials by an empirical leaching method

María Jesús Samper — Tue, 26 May 2020 11:37:36 +0200

The most reliable method to determine the concentration of hydroxyl ions in the aqueous phase of hardened cementitious materials is the squeezing of concrete at high pressures. However, this method needs special equipment as well as a relatively high amount of sample to be carried out. In present research, the determination of the OH concentration in the concrete pore solution is undertaken by a leaching method in granulated samples. The experimental program has been made using mortars with 5 different binders and three different leaching solutions. In the treatment of the results, different phenomena (dilution + dissolution of solid phases) occurring during leaching have been taken into account until reaching the target values validated by comparison with those obtained by means of the high pressure technique. The agreement found is good enough, for every binder tested, in spite of the fact that fully understanding of the leaching mechanism is not achieved and that concentrations and not activities of the ions are taken into account in the calculations. Therefore, the method suggested is empirical at present stage.

Avances en el modelado de la penetración de cloruros en estructuras de hormigón expuestas al ambiente marino

María Jesús Samper — Tue, 26 May 2020 09:34:06 +0200

El transporte de iones cloruro a través de los poros del hormigón presenta un gran interés en relación con la durabilidad de las estructuras de hormigón armado, ya que éstos iones son los agentes más agresivos para las armaduras. Por ello, en los últimos años y en la actualidad se está llevando a cabo un gran esfuerzo de investigación para modelizar la penetración de cloruros así como el umbral límite que produce la despasivación de las armaduras. Sin embargo, el fenómeno es muy complejo, ya que viene condicionado por la propia estructura de la red porosa del hormigón, por la fuerza iónica de la fase acuosa de los poros, así como por las condiciones medioambientales (macroclima y microclima en las que se sitúa la estructura). La vida útil o tiempo hasta corrosión se estima actualmente a través del cálculo de los coeficientes de difusión en estado estacionario, Ds, y no estacionario, Dns, y posterior resolución de la ley de Fick (medio semi-infinito y concentración exterior constante), que ha demostrado no dar resultados fiables, debido precisamente a que la interacción cloruro/material cementante es mucho más compleja de lo que indica la solución a la ecuación de Fick. Se necesita pues avanzar en el conocimiento y establecer condiciones de contorno más reales, así como desarrollar procedimientos, basados en la medida de diversos parámetros de transporte, para realizar determinaciones tanto en laboratorio como en obra. En este artículo se recogen los métodos más utilizados para la determinación de los coeficientes de difusión, así como los modelos que se preconizan en la literatura.

Caracterización de la durabilidad de los hormigones de polvo reactivo (HPR) con fibras metálicas y sin fibras

María Jesús Samper — Tue, 26 May 2020 09:29:48 +0200

La utilización de aditivos reductores de agua y la incorporación de partículas ultra finas en los hormigones, han permitido mejorar considerablemente su rendimiento mecánico así como su durabilidad. La reducción de la porosidad se traduce en una gran resistencia de los hormigones frente a la penetración de agentes agresivos.

En este trabajo la durabilidad de los Hormigones de Polvo Reactivo (HPR) se compara con la de dos hormigones de referencia H-30 y H-80. El HPR presenta una resistencia muy buena frente a la carbonatación, a la penetración de iones cloruro, a la abrasión y a los ciclos de hielo-deshielo. El estudio de la cinética de la corrosión de las armaduras metálicas en el HPR se ha realizado por vía electroquímica. Las medidas experimentales asociadas a cálculos de predicción permiten establecer las velocidades de penetración de los agresivos estudiados y dimensionar el recubrimiento mínimo de las armaduras pretensadas que se deben utilizar.

The CMM-PWD: a feature extraction method of subway fan under piston wind effect

Yongxing SONG — Tue, 26 May 2020 04:02:19 +0200

Subway fans play significant roles in subway system such as ventilation, smoke discharging and cooling. Nowadays, fast and effective condition monitoring of subway fan is highly important for the safety and comfort in subway system. However, as one of the most important monitoring tool, fan vibration signals are strongly interfered by frequent piston winds during train arrival-depart, such effect will cause many unnecessary false alarm and deteriorate the fault detection performance. To overcome this problem, this study proposes a condition monitoring method of subway fan under piston wind effect. Piston wind detection method and feature extraction method two key techniques for CMM-PWD method. The piston wind detection method is based on similarity estimation and a new similarity criterion is proposed in this paper. For feature extraction, cyclostationary analysis is exploited for the cyclic feature extraction. And the proposed approach is verified by the piston wind experiments and bolt looseness experiments of axial flow fan and jet fan, which are widely used in subway ventilation system. The results show that the piston wind is accurately detected by proposed method, and fan fault feature is effectively extracted. More importantly, this approach could have great potential to extend to deal with other background interference in fault diagnosis of rotating machinery.

Ciencia y tecnología de materiales: de las sombras a las luces.

María Jesús Samper — Mon, 25 May 2020 15:30:08 +0200

En este artículo se analiza la presencia de la mujer en las escalas del Consejo Superior de Investigaciones Científicas (CSIC) centrándonos en el Área de Ciencia y Tecnología de Materiales. Los datos indican que algo se ha hecho mal desde el principio para que un área tan joven presente cifiras tan alarmantes de desigualdad de género, con sólo un 3% de Profesoras de Investigación cuando las mujeres representan el 31% del personal científico del área. Es una realidad la existencia de un techo de cristal que impide que las mujeres alcancen los puestos de máxima responsabilidad. Tanto las mujeres jóvenes como los hombres no son aún muy conscientes de su existencia, no se ve, es transparente, sólo te topas con él cuando tratas de atravesarlo. No se manifiesta de igual manera en todos los Centros, en algunos es más fi^ágil, en otros es cristal blindado.

Efecto de la distancia al mar en la agresividad por cloruros en estructuras de hormigón en la costa brasileña

María Jesús Samper — Mon, 25 May 2020 14:54:45 +0200

La influencia de la distancia al mar es un tema clave en el estudio de la agresividad salina en zona de atmósfera marina, ya que permite conocer cómo afecta a la durabilidad de las construcciones cuando aumenta la distancia al mar. Este trabajo presenta resultados de un estudio experimental que valora la situación a través de la medida del depósito de cloruros de la niebla salina y en probetas de hormigón expuestas a distintas distancias desde el mar en la ciudad de Joâo Pessoa, ubicada en la costa noreste de Brasil. Los resultados indican una importante disminución del depósito de cloruros de la niebla salina a medida que se aumenta la distancia al mar, especialmente en los primeros doscientos metros. La concentración de cloruros en el hormigón indica un comportamiento semejante. Sin embargo, la disminución de la concentración de cloruros con la distancia ocurre de forma más suave que en la niebla. A pesar de la necesidad de más investigación, aspectos como la relación entre los cloruros de la niebla y los que se fijan en la superficie del hormigón, los fenómenos que ocurren en el transporte de los cloruros en el hormigón, el efecto del lavado superficial y el efecto piel del hormigón pueden justificar esas diferencias

Influencia del electrolito externo en el flujo electroosmótico inducido por realcalinización

María Jesús Samper — Mon, 25 May 2020 14:24:19 +0200

Los métodos electroquímicos de reparación de estructuras dañadas por corrosión de armaduras se basan en la aplicación de corriente continua entre la armadura y un electrodo auxiliar colocado sobre la superficie del hormigón. En el caso de la realcalinización, el objetivo del tratamiento consiste en restaurar la alcalinidad del hormigón alrededor de la armadura, con lo que se consigue la repasivación de la misma. Esta alcalinización se alcanza por la generación de OH- en la hidrólisis del agua que tiene lugar en el acero que actúa como cátodo, aunque también se postula la penetración de carbonatos presentes en el electrolito externo por el establecimiento de un flujo electroosmótico durante el tratamiento, lo que fue demostrado y cuantificado recientemente por los autores, para hormigón carbonatado. En este artículo, se presentan ensayos realizados con el objetivo de estudiar la influencia del electrolito externo en el flujo electroosmótico. Los experimentos se han llevado a cabo sobre mortero portland normalizado, previamente carbonatado, con 4 disoluciones diferentes de Na2CO3 de concentraciones comprendidas en el rango entre 0,1 a 2M. Los resultados indican que el flujo electroosmótico establecido no es constante durante los experimentos, siendo el pH del electrolito el parámetro que determina el potencial zeta y, consecuentemente, el flujo electroosmótico alcanzándose el máximo, en los experimentos realizados en esta investigación, al pH de la disolución reguladora carbonato/bicarbonato

Efecto de la aplicación de campos eléctricos sobre las interacciones entre los iones cloruro y la matriz de cemento

María Jesús Samper — Mon, 25 May 2020 14:07:23 +0200

La determinación de coeficientes de difusión de los iones cloruro a través del hormigón precisa en muchas ocasiones de la aplicación de campos eléctricos con el fin de obtener resultados en plazos razonables de tiempo. Sin embargo, esta aceleración del transporte podría modificar las complejas interacciones que tienen lugar entre los iones cloruro y la matriz de cemento, haciendo que los coeficientes obtenidos mediante ensayos de migración no fueran representativos de condiciones de difusión natural. Este aspecto se aborda en el presente trabajo mediante la realización de ensayos de migración de cloruros en estado estacionario y no estacionario, así como de difusión natural de cloruros y oxígeno en estado estacionario. Como resultado, se ha podido establecer que cuando el transporte se produce por migración, hasta un campo aplicado de 10.5 V/cm, ésta tiene lugar a través de poros del mismo tamaño que por los que se lleva a cabo la difusión natural, produciéndose una interacción más débil del adsorbato con el sustrato que en difusión natural, lo que debe tenerse en cuenta a la hora de diseñar los ensayos de migración para la determinación de los coeficientes de difusión de cloruros en estado no estacionario.

Opinión de la Secretaria de Estado de Universidades e Investigación

María Jesús Samper — Mon, 25 May 2020 13:29:14 +0200

La puesta en marcha de Plataforma Tecnológica es un hecho que supone una iniciativa novedosa dentro del programa móvil para incentivar la investigación industrial. Los funcionarios de la DG - Investigación han sido siempre entusiastas, promotores de la participación de la empresa en la investigación. La Secretaria de Estado de Universidades e Investigación ha acogido la idea con interés y pretende explorar todas sus posibilidades, por lo que respalda la creación de esta Plataforma nacional de Construcción y nombra un delegado suyo para un seguimiento de su desarrollo.

Influencia del contenido de agua en los conglomerantes fabricados con cemento portland sobre la difusividad del ión cloruro

María Jesús Samper — Mon, 25 May 2020 13:20:05 +0200

En el presente trabajo se propone un método para la determinación del coeficiente de difusión del ión cloruro a través de probetas de hormigón parcialmente saturadas, con contenidos de agua controlados y bien caracterizados. El procedimiento experimental permite depositar una cantidad inicial limitada de cloruro sobre la superficie de hormigón en estudio. Dicho procedimiento está basado en la interacción de la superficie de hormigón con los productos de combustión del PVC, que contienen fundamentalmente cloruro de hidrógeno gaseoso. Tras devolver las probetas de hormigón a sus cámaras de humedad relativa controlada, se puede estudiar la cinética del transporte de cloruro desde la superficie hacia el interior del hormigón. Los perfiles experimentales de concentración de cloruro, obtenidos a intervalos de tiempo seleccionados, han sido ajustados a un modelo matemático difusional de ¿fuente plana instantánea¿, que se corresponde con las condiciones iniciales y de contorno del procedimiento experimental, y permite obtener los coeficientes de difusión del cloruro.

Comportamiento frente a lixiviación de materiales de base cemento

María Jesús Samper — Mon, 25 May 2020 12:05:48 +0200

Cuando los materiales de la construcción son aplicados en el exterior, el agua de lluvia, el agua superficial o las aguas subterráneas, pueden ser responsables de que ocurran procesos de lixiviación o procesos de disolución y transporte de componentes de la fase sólida a una fase acuosa. En su interacción con las aguas, los materiales sufren una serie de transformaciones físicas y químicas; el ataque que se produce depende mucho del régimen hidrodinámico, del tipo de cemento y de la dosificación del hormigón. En el presente trabajo se comunican los resultados de varias investigaciones realizadas con financiación de la UE y de Enresa en el que se estudia el comportamiento frente a la lixiviación. Estos trabajos se han ampliado con financiación de Oficemen, para el estudio del comportamiento frente a la lixiviación de metales pesados y otros elementos, en cementos fabricados con combustibles tradicionales y cementos fabricados con combustibles alternativos.

Influencia del uso de material fotocatalítico como adición al cemento en la durabilidad de las armaduras embebidas en hormigón

María Jesús Samper — Mon, 25 May 2020 11:42:34 +0200

Uno de los aspectos clave de la Innovación en Construcción es el desarrollo de materiales inteligentes. Entre estos materiales se encuentran aquellos que contribuyen a luchar contra la contaminación atmosférica por la inclusión en su composición de agentes fotocatalíticos, como dióxido de titanio, capaces de oxidar contaminantes orgánicos e inorgánicos en presencia de luz ultra violeta.

En este trabajo se ha estudiado la influencia del uso de material fotocatalítico como adición al cemento sobre la corrosión de las armaduras embebidas en hormigón, ya que por un lado, la formación de CO2 por la oxidación de moléculas orgánicas en su superficie podría llevar a la aceleración de la carbonatación de la matriz, y por otra parte, la oxidación de iones cloruro a cloro gaseoso evitaría la corrosión por picaduras inducida por aquellos.

En este trabajo se presentan los resultados preliminares obtenidos con probetas armadas de mortero de cemento blanco con y sin TiO2 sometidas a distintos ambientes.

Nanociencias del cemento

María Jesús Samper — Mon, 25 May 2020 11:08:48 +0200

Con la ayuda de las técnicas de caracterización desarrolladas en las últimas décadas se pudo avanzar en el conocimiento de la microstructura de los materiales y su relación con el comportamiento estructural. Ahora es el turno de profundizar a nivel de la nanoestructura ya que empiezan a existir técnicas capaces de dar información con esa resolución. Se trataría de sentar las bases de las Nanociencias que dan información a nivel atómico. Las Nanotecnologías son entendidas como la capacidad de manipulación de entes del tamaño de nm. En el caso del cemento parece más accesible en el momento actual hablar de nanociencias que de nanotecnologías. Para desarrollar las bases de las Nanociencias del Cemento se ha constituido a nivel europeo la Red Nanocem que integra a unos 120 investigadores permanentes que dirigen en la actualidad unas 60 Tesis Doctorales en universidades y centros de investigación europeos.

Los objetivos que se plantea NANOCEM son: a) Identificar, estudiar y elucidar los mecanismos fundamentales que subyacen en problemas específicos de la industria de la Construcción, b) Generar el conocimiento básico requerido para desarrollar nuevos materiales en base cemento y mejorar los existentes y la tecnología implícita en los procesos. c) Mejorar la sostenibilidad de los procesos relacionados con el cemento y el hormigón, d) Promover avances de alta tecnología en los materiales en base cemento y buscar sus aplicaciones y e) Formar graduados universitarios y facilitar su incorporación a la industria del cemento y del hormigón. Los resultados a largo plazo de NANOCEM se espera que sitúen a sus miembros en la vanguardia mundial de la investigación, y a la industria europea le aporten una más elevada eficiencia en sus procesos con el desarrollo de nuevos materiales y aplicaciones más compatibles con el Medio Ambiente.

En la actualidad se están financiando 3 proyectos con temas avanzados que se describirán brevemente en el trabajo. También se mencionan los miembros actuales y los proyectos aportados por ellos.

Lixivación acelerada de materiales en base cemento por aplicación de campos eléctricos

María Jesús Samper — Mon, 25 May 2020 10:29:39 +0200

Los materiales de base cemento están siendo utilizados cada vez más como matrices confinantes en la inertización de residuos, tanto peligrosos como radiactivos. En su utilización en este ámbito, uno de los principales problemas es el de la degradación a largo plazo, cuya caracterización mediante técnicas tradicionales se hace inviable, por lo que se hace necesario el desarrollo de métodos acelerados, como el basado en la aplicación de campos eléctricos. En este artículo, se presenta un resumen de algunos de los trabajos de los autores en este campo: Monitorización in-situ del tratamiento eléctrico por difracción de neutrones; cuantificación de las fases cristalinas antes y después de un tratamiento acelerado mediante análisis Rietveld de los espectros de difracción de Rayos X con radiación Sincrotrón y por último comparación de los resultados obtenidos por el método acelerado, mediante integración de los perfiles absolutos obtenidos por EDX, con un método estandarizado de lixiviación.

Difusión de cloruros en hormigones expuestos a ambientes marinos. Estudio de 15 años de exposición

María Jesús Samper — Mon, 25 May 2020 10:15:56 +0200

El hormigón armado situado en ambientes marinos puede sufrir la corrosión del acero embebido debido a la penetración de los cloruros. Los fenómenos de transporte de los cloruros en el hormigón son complejos y aunque son controlados principalmente por el mecanismo de difusión, los perfiles de concentración de cloruros no siguen fielmente la segunda ley de Fick. Por lo tanto, resulta de vital importancia para conocer la cinética del fenómeno acceder a datos de penetración de los cloruros a largo plazo.

En el presente trabajo se comentan los perfiles de concentración de iones cloruro obtenidos en bloques de hormigón de 50x50x200 cm que se han conservado semienterrados en una playa de Huelva cedida al Instituto Eduardo Torroja por la Autoridad Portuaria de Huelva para realizar los ensayos. Los bloques fueron fabricados en 1988 con dos cementos portland, uno de ellos con un bajo contenido de C3A. Se comentan los perfiles de cloruros obtenidos así como la variación del coeficiente de difusión y de la concentración superficial a lo largo del tiempo

Análisis no destructivo del estado de degradación en morteros bajo la acción de ciclos hielo-deshielo

María Jesús Samper — Mon, 25 May 2020 09:19:17 +0200

En el presente trabajo se evalúan diferentes morteros, con distinto grado de daño por la acción de ciclos de hielo-deshielo, analizando su estado mediante diferentes métodos de evaluación habituales. Los resultados obtenidos por estos métodos se comparan con un análisis mediante la técnica de espectroscopía de impedancia, analizándose la capacidad de esta técnica para evaluar el estado de los morteros y el grado de daño interno producido.

Evaluación y monitorización de la durabilidad de las cubiertas del Hipódromo de la Zarzuela de Madrid

María Jesús Samper — Mon, 25 May 2020 09:06:19 +0200

En el presente trabajo se describen algunos aspectos que se han tenido en cuenta en la restauración que se ha llevado a cabo recientemente en la emblemática obra de Torroja del Hipódromo de La Zarzuela,. Aunque la estructura presenta un muy buen comportamiento, se han producido algunos deterioros locales debido a la corrosión de la armadura por rotura de la impermeabilización y la carbonatacion del hormigón. Lo primero que se realizó fue una evaluación del grado de la corrosión, para posteriormente acometer el proyecto de reparación, que consistió en la inyección de grietas y en el parcheo de zonas deterioradas. Durante la reparación se procedió a la instalación de un sistema de registro de corrosión con sensores permanentes. Se presentan los resultados de la aplicación de técnicas electroquímicas no destructivas utilizadas en la evaluación de estructuras, y se describen el sistema de sensores instalados y sus primeros resultados

Evaluación de la corrosión en estructuras de contención nuclear mediante el uso de técnicas electroquímicas no destructivas

María Jesús Samper — Fri, 22 May 2020 15:03:02 +0200

Son muchos los planteamientos que se realizan en relación al estado de estas estructuras nucleares y a la posibilidad de prorrogar su vida útil, siendo la corrosión uno de los problemas que más preocupa en la actualidad. Por ello, la evaluación y control de la corrosión en estructuras como los liners de los edificios de contención es extremadamente importante para que éste no sea el motivo que limite la vida de estas estructuras.

En el presente trabajo se muestran resultados de la aplicación de técnicas electroquímicas no destructivas en estructuras reales de contención nuclear para la evaluación de la corrosión de armaduras o elementos metálicos embebidos en el hormigón, como son los liners antes mencionados.

Diez años de estudio del comportamiento higrotérmico de la cubierta del Museo del Prado

María Jesús Samper — Fri, 22 May 2020 14:05:20 +0200

In the current paper we present the results of the monitoring of the hygrothermal behaviour during the last ten years of the El Prado Museum roof. Sensors were installed in the south roof of the museum after it underwent mayor repair following a leak over a very important exhibition hall (the one holding Velazquez’s Las Meninas painting). The liquid water sensors reveal that water is retained at the waterproofing layer. These sensors do not show water presence in lower layers of the roof. The humidity sensors show condensation when the ambient temperature drops. The temperature sensors show the insulating capacity of the different layers of the roof, which effectively attenuate the outside temperature changes. The strain sensors placed on the liquid waterproofing layer show a constant increase of strain with time. In summary, the repaired roof can be considered to perform as intended and no more leaks have been detected

Calculation of the crack propagation rate due to hydrogen embrittlement

María Jesús Samper — Fri, 22 May 2020 13:25:12 +0200

The durability of high strength steels in aggressive media is determined by the presence of hydrogen, in particular hydrogen embrittlement processes. Hydrogen embrittlement is present in many of the failures of structures made with steel components. The effect of interstitial hydrogen within the network of iron has been investigated in previous studies at the atomic level. It is concluded that the main role of hydrogen is not to establish chemical bonds with iron atoms, but to introduce internal stresses that weaken the interactions between iron atoms and decrease fracture toughness. In this work, the spread of a crack has been stimulated inside a matrix of iron in the presence of hydrogen. Hydrogen transport, stress distributions, and the evolution of fracture toughness were analysed together in a multi-physics finite element model. The behaviour in the fracture was simulated using two different models for the cohesive law, one lineal and the other polynomial. Results show that the choice for the cohesive law influences the crack propagation rate and the hydrogen concentration profiles.

Some historical notes on the research in corrosion of reinforcement

María Jesús Samper — Fri, 22 May 2020 13:13:23 +0200

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.

Test methods for on-site corrosion rate measurement of steel reinforcement in concrete by means of the polarization resistance method

María Jesús Samper — Fri, 22 May 2020 12:03:46 +0200

This recommendation covers the description of non-destructive electrochemical test methods for the estimation in large size concrete structures of the instantaneous corrosion current densiti, icor, expressed in gA/cm2, by means of the so called Polarization Resistance technique, Rp, in order to asses the condition of embedded Steel reinforcement related to its corrosion.

The values of icor, can be used to assess the rate of degradation of concrete structures affected by reinforcement corrosión. However, the cannot give information on the actual loss in steel cross section which, at present, only can be assessed by means of direct visual observation.

Values of the free corrosión potential or half-cell potential, Ecorr [V], of the embedded reinforcing Steel and of the electrical concrete resistance, Re [f)], are obtained as preliminary steps of the Rp measurements. Values of the concrete resistivity, P [~m], can be calculated from Re values providing the geometrical arrangement of the electrodes enables this calculation. Both parameters, Ecorr and Re (or P) may be used to complement the reliability of the ico~r measurements.

Revisión sobre el comportamiento de las armaduras galvanizadas en el hormigón

María Jesús Samper — Fri, 22 May 2020 11:19:38 +0200

Esta comunicación pretende ofrecer una panorámica de las ventajas e inconvenientes derivados del empleo de las armaduras de acero galvanizados en el hormigón.

Se resumen las causas que pueden provocar la corrosión de las armaduras embebidas en el hormigón y se analiza la protección suplementaria que el galvanizado puede conferir a dichas armaduras en condiciones especialmente agresivas.

Se mencionan los datos publicados sobre los límites tolerables de cloruros para las armaduras normales, punto en el que se echa en falta la existencia de datos cuantitativos similares para las armaduras galvanizadas y se examina, asimismo, las repercusiones sobre ellas de la carbonatación del hormigón y de la presencia de pilas de aireación diferencial, así como la influencia sobre la adherencia hormigón-armaduras, y el peligro de fragilización de estas, por el hidrógeno desprendido en el curso del fraguado. Finalmente se nombran algunas de las obras donde se han empleado armaduras galvanizadas.

Electrochemical Behavior of Galvanized Steel in a Calcium Hydroxide-Saturated Solution. A Quantitative Assessment of Corrosion Rate.

María Jesús Samper — Fri, 22 May 2020 10:20:34 +0200

An electrochemical study has been carried out involving immersion of galvanized steel in a Ca(OH)//2-saturated solution with and without chloride additions. Results show that galvanized steel corrodes steadily during the first few days; after approximately a week, however, it becomes passive, the passivity being perfectly stable both in the presence and absence of chlorides for the entire test period which lasted for more than 60 days' exposure.

Quantitative measurements of corrosion rate of reinforcing steels embedded in concrete using polarization resistance measurement

María Jesús Samper — Fri, 22 May 2020 10:07:18 +0200

Up to this time all the methods to measure the corrosion rate of reinforcing steels embedded in hardened concrete have been of the destructive type, which requires much time and materials and makes the full scale study of the phenomenon difficult. The authors have applied the polarization resistance method to bars embedded in hardened mortar and immersed in Ca(OH)2‐saturated solution, and have found an acceptable agreement between the gravimetric and the electrochemical weight loss data.

Valores del potencial de corrosión y de a resistencia de polarización de armaduras galvanizadas embebidas en hormigón

María Jesús Samper — Fri, 22 May 2020 09:43:36 +0200

Muchas de las estructuras de hormigón armado se muestran exentas de corrosión aun después de periodos muy prolongados de servicio. Ello es debido a que en el hormigón el electrolito está constituido por la fase líquida que rellena sus poros y que es, fundamentalmente, una disolución saturada de CA(OH)2, con un pH alrededor de 13. A este elevado pH y a los potenciales de corrosión Ecorr, que presentan las armaduras, el acero se encuentra en la zona de pasividad descrita por Pourbaix, permaneciendo protegido indefinidamente mientras no cambien las condiciones del medio.

Este cambio en las condiciones de servicio del hormigón capaz de introducir en la zona de corrosión al acero de las armaduras, se puede producir con relativa frecuencia. Así, la carbonatación del cemento disminuye el pH del hormigón y provoca una corrosión generalizada, la presencia de iones despasivantes o de fisura conduce a corrosión localizada y, finalmente, la acción simultánea de tensiones mecánicas y factores agresivos puede ser la causa de corrosión bajo tensiones.

Así pues, es aconsejable recurrir a una protección suplementaria de los aceros cuando se prevean situaciones que puedas provocar la corrosión de las armaduras. Entre los varios métodos de protección que se utilizan se viene ensayando desde hace varios lustros, con resultados muy contradictorios, la galvanización en caliente de los redondos.

Corrosion of Reinforcing Bars in Carbonated Concrete

María Jesús Samper — Fri, 22 May 2020 08:50:58 +0200

In all published studies of cement carbonation there has been general agreement that it must be considered as a cause of generalised corrosion in reinforcements, but quantitative data have been provided in very few cases. In the present work the intensity of attack has been modified by means of the accelerated carbonation of mortar specimens without additives, with 2% CaCl2, and with 3% NaNO2 It has been shown that a critical level of atmospheric moisture must also be present for considerable attack to occur. The measurement of polarisation resistance (Rp) has been used to evaluate the intensity of corrosion of the reinforcements. This method has already been usefully applied by the authors to investigations of corrosion of steel bars in hardened concrete specimens.

Influencia de la dosificación en cemento sobre la corrosión de armaduras, negras y galvanizadas provocado por lo penetración de Cl- en el mortero

María Jesús Samper — Thu, 21 May 2020 16:01:58 +0200

En el presente trabajo se aborda el estudio de la corrosión de armaduras, tanto desnudas como galvanizadas, producida por la penetración de agua de mar en nueve calidades (dosificaciones y por lo tanto porosidades) diferentes de mortero de cemento portland en el que se embebieron redondos a tres profundidades (0,5-1,5-2,5 cm). Las probeta de 7 X 7 X 7 cm se conservaron sumergidas durante 1 año. Para la evaluación de la velocidad de corrosión se ha utilizado la Resistencia de Polarización, técnica que permite el seguimiento continuo de la despasivación progresiva que provocan los Cl^- al llegar a la armadura. Se aportan resultados sobre la penetración de Cl^-, discutiéndose las relaciones encontradas entre: corrosión, % de Cl^-, porosidad y dosificación de cemento. Finalmente se compara el comportamiento frente a la corrosión de las armaduras de acero desnudo respecto de las galvanizadas.

Effect of Carbonation, Chlorides and Relative Ambient Humidity on the Corrosion of Galvanized Rebars Embedded in Concrete

María Jesús Samper — Thu, 21 May 2020 15:25:01 +0200

The variation with time of the corrosion rates of galvanized steel and bare steel rebars has been studied as a function of the relative ambient humidity, mortar carbonation and the presence or absence of chloride ions. Corrosion rates are estimated from Rp measurements with electronic compensation for the ohmic drop between the working imd reference electrodes.

It is shown that a normal galvanized coating with a continuous layer of practically pure zinc in contact with mortar gives effective protection to the steel reinforcing bars against the aggressive action of carbonation and chlorides. The protective effect of this galvanized coating is much greater under partial immersion conditions of the mortar than in very humid atmospheres, although in the latter case the corrosion rate decreases with time

Techniques electrochimiques qualitatives et quantitatives pour mesurer les effets des additions sur la corrosion des armatures

María Jesús Samper — Thu, 21 May 2020 15:12:25 +0200

Les auteurs resument une serie de considerations theoriques sur l'incidence que les additions actives peuvent avoir dans la corrosion des armatures. Ensuite, ils attirent l'attention sur le manque de normes ou recommandations de travail, qui s'appuient sur des essais suffisants, et qui pourraient permettre de delimiter les causes et conditions qui influent sur la duree des armatures ; finalement ils exposent une systematique d'essais qu'ils ont realisee pour etudier cette incidence au moyen de techniques electrochimiques, et les differences de comportement trouvees entre les differents ciments.

Les effets des cycles d’humidité sur la corrosion des armatures galvanisées dans les mortiers carbonatés et non carbonatés

María Jesús Samper — Thu, 21 May 2020 14:17:41 +0200

Galvanisation of steel reinforcement has been usual practice for the last decades as a protection against certain types of aggressive agents. However, recent results, mostly European, have thrown doubts on the usefulness of galvanisation.

The results presented here contribute to explain this controversy. We have identified three factors that may influence the corrosion kinetics of galvanized steel bars embedded in concrete, although they usually go unheeded: type of galvanized coating, type of cement and humidity during curing and hardening.

From these factors, this report deals mostly with ambient humidity. Corrosion rate was basically estimated from the Polarisation Resistance in reinforced mortar specimens that were cyclically subjected during curing and hardening to different ambient humidities. The influence on the corrosion kinetics of the structure of the galvanized coating which, in turn, depends on the chemical composition of the steel, is also discussed. Finally, the behaviour of bare and galvanized steel are compared, and criteria are given on the usefulness of galvanized coatings.

Corrosion Rate of Galvanized Steel Immersed in Saturated Solutions of Ca(OH)2 in the pH Range 12–13 8

María Jesús Samper — Thu, 21 May 2020 13:45:38 +0200

The influence of the alkaline content of cement on the corrosion kinetics of galvanized reinforcements has been studied, by means of the polarisation resistance method, in saturated solutions of Ca(OH)2 with additions of NaOH, KOH and SO2 4, thus simulating the liquid phase of concrete.It has been established that below a threshold pH the coating protects the surface; above this pH the coating is attacked, disappearing in a few days. Cements with low alkali contents and proper concrete dosage must therefore be used to ensure that the pH remains below the threshold value.

Corrosion rate of galvanized steel immersed in saturated solutions of Ca(OH)2 in the pH Range 12-13.8

María Jesús Samper — Thu, 21 May 2020 13:23:41 +0200

The influence of the alkaline content of cement on the corrosion kinetics of galvanized reinforcements has been studied, by means of the polarisation resistance method, in saturated solutions of Ca(OH)2 with additions of NaOH, KOH and SO²4, thus simulating the liquid phase of concrete. It has been established that below a threshold pH the coating protects the surface; above this pH the coating is attacked, disappearing in a few days. Cements with low alkali contents and proper concrete dosage must therefore be used to ensure that the pH remains below the threshold value.

SEM Study of the Corrosion Products of Galvanized Reinforcements Immersed in Solutions in the pH Range 12·6 to 13·6

María Jesús Samper — Thu, 21 May 2020 12:51:15 +0200

In previous work on galvanized reinforcements in contact with Ca-containing highly alkaline media the authors have reported the existence of a threshold pH below which the Zn in contact with such a medium is passivated, but at pH values above this it corrodes continuously until it totally disappears. In this paper, after a brief literature review concerning the identification of the corrosion products in these media, they report that the passivation detectedfrom the data of the polarisation technique agreed with the results of an SEM study. This showed that below the threshold pH value the surface is covered with a continuous layer of calcium hydr.oxyzinccite, Ca (Zn(OH)3)2.2H2O, and above this pH this layer is increasingly composed ofnon-passivating ZnO, to the detriment of the calcium hydroxyzincate content. They have also established that it is the (Ca2+) ions that control the amount of calcium hydroxyzincate formed, and therefore the likelihood of the formation of a continuous passivating layer. Finally, they report that if the calcium hydroxyzincate isperfectly developed, a later increase of thepH does not affect the stability.

Corrosion rate of three different types of galvanized coatings of steel reinforcements in contact with mortar

María Jesús Samper — Thu, 21 May 2020 11:57:45 +0200

Corrosion of galvanized reinforcements in concrete is controlled by three factors: the type of the cement, the type of metallographic structure and the humidity of conservation of the concrete. The behaviour of three different types of galvanized coating embedded in mortars made with three different Portland cements: low, medium and high alkali content, was studied. The corrosion rate was measured by means of the linear polarization (Polarization Resistance) technique. The results show that the thicker the pure zinc layer is, the greater the resistance against the corrosion of the chlorides.

Effect of four coating structures on corrosion kinetic of galvanized reinforcement in concrete

María Jesús Samper — Thu, 21 May 2020 11:24:11 +0200

In the present work is described the effect of the characteristics of the galvanized coating on corrosion rate of reinforcing bars embedded in a concrete without additives and in another with 2% CaCl2 in terms of cement weight. To this end, the following materials were subjected to the action of a moisture saturated atmosphere for a period of400 days: an annealed-galvanized coating; another one obtained by dipping in a molten Zn bath with0.025% Al and some others produced at450 and430°C in an ordinary bath.

The attack evolution vs time was controlled by measuring the polarization resistance. The electrochemical determinations were gravimetrically verified and supplemented by a metallographic examination of tests coatings.

In the absence of chlorides, the attack is fully tolerated. Chlorides radically change the corrosion behaviour of galvanized steel and increase the attack by a factor of2.8 in the most favourable case, but in these conditions, coatings with thick, homogeneous η layer outperform the usual ones, and specially the annealed ones.

Corrosion of galvanized steel reinforcements in alkaline solutions: Part 2: SEM study and identification of corrosion products

María Jesús Samper — Thu, 21 May 2020 11:09:58 +0200

A report is presented of the morphology and composition of the corrosion products formed on galvanized corrugated steel reinforcing bars immersed in 0·05–1·5M KOH solutions designed to simulate concrete pore environments. The morphology was studied by SEM of the in situ corrosion products and optical examination of transverse sections of the bar; phase identification was performed by X-ray diffraction and IR absorption analyses. Passivation events on the corrosion potential and corrosion intensity curves can be related to precipitation of prismatic Zn (OH)2 crystals which form a compact layer on the surface. Active corrosion is associated with formation of porous ZnO layers or precipitation of Zn(OH)2 in the solution rather than on the galvanized surface. A solution-precipitation mechanism involving ZnO and Zn(OH)2− 4 intermediate species is proposed for formation of the passivating Zn(OH)2 coating, although this scheme must be complemented to take account of the localized corrosion observed at pH < 12 in the first part of this study

Corrosion of galvanized steel in dilute Ca(OH) 2 solutions (pH 11·1–12·6)

María Jesús Samper — Thu, 21 May 2020 10:03:47 +0200

The corrosion behaviour of. galvanized bars was studied in 0·1–3 g Ca(OH)2 (pH 11·1–12·6) solutions designed to simulate the aqueous phase found in concrete pores. Corrosion potential and current density were monitored over the course of the 33 day tests and the corrosion products were examined by light and electron microscopy, X-ray diffraction, and IR absorption spectroscopy. Most specimens showed high initial corrosion rates which fell to a lower, nearly constant level after ∼6 days. The corrosion kinetics were found to depend only on solution pH. Ca2+ concentration had no effect other than on the nature of the corrosion products: Ca(Zn(OH)3)2.2H2O is the passivation product in the presence of calcium ions, Zn(OH)2 in their absence. Localized corrosion was observed at pH <11·5.

Corrosion of galvanized steel reinforcements in alkaline solutions: Part 1: Electrochemical results

María Jesús Samper — Thu, 21 May 2020 09:20:12 +0200

The behaviour of galvanized corrugated reinforcing bars has been studied in 0·001–1·5M solutions of KOH and NaOH designed to simulate aqueous environments found in concrete pores. Specimens were immersed for 33 days in polyethylene cells, corrosion potential, corrosion intensity, and pH being monitored throughout. Polarization curves were also obtained after 50 min and ∼ 33 days' immersion. It was possible to establish pH ranges in which localized corrosion (< 12), stability (12–13·4), and complete dissolution of the galvanic coating (> 13·4) occurred. A white, dusty corrosion product was observed on most specimens at the conclusion of the tests. Hydrogen dissolution on the galvanized bars occurred at pH values higher than the threshold level of 12·8±0·1.

Equilibria of the chemical composition of the concrete pore solution. Part I: Comparative study of synthetic and extracted solutions

María Jesús Samper — Thu, 21 May 2020 08:49:26 +0200

A critical review is made on Frattini and Hansen's results on the equilibria of the different ions present in the aqueous solution of cement paste after mixing. These values are compared with those obtained from results of squeezed cement paste specimens drawing the conclusions that the cement paste solution is oversaturated in Ca(OH)2 just after mixing but the ions present in it are not in thermodynamic equilibrium because the solution is continuously evolving during early ages.

Also the increase in the solubility of the Ca+2 ion because of the presence of SO4= is discussed and attributed to the increase in the ionic strength of the solution.

Galvanized steel behaviour in Ca(OH)2 saturated solutions containing SO4 ions

María Jesús Samper — Thu, 21 May 2020 08:04:52 +0200

In previous work on galvanized reinforcements in contact with Ca-containing highly alkaline media the authors have reported the existence of a threshold pH of 13.3 ± 0.1 below which the Zn in contact with such a medium is passivated, but at pH values above this it corrodes continuously until it totally disappears. In this paper, the influence of the presence of SO4 ions on the electrochemical behaviour of the galvanized has been studied.

It has been established that the precipitation of CaSO4 with takes place in the media studied makes that the pH never surpasses the value of 13.3 ± 0.1. This coincidence with the pH threshold previously reported for passivation of the galvanized bars allows conclude that the sulfates not only are innocuous with respect to the galvanized behaviour in media which simulate the concrete but they are beneficial.

Some unpublished results on the research in corrosion of steel in concrete

María Jesús Samper — Wed, 20 May 2020 16:35:29 +0200

Accuracy of different electrochemical laboratory techniques for evaluating corrosion rates of galvanized reinforcements

María Jesús Samper — Wed, 20 May 2020 16:21:42 +0200

In the present paper the accuracy of three electrochemical laboratory techniques in order to evaluate the corrosion rate of galvanized rods inmersed in solutions which simulate the pore solution, is commented. The techniques used were: polarization resistance, electrochemical impedance and harmonic analysis. The corrosion intensity values obtained through these techniques were compared with the gravimetric ones. Values of constant B obtained through polarization curves and the harmonic analysis were compared.

Evaluation of steel durability in a construction system of reinforced mortar-polystyrene-mortar panels

María Jesús Samper — Wed, 20 May 2020 16:13:49 +0200

This paper sumarises the research into steel durability in reinforced sandwich panels made of mortar-polystyrene mortar, which is a new construction system for buildings. In this type of system the main risk of steel corrosion is that of the steel connectors, which cross the polystyrene, and the corrosion of the reinforced mesh, owing to the carbonatation of the mortar coating. The evaluation of different suplementary protection methods which increase expected service life in aggressive environments is also presented.

The different tests carried out are described. The specimens were of small, medium and full size. The corrosion was monitored with electrochemical techniques (polarization resistance). The specimens were submitted to wet and dry cycles and some of them were carbonated. Galvanized, stainless and bare steel were tested. Also addition in the mix of calcium nitrite as an inhibitor was used. Results show that the steel connectors are not the weakest point of the system as previously thought.

Finally, practical recomendations are given which allow a reasonable increase in the service life of the reinforced mortar-polystyrene-mortar system. The specifications are presented considerinng three levels of environmental aggressivity.

Equilibria of the chemical composition of the pore concrete solution Part II: Calculation of the equilibria constants of the synthetic solutions

María Jesús Samper — Wed, 20 May 2020 15:31:06 +0200

The chemical composition of synthetic solutions used to simulate the pore concrete solution was analyzed in Part I. It was not possible to match the experimental results obtained from concentration measurements of the ions present in the solutions with the results obtained from calculations based on the values of pK of Ca(OH)2 and CaSO4. The inconsistency between the experimental values and the theoretical calculations was attributed to the elevated concentrations that exist, and, therefore, the elevated ionic strength.The errors that are committed when applying the Debye-Huckel theory make it imprecise for proper calculations at such high concentrations. As an alternative the use of “apparent constants” is proposed. These are calculated from the values of the concentrations directly measured in the solutions.

Polypropylene Fibre Reinforced Concrete Air Permeability

María Jesús Samper — Wed, 20 May 2020 14:14:50 +0200

The permeability of concrete to gases is of direct importance to the durability of concrete structures, because of carbon dioxide flowing through the concrete favour lime carbonation and reinforcing steel corrosion.

Mortar with and without polypropylene fibres having water/cementitious ratios of 0.30, 0.35 and 0.40 and a cement/sand ratio of 1/1 were studied. Polypropylene dosage varied from 0.1 to 0.3% by volume of cement.

The characterization of mortar permeability was made using cylindrical shaped samples (3 cm height and 15 cm diameter). These specimens were 28 days cured and then dried before the test.

The addition of fibres results in a decrease of air permeability. Variation of the water/cement ratio is of lesser importance than fiber addition.

Quantitative measurement of the corrosion rate using a small counter electrode in the boundary of passive and corroded zones of a long concrete beam

María Jesús Samper — Wed, 20 May 2020 13:54:36 +0200

Recently, in CORROSION-87, one paper was presented which, assuming the electrical model of the 'transmission line' to represent the nonuniform distribution of the current in a concrete beam, demonstrated the calculation of the instantaneous corrosion rate by unit of length of the rebar through mathematical equations. In the present contribution those equations are used in order to determine whether the equations enable distinction between the corroded zones of a rebar and those which remain passive. A concrete beam was fabricated, half of it by mixing chlorides with the cement (and therefore inducing a corrosion in the rebars) and the other half without admixtures (passivated zones of the rebars). The apparent polarization resistance was measured along the beam using a small counter electrode. Through the equations previously proposed, the corrosion rate was calculated. The results obtained confirm that the boundary between corroded and passivated zones can be clearly identified using these formulae. Finally, some comments are given on the relative activity of galvanic macrocells compared with the corrosion microcells.

Initial effort to use the corrosion rate measurements for estimating rebar durability

María Jesús Samper — Wed, 20 May 2020 13:20:06 +0200

The approach presented here is an attempt to implement the values of corrosion intensity which have been measured in laboratory tests, in the framework of the service life prediction analysis for corroding structures. First of all, the model on service life suggested by Tuuti was considered, and only the propagation period model has been analyzed in this paper. In order to expand the proposal, different steps were covered: (1) the definition of an unacceptable level of deterioration, taking into consideration the levels suggested by the Comite Eurointernational du Beton (CEB) in its Bulletin No. 162, in order to define the urgency of intervention in a damaged structure; (2) the reduction in bar diameter or bar section was taken as the determining parameter in failure risk, assuming that this decrease in section occurs either in a generalized form or in the zones of the structure in which the load-carrying capacity may be significantly affected; and (3) the ranges of possible corrosion intensity values were introduced in Tuuti's model for calculating the reduction in bar section in function of the life of the structure. Some examples for bars of 10 and 20 mm Φ were presented. Finally, the limitations and the improvements of the proposal are discussed.

The behaviour of galvanized steel in chloride-containing alkaline solutions-I. The influence of the cation

María Jesús Samper — Wed, 20 May 2020 12:08:23 +0200

The behaviour of galvanized reinforced bars (rebars) in chloride-contaminated concrete is a very controversial matter not yet resolved. An extensive study of the behaviour of galvanized steel in alkaline solutions which simulate the aqueous phase present in concrete pores has been undertaken. This paper describes the modifications that the presence of chloride has on the corrosion behaviour of galvanized steel in alkaline solutions, as well as the influence of the accompanying cation. It was confirmed that the corrosion behaviour of galvanized steel in the presence of chlorides is controlled by the medium pH, which depends on the calcium or sodium salt which provides the chloride ions.

Identificación de presencia de cemento aluminoso en hormigones mediante el uso del pachómetro

María Jesús Samper — Wed, 20 May 2020 11:37:49 +0200

The observation of the premature degradations detected in High Alumina concretes due to the transformation and carbonation of this kind of cement has promoted the interest to develop in-situ testing methods for the fast Identification of HAC presence. In present work, preliminary results are given on the use of magnetic methods (pachometer), usually employed in the concrete cover verification, to identify the existence of HAC in a concrete. The laboratory results have been verified in practice and show that HAC can be clearly distinguished of an OPC concrete with the pachometer used in present experimentation. The research has also indicated that fly ash cements as aluminous one, have a lower magnetic reluctance. La constatación de los daños que se producen en estructuras de hormigón de cemento aluminoso, debido a su rápida transformación y carbonatación, ha llevado a intentar poner a punto diversos métodos de detección acelerada in situ de la presencia del citado cemento. En el presente trabajo se aportan unos primeros resultados sobre el empleo de métodos magnéticos (pachómetro) habituales en la medida del espesor del recubrimiento de armaduras para identificar si un hormigón está fabricado o no con cemento aluminoso. Los resultados de laboratorio se han contrastado en obra pudiéndose comprobar que el pachómetro utilizado es capaz de detectar perfectamente la presencia de aluminoso previa calibración con un hormigón de portland puro. Esta investigación preliminar también ha permitido comprobar que los hormigones de cenizas volantes presentan, como el aluminoso, una menor reluctancia magnética

A reply to the discussion by A. Xu and S. Chandra of the Paper “calculation of chloride diffusion coefficients in concrete from ionic migration measurements”

María Jesús Samper — Wed, 20 May 2020 10:33:07 +0200

Calculation of chloride diffusion coefficients in concrete from ionic migration measurements

María Jesús Samper — Wed, 20 May 2020 10:00:36 +0200

A critical review is offered on the Rapid Chloride Permeability Test standarized by AASHTO, pointing out its limitations and errors but recognizing its contribution to the developing of a simple and quick test for chloride migration. Then another review is made on the electrochemical fundaments of the processes developped in concrete when an electrical field is applied and on the basic equations of mass transport (Nernst-Plank and Nernst-Einstein) which can be applied to calculate ionic movements. The limitations and assumptions needed for a simplified resolution of these equations, are presented, as well as numerical examples of calculation of the Effective Diffusion Coefficient of chlorides, Deff, in steady state condition. Finally, considerations on the possibility of calculation of Deff from simple resistivity measurements are also offered.

Suitability of Assessment Methods for Identifying Active and Passive Zones in Reinforced Concrete

María Jesús Samper — Wed, 20 May 2020 09:19:47 +0200

The ability of various electrochemical techniques to differentiate between areas of reinforcing steel (rebar) with high and low corrosion activity and to define the boundary between such areas was studied. These techniques are based on determining the corrosion potential (E[sub corr]), the galvanic current between an external stainless steel (SS) sensor and the bar (I[sub g]), the apparent polarization resistance (R[sub p][sup ap]), or the polarization resistance (R[sub p]) under electric confinement conditions. Values of E[sub corr] and I[sub g] (the current flowing between a SS counter electrode [CE] and the rebars) were shown to distinguish active areas from passive ones very well when the areas were isolated electrically, but with difficulty when the areas were in electric contact, which is usually the case. Values of R[sub p][sup ap] or i[sub corr] (both calculated using the Stern-Geary equation) were shown to define areas of high corrosion rates in a structure where passivity prevailed much better. However, excessive i[sub corr] values were estimated because the polarized area of the rebar (especially with passive rebars) was much greater than the CE area. Finally, the confinement of signal distribution permitted definition of the exact boundary between active and passive areas, regardless of whether they were isolated or interconnected. In addition, i[sub corr] values obtained with this technique were shown to provide a reliable quantitative index of the damage rate in reinforced concrete structures.

La realcalinización y la extracción electroquímica de los cloruros en las construcciones de hormigón armado

María Jesús Samper — Wed, 20 May 2020 08:47:35 +0200

Realkalisation and electrochemical chloride removal techniques, developed for rehabiliting carbonated and chloride-containing structures, are presented. Electrolysis and electromigration mechanisms and consequences as well as electrochemical conditions at the reinforcement surface are discussed and compared with cathodic protection ones. Furthermore, possible side effects are commented.

Se presentan técnicas electroquímicas de realcanización y extracción de cloruros, desarrolladas con el fin de rehabilitar estructuras carbonatadas y que contengan cloruros. Se discuten y comparan los mecanismos y consecuencias de la electrólisis y la electromigración, así como las condiciones electroquímicas en la superficie de las armaduras con los de protección catódica. Se comentan, también, los posibles efectos secundarios.

Mathematical modelling of a concrete surface skin effect on diffusion in chloride contaminated media

María Jesús Samper — Tue, 19 May 2020 16:11:23 +0200

Concrete skin is considered the closest zone to the surface of concrete cover of reinforcements. It usually has a different composition than the internal concrete due to phenomena such as contact with molds or segregation of aggregates. In addition, environmental actions induce a gradient of moisture along the cover depth. These circumstances sometimes produce an irregular chloride profile in the cover, which either exhibits a maximum of chloride content some millimeters inside the outer surface or sometimes shows an anomalously high chloride concentration right at the concrete surface. In the present paper, analytical modeling of chloride diffusion is used to study the relative influence of the skin thickness. This theoretical analysis aims to show that there are cases where, if the diffusivity of the skin and the bulk concrete are very different, an error is introduced when the “skin effect” is not accounted for. The clarification of this error may contribute to understanding the differences found between laboratory experiments and the long-term record of chloride profiles in the same concrete.

Evolution of pH during in-situ leaching in small concrete cavities

María Jesús Samper — Tue, 19 May 2020 14:18:34 +0200

Small amounts (0.4 cc) of neutral water placed in small cylindrical cavities (5 mm diameter) in concrete exposed to 100% relative humidity first developed a pH comparable to that of a saturated Ca(OH)2 solution. The pH then increased over a period of days-weeks toward a higher terminal value. A micro pH electrode arrangement was used. This behavior was observed in samples of 12 different concrete mix designs, including some with pozzolanic additions. The average terminal cavity pH closely approached that of expressed pore water from the same concretes. A simplified mathematical model reproduced the experimentally observed behavior. The model assumed inward diffusional transport of the pH-determining species in the surrounding concrete pore solution. The experimental results were consistent with the model predictions when using diffusion parameters on the order of those previously reported for alkali cations in concrete. The cavity size, cavity water content, and exposure to atmospheric CO2 should be minimized when attempting to obtain cavity pH values approaching those of the surrounding pore water.

Progress Report 1994-97

María Jesús Samper — Tue, 19 May 2020 13:41:35 +0200

L Aniversario

María Jesús Samper — Tue, 19 May 2020 13:26:44 +0200

Editorial

María Jesús Samper — Tue, 19 May 2020 13:20:25 +0200

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

María Jesús Samper — Tue, 19 May 2020 12:21:28 +0200

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.

Towards excellence

María Jesús Samper — Tue, 19 May 2020 11:52:45 +0200

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)