Scipedia: Documents published in 2020

Energy situation in the Republic of Serbia

Dejan Brkić — Wed, 10 Jun 2020 13:53:03 +0200

Paper presents the energy policy of the Republic of Serbia with special attention to the energy situation on the government controlled territory. South Serbian autonomous province of Kosovo and Metohija is under UN jurisdiction since the 1999 according to UNSC Resolution 1244. Renewable energy sources are rarely used in Serbia with exception of energy from hydropower plants, but in this sector priorities in geothermal and energy coming from biomass recently increased. In natural gas sector, Serbia has the deal with Russia for construction of South Stream gas-line through Serbia and for construction of the first underground storage in depleted gas reservoir in Banatski Dvor. In 2008, Serbia also sold 51% of the government founded petroleum industry – NIS which has exclusive monopoly for exploitation of crude oil. Serbian government has complete monopoly in electric power sector. Electric power infrastructure became technologically obsolete, and operative efficiency is at very low level. Serbia has not yet decided whether Serbian Electric Power Industry – EPS will be privatized. District heating sector mostly natural gas fuelled is highly inefficient and it is in jurisdiction of local municipalities but also has social component dictated by central government.

Similarities and differences in optimization of water-and gas-distribution pipeline networks

Dejan Brkić — Wed, 10 Jun 2020 13:22:02 +0200

Two efficient methods for gas distributive network calculation

Dejan Brkić — Wed, 10 Jun 2020 13:14:02 +0200

Today, two very efficient methods for calculation of flow distribution per branches of a looped gas pipeline are available. Most common is improved Hardy Cross method, while the second one is so-called unified node-loop method. For gas pipeline, gas flow rate through a pipe can be determined using Colebrook equation modified by AGA (American Gas Association) for calculation of friction factor accompanied with Darcy-Weisbach equation for pressure drop and second approach is using Renouard equation adopted for gas pipeline calculation. For the development of Renouard equation for gas pipelines some additional thermodynamic properties are involved in comparisons with Colebrook and Darcy-Weisbach model. These differences will be explained. Both equations, the Colebrook’s (accompanied with Darcy-Weisbach scheme) and Renouard’s will be used for calculation of flow through the pipes of one gas pipeline with eight closed loops which are formed by pipes. Consequently four different cases will be examined because the network is calculated using improved Hardy Cross method and unified node-loop method. Some remarks on optimization in this area of engineering also will be mentioned.

Analysis of stability of earth dams in overtopping scenarios with the particle finite element method

María Jesús Samper — Wed, 10 Jun 2020 13:11:56 +0200

The aim of this work is to study the consequences of an overtopping on the stability of earth dams and its possible failure mode. Rehabilitation and safety analysis of existing dams is nowadays an open field of research. The possibility to define a numerical instrument to provide support for analyzing the failure of a dam is a big step ahead for organizing the intervention measures and for optimizing the economic plan. In fact many existing dams have now to be modified due to the revision of previous design criteria in order to increase their safety. The objective of our work is to develop and validate a new computational method of general applicability that allows treating the above problems. The method will combine advanced finite element and particle techniques. Fluid-structure interaction effects and non-linear geometrical and mechanical effects in the dam material are considered. A mixed Lagrangian and Eulerian approach is used. The fluid behavior is described using a modified form of the Navier Stokes equations in order to consider the effect of a variable porosity. A non linear Darcy law is included in the momentum equation. A level set function is chosen to follow the movement of the free surface inside and outside the porous medium. The structure is described using a purely lagrangian PFEM formulation [1] and [2]. The specific features of PFEM make it appropriate to treat the rockfill material and its large deformations and shape changes. A projection technique allows to perform the data transfer between the fluid and the structure non matching meshes. Peer Reviewed Postprint (published version)

Multidimensional gas distribution networks

Dejan Brkić — Wed, 10 Jun 2020 13:03:02 +0200

Coupling eulerian and lagrangian models to simulate seepage and evolution of failure in prototype rockfill dams

María Jesús Samper — Wed, 10 Jun 2020 12:48:18 +0200

This work presents a model which allows considering the interaction between rockfill dams and the water. The fluid behaviour is analyzed on an Eulerian fixed mesh. A level set technique is employed to tack the evolution of the free surface. An edge based approach is used to solve efficiently the modified form of the Navier‐Stokes equations. The dam response is evaluated on a Lagrangian moving mesh using PFEM. A visco‐rigid constitutive model is used to describe the structural behaviour and collapse of rockfill under fluid dynamic forces. Mohr‐Coulomb is the failure criteria adopted in the calculation. Finally a nodal projection algorithm allows the transferring of information through non matching meshes.

Accuracy increasing of gas distribution network calculation after Hardy Cross method

Dejan Brkić — Wed, 10 Jun 2020 12:43:02 +0200

Safety analysis of rockfill dams during overspill phenomena

María Jesús Samper — Wed, 10 Jun 2020 12:36:47 +0200

An increasing interest is rising on the study of rockfill embankment dams during overspilling. Design criteria of earth dams are being reviewed in many countries to guarantee an increasing safety level in front of an exceptional flooding. The possibility of studying the failure process is currently limited by the lack of a precise knowledge and by the absence of a suitable computational method which can predict accurately the onset and evolution of breaching. The analysis of the possible consequences of an accidental overspill is then impossible or very imprecise and the necessary economical measures for solving the problem are then inefficient. An appropriate computational method will help to reduce the economic impact of the investments in dam safety and in emergency plans for embankment dams. The dam failure is mainly due to the hydrodynamic forces acting on the rockfill material in the downstream face. Two failure mechanisms occur in an alternative or combined mode: dragging of rockfill particles with erosive effects, and loss of stability of a part of the downstream region due to the slippage of a bulk mass of the rockfill material. The loss of a relevant part of the rockfill material in the downstream side of the dam, can lead to mechanical failure of the impervious region, either if this is formed by a concrete (or asphalt) face, or by a clay core. In the latter case, erosion of the cohesive material can also influence the failure process, but the scale time of appearance of this erosion phenomenon is so different from the principal erosion of the rockfill part, that this second one is not taken into account. The objectives of the current work is to develop and validate a new computational method of general applicability that allows treating above problems. The method will combine advanced finite element and particle techniques. Fluid-structure interaction effects and non-linear geometrical and mechanical effects in the dam material will be considered. The specific features of the analysis method proposed make it appropriate to treat the rockfill material adjacent to the downstream surface where a transfer of momentum between the water running over the dam surface and that moving through the interior due to seepage occurs

Centralised system options of demo setlement energy suplying

Dejan Brkić — Wed, 10 Jun 2020 12:16:02 +0200

Calculation of the ﬂow distribution in looped pipeline networks with the node-loop method

Dejan Brkić — Wed, 10 Jun 2020 11:53:02 +0200

Theme B: simulation of the behavior of prototypes of rockfill dams during overtopping scenarios: seepage evolution and beginning of failure

María Jesús Samper — Wed, 10 Jun 2020 11:44:35 +0200

In recent years the technology on embankments dams has developed sensibly due to the advances in soil mechanic, and in all related sciences. Nevertheless their vulnerability to overtopping still remains their weakest point in comparison with concrete structures. The principal aim of this theme is the simulation of the initial stage of failure of the dam when an overtopping or an exceptional flood occurs. A fluid-structure coupled problem has to be considered. The sudden variation of the upstream conditions induces a quick evolution of a seepage line in the downstream shoulder. Non linear Darcy law has to be taken into account. On the other hand the water, emerging from the toe of the dam, induces dragging of particles and possible mass sliding, depending on geometrical and material conditions. UPM and CEDEX have carried out more than 70 experiments during the last two years. They analyzed the influence of a series of parameters on the failure mechanisms. These parameters are, for instance, the dimension of the rocks, the slope of the downstream part of the dam, the type of impermeable element used, and so on. We propose to reproduce numerically three experiments analyzing the evolution of seepage and following initial stage of failure in the case of a homogeneous dam, of a dam with impermeable upstream face and of a dam with internal core. Experimental data, bottom pressure distribution and topographic analysis of the geometry of the dam during the failure can be compared with numerical results.

Improvement of loop method adjusted for calculation of gas distribution networks

Dejan Brkić — Wed, 10 Jun 2020 11:08:02 +0200

Optimization of pipe diameters in looped pipeline network after the modified loop method

Dejan Brkić — Wed, 10 Jun 2020 11:02:02 +0200

Software for deep-well designing

Dejan Brkić — Wed, 10 Jun 2020 10:53:01 +0200

Simulation of the beginning of failure in rockfill dams caused by overtopping

María Jesús Samper — Wed, 10 Jun 2020 10:31:47 +0200

This paper presents the work carried out during the last years for the creation of a numerical model to simulate transient seepage phenomena in rockfill dams when overtopping occurs. The objective is to analyze the trigger of failure mechanism in the downstream slope due to hydrodynamic forces. The current work aims to give a contribution to this field proposing a new computational method of general applicability for simulating, with a unique formulation, the flow throughout and over the dam while failure occurs together with the dam structural response. The numerical results are validated with experiments on scale models rockfill dams.

Simulation of two and three-dimensional viscoplastic flows using adaptive mesh refinement

María Jesús Samper — Wed, 10 Jun 2020 09:48:01 +0200

This paper presents a finite element solver for the simulation of steady non‐Newtonian flow problems, using a regularized Bingham model, with adaptive mesh refinement capabilities. The solver is based on a stabilized formulation derived from the variational multiscale framework. This choice allows the introduction of an a posteriori error indicator based on the small scale part of the solution, which is used to drive a mesh refinement procedure based on element subdivision. This approach applied to the solution of a series of benchmark examples, which allow us to validate the formulation and assess its capabilities to model 2D and 3D non‐Newtonian flows.

Comparison of a Material Point Method and a Galerkin Meshfree Method for the Simulation of Cohesive-Frictional Materials

María Jesús Samper — Wed, 10 Jun 2020 09:18:16 +0200

The simulation of large deformation problems, involving complex history-dependent constitutive laws, is of paramount importance in several engineering fields. Particular attention has to be paid to the choice of a suitable numerical technique such that reliable results can be obtained. In this paper, a Material Point Method (MPM) and a Galerkin Meshfree Method (GMM) are presented and verified against classical benchmarks in solid mechanics. The aim is to demonstrate the good behavior of the methods in the simulation of cohesive-frictional materials, both in static and dynamic regimes and in problems dealing with large deformations. The vast majority of MPM techniques in the literatrue are based on some sort of explicit time integration. The techniques proposed in the current work, on the contrary, are based on implicit approaches, which can also be easily adapted to the simulation of static cases. The two methods are presented so as to highlight the similarities to rather than the differences from "standard" Updated Lagrangian (UL) approaches commonly employed by the Finite Elements (FE) community. Although both methods are able to give a good prediction, it is observed that, under very large deformation of the medium, GMM lacks robustness due to its meshfree natrue, which makes the definition of the meshless shape functions more difficult and expensive than in MPM. On the other hand, the mesh-based MPM is demonstrated to be more robust and reliable for extremely large deformation cases.

A Finite Element Implementation for the Three Variable Biot Model and an Introduction to its Application to Sugar Cane Milling Processes

María Jesús Samper — Tue, 09 Jun 2020 15:35:15 +0200

This document presents a step-by-step derivation for the formulation of a Biot model for saturated porous media, this formulation is apt to be implemented both in two and three dimensions. Afterwards, the spatial and temporal discretization for the model is also presented, focusing on a symbolic representation around the Gauss points for a particular element in an implementation. Lastly, the results for a couple of test cases are shown, and of special interest, the test case that constitutes the first approximation towards an implementation of this model for the simulation of sugar cane milling processes.

Soil-structure interaction simulation of landslides impacting a structure using an implicit material point method

María Jesús Samper — Tue, 09 Jun 2020 14:30:59 +0200

Global warming and climate changes have been one of the many causes that triggered numerous catastrophic landslide and mudflow disasters in the past twenty years. The increase of earth temperature has contributed to the increase of precipitation and undisputedly affected the soil slope stability, which by further may cause landslides in various scale and speed. This large soil deformation phenomenon carries along huge rocks and heavy materials that often results in extensive damage in civil infrastructures both directly or indirectly. Coming with this motivation, a soil-structure interaction simulation based on the implicit material point method (MPM) has been implemented within the Kratos Multiphysics framework for the objective of predicting structural deformation and, furthermore, structural failure caused by environmental flow problems such as landslides. In the current study, the soil is modeled using a non-associated Mohr-Coulomb-based elastoplastic law, while the structure is modeled as elastic and Neo-Hookean hyperelastic materials. In the numerical tests conducted, the equivalent stress and displacement measured on both rigid and flexible structures show a good qualitative agreement. In the future works, a more adequate consideration of the soil and structural model will be investigated before conducting a real-scale landslide simulation.

Corrigendum to “Modelling of Bingham and Herschel-Bulkley flows with mixed P1/P1 finite elements stabilized with Orthogonal Subgrid Scale” [J. Nonnewt Fluid Mech, 228, 2016, p. 1–16]

María Jesús Samper — Tue, 09 Jun 2020 14:07:47 +0200

This corrigendum provides some missing data and a reference for the paper Modelling of Bingham and Herschel-Bulkley flows with mixed P1/P1 finite elements stabilized with Orthogonal Subgrid Scale, as well as it corrects a mistaken unit of measure in the caption of a figure.

The authors apologise for the inconveniences caused.

Corrigendum

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The caption of Figure 14 should read:

Cylinder in an Herschel-Bulkley fluid. Drag force coefficient in terms of the relation L:R for Bn∗ = 10.

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The flow index n in the sub-captions of Figure 17(a)-17(l) is nondimensional.

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The following Reference should be added: [71] E. Moreno, M. Cervera "Elementos finitos mixtos estabilizados para flujos confinados de Bingham y de Herschel-Bulkley Parte II: soluciones numéricas" Revista Internacional de Métodos Numéricos para Cálculo y Diseño en Ingeniería, 2016; 32(3); 131-138.

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The captions of Figures 2, 4-7, 22-25 should include the following text at the end:

(Reproduced with permission from [71]).

Coupled Soil-Structure Interaction Modeling and Simulation of Landslide Protective Structures

María Jesús Samper — Tue, 09 Jun 2020 13:35:40 +0200

Within the past two decades, mass movements hazards involving fast and large soil deformation have increased significantly in frequency and magnitude due to their strong relation to climate changes and global warming. These phenomena often bring along rocks, debris, and heavy materials that can extensively damage and destroy the landscape and infrastructures, causing devastating economic loss, and often, human casualties. The risk of future disasters continues to escalate with the increase of real estate development in suburban areas, including mountainous regions. Further assessment and prediction on such disasters and their countermeasures are, therefore, in high economic demands. One of the most intuitive ways is to install protective structures in mountain slopes and valleys that can hold the materials brought by the moving landslides. While the current state of the art of landslide prediction using numerical methods has been mainly dominated by the development of advanced geomechanical models suited for different types of soil materials, e.g. multi-phase unsaturated soil model, this study focuses more on the interaction of such phenomena with the installed protective structures. Here, an implicit formulation of material point method (MPM) is implemented to model the landslides considering finite strain assumption. Furthermore, a staggered coupling scheme with traditional Finite Element Method (FEM) is proposed to simulate accurately and robustly the dynamic force and displacement coupling of soil-structure interaction (SSI). All developments of the method are implemented within the Kratos-Multiphysics framework and available under the BSD license (https://github.com/KratosMultiphysics/Kratos/wiki). In the future works, more adequate consideration of coupling scheme and material models considering damage and fracture will be investigated before conducting a real-scale landslide simulation.

A procedure to design toe protections for rockfill dams against extreme through-flows

María Jesús Samper — Tue, 09 Jun 2020 13:16:34 +0200

This article presents a procedure for designing rockfill toe protections with a highly permeable downstream shoulder to avoid mass sliding in dams during extremely high through-flow episodes. This accidental through-flow may be caused by reasons such as overtopping or leakage flow due to the loss of sealing at the impervious element of the dam or its foundation. The proposed protection is located at the downstream toe of the dam, and it is composed of highly permeable material, typically compacted rockfill. This material can be different from the rockfill forming the downstream shoulder of the main dam. The work is a result of a combination of numerical and experimental research carried out to analyze the influence of the geometry of the toe protection for given material properties of both dam shoulder and protection, when they can be considered highly isotropic. As a result of these studies, a design methodology is obtained. A series of validation tests are presented to support the reliability of the method.

Estudio de la capacidad de desagüe de aliviaderos con compuertas mediante modelación numérica. Aplicación a la presa de Oliana

María Jesús Samper — Tue, 09 Jun 2020 12:56:35 +0200

En el presente trabajo se estudia la capacidad de desagüe de aliviaderos con compuertas radiales mediante la aplicación de un código de cálculo numérico al caso del aliviadero de la presa de Oliana.

Numerical modeling of the hydraulic performance of Oliana dam spillway using Kratos

María Jesús Samper — Tue, 09 Jun 2020 12:40:28 +0200

Head-discharge curves in gated spillways are commonly obtained by means of the application of empirical formulations. The most popular one, recommended by SPANCOLD [1], was developed by the U.S. Army Corps of Engineers [2]. It is based in several experimental campaigns whose results were used to define a chart which provides the value of the discharge coefficient depending on the gate position. This formula does not take into account the effect of side contractions, which depends on the length-height ratio of the bays, as well as the head, the inflow conditions and spillway geometry. Thus, it is necessary to carry out specific experimental tests for every new spillway. The aim of the work is the analysis of the discharge capacity of radial gated spillways. The accuracy of empirical formulations has been studied, and Oliana Dam spillway has been investigated via numerical simulation.

Applications of the particle finite element method in dam engineering

María Jesús Samper — Tue, 09 Jun 2020 11:39:46 +0200

The paper presents the results of the application of the Particle Finite Element Method (PFEM) to the analysis of some of the more complex phenomena related to dam hydraulics: shock waves in spillways, aeration in bottom outlets, and erosion in the downstream river bed. Furthermore, the method has been applied to the study of the consequences of landslides in reservoirs: the wave generation, its propagation, and the affection to the dam.

Numerical modeling of air-water interaction in bottom outlets. Application to susqueda dam

María Jesús Samper — Tue, 09 Jun 2020 11:06:00 +0200

The convenience of installing an aeration system in dam bottom outlets is well known nowadays. Otherwise, damages due to cavitation and vibration are frequently serious, as could be observed in several dams built in the beginning of the 20 th century. Several empirical formulas have been developed for calculating the maximum air demand, but their results are very sensitive to the variation of the geometrical characteristics of the installation. The Ministry of Science and Innovation of Spain has funded a project to address this problem using numerical modeling. The interaction of two fluids (air and water) with very different physical characteristics is the greatest difficulty to be overcome. To deal with this challenge, the Particle Finite Element Method (PFEM) has been used. The method has being applied to verify the performance of the new flat-seat circular-section valves, which design is being developed by INHISA as an alternative to the traditional Bureau-Type. Firstly, a case comprising the mentioned valve in a standard facility was analyzed for validation purposes, as well as for studying the influence of the different parameters in the air flow. Then, the method has been used for the analysis of the performance of the bottom outlets of Susqueda Dam.

Protecciones de presas mediante repiés de escollera y bloques en forma de cuña

María Jesús Samper — Tue, 09 Jun 2020 10:39:01 +0200

Las conferencias presentadas durante la Jornada Técnica sobre Avances en investigación aplicada en seguridad hidráulica de presas organizada por el Centro de Estudios Hidrográficos del CEDEX y la Universidad Politécnica de Madrid el mes de junio de 2013 versan sobre la mejora de la seguridad hidráulica de las presas, una materia de especial importancia en nuestro país (habida cuenta del elevado número de infraestructuras de regulación en servicio y de su antigüedad media) y constituye una tarea en la que tanto el CEDEX como la Universidad Politécnica de Madrid han trabajado activamente en los últimos años. En este artículo se van a tratar dos tipos de protecciones de carácter muy diferente: las protecciones tipo repié y las protecciones mediante bloques prefabricados en forma de cuña (en adelante, BFC). En el caso de las protecciones tipo repié, aplicables a presas de materiales sueltos con espaldón de aguas abajo de escollera, se realiza una breve descripción del estado del arte de la tecnología y de sus aplicaciones así como de la innovación conseguida en este campo a partir de las investigaciones desarrolladas en la Universidad Politécnica de Madrid (UPM), en colaboración con el Centro de Estudios Hidrográficos del CEDEX y el Centro Internacional de Métodos Numéricos en la Ingeniería (CIMNE), en el marco del proyecto de investigación del Plan Nacional denominado EDAMS, y cuyo resultado directo ha sido la tesis doctoral titulada “Mejora de la seguridad de las presas de escollera frente a percolación accidental mediante protecciones tipo repié” (Morán, 2013). En la parte dedicada a la protección mediante BFC`s se describe la tecnología, sus posibilidades de utilización dentro de la ingeniería de presas y se presenta el caso de la presa de Barriga (Burgos), como primera aplicación mundial de esta tecnología para el diseño de un aliviadero de servicio sobre el propio cuerpo de una presa de materiales sueltos en explotación.

Interpretación de los datos de auscultación de presas por métodos no convencionales

María Jesús Samper — Tue, 09 Jun 2020 10:00:54 +0200

Nuevos métodos para el análisis de datos de auscultación de presas: la herramienta iComplex

María Jesús Samper — Tue, 09 Jun 2020 09:41:45 +0200

Los avances en los instrumentos de medida y en las técnicas de transmisión y almacenamiento de información han permitido aumentar el control de la seguridad de las presas, con medidas más fiables, precisas y frecuentes. En general, estos avances no han sido acompañados por una mejora en las técnicas de tratamiento y análisis de los datos de auscultación, que con frecuencia se limitan a gráficos y modelos estadísticos sencillos, como el modelo HST. Los autores están trabajando en la integración de tecnologías avanzadas de análisis de datos para extraer la mayor información posible acerca del estado de seguridad de la presa. Como resultado, se está desarrollando una herramienta que contiene: a) un módulo gráfico flexible y dinámico, que permite explorar los datos de forma interactiva, b) herramientas para el pretratamiento de datos para filtrar valores anómalos, completar series y calcular series modificadas, y c) una librería de herramientas estadísticas y de inteligencia artificial (HST, redes complejas y redes neuronales, entre otras) para seleccionar el modelo predictivo más adecuado en cada caso. Palabras clave: Seguridad de presas, auscultación, análisis de datos, modelos de predicción, bases de datos.

Procedimiento de diseño de protecciones tipo repié para evitar la rotura por deslizamiento en masa de presas de escollera sometidas a percolaciones extremas

María Jesús Samper — Mon, 08 Jun 2020 16:10:56 +0200

Síntesis del procedimiento de diseño formulado en la tesis doctoral de Rafael Morán. La demanda de seguridad en infraestructuras críticas ha aumentado en los últimos años, especialmente en los países con mayor nivel de desarrollo económico y social. En estos países, el control del estado de la seguridad de estas infraestructuras y las medidas para disminuir los riesgos asociados en caso de avería están adquiriendo una gran relevancia, lo que se ha plasmado en unas normativas más exigentes. Las presas están dentro de este tipo de infraestructuras tanto por su interés estratégico como por los daños que pueden llegar a ocasionar en caso de un mal funcionamiento o de su eventual rotura. La tecnología de protecciones de presas surge como respuesta a esta demanda de seguridad y, por este motivo, ha experimentado un gran avance en las últimas décadas. Dentro de este artículo se va a describir la protección tipo repié y el procedimiento de diseño propuesto para evitar el deslizamiento en masa de presas con espaldón de aguas abajo de escollera, cuando se produce una filtración anormalmente elevada debido a un fallo en la impermeabilidad en el conjunto presa-cimiento. El artículo describe brevemente el estado del arte de la tecnología y de sus aplicaciones así como de la innovación conseguida en este campo a partir de las investigaciones desarrolladas en la Universidad Politécnica de Madrid (UPM), en colaboración con el Centro de Estudios Hidrográficos del CEDEX y el Centro Internacional de Métodos Numéricos en la Ingeniería (CIMNE), en el marco del proyecto de investigación del Plan Nacional denominado EDAMS.

Discussion on “Thermal displacements of concrete dams: Accounting for water temperature in statistical models”

María Jesús Samper — Mon, 08 Jun 2020 15:24:55 +0200

A discussion on the paper by Tatin et al. (2015) is presented. The paper described an innovative statistical model to interpret dam behaviour, which was validated with artificial data and then applied to seven dams in operation. This discussion provides several comments about the model performance evaluation, as well as suggestions for further analysis of the monitoring data.

Corrigendum to “An empirical comparison of machine learning techniques for dam behaviour modelling” [Struct. Saf. 56 (2015) 9–17]

María Jesús Samper — Mon, 08 Jun 2020 15:01:41 +0200

The authors wish to report an error in Fig. 1 of the above-mentioned article. The correct position of the monitoring devices is shown below.

A methodology for dam safety evaluation and anomaly detection based on boosted regression trees

María Jesús Samper — Mon, 08 Jun 2020 14:14:46 +0200

Many countries are implementing new dam safety regulations that often include more restrictive standards. This, together with the increasing average age of dams, results in a greater need for dam control and maintenance works. The advances in information and communications technologies improved the performance of dam monitoring systems, so a large amount of information on the dam behaviour can be collected. This has led to the use of more powerful tools for its analysis, many of which were first developed in the field of machine learning (e. g. neural networks). They offer some advantages over the conventional statistical methods. However, their capacity for early detection of anomalies has seldom been studied. As a result, they are far from being fully accepted by practitioners, whose analyses are often restricted to the interpretation of simple plots of time series data, together with basic statistical models. The present work describes a methodology for anomaly detection in dam behaviour, with the following features: a) The prediction model is based on boosted regression trees (BRTs). b) Causal and auto-regressive models are combined to detect different types of anomalies. c) It is checked whether the values of the external variables fall within the range of the training data. The performance of the proposed methodology was assessed through its application to a test case corresponding to an actual 100-m height arch dam, in operation since 1980. Artificial data were generated by means of a finite element model. Different anomalies were later added in order to test the anomaly detection capability. The method can be applied to other response variables and dam typologies, due to the great flexibility of BRTs, which automatically select the most relevant inputs.

Modelación física y numérica de aliviaderos en laberinto con fondo poliédrico

María Jesús Samper — Mon, 08 Jun 2020 10:57:03 +0200

Un número importante de presas en España deben ampliar sus aliviaderos para cumplir criterios de seguridad distintos a los de su construcción. En este contexto, cobran interés soluciones de aliviaderos no convencionales como los aliviaderos en laberinto, que permiten aumentar la capacidad de desagüe de estructuras existentes con una inversión moderada. Para la optimización del diseño de este tipo de aliviaderos se desarrolla el proyecto POLILAB, en cuyo marco se llevaron a cabo las campañas de modelación física y numérica que se exponen en este artículo. Se describen los resultados más relevantes en lo relativo a la inclusión de fondos poliédricos en aliviaderos en laberinto como refuerzo estructural, contemplando además las modificaciones que implican con respecto a soluciones en laberinto con fondo plano, en lo relativo a capacidad de desagüe, patrón de flujo y acciones hidrodinámicas sobre los contornos del laberinto.

Hydraulic and stability analysis of the supporting layer of wedge-shaped blocks

María Jesús Samper — Mon, 08 Jun 2020 10:08:31 +0200

Wedge shaped blocks (WSB) are attracting increasing attention as protection against overtopping for earth and rock-fill dams. However, there are limited examples of application and some aspects of the technology merit additional research and improvement. One key issue is the design of drainage and supporting layer for WSB protections. During overtopping, part of the overflow leaks through the joints between blocks, hence circulating through the granular material. The permeability and thickness of the supporting layer must be sufficient to prevent the flow from generating pressure on the bottom side of the blocks, which contributes to its destabilization. However, it must also be structurally stable to avoid undesirable deformations on the downstream face. Both the material permeability and the layer thickness determine the hydraulic behavior of this element. These, together with the weight of the blocks and the slope of the downstream face, directly influence mass and block stability. These aspects should be taken into account for the numerical modeling of seepage through the supporting layer. To this end, an application of the open source software Kratos Multi-physics was employed. A parametric study was conducted to quantify the influence of each design variable in the safety factor against mass sliding of the supporting and drainage layer.

Applications of numerical methods in design and evaluation of overtopping protection systems

María Jesús Samper — Mon, 08 Jun 2020 09:50:21 +0200

The development of overtopping protection systems often requires detailed analyses of complex physical phenomena. This hinders the comprehensive knowledge of their behavior, and therefore the development of suitable design criteria. In recent years, the authors have developed and validated different methods, combining continuous, particle and discrete numerical techniques, to obtain accurate and reliable solutions of different numerical problems involving fluid-soil-structure interaction. In this contribution, some applications of these methods to the study of dam protection against overtopping are presented. The main advantages of this approach include the ability to extract results of the governing variables (pressure, velocity) at any location of the domain, and the possibility to consider scenarios without the restrictions of the experimental facilities (flow rates, size, scale effects). In particular, the contribution gathers examples of application of numerical methods in a) analysis of rockfill dam stability against overtopping, including seepage evolution and deformation of the downstream shoulder, and b) stability analysis of wedge-shaped-blocks subjected to vandalism.

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.

Are fossil fuels the main cause of today's global warming?

Dejan Brkić — Thu, 28 May 2020 15:27:02 +0200

Gas will increasingly be seen as the fossil fuel of choice, especially when considering environmental impacts. Natural gas is the chance for Serbia for sustainable development and with its intensive consumption in the XXI century to conciliate the 4Es (Energy, Economy, Efficiency and Environment). In this paper we will compare the impact of different fossil fuels used for domestic heating with a special emphasis on natural gas. Some other causes of climate changes will be also discussed such as the Milanković astronomical cycles. These factors will be compared with climate changes caused by the consumption of fossil fuels.

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).

Natural gas heating in Serbian settlements according to urbanity parameters

Dejan Brkić — Thu, 28 May 2020 15:20:02 +0200

Natural gas can be directly used for heating of flats by gas distribution system. Indirectly, heating power plant can disburse natural gas and deliver hot water or steam for heating of flats. Decision of optimal way for gas heating usage is done based on spatial disposal of building, number and size of buildings in settlement, etc. Optimal solution, between gas distribution and district heating system (local or district heating by natural gas), can be done according to methodology (model approach) shown in this paper. According to variety of Serbian settlements (in density, size and layout of buildings) model which has ability to represent their different characteristics is formed. This model could be simple and useful tool for initial decision about energy supply system.

Natural gas distribution and domestic usage efficiency

Dejan Brkić — Thu, 28 May 2020 15:09:03 +0200

http://nardus.mpn.gov.rs/123456789/2654

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.