Effect of a Crystalline Admixture on the Permeability Properties of Concrete and the Resistance to Corrosion of Embedded Steel

Reinforced concrete structure durability hinges on concrete permeability, which relies on the characteristics of the inner porous network. Harmful ions and gases can accelerate steel corrosion. Permeability-reducing admixtures (PRA), including crystalline admixtures (CA), are commonly used to mitigate this. This study examines a commercial CA’s impact on durability-related aspects in concrete specimens. Two concrete mixtures with matching proportions were prepared: a reference mix and another mix with a commercial crystalline admixture. Several properties were studied, such as compressive strength, density, porosity, electrical resistivity, water absorption capacity, chloride diffusion, air permeability, and corrosion resistance. The studied admixture in concrete yields several positive outcomes such as a slight reduction in mixing water, a potential 6% increase in concrete’s compressive strength and the development of a denser and less permeable structure with 3% lower porosity and water absorption than the reference mix. Electrical resistivity improves by 10%. Unidirectional chloride diffusion tests show no differences. Air permeability decreases by from 36% to 55%, and the water absorption rate diminishes by 23%. The admixture potentially reduces the scatter in corrosion initiation periods for steel reinforcements, delaying corrosion onset by around 60 days, although more extensive experiments are needed for definitive conclusions.This research was funded by the Spanish Agencia Estatal de Investigación (grant code BIA2016-80982-R) and by the European Regional Development Fund (grant code BIA2016-80982-R)

An improved procedure for obtaining and maintaining well characterized partial water saturation states on concrete samples to be used for mass transport tests

A conditioning procedure is proposed allowing to install into the concrete specimens any selected value of water saturation degree with homogeneous moisture distribution. This is achieved within the least time and the minimum alteration of the concrete specimens. The protocol has the following steps: obtaining basic drying data at 50 °C (water absorption capacity and drying curves); unidirectional drying of the specimens at 50 °C until reaching the target saturation degree values; redistribution phase in closed containers at 50 °C (with measurement of the quasi-equilibrium relative humidities); storage into controlled environment chambers until and during mass transport tests, if necessary. A water transport model is used to derive transport parameters of the tested materials from the drying data, i.e., relative permeabilities and apparent water diffusion coefficients. The model also allows calculating moisture profiles during isothermal drying and redistribution phases, thus allowing optimization of the redistribution times for obtaining homogeneous moisture distributions.We thank the funding received for this research from the Ministerio de Ciencia e Innovación and Ministerio de Economía y Competitividad of Spain and Fondo Europeo de Desarrollo Regional (FEDER) through project BIA2010-20548, and from the Ministerio de Fomento of Spain through project C34/2006

Shape Effect of Electrochemical Chloride Extraction in Structural Reinforced Concrete Elements Using a New Cement-Based Anodic System

This article shows the research carried out by the authors focused on how the shape of structural reinforced concrete elements treated with electrochemical chloride extraction can affect the efficiency of this process. Assuming the current use of different anode systems, the present study considers the comparison of results between conventional anodes based on Ti-RuO2 wire mesh and a cement-based anodic system such as a paste of graphite-cement. Reinforced concrete elements of a meter length were molded to serve as laboratory specimens, to closely represent authentic structural supports, with circular and rectangular sections. Results confirm almost equal performances for both types of anode systems when electrochemical chloride extraction is applied to isotropic structural elements. In the case of anisotropic ones, such as rectangular sections with no uniformly distributed rebar, differences in electrical flow density were detected during the treatment. Those differences were more extreme for Ti-RuO2 mesh anode system. This particular shape effect is evidenced by obtaining the efficiencies of electrochemical chloride extraction in different points of specimens.This research was funded by the Spanish Ministerio de Economía y Competitividad (and formerly by the Spanish Ministerio de Ciencia e Innovación) and ERDF (European Regional Development Fund) through projects BIA2010-20548 and MAT2009-10866, and also through the project PROMETEO/2013/035 of Generalitat Valenciana (Spain)

Moisture Distribution in Partially Saturated Concrete Studied by Impedance Spectroscopy

The moisture content and its spatial distribution has a great influence on the durability properties of concrete structures. Several non-destructive techniques have been used for the determination of the total water content, but moisture distribution is difficult to determine. In this paper impedance spectroscopy is used to study the water distribution in concrete samples with controlled and homogeneously distributed moisture contents. The technique is suitable for the determination of water distribution inside the sample, using the appropriate equivalent circuits. It is shown that using the selected drying procedures there is no change in the solid phase of the samples, although the technique can only be used for the qualitative study of variations in the solid phase when samples are too thick. The results of this work show that for a wide range of concrete percentages of saturation, from full to 18 % saturation, practically all the pores keep at least a thin layer of electrolyte covering their walls, since the capacitance measurement results are practically independent of the saturation degree.The authors would like to thank the Spanish “Ministerio de Economía y Competitividad” (formerly the “Ministerio de Ciencia e Innovación”) for their financial support through projects BIA 2010-20548 and BIA 2011-25721

Prácticas de laboratorio para asignaturas relacionadas con la microestructura, durabilidad y corrosión en materiales base-cemento

La llegada del Espacio Europeo de Educación Superior ha traído consigo una importante transformación de las titulaciones que se impartían en la universidad española. Entre estos cambios, destaca la aparición de los másteres universitarios que, entre otros, tienen como objetivo mejorar el grado de especialización de los egresados. Entre ellos, en la Escuela Politécnica Superior de la Universidad de Alicante, se puso en marcha el Máster en Ingeniería de los Materiales, Agua y Terreno. Dentro de este máster hay varias asignaturas que tratan aspectos relacionados con la microestructura, durabilidad y estudio de la corrosión en materiales base cemento, que cuentan con una serie de horas dedicadas a prácticas de laboratorio. En vista de ello, en esta red se ha elaborado una propuesta de prácticas de laboratorio, coordinadas entre esas asignaturas, estableciendo los contenidos cuyo aprendizaje puede ser más efectivo a través de las prácticas de laboratorio y optimizando así el proceso de enseñanza-aprendizaje

Chloride Penetration Prediction in Concrete through an Empirical Model Based on Constant Flux Diffusion

An empirical model based on constant flux is presented for chloride transport through concrete in atmospherical exposure conditions. A continuous supply of chlorides is assumed as a constant mass flux at the exposed concrete surface. The model is applied to experimental chloride profiles obtained from a real marine structure, and results are compared with the classical error-function model. The proposed model shows some advantages. It yields a better predictive capacity than the classical error-function model. The previously observed chloride surface concentration increases are compatible with the proposed model. Nevertheless, the predictive capacity of the model can fail if the concrete microstructure changes with time. The model seems to be appropriate for well-maturated concretes exposed to a marine environment in atmospherical conditions.The authors thank the Ministerio de Economía y Competitividad of Spain and Fondo Europeo de Desarrollo Regional (FEDER) for the funding received for this research through project BIA2010-20548. M. P. López is grateful for a fellowship with the Formación Personal Investigador (FPI) program (reference BES-2011-046401)

Early Detection of Corrosion-Induced Concrete Micro-cracking by Using Nonlinear Ultrasonic Techniques: Possible Influence of Mass Transport Processes

This work presents results allowing an unequivocal correlation of the observations of strong nonlinear elastic features of ultrasonic waves (values of the nonlinearity parameters exceeding the thresholds corresponding to undamaged states), with the critical events of the corrosion-induced surface cracking of reinforced cement-mortar specimens. These observations point to the possibility of the early detection of cracking using nonlinear ultrasonic (NLU) techniques. Experimental evidence is presented on the existence of active net mass transport processes, due to wick action, in the course of the corrosion tests, in the experimental conditions of this work. These phenomena might explain the observed abrupt shifting of the nonlinear parameter values (typically increasing and then decreasing post-peak, even reaching values typical of the undamaged state), and, partially, the high variability obtained for the values of the nonlinear parameters in damaged (cracked) states. Finally, some consequences are derived from the point of view of use of the NLU techniques in engineering practice, i.e., in surveys aimed at evaluating reinforced concrete structures affected by corrosion.This research was funded by the Spanish Agencia Estatal de Investigación (grant code BIA2016-80982-R) and by the European Regional Development Fund (grant code BIA2016-80982-R). M.M. acknowledges a pre-doctoral fellowship from the Spanish Ministerio de Educación, Cultura y Deporte (FPU16/04078)

Rebar Shape Time-Evolution During a Reinforced Concrete Corrosion Test: An Electrochemical Model

An electrochemical model is presented to calculate the rebar shape time-evolution in reinforced mortar specimens during forced corrosion tests. This provides a more realistic description than the usually used geometric models. The current distribution along the rebar perimeter is calculated by using Finite Element Method (FEM) to solve Laplace equation. Then, Faraday’s law is used to relate current distribution to rebar volume increase due to corrosion products creation. The shape of the rebar section is obtained as a function of corrosion time.We thank the funding received for this research from the Spanish Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER) through project BIA2016-80982-R. One of us (M. Miró) acknowledges a pre-doctoral fellowship from the Spanish Ministerio de Educación (FPU16/04078)

Use of Non-Linear Ultrasonic Techniques to Detect Cracks Due to Steel Corrosion in Reinforced Concrete Structures

In this work, non-linear ultrasonic wave techniques have been used to detect the onset of micro-cracking due to steel corrosion in model reinforced concrete elements. The specimens were of prismatic shape with a single steel rebar. The corrosion was forced by admixing an appropriate amount of sodium chloride at the moment of preparing the concrete mix, and by the application of an electric field, using a constant current density power source, and making the steel rebar work as the anode, and an external counter-electrode as the cathode. The preliminary results indicate that the onset of cracking seems to be accompanied by the appearance of higher-harmonic generation at the output signal (harmonic distortion), when the system is excited by the means of an ultrasound wave with a burst central frequency. Other phenomena related to the micro-cracks induced by corrosion, such is the parametric generation with respect to the fundamental amplitude, have not been observed until now.This research was funded by the Spanish Agencia Estatal de Investigación (grant code BIA2016-80982-R) and by the European Regional Development Fund (grant code BIA2016-80982-R). M. M. acknowledges a pre-doctoral fellowship from the Spanish Ministerio de Educación, Cultura y Deporte (FPU16/04078)

Modificaciones en el planteamiento docente de la asignatura Fundamentos Químicos de la Ingeniería Civil del Grado en Ingeniería Civil

Es un problema actual la falta de motivación de los estudiantes del grado en Ingeniería Civil, especialmente en las asignaturas básicas. En esta red se ha planteado un cambio tanto de programa como de metodología docente para el caso de Fundamentos Químicos de la Ingeniería Civil, a fin de mejorar los resultados del aprendizaje de los estudiantes. Se ha realizado en primer lugar una investigación de los programas y metodologías docentes utilizados en otras universidades españolas para materias equivalentes y los resultados de esa búsqueda, junto con el estudio y la reflexión sobre la aplicabilidad de nuevas metodologías docentes ha dado lugar a una propuesta de metodología/programa que se pretende implementar en el curso 1016-17 y seguir analizando de forma crítica para mejorarlo. Se propone el uso de la metodología del aprendizaje basado en proyectos para la selección de materiales óptimos para una obra de Ingeniería Civil, y el desarrollo, a partir de la información obtenida por los alumnos y modulada por el equipo docente tendrá como resultado la adquisición de todas las competencias y cubrirá todos los descriptores incluidos en la memoria verificada del grado