Aprendizaje Centrado en el Proyecto de Estructuras Adaptados a la Enseñanza Universitaria

The establishment of the European higher education area (EHEA) and the Bologna process tries to improve student’s motivation and the development of personal skills, communication, teamwork, etc. through theoretical and practical similar experiences to those they will find in their future career. In this regard, this work pretends to perform the design and calculation of structures by a realistic project adapted to the academic field. The project must follow a series of guidelines established, so that students have to analyse possible solutions, make decisions, as well as, develop teamwork skills. At the end of the course, all the groups make a public presentation of their project and the students act as participants in the evaluations of their peers, thus encouraging a constructive critical discussion of the projects and the decision-making made.Con la instauración del marco educativo común en Europa y del proceso de Bolonia se pretende mejorar la motivación de los estudiantes y desarrollar sus habilidades personales, de comunicación, de trabajo en equipo, etc. mediante experiencias teórico-prácticas similares a las que encontrarán en su futura carrera profesional. Para ello, en este trabajo se propone la realización del diseño y cálculo estructural de un proyecto realista adaptado al ámbito académico. Se establecen una serie de condicionantes que debe cumplir el proyecto, de manera que los alumnos tienen que analizar posibles soluciones, tomar decisiones, así como, desarrollar habilidades de trabajo en equipo. A final de curso todos los grupos realizan una exposición pública de sus trabajos y los propios alumnos son los que evaluarán los trabajos de sus compañeros de manera que se fomente una discusión crítica-constructiva de los proyectos y de la toma de decisiones realizada

Microstructural analysis of heated ultra-high-performance fibre-reinforced-concrete under cyclic loading.

Concrete is currently the structural material more used in civil engineering and building construction. Nowadays, the application of the technological advances of the chemical industry in the processes of concrete manufacture, as well as the addition of fibres as reinforcement of the cementitious matrix, has meant a significant improvement in the mechanical and fracture behaviour of these materials. High performance and especially, ultra‐high‐performance concretes are examples of such advances. One of the advantages of the use of concrete as structural material is its high resistance in fire situations compared to other types of materials, like steel. However, the maximum service temperature of structural concrete is essentially limited by the internal damage caused by them. This thermal damage is evidenced by the generation of cracks on the border of the pore matrix, as a consequence of the pressure inferred by the evaporation of the free water and dehydration of the compounds arisen from the cement hydration. One of the alternatives to mitigate the thermal damage of the cementitious matrix is the addition of polymer fibres, which are melted at relatively low temperatures (approximately 160 oC). The melting of the fibres generates a network of micro‐channels that allow the evacuation of the evaporated water more efficiently, so that the pressure inside the pores of the matrix is reduced and consequently the thermal damage. Another alternative is the use of steel fibres as reinforcement of the concrete matrix. The presence of steel fibres, well‐distributed and in the right amount, hinders the free crack propagation because they act as barriers. Nevertheless, the addition of fibres generates a greater heterogeneity of the matrix that can induce the alteration of its microstructure and affect the mechanical and fracture properties of concrete. This effect, together with the high packing density of high‐performance concrete and, more significantly in ultrahigh‐ performance concrete, leads to the thermal damage produced in the matrix of the material must be conveniently analysed using the appropriate techniques, like the computed tomography. In some applications, the concrete elements must bear thermal and mechanical loads simultaneously at moderately temperatures, but for long periods of time. In these cases, the microstructure of the matrix, as well as its degradation by thermal damage, is closely related to the mechanical strength and fracture behaviour of the material. In other applications, concretes are subjected to cyclic thermo‐mechanical loads that entail the generation and propagation of cracks as a result of thermo‐mechanical fatigue. The reinforcement of concretes with a high number of steel fibres, as in the case of ultrahigh‐performance concretes, allows to reach very high values of the tensile and flexural strength. Thus, it is possible to reduce or dispense the use of prestressed reinforcement in those applications where it is necessary that the material resists high tensile stress without cracking. In all these cases, the analysis of the macro‐mechanical behaviour (mechanical and fracture properties) and its time evolution is closely related to the microstructure of the material and the mechanisms produced in the micro‐scale by the addition of fibres, the thermal degradation and the crack growth by cyclic loading. This thesis begins with the study of the microstructural behaviour and its effect on the macroscopic properties of high‐strength concrete reinforced with polypropylene fibres of different length and subjected to high temperatures (Chapter 2). The discussion focuses on the connection between the microstructure and the mechanical and fracture properties of the different concretes. In the Chapter 3, it is analysed the effect that the addition of different steel fibres has in the microstructure of an ultra‐high‐performance concrete and to determine its influence on the microstructure and the mechanical and fracture properties. In the next chapter, it is analysed the effect of temperature on the internal structure of the ultra‐high‐performance concrete of Chapter 3, as well as the influence of thermal damage on its mechanical and fracture properties. Chapter 5 focuses on the validation of a fatigue failure probability model in compression developed by Saucedo et al., for its application in flexural fatigue tests on high and ultrahigh‐ performance fibre‐reinforced concrete and the evaluation of the effect of fibres on the model parameters. Finally, in Chapter 6, the fatigue behaviour of an ultra‐highperformance concrete subjected to different temperatures is analysed by determining the Wöhler curves through a fatigue failure probability model developed by Castillo and Fernández‐Canteli. All the analysis carried out have focused on relating the effect of thermal damage and the influence of fibres on the microstructure, with the obtained macro‐mechanical properties.Premio Extraordinario de Doctorado U

Effect of mix design on the size-independent fracture energy of normal- and high-strength self-compacting concrete

Self-compacting concrete has a characteristic microstructure inherent to its specific composition. The higher content of fine particles in self-compacting concrete relative to the equivalent vibrated concrete produces a different fracture behavior that affects the main fracture parameters. In this work, a comprehensive experimental investigation of the fracture behavior of self-compacting concrete has been carried out. Twelve different self-compacting concrete mixes with compressive strength ranging from 39 to 124 MPa (wider range than in other studies) have been subjected to three-point bending tests in order to determine the specific fracture energy. The influence of the mix design and its composition (coarse aggregate fraction, the water to binder ratio and the paste to solids ratio) on its fracture behavior has been analyzed. Moreover, further evidence of the objectivity of the size-independent fracture energy results, obtained by the two most commonly used methods, has been provided on the self-compacting concrete mixes.Influencia de la composición de la mezcla sobre la energía de fractura de hormigones autocompactantes de resistencias media y alta. Los hormigones autocompactantes tienen una microestructura interna inherente a su composición específica. Su mayor contenido de partículas finas, en comparación con hormigones vibrados equivalentes, provoca un comportamiento diferente en fractura que afecta a los principales parámetros de fractura. En este trabajo, se ha realizado una amplia investigación experimental del comportamiento en fractura de hormigones autocompactantes. Así, se han realizado ensayos de flexión en tres puntos para determinar sus propiedades de fractura sobre 12 hormigones autocompactantes de diferente composición, con resistencias a compresión que van desde 39 hasta 124 MPa (mayor que en otros estudios). De esta forma, se ha analizado la influencia de la dosificación del hormigón y su composición (contenido en árido grueso, relación agua-cemento y pasta-sólidos) sobre su comportamiento en fractura. Además, se ha validado, para hormigones autocompactantes, la objetividad de los resultados obtenidos mediante los dos métodos habitualmente empleados para la determinación de la energía de fractura.Ministerio de Economía y Competitividad BIA2016- 75431-

Analysis of the tensile fracture properties of ultra-high-strength fiber-reinforced concrete with different types of steel fibers by X-ray tomography

This study is concerned with the analysis of the tensile properties of an ultra-high-strength fiber-reinforced concrete manufactured with short and long steel fibers. The analysis involve using different techniques - from mechanical tests to X-ray computed tomography - to relate the observed variation of the mechanical properties of the mixes with their porosity. A comprehensive study of the porosity distribution was conducted on the basis of the analysis of X-ray computed tomography images and porosimetry. The study shows the influence of the type of fiber used in the reinforcement on the pore size and distribution of the concrete matrix and consequently on its tensile properties. The tensile properties are obtained with an inverse analysis method available in the literature that yielded the first-cracking tensile strength (f t ) and the ultimate tensile strength (f tu ) and related with the inner structure of the concrete matrix. Our results prove that the tensile properties, especially the first-cracking strength, vary depending on the fibers used. These findings help mix designers make a decision about the type of fibers that should be used when a high first-cracking tensile strength is needed and make it possible to quantify the effect of the fiber.Ministerio de Economía y competitividad BIA2016-75431-RMinisterio de Economía y Competitividad DPI2015-66534-RAcademia de Ciencias de la República Checa 16-18702

Probabilistic Flexural Fatigue in Plain and Fiber-Reinforced Concrete

The objective of this work is two-fold. First, we attempt to fit the experimental data on the flexural fatigue of plain and fiber-reinforced concrete with a probabilistic model (Saucedo, Yu, Medeiros, Zhang and Ruiz, Int. J. Fatigue, 2013, 48, 308–318). This model was validated for compressive fatigue at various loading frequencies, but not for flexural fatigue. Since the model is probabilistic, it is not necessarily related to the specific mechanism of fatigue damage, but rather generically explains the fatigue distribution in concrete (plain or reinforced with fibers) for damage under compression, tension or flexion. In this work, more than 100 series of flexural fatigue tests in the literature are fit with excellent results. Since the distribution of monotonic tests was not available in the majority of cases, a two-step procedure is established to estimate the model parameters based solely on fatigue tests. The coefficient of regression was more than 0.90 except for particular cases where not all tests were strictly performed under the same loading conditions, which confirms the applicability of the model to flexural fatigue data analysis. Moreover, the model parameters are closely related to fatigue performance, which demonstrates the predictive capacity of the model. For instance, the scale parameter is related to flexural strength, which improves with the addition of fibers. Similarly, fiber increases the scattering of fatigue life, which is reflected by the decreasing shape parameter.Ministerio de Economía y Competitividad BIA2016-75431-RMinisterio de Economía y Competitividad BIA2015-68678-C2-1-RJunta de Comunidades de Castilla-La Mancha PEII-2014-016-

Analysis of the mechanical and fracture behavior of heated ultra-high-performance fiber-reinforced concrete by X-ray computed tomography

Artículo premiado 2º Trimestre 2019 en la Escuela Técnica Sup. de Ingeniería de SevillaThis work analyzes the effects of temperature (300 °C) on mechanical and fracture behavior of an ultra-high-performance steel-fiber-reinforced concrete. The deterioration of the pore structure due to thermal damage of the fiber-reinforced concrete and its un-reinforced matrix was analyzed by X-ray computed tomography. Complementarily, a thermogravimetric analysis was performed to relate the observed phase changes, due to dehydration and decomposition, with the deterioration of pore structure. Additionally, an analysis of their mechanical and fracture properties was also done at room temperature and 300 °C. Finally, a connection between the damage within the concrete matrix and its corresponding mechanical behavior was established. From the results, it has been ascertained that the propagation of thermal damage within the matrix affects the mechanical and fracture behavior in different ways depending on the pore-size. The presence of fibers modifies the pore structure and consequently the evolution of the thermal damage in the ultra-high-performance concrete, inferring its mechanical and fracture behavior.Ministerio de Economía y Competitividad BIA2016-75431-RCzech Academy of Sciences Project No. 16-18702

Influencia del tiempo de exposición a altas temperaturas en el comportamiento en fractura de hormigones autocompactantes reforzados con fibras

En el presente trabajo se analiza la influencia del tiempo de exposición a altas temperaturas sobre el comportamiento mecánico, en especial en fractura, de hormigones autocompactantes de alta resistencia con y sin refuerzo de fibras de polipropileno. Para ello, se han realizado ensayos normalizados de caracterización de los distintos hormigones y ensayos a flexión en tres puntos para las distintas temperaturas y tiempos de exposición. Las propiedades se han determinado en caliente, no tratándose de propiedades residuales. Los resultados muestran una influencia del tiempo de exposición, así como del refuerzo con fibras, mitigando en este caso los efectos nocivos que las altas temperaturas puedan generar sobre la matriz del hormigón.In this work, the influence of the exposure time to high temperatures on the mechanical behaviour of high-strength selfcompacting concrete mixes, plain and polypropylene fibre reinforced concrete, is analysed. Special attention is paid on their fracture behaviour. In this way, standardized tests in order to mechanical characterization of the different mixes are conducted for the different temperatures and time of exposition. The properties are measured directly on heated concrete and not on cooling concrete. The results show the influence of the exposure time, as well as the effect of the fibre reinforcement of the mixes. The presence of polypropylene fibres mitigates the harmful effects that the high temperatures generate in the concrete matrix

Analysis of the Utilization of Air-Cooled Blast Furnace Slag as Industrial Waste Aggregates in Self-Compacting Concrete

In this work, the effects of replacing the aggregates of self-compacting concrete by air-cooled blast furnace slag have been analysed. Different mixes have been manufactured by substituting the fine and coarse natural aggregates by air-cooled blast furnace slag. The fracture energy and the tensile and compressive strength have been determined for each mix. The self-compacting properties of the mixes, or the absence of them, have been observed. The main goals of this research are the decrease of the price of aggregates, reduction of the industrial waste, and attenuation the rate of consumption of natural resources. The results show that the self-compactability of the concrete is gradually lost as the slag content is increased, thus, when the ratio of replacement is low, the concrete keeps the self-compacting properties. Nevertheless, the loss of self-compaction affects the mechanical properties by increasing its strength. An air-cooled blast furnace slag did not present problems of heavy metals leaching.Ministerio de Economía y Competitividad BIA2016-75431-RUniversidad de Sevilla VI Plan Propio de Investigació

Soil contamination in nearby natural areas mirrors that in urban greenspaces worldwide

Soil contamination is one of the main threats to ecosystem health and sustainability. Yet little is known about the extent to which soil contaminants differ between urban greenspaces and natural ecosystems. Here we show that urban greenspaces and adjacent natural areas (i.e., natural/semi-natural ecosystems) shared similar levels of multiple soil contaminants (metal(loid)s, pesticides, microplastics, and antibiotic resistance genes) across the globe. We reveal that human influence explained many forms of soil contamination worldwide. Socio-economic factors were integral to explaining the occurrence of soil contaminants worldwide. We further show that increased levels of multiple soil contaminants were linked with changes in microbial traits including genes associated with environmental stress resistance, nutrient cycling, and pathogenesis. Taken together, our work demonstrates that human-driven soil contamination in nearby natural areas mirrors that in urban greenspaces globally, and highlights that soil contaminants have the potential to cause dire consequences for ecosystem sustainability and human wellbeing