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This paper presents the material and process-related research that underpinned the realisation of the Parque de Castilla Footbridge in Madrid in 2016, going from the laboratory to the industrial scale. The fibre-reinforced cement-based composite was first developed and tested in a small-scale particle bed printer focusing on evaluating the influence of the material and process on the mechanical response and density of the printed parts. The solution was then upscaled to a full-size particle bed printer that underwent technical modifications to ensure adequate control and production quality of the footbridge segments. The observations derived from the study provide valuable insights on relevant process-related differences induced by the technology upscaling that can inform future applications of the technology., The authors acknowledge ACCIONA, S.A., for the funds provided. The authors also acknowledge Mr. Enrico Dini for his seminal role in the popularisation and visibility of particle bed 3D printing, holding the Application Patents of this system. The experimental program carried out at the Laboratory of Structures and Materials (LATEM) of the Polytechnic University of Catalonia (UPC, BarcelonaTECH) allowed identifying the parameters that govern the mechanical performance of the fibre reinforced cement-based composite designed and oriented to the manufacturing of structural components with particle bed 3D-printing systems. Additionally, the first and third author want to express their gratitude to AGAUR-FEDER for the financial support through the project 2019PROD00066., Peer Reviewed, Postprint (published version)

The present paper deals with an experimental study on the flexural fatigue behaviour of pre-cracked polypropylene fibre reinforced concrete with two different volume of fibre. Mechanical response was evaluated through compressive strength, elastic modulus and static bending test. Fatigue test considered an initial crack width accepted in the service limit state and the evolution of the crack opening displacement of the beams subjected to a prescribed number of cycles (1,000,000 or 2,000,000). After the cyclic load, the post-fatigue residual strength was evaluated and compared to the static response. Results suggest that the mechanism of crack development is independent of the adopted fibre content. The post-fatigue strength seems to be unaffected by accumulated damage due to cyclic load and the static load-crack opening displacement curve might be used as a criterion to predict the residual strength. Furthermore, a conceptual model is proposed to predict the crack opening as a function of number of cycles in view of accumulated fatigue damage. The equation was validated for different fibre content and polypropylene fibres., The first author thanks the Brazilian National Council for Scientific and Technological Development for the scholarship granted (233980/2014-8). This research was enabled by funds provided by the SAES project (BIA2016-78742-C2-1-R) of Spanish Ministerio de Economía, Industria y Competitividad., Peer Reviewed, Postprint (published version)

This paper presents an experimental investigation on the post-crack flexural fatigue behaviour of a steel macrofiber reinforced concrete (SFRC) and a high performance steel microfiber reinforced concrete (HPFRC), on notched beams considering the crack opening for serviceability condition. Different load levels were applied by means of three-point bending tests in order to verify the fatigue life. Performance of SFRC and HPFRC was compared under cyclic dynamic tests. Higher load levels seem to lead to failure through a continuous pull-out of the fibres, generating a more ductile response. Smaller load levels can be responsible for the progressive weakening of the fibre-matrix interface through micro-cracks. The conducted probabilistic approach has demonstrated to be suitable to predict the flexural fatigue life of pre-cracked SFRC and HPFRC for a desired probability of failure. From the experimental intrinsic scatter of the fatigue phenomenon, in particular for high levels of applied fatigue load, the amount of fibres in the cracked cross section seems to play an important role in withstanding the fatigue load., The first author would like to thank the Brazilian National Council for Scientific and Technological Development for the scholarship granted (233980/2014-8). This research has been possible owe to the economic funds provided by the SAES project (BIA2016-78742-C2-1-R) of Spanish Ministerio de Economía, Industria y Competitividad., Peer Reviewed, Postprint (published version)

The development of early age properties of sprayed concrete is a key factor that governs its mix design and safe application. The conventional methods to evaluate the evolution of mechanical strength in sprayed concrete present a large interval between each set of measurements and results present a high scatter. In this context, the objective of this study is to characterize the early age properties of sprayed mortars through a novel continuous monitoring system based on in situ ultrasound measurements. Sprayed mortars were also analyzed by isothermal calorimetry, needle penetration and stud driving method. Results indicate that the system developed here can monitor the evolution of early age properties of sprayed mortars continuously without the common drawbacks observed in penetration tests. This research may lead to the development of a more reliable procedure to characterize the early age mechanical properties of sprayed materials in the worksite under safer conditions., This research was financially supported by the project RTC-2015- 3185-4 (MAPMIT), co-funded by the Ministerio de Economía y Competitividad of Spain in the Call Retos-Colaboración 2015 and by the European Union through FEDER funds under the objective of promoting the technological development, innovation and high quality research. Furthermore, the authors thank Industrias Quimicas del Ebro (IQE) and, especially, Dr. Miguel Cano and Dr. Jorge Pérez for their active collaboration and technical support on accelerating admixtures. Finally, authors extend their acknowledgements to the staff at the Laboratory of Technology of Structures Luis Agulló and, especially, Robert and Jordi for their technical support on the experimental campaign., Peer Reviewed, Postprint (author's final draft)

In the context of the evaluation of the load-bearing capacity of a steel fibre reinforced concrete (SFRC) elevated slab recently built in northern Italy, this paper presents the study addressing the effects of fibre distribution and orientation. An extensive experimental programme was carried out in a collaboration between Politecnico di Milano and Universitat Politècnica de Catalunya. The programme included mechanical tests on four shallow beams and six notched standard beams. Additionally, uniaxial tensile tests (UTTs), double edge wedge splitting tests (DEWSTs) and double punching tests (DPTs) on 192 drilled core samples extracted from the shallow beams were performed. Inductive tests, measuring the self-induction change that occurs when a SFRC sample is placed inside a coil, were performed on all samples subjected to DPTs to assess fibre distribution. This paper compares direct and indirect tensile tests for the definition of the FRC post-cracking constitutive law, highlighting advantages and disadvantages of each test type. A comparison between standard and non-standard mechanical tests is also presented. Mechanical and non-destructive tests on drilled core samples extracted in different directions and at different locations have allowed the evaluation of the effects of fibre distribution and fibre orientation which provide an estimation of the possibility of using these tests as simplified tests for production control., Peer Reviewed, Postprint (published version)

The objective of this paper is to analyse the mechanical behaviour of polypropylene fibre reinforced concrete subjected to load cycles and propose a model to predict the crack-opening increase and mechanical performance evolution over the cycles. Fatigue tests were performed in pre-cracked specimens with two fibre types and contents to assess the evolution of the crack-opening for prescribed numbers of load cycles. The residual flexural tensile strength was assessed before and after these tests to estimate the impact of the cycles in the remaining resistant capacity of the specimens. Results suggest that the mechanism of crack propagation is independent of the fibre type and content. The accumulated damage due to the cycles produces an offset in the quasi-static residual tensile strength curve. These findings underpin the proposal of a model to predict the evolution of the crack-opening and the remaining resistant capacity. An optimisation procedure is proposed to derive the model parameters using a limited number of initial load cycles., The first author thanks the Brazilian National Council for Scientific and Technological Development for the scholarship granted (233980/2014-8). This research was enabled by funds provided by the SAES project (BIA2016-78742-C2-1-R) of Spanish Ministerio de Economía, Industria y Competitividad. Likewise, this work was only possible thanks to the support from the Laboratory of Technology of Structures and Materials “Lluis Agulló" of Polytechnic University of Catalonia., Peer Reviewed, Postprint (author's final draft)

The paper presents an experimental program carried out to check the load bearing capacity of a steel fibre reinforced concrete (SFRC) floor in northern Italy. The extensive mechanical characterization focused on the suitability of 3 non-standardized test methods for quality control and tensile constitutive curve assessment was performed, this consisting of: uniaxial tensile test (UTT), double edge wedge splitting test (DEWST) and double punching test (DPT) to characterize the post-cracking mechanical properties of the material. The joint experimental programme, carried out at the Politecnico di Milano and at the Universitat Politècnica de Catalunya, included the flexural characterization of four shallow beams (1.5 × 0.5 × 0.25 m3) and six standard notched beams (0.55 × 0.15 × 0.15 m3). All the samples were produced from the same batch and with the same SFRC mix which was applied for the floor. After that, 192 cores were drilled from the shallow beams and subjected to either UTTs, DEWSTs or DPTs. The stress level, the scatter and the constitutive curves derived from the non-standardized tests were identified and analysed. The calculated constitutive curves were used to predict the behaviour of the shallow beams., Peer Reviewed, Postprint (published version)

The distribution and orientation of fibers in Steel Fiber Reinforcement Self-Compacting Concrete (SFRSCC) are paramount given its influence in the mechanical properties of the material/structural elements. A two-way coupled model based on Discrete Element Method (DEM) to simulate the flow of clumps of particles with the high aspect ratio as fibers and two-phase particles as concrete is developed and introduced briefly in this paper. The framework is capable of modelling of the movement (translation and rotation) including the separation and contact detection of the particles. The interaction of the particles is treated as a dynamic process with a developing state of equilibrium whenever the internal forces are in balance. Newton’s laws of motion provide the fundamental relationship between particle motion and the forces causing that motion. Several experiments were conducted and analyzed by means of the inductive test method (a non-destructive method to assess steel fiber content and orientation). Orientation numbers coming from the inductive test method were compared with the simulation to verify the ability of the model to properly represent the flow of the fresh state SFRSCC. Through comparison with the experimental data, it is shown that the numerical model predicts the final distribution and orientation of the fibers sufficiently accurate and in a reasonable amount of time. The results obtained represent a step forward, showing that it is possible to apply advanced numerical tools for a preliminary assessment of the performance of SFRSCC, which might have positive implications through improved reliability of the design procedures., The first author thanks the AGAUR FI Catalan government for the scholarship granted (2017 FI_B 00748). Likewise, this work was only possible thanks to the support from the Laboratory of Technology of Structures and Materials “Lluis Agulló” of Polytechnic University of Catalonia., Peer Reviewed, Postprint (published version)

Fibre reinforced concrete (FRC) is recognized as suitable material for structural applications. The number of national codes that have approved it is an evidence. Structures where FRC is generally used can be subjected to fatigue loads and are expected to resist millions of cycles during their service life. Cyclic loads affect significantly the characteristics of materials and can cause fatigue failures. The most demanded cross-sections being cracked under tensile stresses due to direct loads or imposed deformations. Commonly, publications report fatigue behaviour of concrete under compression and are valid for uncracked sections. Imprecision in fatigue prescriptions are reflected through formulation of models that contemplate a probabilistic approach, or an introduction of high safety coefficients within construction codes. The aim of the present doctoral thesis is to perform a structural design oriented analysis on the behaviour of pre-cracked FRC subjected to flexural fatigue loads. FRC with steel and polypropylene fibre with different volume content were investigated by means of three-point bending tests, considering an initial crack width accepted in the service limit state. The mechanical behaviour of FRC were analysed in terms of applied load level, crack opening displacement (CMOD) and fatigue life. The residual flexural tensile strength was assessed after these tests to estimate the impact of the cycles in the remaining resistant capacity of the specimens. Results suggest that the mechanism of crack propagation is independent of the fibre type and content and the monotonic load-crack opening displacement curve might be used as deformation failure criterion for FRC under flexural fatigue loading. The conducted probabilistic approach allows predicting the fatigue strength of concrete reinforced with steel fibres. The findings postulate the proposal of a model to predict the evolution of the crack-opening and the remaining resistant capacity. An optimisation p, El hormigón reforzado con fibra (FRC) se reconoce como material adecuado para aplicaciones estructurales. El número de normativas que lo han aprobado es una evidencia. Las estructuras donde generalmente se usa FRC pueden estar sujetas a cargas de fatiga y se espera que resistan millones de ciclos durante su vida útil. Las cargas cíclicas afectan significativamente a las características de los materiales y pueden causar roturas por fatiga. Las secciones transversales más demandadas se fisuran bajo tensión debido a cargas directas o deformaciones impuestas. Comúnmente, las publicaciones informan del comportamiento de fatiga del hormigón bajo compresión y son válidas para secciones no fisuradas. La imprecisión de las recomendaciones se refleja a través de la formulación de modelos que contemplan un enfoque probabilístico o la introducción de altos coeficientes de seguridad dentro de los códigos de construcción. El objetivo de la presente tesis doctoral es realizar un análisis orientado al diseño estructural sobre el comportamiento del FRC pre-fisurado sometido a cargas de fatiga por flexión. Se investigaron FRC con fibras de acero y polipropileno con diferentes contenidos de fibras mediante pruebas de flexotracción a tres puntos, considerando un ancho de fisura inicial aceptado en el estado límite de servicio. El comportamiento mecánico del FRC se analizó en términos de nivel de carga aplicada, desplazamiento de apertura de fisura (CMOD) y vida útil bajo fatiga. La resistencia residual a flexotracción se evaluó después de los ciclos de fatiga para estimar el impacto de los ciclos en la capacidad de resistencia restante de las muestras. Los resultados sugieren que el mecanismo de propagación de fisuras es independiente del tipo y contenido de fibra y la curva monotónica de CMOD podría ser utilizada como criterio de falla de deformación para FRC bajo carga de fatiga por flexotracción. El enfoque probabilístico realizado permite predecir la resistencia a la fatiga del hor, Postprint (published version)

High performance fiber reinforced concrete (HPFRC) is recognized as suitable material for structural applications. The number of national codes that have approved it is an evidence. Structures where HPFRC is generally used can be subjected to fatigue loads and are expected to resist millions of cycles during their service life. Cyclic loads affect significantly the characteristics of materials and can cause fatigue failures. The most demanded cross-sections being cracked under tensile stresses due to direct loads or imposed deformations. Commonly, publications report fatigue behavior of concrete under compression and are valid for uncracked sections. Imprecision in fatigue prescriptions are reflected through formulation of models that contemplate a probabilistic approach, or introduction of high safety coefficients within construction codes. The aim of the present research is to perform a structural design oriented analysis on the behavior of pre-cracked HPFRC subjected to flexural fatigue loads. Seven load levels were applied by means of three-point bending tests, considering an initial crack width accepted in the service limit state. Results showed that the monotonic load-crack opening displacement curve might be used as deformation failure criterion for HPFRC under flexural fatigue loading. The conducted probabilistic approach allows predicting the fatigue strength of HPFRC cracked sections., The first author would like to thank the Brazilian National Council for Scientific and Technological Development for the scholarship granted (233980/2014-8). The development of this research has also been possible owe to the economic funds provided by the SAES project (BIA2016-78742-C2-1-R) of Spanish Ministerio de Economía, Industria y Competitividad. Likewise, this work has been possible thanks to the support provided by the Laboratory of Technology of Structures and Materials “Lluis Agulló” of Polytechnic University of Catalonia., Peer Reviewed, Postprint (author's final draft)

Studies on the diagnosis of pathologies of concrete dams are a valuable reference for professionals managing such assets. However, detailed information is rarely reported in the literature. This paper compiles the most important lessons learned during 30 years of practical experience on this area. The diagnostic procedure is illustrated through 4 of the most interesting dams analysed and monitored by the authors. All were subjected to a first stage that included inspection and analysis of historical documentation, leading to the proposal of a diagnose hypothesis. This was followed by a second stage that included an experimental programme with laboratory tests and, in some cases, numerical simulations to confirm or reject the hypothesis. The analysis of the information shows different pathologies and provide a wide spectrum of boundary conditions, symptoms and diagnoses (from internal sulphate attack and alkali-aggregate reaction to soil-structure interaction)., Peer Reviewed, Postprint (author's final draft)

A significant part of the pathologies found in concrete dams is related with the presence of unsound aggregates that react with the cement paste. Such reactions may lead to expansions, causing damage and compromising the durability of the structure. Despite of the most frequent and studied in the literature is the alkali aggregate reaction (AAR), others reactions may cause similar consequences. This is the case of the internal sulfate attack (ISA) from the use of aggregates contaminated with iron sulfides. In presence of oxygen and water these compounds oxidase releasing sulfates which react with the portlandite and aluminates of the concrete. As a result, the secondary gypsum and secondary ettringite generated lead to expansive phenomena. In spite of the increased number of studies considering ISA and its consequences, deeper insight regarding uncertainties such as how the ISA develops, its differences with respect to AAR from the diagnostic point of view, and if the ISA may occur combined with the AAR is required. In this line, specific experimental methods to predict the risk of ISA is also needed. The strategy adopted by most of the standards and guidelines limit the maximum content of iron sulfides and/or total sulfates present in the aggregate used to produce the concrete. Taking account that part of the iron sulfides do not react due to the protection of the interlocking rock, methods capable to quantify the effective amount that oxidize and is free to react with the phases present in the concrete are required. The objective of this doctoral thesis is to answer these questions providing information regarding the accelerated evaluation of the sulfates releasing from the oxidation of the iron sulfides. Likewise, deeper study of the ISA in two real damps provides evidences of its development in parallel with the AAR. The work addresses complementary aspects which include the study of different accelerated procedures to evaluate the potential reactivity of the ag, Gran parte de las patologías encontradas en las presas de hormigón están relacionadas con la presencia de áridos inadecuados que reaccionan con la pasta de cemento, dando lugar a expansiones que causan daños y comprometen la durabilidad de la estructura. Si bien la reacción más frecuente y estudiada en la literatura es la álcali-árido (RAA), existen otras que también puede causar consecuencias similares. Este es el caso, por ejemplo, de la reacción sulfática interna (RSI) ocasionada por el uso de áridos contaminados con sulfuros de hierro. En presencia de oxígeno y agua, estos compuestos se oxidan, liberando sulfatos que reaccionan con la portlandita y los aluminatos presentes en el hormigón para producir yeso secundario y etringita secundaria, dando lugar a un fenómeno expansivo. A pesar del creciente número de estudios sobre la RSI y sus consecuencias, todavía se requieren más trabajos que permitan entender cómo se desarrolla la RSI, sus diferencias con respecto a la RAA desde el punto de vista de diagnóstico y si la RSI puede producirse en combinación con la RAA. Otro punto todavía pendiente de desarrollar son los métodos experimentales específicos para evaluar el riesgo de la RSI. La estrategia adoptada por la mayoría de las normativas es limitar el contenido máximo de sulfuro de hierro y/o sulfatos totales presentes en el árido utilizado para fabricar el hormigón. Sin embargo, parte de los sulfuros de hierro presentes no reaccionan al estar protegidos por la roca encajante por lo que se requieren métodos capaces de cuantificar lo que efectivamente se oxida y queda libre para reaccionar con las fases encontradas en el hormigón. La presente tesis doctoral tiene como objetivo responder a esas cuestiones, aportando información sobre la evaluación acelerada de la liberación de sulfatos a partir de la oxidación de los sulfuros de hierro. Asimismo, se ahonda en el estudio de la RSI en 2 presas reales, aportando evidencias del desarrollo de la reacción en paralelo a la, Postprint (published version)

Design codes promote a limitation of permeability (indirectly of porosity) to reduce the sulphate ingress and improve the resistance of concrete and mortar to external sulphate attack (ESA). However, porosity could also have a positive effect on durability by generating additional space to accommodate the expansive phases. The aim of this study is to evaluate the role of porosity in ESA. For that, changes at the macro-scale, phase composition and pore network are monitored for mortar compositions with different pore-size distribution. Results indicate the existence of two mechanisms: the capacity to accommodate expansive phases controls the durability during the initial stages of the attack, while at later stages durability is defined by the permeability. Results from specimens with air-entrainer suggest that the intentional increase of porosity towards maximising the capacity to accommodate expansive products might be a valid approach in order to reduce the expansive forces generated during ESA., Peer Reviewed, Postprint (author's final draft)

Research on external sulfate attack (ESA) is usually performed on small scale specimens under free expanding conditions. However, most field structures cannot expand freely due to confinement induced by the ground or other elements from the structure. As a result, ESA usually develops in confined conditions. This work aims to assess the interaction of gradual biaxial compression stresses generated by confinement with the ESA. Visual appearance, mass and ultrasonic velocity were monitored to characterize the macro-scale behavior of free and restrained mortar samples. Changes on phase composition and crystal morphology induced by confinement were evaluated by X-Ray diffraction and scanning electron microscopy. The confining stresses generated were estimated during the attack. Results indicate that ESA is not developed equally in free and confined specimens. The confinement limits sulfate availability, reduce the amount of ettringite precipitated and might induce changes on crystal morphology that reduce the degradation caused by the ESA., Peer Reviewed, Postprint (author's final draft)

Sprayed materials must present short setting times and a fast early strength development for safety and productivity reasons. In order to improve these characteristics, the construction industry has focused on the development of new formulations of accelerators. Research and improvement of other components of the mix, such as cement or additions, have not advanced at the same rate despite being also crucial for the reaction kinetics. The objective of this work is to evaluate the influence of gypsum content on the hydration and mechanical strength development in sprayed mixes. Sprayed pastes and mortars were prepared with one type of cement, two types of accelerators and different gypsum contents. Kinetics, mechanisms of hydration and mechanical properties were evaluated. Results showed a better performance in sprayed mixes that contain ideal doses of gypsum. Such approach provides valuable information for the improvement of the formulation of cement used in sprayed concrete applications., Peer Reviewed, Postprint (author's final draft)

The durability of concrete mixes with EAF slag as aggregate (HS) is studied; mixes with limestone (HC) and barite (HAB) aggregates were used as reference for structural and heavy-weight applications, respectively. Compressive strength, elastic modulus, water penetration under pressure, wet-dry cycles, freeze-thaw cycles, influence of environmental condition and leaching tests were conducted. The results indicate that HS tends to present higher depth of water penetration under pressure, a slightly higher expansion, higher carbonation depth and similar compressive strength than reference HC. Should be payed attention to the formation of stain points on HS concrete surface subjected to wet-drying cycles., Peer Reviewed, Postprint (author's final draft)

Improvements in concrete technology, reinforcing systems and manufacturing enable the use of longer reinforced precast concrete girders, contributing to the competitiveness of this solution for bridge decks. The weight of the girders should be limited in order to achieve an optimum between span length, transportation costs and lifting costs. The current tendency in design is to minimize the width of the flanges of the girder. This makes the element more flexible to lateral deformation and increases the risk of lateral instability in temporary situations without lateral supports. This is reflected in an increment of the number of accidents and damages associated with such phenomenon. The main objective of this study is to describe a real case study of lateral instability of a 46¿m long prestressed concrete girder during lifting operations as well as to perform a parametric study to understand the limits of the problem observed. In addition to presenting the case study, simplified formulations and numerical simulations are used to assess the safety margins against lateral instability. Special attention is paid to the evaluation of the provisions gathered in codes and guidelines regarding the lateral stability since they might not cover extreme cases., Peer Reviewed, Postprint (author's final draft)

The final publication is available at Springer via http://dx.doi.org/10.1617/s11527-018-1156-5, Sprayed steel fibre reinforced concrete (SSFRC) is a material that tends to present anisotropy, due to the action of the spraying process inducing preferential fibre orientation. Despite numerous applications worldwide since the 1980s, no study has been found of the assessment of fibre distribution and its influence on the residual tensile strength of SSFRC. This work addresess this issue from a quantitative standpoint through an experimental programme with specimens extracted in various orientations within a SSFRC panel. The fibre content and 3D orientation were quantified using the inductive method and correlated with an indirect tensile behaviour for the same specimen with the Barcelona test. The results confirm the high level of anisotropy of SSFRC. The fibre orientation number parallel to the spraying direction is three times bigger than that found in the perpendicular direction. Similar differences were observed between the residual tensile response measured in those directions. Comparison of test results suggest that the preferential fibre orientation creates weaker planes that favours the increase of crack opening at lower load levels., Peer Reviewed, Postprint (author's final draft)

The construction and conservation of road networks represent a major part of public expenditure. For instance, the EU-28 countries annually spend approximately EUR 20.000 million on roadway preservation. These figures highlight the need to develop more efficient methods for the design, construction and maintenance of pavements. Concrete pavements, including both new construction and strengthening (whitetoppings and overlays), offer many advantages over bituminous ones. These advantages provide more cost-effective and environmentally sustainable solutions. This is because their longer lifetime, lower cost at the long term, the capacity to reduce fuel consumption, etc. Nevertheless, some countries such as Spain have no tradition in the use of concrete as a road construction material. This is confirmed by the fact that more than 99% of the roads belonging to the “Red de Carreteras del Estado” (National Highway Network) are asphalt roads. Consequently, technicians are not committed to implement the use of concrete and asphalt pavements tend to be perpetually applied. The limited application of concrete pavements at the state level might be explained due to limitations in pavement-design software and the low availability of specialized machinery, among other causes. Furthermore, whitetoppings and overlays present inherent uncertainties related to the interfacial bond strength that may have a negative effect on the structural performance and make its use even more difficult. This doctoral thesis addresses these aspects with the global objective of facilitating the use of concrete in both newly constructed pavements and road preservation. To this end, a cross-sectional study work has been conducted, involving the development of a new pavement calculation software, an experimental program and the construction of four real-scale pavements. The software allows the design and checking of multilayer pavements adopting different calculation methodologies depending on the structu, La construcción y el mantenimiento de las redes viarias suponen una parte importante del gasto público. Por ejemplo, los 28 países de la Unión Europea destinan anualmente unos 20.000 millones de € al mantenimiento de sus carreteras. La magnitud de estas cifras indica la necesidad de dedicar esfuerzos a obtener mejoras en el diseño, la construcción y la reparación de firmes. Los pavimentos de hormigón, tanto de nueva construcción como de reparación de firmes asfálticos (whitetoppings) y rígidos (overlays), tienen una serie de ventajas respecto a los bituminosos que permiten obtener soluciones más económicas y medioambientalmente sostenibles. Ello se debe a su mayor vida útil, su menor coste a largo plazo, su capacidad para reducir el consumo de carburante de los vehículos pesados, etc. Sin embargo, en países como España apenas hay tradición de uso del hormigón como material para la construcción de carreteras, dato que corrobora el hecho de que más del 99% de la Red de Carreteras del Estado está construida con firme asfáltico. Ello hace que los técnicos apenas contemplen el hormigón como una alternativa real, perpetuando así el uso del asfalto como material predominante. La escasa aplicación a nivel estatal de los pavimentos de hormigón puede explicarse por, entre otras causas, las limitaciones de los programas de diseño y la poca disponibilidad de maquinaria especializada. Además, en la construcción de whitetoppings y overlays existen también incertidumbres asociadas a la resistencia mecánica de su interfase con el firme reparado, que pueden afectar negativamente al desempeño estructural y dificultar todavía más su uso. Esta tesis doctoral afronta estos aspectos con el objetivo general de facilitar el uso del hormigón en pavimentos de nueva construcción y en la reparación de firmes existentes. Para ello se ha realizado un extenso trabajo transversal que comprende el desarrollo de un nuevo programa de cálculo de pavimentos, una campaña experimental a escala de laborat, Postprint (published version)

The shrinkage of concrete and the current methods to mitigate this phenomenon are mainly based on the realization of retraction joints approximately 24 hours after the mixing. These joints represent a critical point in the pavements due to the fact that they can trigger pathological processes. These processes go from the rupture of the lips of the joint to the filtration of substances that can be harmful to the concrete. The different pathologies arising from the realization of the joints, as well as the concrete cracking of the concrete have raised the use of materials with compensated shrinkage in order to reduce the number of joints and mitigate the cracks that appear in the element. In this doctoral thesis the effect of the addition of CaO to the cemetícia mixture for the realization of compensated shrinkage concretes (SCC) has been studied. The first line of research is based on the study of the chemical interaction between cement and lime, considering the variation of three main variables such as the ratio w/c, the percentage of lime added and the type of lime used. The results have shown that there is a synergy between cement and lime during hydration, as well as competition during the hydration of CaO with some of the phases present in the cement. Likewise, the addition of lime modifies the setting times of the different mixtures studied, generating mixtures that set in a shorter time than a cement paste without the addition of lime. The second line of research has shown the impossibility of measuring the expansion process that occurs in this type of material during the first 24 hours after mixing by using standardized tests. The obtained results indicate that both the process of expansion and the generation of tensions occur, mainly, during this period of time. Due to this fact it has been necessary to propose new tests in order to characterize both processes. The method of the mixed mould has allowed to determine the influence of the addition of lime in mo, La retracción del hormigón y los métodos actuales para mitigar este fenómeno se basan principalmente en la realización de juntas de retracción a las 24 horas, aproximadamente, del amasado de la mezcla. Estas juntas representan un punto crítico en los pavimentos debido a que pueden llegar a desencadenar procesos patológicos que van desde la rotura de los labios de la junta hasta la filtración de sustancias perjudiciales para el hormigón. Las distintas patologías surgidas de la realización de las juntas, así como de la fisuración propia del hormigón han planteado el uso de materiales con retracción compensada para poder reducir la cantidad de juntas y mitigar las fisuras que aparecen en el elemento. En esta tesis doctoral se ha estudiado el efecto de la adición de CaO a la mezcla cemetícia para la realización de hormigones de retracción compensada (HRC). La primera línea de investigación se ha basado en el estudio a nivel de interacción química entre el cemento y la cal, contemplando la variación de tres variables principales como son la relación a/c, el porcentaje de cal añadido y el tipo de cal usado. Los resultados han evidenciado que existe una sinergia entre el cemento y la cal durante su hidratación, así como una competencia durante la hidratación del CaO con algunas de las fases presentes en el cemento. Así mismo, la adición de cal modifica los tiempos de fraguado de las distintas mezclas estudiadas, generando mezclas que fraguan en un tiempo menor al de una pasta de cemento sin adición de cal. La segunda línea de investigación ha dejado patente la imposibilidad de medir el proceso de expansión que se da en este tipo de materiales durante las primeras 24 horas posteriores al mezclado mediante ensayos normalizados. Los resultados obtenidos indican que tanto el proceso de expansión como el de generación de tensiones se dan, principalmente, durante este período de tiempo, por lo que ha sido necesario plantear nuevos ensayos de diseño propio para poder caracterizar, Postprint (published version)

Concrete dams with expansions from different origins are rare and scarcely documented in the literature, therefore their study gains special interest. This study presents the case of a 62-year-old concrete dam with signs of deterioration due to expansive reactions. Several tests performed on the samples extracted from the dam such as X-ray diffraction, scanning electron microscope with energy dispersive spectroscopy mode and petrography suggest that the expansions are due to a delayed ettringite formation and a subsequent alkali-silica reaction. Thermal and mechanical models developed in the study support this diagnosis., Peer Reviewed, Postprint (author's final draft)

Las mejoras tecnológicas de la prefabricación con hormigón han hecho competitivo el uso de vigas prefabricadas de luces cada vez mayores en comparación con otras alternativas. Sin embargo, el peso de las vigas es limitante en las operaciones de izado y transporte, por lo que se tiende a reducir el ancho de las alas, produciendo elementos más propensos a la inestabilidad lateral. En este artículo se describe un caso de estudio real de inestabilidad lateral de una viga pretensada de puente de gran luz y realizar un estudio paramétrico. Se analizan las actuales provisiones del Código Modelo 2010 y se muestra que pueden resultar inseguros en casos límites., Peer Reviewed, Postprint (author's final draft)

High performance steel fibre reinforced cementitious composites (HPSFRCCs) show enhanced structural performance and durability. The improved properties favour its use in agressive conditions (such as marine environment) prone to corrosion. Despite the remarkable advances in the knowledge about corrosion of conventional reinforced concrete structures, questions still remain about its effects on the durability of HPSFRCC. The governing mechanisms of corrosion, the presence of cracks, the high steel fibre content, and the long-term chloride exposure still need to be properly evaluated. Given the increased application of HPSFRCC with structural responsibility and the high steel fibre content commonly used in the mixes, it is of great importance to understand the main mechanisms governing the chloride corrosion and its effects on the durability of the real-scale structures constructed with the material. To overcome these barriers and the uncertainty mentioned, this doctoral thesis adresses the following key issues: the effect of chlorides in uncracked HPSFRCCs under constant conditions; the influence of chloride corrosion in uncracked HPSFRCCs under wet-dry cycles with chlorides; the effect of corrosion in pre-cracked HPSFRCCs subjected to the same cycles and the proposal of a simplified model to consider the structural effects of corrosion. The first subject concerns the assessment of chloride corrosion on the aesthetic aspect and on the mechanical behaviour of HPSFRCCs by means of an accelerated test. For that, HPSFRCCs specimens with and without chlorides added to the mixes and with different fibre contents were tested. The preliminary experimental programme shows that, in general, the chlorides produce a level of surface corrosion with aesthetic consequences but have small influence on the mechanical performance. In the second subject, the influence of cycles was assessed in accelerated tests with uncracked HPSFRCCs prisms. The results reveal that, for uncracked HPSF, Los compuestos cementicios de alta resistencia reforzados con fibra de acero (CCARRFA) muestran un mayor rendimiento estructural y durabilidad. Las mejoras en las propiedades del CCARRFA debido a la inclusión de fibras de acero favorecen su uso en condiciones agresivas (tales como el ambiente marino) propensas a la corrosión. A pesar de los notables avances en el estudio de la corrosión de estructuras de hormigón armado, aún quedan cuestiones sin resolver respecto a sus efectos en la durabilidad del CCARRFA. En relación a ello, los mecanismos que gobiernan la corrosión, la presencia de fisuras, el alto contenido de fibra de acero y la exposición prolongada a los cloruros deben ser evaluados adecuadamente. Dado el aumento de la utilización de CCARRFA con responsabilidad estructural y el alto contenido de fibra de acero comúnmente utilizado en las mezclas, resulta de gran importancia comprender los principales mecanismos que gobiernan la corrosión, así como sus efectos en la durabilidad de estructuras a escala real construidas con este material. Para superar estas barreras y las incertidumbres mencionadas, esta tesis doctoral tratará los siguientes aspectos clave: el efecto de los cloruros en CCARRFA no fisurado en condiciones constantes; la influencia de la corrosión por cloruros en CCARRFA no fisurado sometido a ciclos de mojado y secado con cloruros; el efecto de la corrosión en CCARRFA fisurados sometidos a los mismos ciclos y una propuesta de modelo simplificado para considerar los efectos estructurales de la corrosión. El primer aspecto aborda la evaluación de la corrosión por cloruros desde un punto de vista estético y del comportamiento mecánico del CCARRFA mediante un ensayo acelerado. Para ellos, se han ensayado probetas de CCARRFA con y sin cloruros añadidos a las mezclas con diferentes contenidos de fibra. La campaña experimental preliminar mostró que, en general, los cloruros producen un nivel de corrosión superficial con consecuencias estéticas, pero con, Postprint (published version)

Sprayed cementitious materials are widely used in the construction industry, from buildings to infrastructure. The process of construction consists of spraying a concrete mix that consolidates once it reaches the substrate. The sprayed mix must have an adequate consistency and setting time to enable the build-up of layers with proper thicknesses. To reduce the setting times and increase the early strength of the matrix, accelerators are commonly employed. These chemicals alter cement hydration, affecting the mechanical properties at short and long term. Despite the recent advances on the field of sprayed cementitious materials, several topics still require further studies. For instance, the properties of the sprayed material depends on the cement-accelerator compatibility. Research and industrial development have focused on the improvement of accelerators, paying little attention to the improvement of cements. Moreover, few studies are found in the literature about the durability of sprayed cementitious materials with accelerator. One of the areas of concern is the external sulfate attack (ESA). The use of sulfate resistant cements might not be enough to guarantee the durability given the particular microstructure of the sprayed cementitious material and the additional content of aluminum provided by accelerators. This study extends the knowledge in this field through the following objectives: evaluate the compatibility cement-accelerator considering the inclusion of addition gypsum and evaluate the durability of sprayed mixes exposed to ESA. The first part of the research focuses on the study of the compatibility between typical cements and accelerators applied in sprayed mixes from chemical and mechanical standpoints. The experimental campaign performed highlights the importance of a proper sulfate content in the positive evolution of the mechanical properties. Continuing in this line, the second part of the research focuses on the influence of the gypsum content, Las proyecciones de materiales cementicios son ampliamente utilizadas en la industria de la construcción, desde edificación hasta obra civil. El proceso constructivo consiste en proyectar una mezcla de hormigón que se consolide una vez alcanzado el substrato. La mezcla debe tener una consistencia y tiempo de fraguado óptimos para ser capaz de formar capas con espesores adecuados. Para reducir el tiempo de fraguado e incrementar las prestaciones a edades tempranas, los acelerantes son comúnmente empleados en el hormigón proyectado. Estos aditivos alteran la hidratación del cemento, afectando las propiedades mecánicas a corto o largo plazo. A pesar de los recientes avances en el campo de los materiales proyectados, muchos temas aún requieren más estudios. Por ejemplo, las propiedades del material proyectado dependen de la compatibilidad cemento-acelerante. Las investigaciones y el desarrollo industrial han enfocado su esfuerzo en el mejoramiento de los acelerantes, poniendo poca atención a la mejora de los cementos. Además, pocos estudios se han encontrado acerca de la durabilidad de materiales cementicios proyectados con acelerantes. Una de las áreas a enfocar la atención es el ataque sulfatico externo (ASE). El uso de cementos sulforresistentes pueden no ser suficientes para garantizar la durabilidad, debido a la particular microestructura de las matrices proyectadas y al contenido adicional de aluminio de los acelerantes. Este estudio extiende el conocimiento en este campo a través de los siguientes objetivos: evaluar la compatibilidad cemento-acelerante considerando la inclusión de yeso adicional y evaluar la durabilidad de las mezclas expuestas al ASE. La primera parte de esta investigación se enfoca desde puntos de vista químicos y mecánicos en el estudio de la compatibilidad entre cementos típicos y acelerantes aplicados en mezclas proyectadas. La campaña experimental realizada muestra la importancia del contenido de sulfatos en la evolución positiva de las pro, Postprint (published version)

There are very few methods that can be used for the assessment of pavement conditions. Their application to urban networks tends to be complex, given the wide variety of urban pavement types (concrete, asphalt, and paving tiles) and their different functions (traffic, pedestrian, or both). A flexible method that can address the complexity of different areas is therefore proposed in this paper through a case study of pavement conditions. Hence the interest of this new approach for pavement management that employs a multi-criteria method adaptable to various urban environments: the Integrated Value Model for Structural Assessment (MIVES). It incorporates the Value Function (VF) concept in an Analytic Hierarchy Process (AHP), combining both Multi-criteria Decision Making and Multi-Attribute Utility Theory. The methodology is presented and its sensitivity is evaluated by means of a case study in the city of Barcelona. The quality index of various pavements is assessed through a survey of pavement distresses in a systematic categorisation of urban network pavement categories that is accurate, consistent, and repeatable, Peer Reviewed, Postprint (author's final draft)

El uso del hormigón reforzado con fibras (HRF) para la producción de dovelas para túneles construidos mediante tuneladora es una tendencia que ha ido creciendo con los años. Sin ir más lejos, a día de hoy se han construido más de 50 túneles con este material estructural, usando en algunos de los casos únicamente fibras como refuerzo. Diversas guías de diseño (p. ej. fib Model Code 2010) ya incluyen el HRF como material estructural. Además, existen también algunas guías específicas que contemplan el diseño de dovelas prefabricadas de HRF (p. ej. ITAtech Report/7-15 y ACI 544.7R-16). Estas guías tratan el aspecto de diseño del HRF considerando el formato de seguridad tradicional de los Estados Límite. Así pues, se consideran coeficientes parciales de seguridad tanto para las cargas (γQ) como para las resistencias de los materiales (γM). En particular, la magnitud del γM considerado es el mismo tanto para esfuerzos a compresión como a tracción. Sin embargo, esta suposición puede ser poco realista, sobretodo en términos de resistencia residual a flexotracción (fR), ya que esta propiedad presenta una dispersión mayor que la de la resistencia a compresión (fc). Este suceso se acentúa con elementos con una superficie de rotura reducida (p. ej. vigas) debido al gran impacto que las incertidumbres del material como la orientación y distribución de las fibras tienen sobre la variabilidad de fR. Consecuentemente, esta suposición puede llevar a índices de fiabilidad (β) más bajos que los establecidos para estructuras de hormigón con armado tradicional. Aun así, esta variabilidad tiende a reducirse cuando el ancho de la sección fisurada aumenta (p. ej. losas). En este trabajo se presentan los resultados de un análisis de fiabilidad estructural realizado para calibrar el coeficiente parcial de seguridad de fR. Para ello se han considerado ensayos a escala real a flexotracción ejecutados sobre dovelas prefabricadas con diferentes dimensiones, cantidades y tipos de fibra. Además, s, The use of fibre reinforced concrete (FRC) to produce segmental linings of TBMconstructed tunnels is an increasing tendency. So far, more than 50 tunnels have been constructed with this structural material, in some of these even using solely fibres as reinforcement. Moreover, several design guidelines (e.g., fib Model Code 2010) already include the FRC as structural material. There also exist specific guidelines for the design of FRC precast segment linings (e.g., ITAtech Report/7-15 and ACI 544.7R-16). These guidelines deal with the design of FRC considering the traditional limit state safety format. Therefore, partial safety factors for both the loads (γL) and material strengths (γM) must be considered. In particular, the magnitude of γM considered for compressive and tensile FRC strengths are assumed to be the same. Nonetheless, this assumption can be unrealistic, particularly in terms of flexural residual strength (fR) since this property presents higher scatter than the compressive strength (fc). This is particularly true for elements with a reduced cracking surface (e.g., beams) due to the higher impact that uncertainties like fibre orientation and distribution have on the variability of fR. Therefore, this assumption can lead to lower reliability indexes (β) than those established for traditional reinforced concrete structures. However, this variability tends to decrease with the increase of the width of the cracked sections (e.g., slabs). The results of a structural reliability analysis carried out to calibrate the partial safety factor for fR are presented. Full-scale bending tests on precast segments with different dimensions, amounts and type of fibres were considered. Furthermore, the scatter variability of FRC due to the size effect has been studied.

In order to evaluate the fatigue behaviour of Ultra-High Performance steel Fibre Reinforced Concrete (UHPFRC) in bending an experimental campaign with prismatic specimen of 75 x 75 x 275 mm was carried out. Fatigue tests were performed considering four different values for the upper limit of the applied load (S): 65%, 70%, 75% and 80% of the maximum strength obtained through the bending test. The results of the fatigue tests were analysed as a function of the crack mouth opening displacement (CMOD) and total number of cycles (N), as well as with Wöhler curves (S-N curves). In addition, the results considered the crack opening range and the toughness of the material. It was observed that when subjected to cyclic loadings of 65% and 70%, the residual strength of the specimens appears to be unaffected even after they are cracked. Through analytical relations, it can be verified that the cracked specimens of UHPFRC behave as a rigid solid. The obtained results suggest that the fatigue strength limit of UHPFRC is about 67% of the maximum flexural strength, which is in agreement with the literature., Postprint (published version)

Las mejoras tecnológicas de la prefabricación con hormigón han hecho competitivo el uso de vigas prefabricadas de luces cada vez mayores en comparación con otras alternativas. Sin embargo, el peso de las vigas es limitante en las operaciones de izado y transporte, por lo que se tiende a reducir el ancho de las alas, produciendo elementos más propensos a la inestabilidad lateral. En este artículo se describe un caso de estudio real de inestabilidad lateral de una viga pretensada de puente de gran luz y realizar un estudio paramétrico. Se analizan las actuales provisiones del Código Modelo 2010 y se muestra que pueden resultar inseguros en casos límites., Postprint (published version)

The objective of this paper is to evaluate the influence of sulfate exposure on the pore network development of several Portland cement matrices. MIP, XRD and SEM analysis were performed at different ages in samples exposed to sulfates after 2 days of casting. Results suggest that patterns of precipitation of the expansive products are linked to the degree of refinement of the pore network. During early stages of exposure, large pores concentrate a higher proportion of the expansive product formed. At later stages, precipitation evolves towards finer pore sizes., Peer Reviewed, Postprint (author's final draft)

Underground structures and foundations, including piles, constructed with reinforced concrete may be in contact with sulphate-rich soils and water. Structural elements exposed to these conditions may be affected by an expansive process known as external sulphate attack (ESA) that generally leads to an increase in volume, hence displacements and cracking of the concrete. The most widely accepted approach to mitigate such problems is to use cement(s) with a small content of aluminates. The objective of this research was to assess the potential damage induced by ESA using a simplified analytical model that is able to consider parameters such as the cement content and size of the pile, which may also affect the risk of damage. A parametric study was performed with different pile sizes and aluminate and cement contents. The structural integrity of the elements was verified considering a life span of 50 years and three possible failure modes (tensile failure in the core, and shear or tensile failure in the interface between the damaged and undamaged regions). The results suggest that the recommendations based solely on the maximum aluminate content present in the cement are inaccurate and might lead to very different outcomes depending on the characteristics of the elements. The study indicates that other parameters should also be taken into account in order to reduce the risk of ESA in real structures, such as the size of the element or the cement content per unit volume of concrete. This work has implications for the design of pile foundations in ground conditions prone to sulphate attack., Postprint (published version)

The Barcelona test (BCN) is an alternative method to characterize the post-cracking behaviour of fibre reinforced concrete (FRC). Given its simplicity, the reduced scatter of the results and low material consumption, the BCN may represent a suitable method for the quality control of FRC. For that, a correlation between the results of the BCN and the bending test is currently required since the latter is considered the reference for the characterization of the material and for deriving the constitutive design equations. The objective of this paper is to propose such correlation following an approach that takes into account the intrinsic variability of FRC. An experimental program involving 21 mixes of conventional and self-compacting FRC with either steel or plastic fibres was performed. Several analyses were conducted both for selecting the most relevant parameters and for maximizing the degree of correlation between the tests. The highest correlation coefficient between tests was obtained for the mixes with plastic fibres. In such case, the formulation proposed is able to predict the results with accuracy up to 75%. The correlation found is an interesting tool towards a simple and reliable quality control of FRC based on the BCN mainly oriented to large scale concrete production., Peer Reviewed, Postprint (published version)

The superadobe is a construction technique that consists on building using bags filled with soil and adding barbwire between the courses. It is a simple, durable, sustainable, and affordable technique that has increased in popularity over the last years. Moreover, a remarkable effort was performed in the past years in order to analyse the structural behaviour and characterize the mechanical properties of these constructions. However, since it is a relatively recent technique, no previous studies of complete structures have been performed using numerical strategies and there is still a lack of knowledge regarding its structural response. Consequently, the present thesis attempts to analyse these type of structures using the finite element method, assessing its suitability and applicability to the superadobe. For this purpose, several models of both walls and arches are studied, subjected to different load dispositions and considering three construction types, plain, adding barbwire and stabilizing the infill. Initially two possible constitutive models are considered, Mohr Coulomb and Total strain crack based, and they are evaluated and compared in order to select the most suitable for all the cases studied. Afterwards, all the analyses are performed and calibrated to match the results obtained from the experimental campaigns developed in the University of Bath by Pelly (2009), Vagdama (2010) and Croft (2011). Finally, a sensitivity analysis is also carried out to examine the influence of certain parameters, which had to be adjusted during the analyses, into the structural response of the models., El superadobe es una solución constructiva que consiste en la utilización de bolsas rellenas de tierra apisonadas a las que se les añade alambre de espino entre ellas para aportar cohesión y Resistencia a tracción al conjunto. Es una técnica simple, duradera, sostenible y asequible cuya popularidad ha ido creciendo durante los últimos años. Además, recientemente se ha realizado un notable esfuerzo con el fin de analizar el comportamiento estructural y determinar las propiedades mecánicas del superadobe. No obstante, al tratarse de una técnica relativamente nueva, no se han desarrollado aún estudios de estructuras completas utilizando estrategias numéricas, y existe todavía una carencia de información en lo que respecta a la respuesta estructural de estas construcciones. Por consiguiente, la presente tesis tiene como objetivo el análisis de estas estructuras utilizando el método de los elementos finitos, evaluando su compatibilidad y aplicabilidad al superadobe. Con este fin, se estudian varios modelos, tanto de muros como de arcos, sujetos a diferentes disposiciones de carga y considerando tres tipos de construcción, simple, añadiendo alambre de espino y estabilizando el relleno de las bolsas. Inicialmente se consideran dos posibles modelos constitutivos, Mohr Coulomb y Total strain crack based, se evalúan y comparan a fin de seleccionar el que más se adecúa a todos los casos estudiados. Posteriormente, se llevarán a cabo y calibrarán todos los análisis para hacer coincidir los resultados con los obtenidos en las campañas experimentales desarrolladas en la Universidad de Bath por Pelly (2009), Vagdama (2010) y Croft (2011). Finalmente, también se realizará un estudio de sensibilidad para examinar la influencia de ciertos parámetros, que han debido ser ajustados durante los análisis, en la respuesta estructural de los modelos.

A través de los años se ha visto de manera muy notable la utilización de mezclas proyectadas para diferentes tipos de construcción, como túneles, refuerzo de taludes, además de construcción de viviendas proyectadas, entre otras. Se ha dado la necesidad de seguir estudiando su comportamiento debido al incremento rápido y continúo de este material, siendo utilizado en áreas y volúmenes cada vez mayores. La presente investigación está fundamentada en una campaña experimental centrada a estudiar las diferentes propiedades mecánicas y físicas del hormigón proyectado, en este caso, su anisotropía y homogeneidad, y ver la influencia que existe en la dirección perpendicular al proyectado, además de analizar la zona localizada entre el refuerzo de barras para ver el impacto generado por el efecto sombra al momento de proyectar el hormigón y la adherencia de barras. Para ello fue necesaria la extracción de muestras proyectadas de la obra en construcción “Túnel B-40 Viladecavals”, en artesas con diferentes características, utilizando el equipo de hormigón proyectado del túnel, y obteniendo una serie de muestras que han sido analizadas con diferentes ensayos con equipos especializados y las normas adecuadas para obtener diferentes características del hormigón proyectado como adherencia, ultrasonidos, módulos de elasticidad, resistencia a compresión y densidades. Con los resultados obtenidos podremos ver la influencia que se genera en la dirección perpendicular, la influencia del efecto que existe en el hormigón localizado entre barras llamado “efecto sombra” y además hacer comparativas con un hormigón proyectado con probetas verticales y comparar también con un hormigón convencional., Over the years, the use of mixtures designed for different types of construction, such as tunnels, reinforcement of slopes, as well as construction of projected dwellings, among others, has been very noticeable. It has been necessary to continue studying its behavior due to the rapid and continuous increase of this material, being used in areas and volumes increasing. The present investigation is based on an experimental campaign focused on studying the different mechanical and physical properties of the projected concrete, in this case, its anisotropy and homogeneity, and to see the influence that exists in the direction perpendicular to the projected one, besides analyzing the localized zone between the reinforcement of bars to see the impact generated by the shadow effect at the time of projecting the concrete and the bond stress. To do this, it was necessary to extract projected samples from the construction site "Tunnel B-40 Viladecavals", in troughs with different characteristics, using the concrete equipment projected from the tunnel, obtaining a series of samples that have been analyzed with different tests with specialized equipment and appropriate standards to obtain different characteristics of the projected concrete such as bond stress, ultrasound velocity, modulus of elasticity, compressive strength and densities. With the results obtained we can see the influence that is generated in the perpendicular direction, the influence of the effect that exists in the concrete located between bars called "shadow effect" and also make comparative with a projected concrete with vertical specimens and also compare with a concrete conventional.

Improvements in concrete technology, reinforcing systems and manufacturing processes enable the use of increasingly long reinforced precast concrete girders, contributing to the competitiveness of girders in concrete in comparison with other alternatives. The weight of the girders should be limited however, in order to achieve an optimum between span length and lifting and transportations costs. The current tendency in design is to minimize the width of the flanges, thus the girder becoming more flexible laterally and more prone to suffer instability phenomena during transient loading situations. An increasing number of accidents and damages associated with this instability problem are reported in the technical literature (e.g., Hurff 2010; Rose 2013). The main objective of this study is to describe a real case of lateral instability of a long prestressed concrete bridge girder during lifting as well asto perform a parametric study to understand the limits of the problem observed. Special attention is paid to the evaluation of the provisions gathered in the Model Code 2010 (MC - 2010) regarding the lateral stability, since these might not be sufficient to cover limit cases., Peer Reviewed, Postprint (author's final draft)

A bonded concrete overlay consists of a concrete layer poured over a deteriorated pavement. Its mechanical performance depends on the quality of the bond between the lower and the uppermost layers. This paper reports an extensive experimental program to evaluate bond strength between Conventional Concrete (CC) and Asphalt Concrete (AC) substrates and Self-Compacting High-Performance Concrete (SCHPC) overlays. In all, 8 interface treatments are tested under Direct Tension, pure shear “LCB”, and compressive Slant Shear tests. The results show that direct pouring of the SCHPC overlay over CC and AC substrates produces similar or higher strengths than the other treatments analyzed., Peer Reviewed, Postprint (author's final draft)

Sprayed concrete is widely used as structural support for underground constructions. Although the sprayed concrete technology advanced significantly over the past years, questions continue to arise regarding its performance, efficient use and optimized design. One of the main subjects that requires further research is the behavior of sprayed cement matrices containing accelerators at low temperature, since the application of sprayed concrete may be hindered in regions with cold weather due to the difficulties to fulfill the requirements of fast setting and early age strength development under such conditions. Understanding the behavior of set accelerator at low temperature can provide useful information for predicting mechanical strength evolution and identifying the most efficiency mix proportions for real practice and constructions. In this context, a study of Vicat test and calorimetry test covering the main factors, which affect the behavior of cement matrices, including temperature, types of cement, types of set accelerator and content, was launched. About the Vicat test, four different temperature degrees: 20⁰C, 15⁰C, 10⁰C, 5⁰C were compared, for cement matrices, two types of cement: CEM I and CEM II were used, four types of set accelerator: ALNA73, AKF63, AKM55, AKF125 were added, with two dosages: 5% and 7%, excepting for mixes with ALNA73 which using a typical 3% content for alkaline based type. The composition of cement matrices for calorimetry test is the same with Vicat test, however experiments for mixes at 5⁰C was unable to reach due to some technical problem. The factor temperature; results from Vicat test present that low temperature delay the setting time of cement matrices in absolute terms, the alkaline accelerator, ALNA73 shows a general better performance over alkali-free set accelerators for cement matrices at low temperature. In relative terms alkali-free accelerator AKM55 and AKF125 are the most efficient accelerators, since they experience a

This paper focuses on the characterization of setting and hardening of accelerated cementitious matrices by ultrasound propagation velocity, correlating these processes with chemical parameters and the phase evolution obtained by in situ XRD. Evolution of temperature and determination of setting times complemented this analysis. The technique employed provided a continuous monitoring of the setting and hardening of the hydrating matrix and was susceptible to changes in accelerator reactivity and phase composition. Results showed that ettringite formed by accelerator reaction improves the solid-phase interconnectivity and increases initial ultrasound velocity. P-wave propagation during the acceleration period is directly proportional to alite and C3A degrees of hydration. The influence of AFm phases to increase ultrasound velocity is stronger than ettringite and C-S-H. Based on an extensive statistical analysis, multivariate linear regressions were established between ultrasound velocity and the main chemical properties influencing its evolution, leading to a better comprehension of how these parameters are related., Peer Reviewed, Postprint (author's final draft)

Los pavimentos pueden representar más de la mitad de la superfi cie del espacio público de las ciudades, por lo que su preservación y mantenimiento requieren de una gestión adecuada. Debido a que éstos tienen infl uencia sobre la calidad de vida de los ciudadanos, también pueden considerarse una gran fuente de oportunidades para la transformación de las ciudades. El uso de hormigones con propiedades mejoradas en la pavimentación de las ciudades puede añadir nuevas funcionalidades a los fi rmes, las cuales tienen aplicación evidente en las smart cities. En este trabajo se muestra una visión global sobre la gestión de los pavimentos urbanos, mostrando algunas de las tendencias más actuales para su reparación mediante el uso de hormigón. El trabajo se ha estructurado en tres bloques. En el primero de ellos se presentan el uso de índices de estado de pavimentos como estrategia de mantenimiento y los refuerzos de tipo whitetopping como una solución constructiva óptima para el refuerzo y la rehabilitación de fi rmes. En el segundo bloque se describe la contribución de los fi rmes rígidos en la mitigación de los efectos de las islas de calor en las ciudades y cómo plantear su diseño para optimizar la absorción, almacenamiento e irradiación de calor. Finalmente, en el último bloque se presentan algunas de las últimas innovaciones en el ámbito de los hormigones para pavimentos de smart cities. Estas mejoras signifi cativas en las prestaciones y estrategias de mantenimiento de los pavimentos podrían situar a las empresas que aportan estas tecnologías en el papel protagonista que actualmente ejercen las empresas de construcción, lo que podría derivar en un cambio de paradigma en el sector., Postprint (published version)

The flexural creep of plastic fiber reinforced concrete (PFRC) is a controversial issue since significant doubts regarding the suitability of this type of fiber and its influence in the long-term behavior of the material still exist. The objective of this paper is to evaluate the post-cracking creep response of PFRC beams under flexural load in comparison with that of steel fiber reinforced concrete (SFRC) beams. The aim is to explore how the pre-crack opening and the environmental condition affect the long term behavior of each material and identify differences. An experimental program was conducted with 30 concrete beams with dimension of 150 × 150 × 600 mm reinforced with plastic or steel fibers subjected to a 4-point bending creep test for 5 months under 2 environmental conditions. Results showed that the flexural creep coefficient of PFRC is 2 times bigger than that of SFRC. Despite that, the use of plastic fibers as reinforcement should not be rejected as long as the additional creep is considered in the design and the crack widths are limited to reduce the risk of tertiary creep., Peer Reviewed, Postprint (author's final draft)

The use of fibre reinforced concrete (FRC) to produce segmental linings of TBM-constructed tunnels is an increasing tendency. So far, more than 50 tunnels have been constructed with this structural material, in some of these even using solely fibres as reinforcement. Moreover, several design guidelines (e.g., fib Model Code 2010) already include the FRC as structural material. There also exist specific guidelines for the design of FRC precast segment linings (e.g., ITAtech Report/7-15 and ACI 544.7R-16). These guidelines deal with the design of FRC considering the traditional limit state safety format. Therefore, partial safety factors for both the loads (¿L) and material strengths (¿M) must be considered. In particular, the magnitude of ¿M considered for compressive and tensile FRC strengths are assumed to be the same. Nonetheless, this assumption can be unrealistic, particularly in terms of flexural residual strength (fR) since this property present higher scatter than the compressive strength (fc). This is particularly true for elements with a reduced cracking surface (e.g., beams) due to the higher impact that uncertainties like fibre orientation and distribution have on the variability of fR. Therefore, this assumption can lead to lower reliability indexes (ß) than those established for traditional reinforced concrete structures. However, this variability tends to decrease with the increase of the width of the cracked sections (e.g., slabs). The results of a structural reliability analysis carried out to calibrate partial safety factors for fR is presented. Full-scale bending tests on precast segments with different dimensions, amounts and type of fibers were considered. This partial safety factors could be used in the design of future precast FRC tunnel linings., Peer Reviewed, Postprint (author's final draft)

The most singular characteristic of pervious concrete is its interconnected porosity that allows water to flow through at high rates. The objective of this paper is to develop and validate an advanced DEM-CFD model to assess the permeability of pervious concrete numerically, taking into account the influence of the composition and of the compaction process. An extensive experimental program with 1 aggregate grading size, 4 paste contents and 3 degrees of compaction was conducted to validate the numerical approach. Results show that the DEM-CFD model is capable of predicting the permeability depending on the variables considered here. Moreover, flow parameters derived from the numerical simulations help understand the experimental results. The study confirms that, instead of relying on trial and error experiments, it is possible to use advanced numerical models to accelerate the definition of mixes and the production process, reducing the time, efforts and costs required., Peer Reviewed, Postprint (author's final draft)

Installing utility pipelines generates a significant amount of trench arisings, which are usually transported to landfills instead of being reused as backfill material. This practice generates CO2 emissions and wastes raw materials. This paper presents a more sustainable solution, an eco-trench, which is based on re-using trench arisings as backfill and adding a top layer of expansive concrete to improve the eco-trench’s structural performance. The technical feasibility of the eco-trench was evaluated through a finite element model, which identified the degree of expansion in concrete required to avoid failure or subside the stresses caused by traffic. The potential expansion of concrete was measured under confined conditions in the laboratory by means of a novel test developed for this purpose. The results showed that adding calcium oxide generates the required internal stress. The results were then confirmed in a pilot experience., Peer Reviewed, Postprint (published version)

El projecte preten trobar la millor solució als esforços a soportats pel cércol perimetral d'un cobert agrícola de formigó alleugerit armat amb Bambusa guadua mitjançant un estudi estructural utilitzant el programa d'elements finits SAP2000. El cobert està situat a la La Garrotxa, a Puigsestorres, a les Planes d'Hostoles, i forma part d'una estructura amb la finalitat de satisfer les necessitats d'emmagatzematge d'activitats agrícoles.