Influencia de la composición de distintos hormigones en los mecanismos de transporte de iones agresivos procedentes de medios marinos

La mayoría de las estructuras de hormigón en el ambiente marino muestran signos de degradación debido a la agresividad química de los constituyentes del agua de mar sobre los productos de hidratación del cemento, en especial al sulfato y al magnesio, así como a la corrosión de las armaduras en la presencia de cloruros. Los medios por los cuales los iones penetran en el hormigón son complejos y dependen en gran medida de las condiciones del material, especialmente en el momento de la exposición. Para describir los procesos que intervienen en la degradación del hormigón es imprescindible estudiar los diferentes tipos de mecanismos de transporte en el seno del mismo, junto con los efectos de las interacciones entre los iones presentes en el agua de mar y los productos de la hidratación del cemento. El objetivo principal de esta tesis ha sido estudiar el comportamiento de un cemento resistente a sulfatos con adiciones minerales y el de un cemento de escoria en comparación con el que tiene un cemento portland resistente a sulfatos. Se ha estudiado la evolución mecánica y durable de los mismos en ambientes agresivos que contienen cloruros, sulfatos y magnesio presentes también en medios marinos. El fin primordial con el que se planteó era intentar establecer una relación entre la microestructura, la porosidad y la permeabilidad, sobre la que fundamentar la utilización de estos parámetros, junto con otros factores, además de la resistencia, como criterios a considerar en el diseño de una mezcla adecuada de la que resulte un hormigón durable para usar en este ambiente. El uso de cementos que contienen adiciones minerales tales como escoria de alto horno, cenizas volantes y humo de sílice tienen un papel importante en la durabilidad de hormigones expuestos a ambientes marinos. En este trabajo se ha diseñado una amplia campaña experimental con cuatro dosificaciones diferentes de hormigón para estudiar la influencia de las principales adiciones utilizadas en este medio. Los hormigones fueron dosificados con una relación agua/material cementicio de 0,45 y ensayados a edades de 7, 28 y 91 días. El efecto de las distintas adiciones minerales (humo de sílice, cenizas volantes y escoria de alto horno) se analizó por medio de análisis térmico diferencial (DTA), difracción de rayos X (DRX), porosimetría por intrusión de mercurio (MIP), permeabilidad a los gases, difusión de iones (cloruro, sulfato y magnesio), así como las propiedades mecánicas del hormigón (resistencia a compresión, resistencia a tracción y módulo de elasticidad). Para simular la agresividad del medio marino los hormigones se sumergieron en disoluciones conteniendo cloruro sódico, sulfato sódico y sulfato magnésico respectivamente con una concentración de 1 molar. Posteriormente se evalúa su comportamiento a distintas edades de exposición: 6, 12 y 18 meses. Además en este trabajo se ha desarrollado un modelo numérico para simular la difusión de los iones agresivos (cloruros y sulfatos) en el hormigón. Este modelo se basa en una solución de la ecuación de difusión-reacción que es alimentada por parámetros relativos a la dosificación, composición del material y estructura porosa. Se trata pues de un modelo de carácter predictivo que pueda anticipar los daños en el material. Los datos obtenidos en todas las dosificaciones estudiadas han mostrado que el comportamiento mecánico y la capacidad de transporte de fluidos en el hormigón vienen determinados por la estructura porosa del material. También se ha observado que la incorporación de la adición de humo de sílice, cenizas volantes y escoria de alto horno al hormigón, mejoran sus propiedades mecánicas, la resistencia a la penetración de los iones cloruros y la estructura porosa. La utilización de cementos resistentes a sulfatos (I 42,5 R/SR y III/B 42,5 L/SR) en el hormigón, han mejorado las propiedades mecánicas, la permeabilidad al gas y la resistencia a la penetración de los iones sulfato y magnesio. Los resultados numéricos de difusión de iones cloruros y sulfatos obtenidos a partir del modelo se han comparado con los obtenidos experimentalmente en este estudio, obteniendo una buena correlación. De esta forma el modelo puede ser de utilidad para predecir la penetración de cloruros y sulfatos con el tiempo, siendo posible utilizarlo de base para buscar una calidad adecuada del hormigón a utilizar en ambiente marino sumergido.ABSTRACT A vast majority of concrete structures in marine environment shows signs of degradation due to aggressive chemical constituents of seawater on the cement hydration products, especially sulfate and magnesium, and the corrosion of the reinforcement in the presence of chlorides. The means by which ions penetrate the concrete are complex and depend on a large extent of conditions of the material, especially at the time of exposure. The description of the processes involved in the degradation would require studying the different types of transport mechanism inside the material, together with the effects of interactions between ions in seawater and the products of cement hydration. The main aim of this thesis was to study the behavior of sulfate resistant cement with mineral additions and slag cement compared to sulfate resistant cement. We have studied their mechanical and durable evolution in aggressive environments containing chloride, sulfate and magnesium, which are also present in marine environments. The primary purpose with the one that was designed to establish a relationship between the microstructure, porosity and permeability, and to support accounting for these parameters to other factors besides strength, as criteria to be considered in mix design to achieve a durable concrete. The use of blended cements incorporating materials such as blast furnace slag, fly ash or silica fume have an important role in the long-term durability of concrete exposed to marine environments. In this work we have designed an experimental campaign with four different dosages of concrete to study the influence of the principal additions used in marine environments. The concretes were prepared with the water– cementitious material ratio of 0.45 and tested at ages of 7, 28 and 91 days. The effect of material composition [Sulfate Resistant Portland Cement (CPRS), Blast Furnace Slag Portland Cement (EHA), Silica Fume (HS) and Fly Ash (CV) with four different mix designs] was performed by means of differential thermal analysis (DTA), X - ray diffraction (XRD), mercury intrusion porosimetry (MIP), gas permeability, chloride, sulfate and magnesium diffusion and mechanical properties of concrete. The experimental procedure presented gives reliable information to evaluate the homogeneity of different concretes in terms of air permeability. To simulate the aggressiveness of the marine environment of concrete were immersed in solutions containing sodium chloride, sodium sulfate and magnesium sulfate, with 1 molar concentration. Their behaviour was evaluated at different exposure ages 6, 12 and 18 months. Also in this work, we developed a numerical model to simulate the diffusion of aggressive ions (chlorides and sulfates) in concrete. This model is based on a numerical solution of the diffusion-reaction equation which is input by parameters related to the dosage, composition and pore structure of material. Therefore, it is a predictive model that can anticipate the material damage. The results that we obtained of all examined concrete showed that the mechanical and fluid transport capacity, are determined by pore structure of the material. It was also noted that the incorporation of silica fume, fly ash and blast furnace slag in concrete, improved its mechanical properties, resistance to chloride ion penetration and the pore structure. Utilization of sulfate resistant cements (I 42.5 R/SR and III / B 42.5 L/SR) in concrete, improved the mechanical properties, gas permeability and resistance to penetration of sulfate and magnesium ions. The numerical results of diffusion chloride and sulfate ions which obtained from the model have been compared with the experiment results in this study, we observed that the model achieved a good approximation for assay registers. Thus the model can be useful to predict the penetration of chloride and sulfate ions with the time, being possible to use it as a base to look for a suitable quality of the concrete to be used in submerged marine environment

Influencia de la estructura porosa de hormigones utilizados en ambientes marinos frente al transporte generado por gradiente de presión

En los ambientes marinos, donde los hormigones quedan expuestos al ingreso de los iones cloruro y sulfato fundamentalmente, la bibliografía, [1-4], recomienda que se utilicen cementos con bajo contenido en aluminatos (sulforresistentes) o cementos con adiciones minerales, cenizas volantes y humo de sílice principalmente. El objetivo principal de esta elección es intentar minimizar en lo posible las reacciones expansivas entre los iones del medio agresivo y la matriz de cemento. Sin embargo la protección más efectiva será sin duda la que impida la penetración de los agresivos. La entrada de cualquier agresivo en el hormigón viene determinada por la estructura porosa del mismo, y muy especialmente por la porosidad accesible conectada. Esta porosidad queda definida por la dosificación del hormigón y las características químicas del cemento. Los resultados obtenidos muestran claramente que los hormigones con humo de sílice son significativamente menos porosos y menos permeables. En el resto de dosificaciones estudiadas la porosidad es mayor, y es el radio de poro el factor que se presenta como más determinante para definir la permeabilidad del material

PERFORMANCE OPTIMIZATION OF RECTANGULAR SETTLING TANKS IN SMALL WATER TREATMENT PLANTS BY NUMERICAL APPROACH

ABSTRACT Separation of suspended and colloidal materials from water and wastewater by settlement is one of the most widely used process in water and wastewater treatment. Hydraulic retention time is a main parameter for design and optimization of any water treatment tank or reactor. Determination of the retention time distribution at all different locations within the tank gives information about the possibility of presence of dead zones or and short circuits. The presence of dead zones decrease the effective volume of the tanks that may almost result in a short circuit between the inlet and outlet of the tank. some part of the flow exits the tank without spending the retention time required for settling. On the other hand, it also induces high turbulence intensity in other regions, which not only decreases the possibility of particle aggregation and deposition, but may also causes solids re-stabilization. A uniform flow field is essential to increase the efficient performance of settling tank. This enables particles to settle at a constant velocity and in less time. Serious design and selection of a suitable inlet baffle configuration for settling tanks is one method to decrease the regions and size of the dead zones which shall improve the process performance. The objective of this paper is to study the performance of diffusion drums inlet baffle for settling tanks. In this paper, a computational model has been mapped to the commercial FLUENT® solver and applied to simulate the flow within a 3D rectangular water tank. Finally, numerical results shall demonstrate the optimum hydraulic diameter ratios range for diffusion drums sizing

The influence of sulfuric environments on concretes elaborated with sulfate resistant cements and mineral admixtures. Part 1: Concrete exposed to Sodium Sulfate (Na2SO4) = Estudio de la influencia de los medios con presencia de sulfatos en hormigones con cementos sulforresistentes y adiciones minerales. Parte 1: Hormigones expuestos a sulfato sódico (Na2SO4)

The study of sulfate attack in concrete is considered vital for the preservation of the structural integrity of constructions. Its aggressive behaviour causes degradation of the cement matrix which changes the initial properties of the material. In this article, the sulfate resistance of concrete is studied. To that goal, four different concrete mixes were made with sulphur resistant cement. The concretes were tested for compressive strength, transport capacity of sulfates and microstructural properties. An experimental program was proposed in which the concrete samples were submerged in sodium sulphate (Na2SO4) solution. The obtained results were compared with reference values of concretes cured in calcium hydroxide [Ca(OH)2]. According to the results the concrete with ground granulated blast-furnace slag presented the best behavior when exposed to sodium sulphate (Na2SO4) solution. El estudio del ataque de sulfatos en el hormigón se considera de gran importancia para la conservación de la integridad estructural de las construcciones. Su agresividad se basa en la degradación de la matriz cementicia modificando las características iniciales de diseño. En el presente trabajo se estudia la resistencia del hormigón al ataque de sulfatos provenientes de sulfato sódico (Na2SO4). Para llevar a cabo la investigación se diseñaron cuatro dosificaciones de hormigón empleando cementos sulforresistentes y adiciones minerales. Se llevó a cabo una propuesta experimental donde las muestras de hormigón se sumergieron en disolución de sulfato sódico (Na2SO4) de concentración 1M. Posteriormente se realizaron ensayos de resistencia mecánica, capacidad de transporte de sulfatos y propiedades microestructurales, a distintas edades. Los resultados obtenidos se compararon con valores de referencia de mezclas de hormigón curadas expuestas a hi-dróxido cálcico [Ca(OH)2]. De acuerdo a los resultados obtenidos, el hormigón con escoria de alto horno presentó las mejores características de durabilidad frente a sulfatos provenientes de sulfato sódic

The influence of sulfuric environments on concretes elaborated with sulfate resistant cements and mineral admixtures. Part 2: Concrete exposed to Magnesium Sulfate (MgSO4) = Estudio de la influencia de los medios con presencia de sulfatos en hormigones con cementos sulforresistentes y adiciones minerales. Parte 2.Hormigones expuestos a sulfato magnésico (MgSO4)

The present work studies the resistant of the concrete against magnesium sulfate (MgSO4) and compare the results with values obtained previously of the same concretes exposed to sodium sulfate (Na2SO4). Thus, it is possible analyze the influence of the cation type. To that end, four different concrete mixes were made with sulfur resistant cement and mineral admixtures (silica fume, fly ash and blast furnace slag). The concretes were submerged for different period in magnesium sulfate (MgSO4). After that, different tests were carried out to define mechanical and microstructural properties. The results obtained were compared with reference values of concretes cured in calcium hydroxide [Ca(OH)2]. According to the results, the concrete with blast furnace slag presented the best behavior front MgSO4, meanwhile the concretes with silica fume and fly ash were the most susceptible. The resistance of the concrete with blast furnace slag could be attributed to the characteristics of the hydrated silicates formed during the hydration time, which include aluminum in the chemical chain that hinder its chemical decomposition during the attack of magnesium. The magnesium sulfate solution was most aggressive than sodium sulfate solution. El presente trabajo estudia la resistencia de hormigones al ataque de sulfatos provenientes de sulfato magnésico (MgSO4) y compara estos valores con resultados previos de los mismos hormigones atacados con sulfato sódico (Na2SO4). De esta manera se estudia la interacción del catión que acompaña al ion sulfato durante su afectación a la matriz cementicia. Para lo anterior, se diseñaron cuatro dosificaciones empleando cementos sulforresistentes y adiciones minerales (humo de sílice, ceniza volante y escoria de alto horno). Los hormigones se sumergieron, por distintos periodos de tiempo, en disolución de sulfato magnésico (MgSO4) de concentración 1M, para después realizarles ensayos mecánicos y a nivel microestructural. Los valores obtenidos se compararon con los obtenidos en el hormigón de referencia curado en hidróxido cálcico. El hormigón con escoria de alto horno presentó el mejor comportamiento frente a MgSO4, siendo las mezclas de humo de sílice y ceniza volante las más susceptibles. La resistencia del hormigón con escoria se atribuye a las características de los silicatos hidratados formados durante la hidratación, los cuales incorporan aluminio en las cadenas impidiendo su descomposición ante un ataque por magnesio. El medio con sulfato magnésico mostro una mayor agresividad que el medio con sulfato sódico

Analysis of semiconductor laser dynamics under gigabit rate modulation

金沢大学大学院自然科学研究科電子科学金沢大学工学部A theoretical study of the dynamics of semiconductor lasers subjected to pseudorandom digital modulation at gigabit rates is presented. The eye diagram, turn-on jitter (TOJ), and power fluctuations in the modulated laser wave form are analyzed. The study is based on numerical large-signal analysis of the laser rate equations. Influences of the biasing and modulation currents on the eye diagram and TOJ are examined. The degree of eye opening is measured in terms of a Q factor of the laser signal analogous to the Q factor determining the bit-error rate in transmission systems. Influence of optimizing both the sampling and decision times on the signal Q factor is modeled. We show that the most eye opening corresponds to shortening the sampling time associated with lengthening the decision time. We also assess the relative contributions of the laser intrinsic noise and pseudorandom bit pattern to the TOJ. The results show that the bit pattern is the major contributor to the TOJ when the setting time of the relaxation oscillation is longer than the bit slot. © 2007 American Institute of Physics

Numerical analysis of optical feedback phenomenon and intensity noise of fibre-grating semiconductor lasers

金沢大学大学院自然科学研究科電子科学金沢大学工学部This paper demonstrates numerical analysis of the dynamics and intensity noise of fibre-grating semiconductor lasers (FGSLs). The induced phenomenon of strong optical feedback (OFB) is analysed. The simulations are based on an improved time-delay rate equations model of a single-mode laser that takes into account the multiple round-trips of the lasing field in the fibre cavity. The analyses are performed in terms of the temporal trajectory of the laser intensity, bifurcation diagram and relative intensity noise (RIN). We explore influence of the fibre-cavity length on the dynamics and RIN. The results show that when the fibre cavity is short, the regime of strong OFB is characterized by either continuous-wave (CW) operation or periodic pulsation. The pulsation frequency is locked at the frequency separation of either the compound-cavity modes or the external fibre-cavity modes. The corresponding RIN level is close to or higher than the level of the solitary laser depending on pulse symmetry. When the fibre cavity is long, the laser exhibits unstable dynamics over wider range of OFB. Moreover, the strong-OFB pulsation becomes beating quasi-periodic at the relaxation oscillation frequency and the fibre-cavity mode-separation frequency. Copyright © 2007 John Wiley & Sons, Ltd

Surgical Outcome of Three-Dimensional Correction of Adolescent Idiopathic Scoliosis

Background: Adolescent idiopathic scoliosis is an abnormal curvature of the spine that appears in late childhood or adolescence. Instead of growing straight, the spine develops a side-to-side curvature, usually in an elongated "S" or "C" shape; the bones of the spine are also slightly twisted or rotated. To prevent further curve progression and obtain a balanced spine, surgery remains the mainstay of treatment for idiopathic scoliosis (IS). Objective: This study aimed to discuss three dimensional surgical techniques used for correction of adolescent idiopathic scoliosis, evaluating their feasibility, efficacy and safety. Patients and methods: This study was conducted in Mansoura University Hospital and Alexandria University Hospitals between September 2018 and April 2021. 3D surgical correction was performed for 91 patients complaining of idiopathic scoliosis, and not responding to conservative measures and not associated with neurological affection. Results: According to Lenke classification, there were 56 patients (61.5%) with type 1 curve type , 9 patients (9.9%) with type 2, 7 patients (7.7%) with type 3, 7 patients (7.7%) with type 5 and 12 patients (13.2%) with type 6. Mean preoperative height was 1.60 m while mean postoperative height was 1.66 m. with significant increase in height postoperatively (p < 0.001). Mean percentage height gain was 3.91%. Conclusion: We do believe that the posterior only approach 3D correction is an effective method in management of AIS concerning correction of Cobb angle, shoulder balance and spinopelvic parameters and recommend it as the best way nowadays to treat this disease

Surgical Outcome of Three-Dimensional Correction of Adolescent Idiopathic Scoliosis

Background: Adolescent idiopathic scoliosis is an abnormal curvature of the spine that appears in late childhood or adolescence. Instead of growing straight, the spine develops a side-to-side curvature, usually in an elongated "S" or "C" shape; the bones of the spine are also slightly twisted or rotated. To prevent further curve progression and obtain a balanced spine, surgery remains the mainstay of treatment for idiopathic scoliosis (IS). Objective: This study aimed to discuss three dimensional surgical techniques used for correction of adolescent idiopathic scoliosis, evaluating their feasibility, efficacy and safety. Patients and methods: This study was conducted in Mansoura University Hospital and Alexandria University Hospitals between September 2018 and April 2021. 3D surgical correction was performed for 91 patients complaining of idiopathic scoliosis, and not responding to conservative measures and not associated with neurological affection. Results: According to Lenke classification, there were 56 patients (61.5%) with type 1 curve type , 9 patients (9.9%) with type 2, 7 patients (7.7%) with type 3, 7 patients (7.7%) with type 5 and 12 patients (13.2%) with type 6. Mean preoperative height was 1.60 m while mean postoperative height was 1.66 m. with significant increase in height postoperatively (p < 0.001). Mean percentage height gain was 3.91%. Conclusion: We do believe that the posterior only approach 3D correction is an effective method in management of AIS concerning correction of Cobb angle, shoulder balance and spinopelvic parameters and recommend it as the best way nowadays to treat this disease