Utilización de fibras desechas de procesos industriales como estabilizador de mezclas asfálticas sma

Las mezclas tipo SMA (Stone Mastic Asphalt) son mezclas asfálticas calientes de gradación discontinua desarrolladas para maximizar la resistencia al ahuellamiento y la durabilidad. Esta mezcla está compuesta de dos partes: un esqueleto de agregados gruesos y un mastic rico en asfalto, sin embargo, estas dos partes hacen que la mezcla asfáltica presente segregación entre los agregados y el asfalto, y como consecuencia de ello escurrimiento del mismo asfalto. Es por esto que la mezcla requiere del uso de fibras que inhiban el escurrimiento, y para ello los manuales de diseño específicos para este tipo de mezcla exigen el uso de fibras de celulosa peletizadas y premezcladas con asfalto. Este tipo de fibras actualmente no se producen en el país, por lo que su importación eleva el costo de la mezcla respecto al costo de una mezcla convencional.SMA mixtures (Stone Mastic Asphalt) are hot asphalt mixtures discontinuous gradation developed to maximize rutting resistance and durability. This mixture is composed of two parts: a coarse aggregate skeleton and asphalt rich mortar, however, these two parts make present asphalt mixture segregation of the aggregates and asphalt and as a consequence asphalt draindown. That is why the mixture requires the use of fibers that inhibit runoff, and for these specific design manuals for this type of mixture require the use of cellulose fibers and premixed pelletized asphalt. This type of fiber is not currently produced in the country, so import raises the cost of the mixture in relation to the cost of a conventional mixture.Ingeniero (a) CivilPregrad

Utilización de fibras desechas de procesos industriales como estabilizador de mezclas asfálticas tipo SMA

Las mezclas tipo SMA (Stone Mástic Asphait) son mezeias asfálticas calientes de gradación discontinua desarrolladas para maximizar la resistencia al ahuellamiento y la durabilidad. Por su gradación discontinua la mezcla requiere del uso de fibras que inhiban el escurrimiento del asfalto, y para ello los manuales de diseño específicos para este tipo de mezcla exigen el uso de fibras de celulosa peletizadas y premezcladas con asfalto. Este trabajo de grado se enfocó en encontrar una alternativa para reemplazar de forma eficiente la fibra de celulosa, para esto se utilizaron dos fibras producto de desechos industriales en el país, como son la fibra de polipropileno proveniente de la producción de elementos de higiene y seguridad, y la fibra de la cáscara de coco. Estos productos, al ser desechos industriales, no generan mayores costos en la elaboración de las mezclas asfálticas tipo SMA, comparado con la mezcla SMA elaborada con fibra de celulosa. Para ello se diseñó una mezcla asfáltica de tipo SMA con fibra de celulosa peletizada premezclada con asfalto, así como también con fibras de polipropileno y coco. Estas tres mezclas fueron sometidas a pruebas de desempeño mecánico como módulo resiliente, deformación plástica, y susceptibilidad a la humedad. Los resultados obtenidos en este trabajo indicaron que las fibras producto de desechos industriales son capaces de inhibir el escurrimiento del asfalto y no alteran de forma considerable las propiedades mecánicas estudiadas de la mezcla asfáltica tipo SMA comparado con los resultados obtenidos en esta mezcla con fibra de celulosa.SMA mixtures (Stone Mástic Asphalt) are hot asphalt mixtures discontinuous gradation developed to maximize rutting resistance and durability. That is why the mixture requires the use of fíbers that inhibit runoff, and for these specific design manuals for this type of mixture require the use of cellulose fíbers and premixed pelletized asphalt. Under this argument, this degree work focused on finding an alternative for effíciently replace cellulose fiber and for this we used two fiber industrial waste producís in the country, such as polypropylene fiber production ffom elements health and safety, and fiber ffom coconut shell. These products, when industrial wastes, generate higher costs in the development of SMA asphalt mixture compared to the SMA mixture made with cellulose fiber. We designed an asphalt mixture of SMA with pelletized cellulose fiber premixed with asphalt, as well as polypropylene fiber and coconut. These three mixtures were tested for mechanical performance as resilient modulus, creep, and moisture susceptibility. The results obtained in this study indicate that the industrial waste product fíbers can inhibit the draindown of the asphalt and not significantly alter the mechanical properties of the asphalt mix studied SMA compared with the results obtained in this mixture of cellulose fiber.Ingeniero (a) CivilPregrad

Modeling of Drying Curves of Silica Nanofluid Droplets Dried in an Acoustic Levitator Using the Reaction Engineering Approach (REA) Model

The use of nanoparticles has become of great interest in different industrial applications. The spray drying of nanofluids forms nanostructured grains, preserving the nanoparticle properties. In this work, individual droplets of silica nanofluids were dried in an acoustic levitator. Tests were carried out under different experimental conditions to study the influence of the variables on the drying process. The drying curves were experimentally obtained and an REA model was used to obtain the theoretical curves and the correlations for the activation energy. The critical moisture content theoretically obtained was used to predict the grain diameter

Influence of Particle Size on the Drying Kinetics of Single Droplets Containing Mixtures of Nanoparticles and Microparticles: Modeling and Pilot-Scale Validation

The particle size of the primary particles is an important parameter influencing the drying behavior of droplets. In this work, the influence of particle size on the drying kinetics and grain properties was analyzed for droplets containing silica nanoparticles, microparticles, and mixtures of the two. The presence of microparticles was found to increase the drying rate and shrinkage of the droplet. The drying curves were modeled using a reaction engineering approach (REA) model. Finally, different suspensions were dried in a pilot-scale spray dryer in order to prove the influence of the particle size obtained in the levitator tests

El proceso de secado por atomización: formación de gránulos y cinética de secado de gotas

Spray drying is a unit operation very common in many industrial processes. For each particular application, the resulting granulated material must possess determined properties that depend on the conditions in which the spray drying processing has been carried out, and whose dependence must be known in order to optimize the quality of the material obtained. The large number of variables that influence on the processes of matter and energy transfer and on the formation of granular material has required a detailed analysis of the drying process. Over the years there have been many studies on the spray drying processing of all kind of materials and the influence of process variables on the drying kinetics of the granulated material properties obtained. This article lists the most important works published for both the spray drying processing and the drying of individual droplets, as well as studies aimed at modeling the drying kinetics of drops.El proceso de secado por atomización es una operación unitaria que interviene en numerosas aplicaciones industriales. Para cada aplicación en concreto, el material granulado resultante debe poseer unas propiedades determinadas que dependen de las condiciones en las que se lleve a cabo el secado por atomización, y cuya dependencia debe conocerse para así optimizar la calidad del material obtenido. El gran número de variables que influyen en los procesos de transferencia de materia y energía que tienen lugar, y en la formación del material granulado, han hecho necesario el análisis en detalle del proceso de secado. A lo largo de los años han sido muchos los estudios realizados sobre el secado por atomización y la influencia de las variables del proceso en la cinética de secado y las propiedades del material granulado obtenido, para todo tipo de materiales. En este artículo se recogen los trabajos más importantes publicados correspondientes tanto al secado por atomización como al secado de gotas individuales, así como los estudios cuyo objetivo es el modelado de la cinética de secado de gotas

Characterization of silica–water nanofluids dispersed with an ultrasound probe: A study of their physical properties and stability

The stability and agglomeration state of nanofluids are key parameters for their use in different applications. Silica nanofluids were prepared by dispersing the nanoparticles in distilled water using an ultrasonic probe, which has proved to be the most effective system and gives the best results when compared with previous works. Results were obtained concerning the influence of the solid content, pH and salt concentration on the zeta potential, electrical double layer, viscosity, elastic and viscous moduli, particle size and light backscattering. Measurement of all these properties provides information about the colloidal state of nanofluids. The most important variable is the solid content. Despite the agglomeration due to high concentration, nanofluids with low viscosity and behaving like liquid were prepared at 20% of mass load thanks to the good dispersion achieved with the ultrasonic treatment. The pH of the medium can be used to control the stability, since the nanofluids are more stable under basic conditions far from the isoelectric point (IEP) and settle at pH = 2. Therefore, stable nanofluids for at least 48 h, with high solid content, can be prepared at high pH value (pH > 7) due to the electrostatic repulsion between particles

Microstructure and mechanical properties of grains of silica nanofluids dried in an acoustic levitator

The microstructure and mechanical properties of spray-dried grains are key factors in many applications. In this work single droplets of silica nanofluids were dried in an acoustic levitator under different experimental conditions of solid mass fraction, pH value, salt concentration, drying temperature and initial droplet volume. ANOVA method was used to determine their influence on the final grain diameter, the shell thickness and the mechanical strength. The solid content and the droplet volume are the variables that exert an influence on these three properties. In addition, the mechanical strength is influenced by the pH value. The maximum packing fraction of the particles inside the shell was obtained by modeling the viscosity data with the Quemada equation. The packing fraction was then used to calculate the shell thickness. The internal microstructure of the grains was observed by SEM and the shell thickness was measured. Experimental and calculated results show good agreemen

Transcription Analysis of Central Metabolism Genes in Escherichia coli. Possible Roles of σ38 in Their Expression, as a Response to Carbon Limitation

The phosphoenolpyruvate: carbohydrate transferase system (PTS) transports glucose in Escherichia coli. Previous work demonstrated that strains lacking PTS, such as PB11, grow slow on glucose. PB11 has a reduced expression of glycolytic, and upregulates poxB and acs genes as compared to the parental strain JM101, when growing on glucose. The products of the latter genes are involved in the production of AcetylCoA. Inactivation of rpoS that codes for the RNA polymerase σ38 subunit, reduces further (50%) growth of PB11, indicating that σ38 plays a central role in the expression of central metabolism genes in slowly growing cells. In fact, transcription levels of glycolytic genes is reduced in strain PB11rpoS− as compared to PB11. In this report we studied the role of σ70 and σ38 in the expression of the complete glycolytic pathway and poxB and acs genes in certain PTS− strains and their rpoS− derivatives. We determined the transcription start sites (TSSs) and the corresponding promoters, in strains JM101, PB11, its derivative PB12 that recovered its growth capacity, and in their rpoS− derivatives, by 5′RACE and pyrosequencing. In all these genes the presence of sequences resembling σ38 recognition sites allowed the proposition that they could be transcribed by both sigma factors, from overlapping putative promoters that initiate transcription at the same site. Fourteen new TSSs were identified in seventeen genes. Besides, more than 30 putative promoters were proposed and we confirmed ten previously reported. In vitro transcription experiments support the functionality of putative dual promoters. Alternatives that could also explain lower transcription levels of the rpoS− derivatives are discussed. We propose that the presence if real, of both σ70 and σ38 dependent promoters in all glycolytic genes and operons could allow a differential transcription of these central metabolism genes by both sigma subunits as an adaptation response to carbon limitation

¿Cómo influye en el éxito de la transferencia de conocimiento la percepción que el receptor tiene del emisor?

El trabajo aborda el proceso de transferencia de conocimiento, discutiendo la influencia que ejerce la percepción que el receptor de conocimiento tiene de su emisor. Para ello se analiza un caso específico en el que tiene lugar el citado proceso de transferencia de conocimiento: los acuerdos de cooperación tecnológica entre empresa y universidad. Dichos acuerdos constituyen una de las alternativas, junto a la adquisición y el desarrollo interno, de que dispone la empresa en el momento de afrontar el proceso innovador. El análisis se inicia con una aproximación al concepto de conocimiento y a la justificación de la tecnología como forma de conocimiento, tras lo cual se reflexiona sobre su transferencia. Seguidamente se analizan los acuerdos de cooperación tecnológica, entre los que se encuentran los que se establecen con la universidad. A continuación se exponen las principales ideas en relación con la influencia de la percepción del receptor en el éxito de la transferencia. Finalmente los hallazgos teóricos se someten a contraste empírico de manera exploratoria en una muestra de acuerdos de cooperación tecnológica en el ámbito español.This work addresses knowledge transfer by discussing the influence of the recipient’s perception about the source’s reliability. A specific case of knowledge transfer is analyzed: technological cooperation agreements. These agreements are one of the firm’s alternatives in order to culminate the innovative process. The analysis begins with the introduction to the concept of knowledge and the justification of the technology as a type of knowledge, after which a reflection is done on its transfer. Next, technological cooperation agreements are analyzed, specifically university-industry agreements. After that, we address the main ideas linked to recipient’s perception about the source’s reliability in the success of knowledge transfer. Finally, the theoretical findings are tested empirically in a sample of technological cooperation agreement in Spain from an exploratory view

Estudio comparativo de resistencias a la compresión en hormigones de 24 Mpa empleando agregados finos procedente de los ríos de Manabí

  Las arenas de río son materiales empleados para las construcciones de viviendas y demás obras pequeñas que se realizan en los sectores alejados de las canteras, pero a su vez están cerca de meandros de ríos para su extracción y empleo. Por el uso que se da a este material, se creyó necesario realizar los ensayos físicos y mecánicos que tiene las arenas de varios ríos de la provincia de Manabí, exclusivamente los que atraviesan los cantones de Paján, Calceta y Olmedo, para posterior a ello realizar las dosificaciones del hormigón según los establece la ACI 211.1 y las normativas ecuatorianas, se realizaron probetas cilíndricas que permaneciendo en curado húmedo por un tiempo de 28 días, para realizar el ensayo de resistencia a la compresión, también se realizó el ensayo de resistividad superficial según lo establece la ASTM C1 202, 2012, para correlacionar los datos y establecer los usos apropiados de las arenas de los ríos en mención, Finalmente se obtuvieron los datos de los ensayos determinando que las arenas de los ríos mencionados no cumplen con las condiciones para su uso en obras que requieran hormigón de tipo estructural.   Palabras claves: Arena de río, resistencia a la compresión, resistividad superficial.   Abstract River sands are materials used for the construction of houses and other small works that are carried out in sectors far from the quarries, but in turn are close to meandering rivers for their extraction and use. Due to the use that is given to this material, it was believed necessary to carry out the physical and mechanical tests that the sands of several rivers in the province of Manabí have, exclusively those that cross the cantons of Paján, Calceta and Olmedo, to later carry out the concrete dosages as established by ACI 211.1 and the Ecuadorian regulations, cylindrical test tubes were made that, remaining in wet curing for a time of 28 days, to carry out the compression resistance test, the surface resistivity test was also carried out according to It  is established by ASTM C1 202, 2012, to correlate the data and establish the appropriate uses of the sands of the rivers in question.Finally, the data of the tests were obtained determining that the sands of the mentioned rivers do not meet the conditions for their use in works that require structural concrete. Keys Words; River sand, compressive strength, surface resistivit