The use of polymeric materials such as geosynthetics in infrastructure works has been increasing over the last decades, as they bring down costs and provide long-term benefits. However, the aging of polymers raises the question of its long-term durability and for this reason researchers have been studying a sort of techniques to search for the required renewal time. This paper examined a commercial polypropylene (PP) nonwoven geotextile before and after 500 h and 1000 h exposure to ultraviolet (UV) light by performing laboratory accelerated ultraviolet-aging tests. The state of the polymeric material after UV exposure was studied through a wide set of tests, including mechanical and physical tests and thermoanalytical tests and scanning electron microscopy analysis. The calorimetric evaluations (DSC) showed distinct behaviors in sample melting points, attributed to the UV radiation effect on the aged samples. Furthermore, after exposure, the samples presented low thermal stability in the thermomechanical analysis (TMA), with a continuing decrease in their thicknesses. The tensile tests showed an increase in material stiffness after exposition. This study demonstrates that UV aging has effects on the properties of the polypropylene polymer.

Nonwoven geotextiles are geosynthetic products that are highly susceptible to ultraviolet degradation because light can reach a large area of the material due to its fiber arrangement. Even with additives, which delay the degradation process, material decomposition still occurs, and therefore the product’s long-term durability can be affected. In this paper, the mechanical and thermal behavior of a commercial nonwoven polyester geotextile subjected to accelerated ultraviolet aging tests were evaluated. The deterioration was evaluated by comparing the physical properties (mass per unit area, thickness, and tensile strength) and thermal behavior (thermogravimetry—TG, thermomechanical analysis—TMA, and differential scanning calorimetry—DSC) before and after exposure times of 500 h and 1000 h. The results showed that the ultraviolet aging tests induced some damage in the polyester fibers, leading to the deterioration of their tensile strength. For 1000 h of exposure, in which the reduction was larger, scanning electron microscopy (SEM) found some superficial disruption of the fibers, indicative of damage. TG and DSC could not capture the effects of UV radiation on polymer degradation, unlike TMA. This latter technique was effective in showing the differences between specimens before and after UV exposure.

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En este trabajo se ha utilizado el método de precursor polimérico (método de Pechini) para sintetizar dióxido de titanio, proceso que ha permitido tener un mayor control sobre la pureza del óxido y el tipo de fase que ha presentado el material obtenido, fase anatasa en el presente caso. Durante el proceso de síntesis se ha obtenido una resina que se ha caracterizado utilizando la espectroscopia de Resonancia Magnética Nuclear (RMN) y la espectroscopia infrarroja con transformada de Fourier (FTIR) para determinar su estructura y con base en ella se ha propuesto un modelo para la conformación de la misma. Posteriormente esta resina se ha sometido a un tratamiento térmico para obtener los polvos cerámicos que se han caracterizado empleando diferentes técnicas, principalmente, difracción de rayos X (DRX) y microscopia electrónica (MET y MEB). Los resultados indican que se puede obtener TiO 2 fase anatasa a los 450ºC con un tamaño de partícula <100nm. Palabras claves: Óxido de titanio; anatasa; método de Pechini; caracterización. TiO 2 synthesized by the method of polymeric precursor (Pechini): structure of the intermediate resineIn this work, the polymeric precursor method (Pechini method) was used to synthesize titanium dioxide. This process allowed a bigger control on the purity of the oxide and the crystalline phase present in the material. In this case, the principal phase was anatase. The resine obtained in this process was characterized using NMR and IR spectroscopy to determine their structure. With this information we proposed a resine structure model. To finish the process, the resin was thermally treated to obtain TiO 2 . This oxide was characterized using different techniques: ray-X diffraction (RDX) and electron microscopy (TEM and SEM). The results indicated that the TiO 2 anatase phase can be obtained at 450ºC with a particle size <100nm.Keywords: Titanium dioxide; anatase; Pechini method; characterization. INTRODUCCIÓNEl dióxido de titanio, TiO 2 , es un compuesto de gran interés tecnológico. El TiO 2 presenta cuatro fases cristalinas: rutilo (estructura tetragonal), anatasa (estructura octaédrica), brookita (estructura ortorrómbica) y una de alta presión tipo α-PbO 2 [1]. El dióxido de titanio, especialmente en la variedad de anatasa, es ampliamente utilizado como fotocatalizador debido a que posee un adecuado valor de banda prohibida (∼3eV). Además es utilizado como pigmento blanco, recubrimiento anticorrosivo, sensor de gases, absorbente de rayos UV en productos cosméticos y de manera general en la industria cerámica [2]. También es muy utilizado para fotodegradar moléculas orgánicas presentes en el agua y en el aire.El polvo cerámico de dióxido de titano puede ser obtenido utilizando métodos como: Sol-Gel obtener una disolución líquida transparente. Como en el sistema se encuentran presentes cationes es posible que se conformen quelatos polibásicos, ácidos, que posteriormente, por calentamiento, se polimerizan dando origen a una resina viscosa [6,7]. Comúnmente, en el proceso Pechini, se utiliza u...

-Morphology studies assume significant importance in analysis of phenomena of granular systems packaging, in particular with a view to the use of the technique of soil stabilization named particle size correction in forest roads. In this context, this study aimed to develop and operationalize a Sand Grain Image Capture System and, hereby, determine the morphological indices of the sand fractions of two sandy soils called João Pinheiro (JP) and Cachoeira da Prata (CP). Soil samples, air-dried, were sieved (2.0 mm nominal mesh size) for removal of gravels. The materials that passed through the sieve were subjected to dispersion, washing in 0.053 mm nominal mesh size sieve, removal of organic matter and iron oxides to obtain the clean sand fractions. Subsequently, each soil sample was sieved for separation into twelve classes, between the diameters of 0.149 mm and 1.190 mm, using a Rotap shaker. Next, tests were carried out to characterize the morphometric attributes of the twelve classes of sand fractions of the soils studied. For validation of the performance of the Sand Grain Image Capture System, the results were compared to those obtained using a standard procedure for image analysis. The analysis of the results led to the following conclusions: (i) the sand fraction of the JP soil presented higher values for the morphometric indices roundness, elongation and compactness compared to sand fraction of the CP soil; and (ii) the Sand Grain Image Capture System worked properly, with practicality.

El estudio de la seguridad y confiabilidad de una fundación con pilotes se basa en el análisis de los momentos probabilísticos, media y coeficiente de variación asociados a la superficie resistente, donde se impone la existencia de una población finita representada por elementos aislados de la fundación. Este trabajo presenta un análisis de la adaptación de la estadística para estimar los parámetros poblacionales, usando los conceptos de la estadística de orden. Los valores de resistencia y solicitación de las fundaciones analizadas se basaron en los datos experimentales publicados en la literatura técnica, donde la variable resistencia fue medida por medio de pruebas de carga. El número de ensayos de campo indica especialmente que, para la diversidad de las fundaciones analizadas, la estadística de orden puede ser una herramienta bastante útil para estimar la probabilidad de falla de fundaciones con pilotes, cuando el número de pruebas de carga es pequeño.

Where granular materials are not easily available, local cohesive soils are increasingly employed in geosynthetic reinforced soil walls as a cheap and sustainable option. Conventional design methods do not yet account for the beneficial effect of cohesion in reducing the amount of required reinforcement. Similarly, the contribution of the face to stability is rarely accounted for, despite plenty of experimental evidence in its favour. In this paper, a semi-analytical method based on limit analysis is developed for the design of reinforced soil walls in frictional-cohesive backfills accounting for the wall contribution. A parametric analysis was conducted to evaluate the effect of soil cohesion and friction angle, facing batter, block width, location of the reaction force acting on the face, facing-backfill interface friction, facing-foundation interface friction, and reinforcement length. Dimensionless design charts providing the required amount of reinforcement for lengths recommended in design standards are provided for both uniform and linearly increasing reinforcement distributions. It emerges that accounting for the presence of cohesion and the facing element can lead to significant savings in the overall level of reinforcement, and that tension cracks can be particularly detrimental to wall stability for highly cohesive soils so they cannot be overlooked in the design.

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