Contribuição dos revestimentos poliméricos para a durabilidade de betões em ambientes agressivos

Dissertação de Mestrado em Engenharia Civil - Área de Materiais e Reabilitação da ConstruçãoActualmente é consensual que a principal degradação do betão deve-se a acções que ocorrem do exterior para o interior, devido à penetração de humidade, gases activos e iões agressivos, por métodos mecânicos, físicos e químicos, que frequentemente ocorrem juntos. Uma baixa porosidade, permeabilidade e penetração no betão de humidade e gases, são a primeira linha de defesa contra vários mecanismos de deterioração. A durabilidade do betão depende em grande medida da facilidade com que os fluidos (água, dióxido de carbono, oxigénio) na forma líquida ou gasosa, conseguem migrar através do betão. Um dos possíveis métodos de proteger o betão consiste na utilização de revestimentos por pintura, que funcionam como uma barreira entre o ambiente e o betão. Na selecção dos revestimentos por pintura deve ser dada a máxima importância às propriedades de difusão, permeabilidade, durabilidade e resistência química. Os revestimentos por pintura devem ser capazes de impedir a penetração da água e atrasar a influência de agentes agressivos (CO 2 , SO 2 , Cl − ), permitindo que a estrutura “respire” através de um mecanismo de difusão de vapor de água. Uma avaliação das propriedades de transporte da camada superficial deverá fornecer informação quanto à durabilidade de determinado betão. Virtualmente, todos os revestimentos são suficientemente permeáveis à água para serem pouco eficazes no controlo da corrosão mas não da permeabilidade iónica que é mais baixa. O presente trabalho de investigação pretende contribuir para uma melhor compreensão do desempenho do betão revestido em ambientes agressivos, apresentando resultados de capilaridade, permeabilidade, porosidade, difusão iónica, resistividade eléctrica e resistência a soluções agressivas de vários revestimentos por pintura utilizados para proteger o betão. Assim, foi feita a avaliação de nove ensaios diferentes, utilizados para medir parâmetros de durabilidade do betão revestido. Foram utilizados provetes pintados e não pintados, três tipos de resinas poliméricas (silicone, acrílica e epoxídica) e três tipos de composições de betões. Os resultados obtidos mostraram que os revestimentos contribuem para o aumento da durabilidade do betão, em particular os revestimentos epoxídicos que mostraram o melhor desempenho. Os vernizes de silicone tiveram alguns resultados surpreendentes mostrando ser um produto com uma excelente relação qualidade/preço.It is common knowledge that the highest concrete degradation occurs due to external influences, with effects in the bulk material. Mechanical, physical and chemical component mechanisms that frequently act together origins the penetration of moisture, active gases and aggressive ions inside the concrete. A low porosity, permeability and concrete penetration to moisture and gases are the first protective measures to be taken against several deterioration mechanisms. The concrete durability depends largely on how easy fluids in liquid or gas form, particularly water, carbon dioxide, and oxygen, migrate through the material. One of the possible methods to protect the concrete is by using paint coatings that act as a barrier between the environment and the bulk material. When selecting the paint coating for concrete protection, importance should be given to the critical properties of diffusion, permeability, durability and chemical resistance. The paint coatings should be able to stop the penetration of water and delay the influence of aggressive agents (CO 2 , SO 2 , Cl − ions), allowing the structure to “breathe” trough a water vapour diffusion mechanism. An evaluation of the surface layer transport properties should give some information on the durability of a particular concrete. Virtually all coatings are permeable to water, enough to be little effective controlling the corrosion but not the ionic permeability, which is much lower. The present work intends to contribute to a better understanding of the performance of coated concrete in aggressive environments. For this, results are presented for the capillarity, permeability, porosity, ion diffusion, electrical resistivity and resistance to aggressive solutions of several coatings used to protect concrete. The evaluation of nine different trials used to determine coated concrete durability parameters, was performed. Painted and unpainted specimens, three different types of resins (silicone, acrylic and epoxy) and three different concrete compositions were used. The results obtained showed that, in general, all coatings used contribute to the increasing of the concrete durability, in particular the epoxy resins which had the best performance. The silicone varnishes showed surprising results by presenting high quality/price rates

Hydration status and associated dietary factors in children

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Metabolic Effects of an Oral Glucose Tolerance Test Compared to the Mixed Meal Tolerance Tests: A Narrative Review

The oral glucose tolerance test (OGTT) is recommended for assessing abnormalities in glucose homeostasis. Recognised as the gold standard test for diagnosing diabetes, the OGTT provides useful information about glucose tolerance. However, it does not replicate the process of absorption and digestion of complex foods, such as that which occurs with a mixed meal tolerance test (MMTT), an alternative that is still not well explored in the diagnosis of metabolic alterations. The MMTT could be an asset in detecting glucose homeostasis disorders, including diabetes since it has more similarities to the common dietary pattern, allowing early detection of subtle changes in metabolic homeostasis in response to combined nutrients. This alternative has the advantage of being more tolerable and pleasant to patients since it induces a more gradual increase in blood glucose, thus reducing the risk of rebound hypoglycemia and other related complications. The present article reviewed the clinical data available regarding the possibility of screening or diagnosing altered glucose homeostasis, including type 2 diabetes mellitus, with the MMTT

Impact of food eviction on the nutritional status and adequacy of nutritional intake on children with food allergy

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Immunological impact of induced acute physical activity reduction

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Compliant contact force models in multibody dynamics : evolution of the Hertz contact theory

Over the last decades, several compliant contact force models have been proposed. However, no complete and systematic comparison has been done on these models, which provides information on their range of application and accuracy for use in different contact scenarios. Thus, the selection of an appropriate model for a given contact problem is still an important and challenging issue to be addressed. The Hertzian contact theory remains the foundation for almost all of the available force models, but by itself, it is not appropriate for most impacts in practice, due to the amount of energy dissipated during the impact. A good number of contact force models have been offered that augment the Hertzian law with a damping term to accommodate the energy loss during the impact process for small or moderate impact velocities. In this work, the main issues associated with the most common compliant contact force models of this type are analyzed. Results in terms of the dynamic simulations of multibody systems are presented, which allow for the comparison of the similarities and differences among the models considered.Fundação para a Ciência e a Tecnologia (FCT) - DACHOR - Multibody Dynamics and Control of Hybrid Active Orthoses (MIT-Pt/BSHHMS/0042/2008), BIOJOINTS - Development of advanced biological joint models for human locomotion biomechanics (PTDC/EMEPME/ 099764/2008), SFRH/BD/40164/2007, SFRH/BD/64477/200

Systems for superficial protection of concretes

Nowadays, it is consensual that the biggest degradation of concrete happens from outside to inside actions, due to the penetration of moisture, active gases and aggressive ions, by mechanical, physical and chemical causes that frequently act together. A low porosity, permeability and concrete penetration to moisture and gases are the first lines of defence against several deterioration mechanisms. The durability of concrete depends largely on how hard or easy fluids (water, carbon dioxide, oxygen) in liquid or gas form can migrate through the concrete hardened mass. When selecting the paint coating for concrete protection, importance is given to the properties of diffusion and permeability resistance, besides the properties of durability and chemical resistance. The paint coatings must stop the penetration of water and delay the influence of aggressive agents (CO2, SO2, Cl- ions), allowing the structure to breathe by a water vapour diffusion mechanism. Through tests of capillarity absorption, immersion absorption, porosity, water and oxygen permeability, a comparison was made between painted and non painted concrete specimens. Three different coating types were tested: silicon varnish; acrylic and epoxy paints. The results showed that, in general, all coatings reduce the porosity and the permeability. The epoxy paints proved to be the best ones

Diet and Asthma: A Narrative Review

Asthma is a chronic respiratory disease that impacts millions of people worldwide. Recent studies suggest that diet may play a role in asthma pathophysiology. Several dietary factors have been recognized as potential contributors to the development and severity of asthma for its inflammatory and oxidative effects. Some food groups such as fruits and vegetables, whole grains, and healthy fats appear to exert positive effects on asthma disease. On the other hand, a high consumption of dietary salt, saturated fats, and trans-fat seems to have the opposite effect. Nonetheless, as foods are not consumed separately, more research is warranted on the topic of dietary patterns. The mechanisms underlying these associations are not yet fully understood, but it is thought that diet can modulate both the immune system and inflammation, two key factors in asthma development and exacerbation. The purpose of this review is to examine how common food groups and dietary patterns are associated with asthma. In general, this research demonstrated that fruits and vegetables, fiber, healthy fats, and dietary patterns considered of high quality appear to be beneficial to asthma disease. Nonetheless, additional research is needed to better understand the interrelation between diet and asthma, and to determine the most effective dietary interventions for asthma prevention and management. Currently, there is no established dietary pattern for asthma management and prevention, and the nuances of certain food groups in relation to this disease require further investigation