Navegando por Assunto "concreto"
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Item Influência do tipo de medição na determinação do módulo estático de elasticidade do concreto(Universidade Federal de Goiás, 2011-08-15) ARAÚJO, Suélio da Silva; GEYER, André Bortolacci; http://lattes.cnpq.br/0135796530510700; GUIMARÃES, Gilson N.; lattes.cnpq.br/0060821461126304The knowledge of the compressive strength and static modulus of elasticity is fundamental to the study of deformations of concrete, since deformations can cause cracks that compromise both the structural behavior of the element and serve as an entry to deleterious agents. For purposes of correlating values of compressive strength and static modulus of elasticity of concrete, cylinders were cast with different strengths, different types of strain measurements were taken, different specimen sizes and the loading speed of the testing machine. The specimens were tested at the age of 28 days to determine the compressive strength and static module of elasticity according to ABNT NBR 8522:2008, using different types of strain measurement devices: two mechanical dial indicators, surface bonded strain gages, clip gauges and LVDT (Linear Variable Differential Transducer). Two hundred and fifty eight specimens were cast with dimensions 150 mm x 300 mm and 100 mm x 200 mm using conventional normal strength concrete (NC - Class C30) and high strength concrete (HSC - Class C60). The experimental program was divided into two stages. First the static modulus of elasticity of concrete was measured to evaluate the accuracy of the method using different measuring devices and the accuracy of the method to a loading speed of 0.6 MPa/s. Then, the modulus of elasticity using different deformation measuring devices at a loading speed of 0.3 MPa/s and 0.6 MPa/s was measured. As for concrete NC and HSC, it was found that the specimens 100 mm x 200 mm obtained higher dispersion in relation to 150 mm x 300 mm specimens. In the first stage of the research, 100 mm x 200 mm specimens showed a higher dispersion when using mechanical dial gages and LVDT. The 150 mm x 300 mm NC class C30 specimens showed greater dispersion when using in mechanical dial gages and external strain gages. However, the HSC showed higher dispersion when mechanical dial gages and LVDT were used. In both concretes tested, the mechanical dial gages showed greater dispersion. In the second stage of the research, 150 mm x 300 mm specimens tested at the loading speed of 0.3 MPa/s showed greater dispersion when electrical strain gages and clip gauges were used. The 150 mm x 300 mm specimens tested at loading speed of 0.6 MPa/s showed greater dispersion when electrical strain gages and mechanical dial gages were used.Item Estudo de tratamentos com lítio no combate da reação álcali-agregado(Universidade Federal de Goiás, 2009-09-11) CÂNDIDO, Wilson Ferreira; HASPARYK, Nicole Pagan; http://lattes.cnpq.br/4932240949129648The alkali-aggregate reaction (AAR) is one of the deterioration processes of concrete that most affects the structures of hydroelectric plants, concrete dams and bridges. In recent years, the efficiency of lithium based compounds to mitigate RAA has been proven in both the prevention and repair of the affected structures. With regards to treatment, the main challenge nowadays is how to ensure the adequate impregnation of concrete with the lithium solution. Given this difficulty, the objective of this research is to investigate in laboratory conditions, the efficiency of various types of treatment, using a product based on lithium nitrate. The treatments sought to prevent or minimize the residual expansion of AAR, in particular the alkali-silica reaction (ASR), already under development in the concrete and mortar. The study was divided into two stages, the first one performed in concrete prisms, from an adaptation of the Brazilian standard NBR 15577-6/2008, and the second stage in mortar bars, from an adaptation of NBR 15577-4/2008. The treatments were performed after the specimens reached a predetermined level of defined expansion: 0.04% for the concretes and 0.18% for the mortars. In the case of the concretes, the treatments were electrochemical lithium impregnation and surface saturation with lithium, in addition to their respective reference procedures (impregnation and surface saturation with water). For the mortars, the situations tested were: vacuum impregnation with lithium, total saturation in lithium, surface saturation in lithium, water immersion and wrapping in plastic film. After each exposure/treatment condition, the specimens returned to the accelerated expansion attack process in order to evaluate the effectiveness of each treatment. The results demonstrated the efficiency of the lithium based composite to mitigate the residual expansion, both in the concretes as well as in the mortars, with a different behavior depending on the conditions used. The treatment that had the best efficiency in the concrete, under the applied experimental conditions, was the surface saturation of lithium, achieving a 90% reduction in the residual values of expansions at the end of the attack (73 days), taking as reference the surface saturation condition with water. The lithium electrochemical impregnation performed was able to mitigate the residual expansions, but only up to the age of 42 days after treatment, at which time the reduction was of 50%. In fact, at 73 days the expansions were similar to those of the untreated sample. All treatments with lithium performed in the mortars were able to mitigate the residual expansions at levels approaching reduction of expansion (about 87%), with the total saturation in lithium the most efficient condition.Item Concreto projetado como revestimento de túneis na Ferrovia Norte-Sul: análise segundo parâmetros de durabilidade(Universidade Federal de Goiás, 2010-09-24) MENESES, Antônio Davi Barbosa de; CASCUDO, Oswaldo; http://lattes.cnpq.br/3336749062812376The present work aims to analyse the durability parameters of the shotcrete, comparing the dry and wet projection systems, of the concrete resulting from the projection in plates and from the test specimens extracted from the tunnels structures of the North-South Railway, tract 01, in Anápolis-GO. This work considers an experimental research concerning the shotcrete behavior for dry-mix and wet-mix projection systems, by using testing indicators of the main durability parameters coming from national and international specifications. So, the experimental program involves a comparative assessment among the projection systems of current use in shotcrete, considering the comparative analysis between projected plates (control) and extracted test specimens from the tunnels on what refers to meeting the requirements related to durability. Therefore, the experimental program showed as independent variables: type of projection system (whether by means of dry-mix or wet-mix shotcrete) and the extraction of test specimen (from the control plates or from the tunnels structure). For each type of projection (dry-mix and wet-mix shotcrete), three plates were cast (normally used for concrete technological control) in conditions similar to the work-site, with the test specimens extraction been carried out according to pre-established ages. Eight test specimens were extracted from the just-builts tunnels generating thus samples to the durability associated tests, such as: capillary water absorption, immersion water absorption, concrete electric resistivity, water penetration under pressure, penetrability of chloride ions and concrete compressive strenght. Test specimens extracted from the tunnels and the from the plates were also submitted to testings of compressive strenght and mix-proportion reconstruction. The concrete extracted from tunnels showed worse results comparing to the parameters expected from the projected concrete requirements for road and rail tunnels, and it also demonstrated results which were inferior to the ones obtained from the plates. From a general assessment view, we could verify losses of durability properties of the shotcrete extracted from tunnels in reference to the projected plates.Item AVALIAÇÃO DO DESEMPENHO DE CONCRETOS COM ADIÇÕES MINERAIS QUANTO À CORROSÃO DAS ARMADURAS INDUZIDA POR CLORETOS(Universidade Federal de Goiás, 2007-08-29) OLIVEIRA, Andrielli Morais de; CASCUDO, Oswaldo; http://lattes.cnpq.br/3336749062812376The present work aims to study the performance of concrete with regard to the action of chloride ions, evaluating the influence of both mineral additions and water/binder ratio (w/b), considering kinetic and thermodynamic aspects of the corrosive phenomenon. A experimental research was carried out considering the following variables: the presence of mineral additions in partial substitution to the cement weight (10% of silica fume; 25% of fly ash; 10%, 20% and 30% of metakaolin) and the water/binder ratio (0,40 and 0,55). Thus, cubic concrete test specimens were produced, in addition to cylindrical test specimens for concrete characterization in relation to the compressive strength, specific mass, void ratio and capillary water absorption. After 645 days of casting, the cubic concrete test specimens were submitted to the chlorides attack during 308 days, totality 44 weekly cycles of immersion in chlorides aggressive solution. They were monitored, throughout this period, by means of techniques, such as: the concrete electric resistivity, the half-cell potential, the polarization resistance and the electrochemical impedance spectroscopy. At the end of the experiment, visual inspections of reinforcing steels allowed to observe their superficial aspects after attack. As general result, it was gotten that the incorporation of mineral additions to the concretes promoted significant profits in all the evaluated properties, evidencing the beneficial effect of these additions in concretes exposed to aggressive conditions, specially in those in which there are chloride ions. In this direction, the statistical analysis has shown evidences that concretes with silica fume and metakaolin achieved the best results of electrical resistivity. In relation to the half-cell potentials, the reference concrete (without mineral additions) presented the worst performance, with an indication of despassivation in the reinforcing steels accentuated fall in the values of resistance of polarization with the time, proving the susceptibility of these systems to the action of chlorides. The concrete with mineral additions did not present depassivation of the reinforcing steels meaning that these systems possess great durability and service life in relation to those without mineral additions