RESUMO: Este trabalho tem como objetivo avaliar a influência dos fatores de forma nos ensaios de resistência à compressão em testemunhos de concreto. Para isso foram moldadas e extraídas amostras de concreto de 20 e 30 MPa. Variou-se o diâmetro da base das amostras (50 e 100mm) e sua esbeltez (de 1 a 3). Para verificar a diferença entre amostras moldadas e extraídas, no momento da fabricação do concreto foram moldados corpos de prova de 100 x 200 mm e dois blocos de 500 x 630 x 270 mm de onde os testemunhos foram extraídos. Os dados indicam que os valores de resistência à compressão obtidos em testemunhos de 50 mm de diâmetro tenderam a ser mais baixos do que os obtidos com 100 mm. A magnitude desta diferença é afetada pelo nível de resistência do concreto avaliado. Além disso, a resistência dos testemunhos extraídos foi menor ou igual à obtida em corpos de prova moldados, mesmo mantendo as condições de cura constantes entre o bloco e os corpos de prova normalizados. Dessa forma, o que pode ser concluído neste estudo é que, a resistência real da estrutura é minorada pelo procedimento da extração, sendo este influenciado por diversos fatores. Dentre as possíveis variáveis da extração, o diâmetro foi um fator que demonstrou influência significativa na propriedade do material ensaiado
ABSTRACT: This study aims to evaluate the influence of shape ratio in compressive strength tests. Concrete specimens with 20 and 30 MPa was made and extracted. The diameter of the specimen’s base was 50 and 100mm and its slenderness ratio vary 1 to 3. To verify the difference between molded and samples taken at the time of manufacture of concrete molded bodies were evidence of 100 x 200 mm and two blocks of 500 x 630 x 270 mm where witnesses were extracted. The results indicated that the axial compressive strength values obtained with concrete cores extracted of 50 mm diameter tended to be lower than those obtained with 100 mm, and the magnitude of this difference is affected by the resistance level of the evaluated concrete. Furthermore, the resistance of concrete cores extracted was less than or equal to the obtained in the molded test specimens, while maintaining constant the curing conditions between the block and standard specimens. Thus, it can be concluded in this study is that the real strength of the structure is alleviated by the extraction procedure, which is influenced by several factors. Among the possible variables of extraction, the diameter was a factor that showed a significant influence on the property of the material tested.
Large constructions, such as concrete dams, commonly use aggregates extracted from rock masses near the implantation sites, which may contain sulfide minerals in its composition. These aggregates, inside the concrete, may oxidize, forming sulfate ions (SO 2À 4 ), which can cause the internal sulfate attack. Therefore, in order to study aggregates for concrete dosages of these structures, aimed to evaluate on this paper the oxidation process of aggregate containing sulfide minerals in amounts of up to 5.0 %, by way of studies into the effects of particle size and pH of the medium (Study 1) and the pyrite content (Study 2). In Study 1, diabase aggregates containing pyrite (FeS 2 ) were separated into three particle sizes (sand, coarse aggregate 0 and coarse aggregate 2). Samples were analyzed in two groups and immersed in solutions of distilled water and calcium hydroxide, with pH and electric potential measurements. In Study 2, diabase sand from the same origin of Study 1, but in smaller particle size, and natural aggregates (sand) with the addition of pyrite in four levels (0, 0.5, 1.0 and 5.0 %) were immersed in distilled water, with measurements of pH, electric conductivity and total dissolved solids. The results of the tests, under constant oxygenation, showed that the reduced grain size and alkaline medium accelerate the oxidation reactions, in contrast to aggregates immersed in neutral solutions.Comparing the results by ANOVA test indicates the presence of around 0.5 % of sulfide mineral in the diabase aggregates, with better results from monitoring of electric conductivity and dissolved solids in contrast to pH readings.
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