| Summary: | 碩士 === 國立臺灣科技大學 === 營建工程系 === 106 === Porosity is an important factor of concrete. It affects the durability and engineering properties of the concrete. There are two causes for the formation of concrete pores. One is due to the air being entrappd during the concrete mixing and placing, leaving space inside the concrete. The other is due to the addition of air entraining agent to produce millions of small independent air bubbles in the production process in order to increase the workability and durability of the concrete. On the other hand, the pervious concrete increases the porosity of concrete for the purpose of water permeability. Currently most of the related researches on influence of porosity on engineer porperties are focusing on the relationship between porosity and strength. There are few studies for the influence of porosity on elastic modulus and Poisson’s ratio. Becaue the numerical analysis has the advantages of high speed and getting large amount of data from analysis. Therefore, the finite element method is used in this study to establish four kinds of porosity models to find out the relationships among the porosity, the elastic modulus and the Poisson’s ratio.
In this study, standard cylindrical concrete specimens of D100 mm and L200 mm were used with the material properties of density ρ = 2300 kg/m3, elastic modulus E = 30 GPa, Poisson’s ratio ν = 0.3, and four kinds of porosity of 5%, 10%, 20%, 40% respectively. The finite element software of Abaqus was used to simulate the static uniaxial compression test of cylindrical specimens. The resulting Poisson’s ratios of 0.286, 0.271, 0.237, and 0.145, and the elastic modula of 27.069 GPa, 24.165 GPa, 18.251 GPa, and 6.660 GPa were obtained, respectively. By using linear regression, the relational formulas among the porosity, the Poisson’s ratio and the elastic modulus are found. In comparison with the results of publicized research papers, the results of numerical analysis are close to those on the papers.
In addition, after the pervious comcrete standard cylindrical specimens was subjected to the axial pressure, different deformation was shown at the lateral surface of the cylindrical specimen. The larger the porosity, the larger the deformation and the irregularity formed. When the porosity was increased to 40%, some parts of the specimen were concaved. After making statistical analysis of the result data, it was found that the variation of Poisson’s ratio increased as the porosity increased. It shows that when we measure the cylindrical specimen with lager porosity, the error of lateral displacement becomes larger also.
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