| Summary: | 博士 === 國立中興大學 === 土木工程學系所 === 96 === This research investigates the effects of the addition in mortar and concrete with four types of polypropylene fibers including monofilament, staple fibers with crimp, staple fibers, and fibrillated. The experimental results show that all four types of fibers can enhance the properties of mortar and concrete, and the more the fiber content is, the better the properties of concrete are. In addition, the staple fiber with crimp has the best performance among the four types. Because the staple fiber with crimp has higher fineness and better dispersion, it ensures that every unit volume of concrete uniformly contains more quantity of fibers. The evenly dispersed fiber can resist drying shrinkage during the plastic stage and block the expansion of micro cracks, so it achieves optimal plastic crack control. Also, the staple fiber with crimp also has higher elastic modulus and tensile strength, so the numerous fibers that evenly distributed in the concrete can disperse stress and therefore increase compressive strength, splitting tensile strength, flexural strength, impact resistance, and abrasion resistance.
Moreover, this study investigates mechanical properties of steel-polypropylene hybrid fiber-reinforced concrete and polypropylene hybrid fiber-reinforced concrete. In steel-polypropylene hybrid fiber-reinforced concrete, the research focuses on two kinds of steel fibers, including indented steel fiber and hooked-end steel fiber. The fibers are added at three ratios of 15kg/m3, 20kg/m3, and 25kg/m3 to polypropylene fiber-reinforced concrete. The results show that the properties of steel-polypropylene hybrid fiber-reinforced concrete are better than those of steel fiber-reinforced concrete. There is positive correlation between the quantity of steel fiber and the mechanical properties of hybrid fiber-reinforced concrete, such as compressive strength, splitting tensile strength, modulus of rupture, toughness index, and impact resistance.
The quantity of steel fiber also affects abrasion resistance and drying shrinkage strain. Additionally, hooked-end steel fibers can bear more load than indented steel fibers.
On the other hand, the polypropylene hybrid fiber-reinforced concrete is used in two forms of polypropylene fibers including coarse monofilament, and staple fibers. The content of the former is at 3kg/m3, 6kg/m3, and 9kg/m3, and the content of the latter is at 0.6kg/m3. The experimental results show that the properties of polypropylene hybrid fiber-reinforced concrete are better than that of single fiber-reinforced concrete, in terms of the compressive strength, splitting tensile strength, and flexural properties.
The above two forms of fibers work complementarily. The staple fibers have better fineness and dispersion so they can restrain the cracks in primary stage, and the monofilament fibers have higher elastic modulus and stiffness. When the monofilament fiber content is high enough, it is similar to the function of steel fiber. Therefore, they can take more stress during destruction. In addition, hybrid fibers disperse throughout concrete, and they bond with mixture well, so the polypropylene hybrid fiber-reinforced concrete can effectively decrease drying shrinkage strain.
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