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Suggestions on fiber content in cement concrete

wallpapers Green Building 2020-02-18 PDF Format
The most significant change of the mechanical properties of concrete by fibers is not to improve its strength indexes such as compressive strength and flexural strength but to improve the fracture energy and flexibility of concrete significantly. The general indicators of concrete compressive strength, tensile strength, and other properties are used to measure synthetic fiber concrete, which can not fully reflect the improvement of the fundamental properties of concrete by fibers. As mentioned earlier, the role of synthetic fibers in concrete/mortar is comprehensive. It has the dual effects of strengthening and toughening under low dosage (about 0.1% by volume). Especially for high-strength concrete doped with synthetic fibers, mainly its toughening effect is used. From a large amount of laboratory data and engineering trial data, the compressive strength index has increased and decreased. However, both the magnitude of change and the absolute value are not enough to affect the fundamental design requirements of concrete. The reason why some strength indicators are sometimes improved is also due to the additional effects caused by solving some cracks.
How to add fiber content?
From synthetic fiber materials, it is beneficial to concrete in a broad sense because of its acid and alkali resistance and physical toughness and reinforcement. But in the end, what amount is appropriate, the intellectual and engineering circles have different opinions. From the essence of the role of synthetic fibers in concrete, as long as synthetic fibers are added, it will inevitably solve the inherent defect of concrete-brittleness, so there is nothing wrong with adding it. It seems that the fuzzy theory is used to solve a range. The change is better. However, from the perspective of design and construction, there must be quantified indicators. From the standpoint of the workability of concrete, we have to consider adapting to the relevant requirements of development.
 
The amount of fiber should be determined according to the purpose of use, taking into account the specific proportion of concrete, aggregates, and other admixtures. At present, most manufacturers' recommended dosage data come from the theoretical conclusion of the experimental volume data of fiber volume dosage of 0.05% and 0.1%. Fibers made from different materials have different specific gravity. According to the volume blending amount, the fiber blending amount is different. In the application process of more than 1,000 various practical projects in China, Dura fiber has experienced 0.5, 0.67, 0.7, 0.8, 0.9, 1.0, 1.3, 1.36, 1.5 per cubic meter of concrete / mortar mixing for different requirements. In the case of unequal kg, they all belong to low dosing amounts, and all have good engineering effects. When the dosing amount is 0.7--0.9 kg / m3, they can already meet the general requirements of the design. Generally speaking, the amount of anti-cracking, impermeability, and wear resistance is relatively high; the amount of ultra-fine sand is relatively high; the engineering parts and applications with special requirements must have a special ratio. Except for special applications, high dosages are not necessarily applicable in general engineering applications.

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