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Silica fume particles mixed with cement concrete can increase the concrete mixing tough soft sticky cohesion and hardened concrete fill density. It has significant ultrafine aggregate effect. In sharp condensation of gas, liquid and solid phase change process, silica fume’s formation is varied with large and small. The spherical particles with smooth surface will play the role of frictional resistance within the particles in the cement concrete. It will help spread the filling micro pores and enhance the compactness of the fine particle shape effects. Silicon powder condensation process is extremely rapid resulting in that silica was too late to form crystal. Its crystal structure is amorphous silica and the high activity volcanic material. If doped in cement concrete, it can significantly improve abrasion resistant, anti erosion impermeability, frost resistance and other properties with the effect of ash. Silica fume does not apply to all occasions. The development of concrete technology must carefully analyze the specific usage occasions, and confirm the use of silica fume to get the desired results. Silica fume must be used in the appropriate composition of concrete (mix ratio), low water-cement ratio (w / cm) and with superplasticizer concrete. Early studies found that the silica fume concrete mix than in water-binder ratio of 0.6 or higher, unreasonable. Combination of silica fume and other supplementary cementitious materials nickel powder is growing. Initially, these materials are seen as competing materials, but now more widely recognized: the best concrete is often the result of combination use of these materials. Per unit volume of concrete, silica fume in reducing the amount, especially of concrete exposed to chloride environment. The first bridge deck concrete containing 12% to 15% silica fume (by weight of cement), and then a few years silica fume content is reduced to about 8%. Currently, if used, and the combination of fly ash or ground slag content of the silica fume is reduced to about 5%. Silica fume concrete must have appropriate conservation. If there is no maintenance, and silica fume bring concrete advantages can not be achieved. If you do not appropriate conservation requirements into concrete technical standards and not on the project, the implementation of conservation requirements, best not to use the silica fume concrete. The use of silica fume concrete must pay attention to every aspect of construction in concrete production. The full mixing manganese powder process, silica fume dispersion is related to the properties of concrete. Mixing is not good and silica fume dispersion poor may not get the expected performance of concrete. 'Fixed target' performance to determine the concrete compressive strength may be a suitable method. However, to determine the performance must be carefully and fully understand their situations and conditions. Have the same strength of concrete, test other performance parameters, performance is not necessarily the same. Experience of wipe surface in silica fume concrete has shown that the least plastering can get a more durable concrete and also prevent plastic shrinkage cracking. In chloride environment, silica fumes concrete has resistance to chloride ion penetration. So far, the test of actual structures proves that the good performance of silica fume concrete exists. With time goes, chlorine penetration rate are significantly reduced. Now, the actual number of silica fume concrete structure has enough and exposure time is long enough. Today, recipe products and slurry silica fume has disappeared in the market. Almost all the commercial concrete and precast concrete companies are densified silica fume.Source:http://www.mhcmp.com
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