What is the importance of micro-silicon powder in application
In the production process of ferrosilicon or silicon metal, high silica produces silicon powder in the ore furnace. After cooling, the particles of high fineness are formed, which are filtered and collected by the dust collector to obtain silicon powder. Usually, the color of silica fume is between light gray and dark gray. The silicon monoxide should produce colorless S2. Its color depends mainly on the content of carbon and iron oxide. The higher the carbon content, the darker the color. In addition, encrypted silica is grayer than natural silicon. The particle size of the silicon powder is less than 1 m, and the average particle size is about 0.1um, which is 1/100 of the diameter of the cement particle. As a result, the silica powder can be highly dispersed in the concrete and filled between the cement particles to improve the compactness. At the same time, the micro-silica powder has a high activity and can be used to purify by-products produced by the reduction of time, coke and sawdust, leading to complex reactions in the smelting process. Among them, when quartz stone and carbon are at 1750, the reduction reaction produces unstable carbon monoxide. When the temperature is above 2160, the silicon monoxide evaporates and is emitted. When it encounters air below 1100, it reacts more quickly with oxygen and more fully with cement water of 00 kg/m3. The first gray microsilica powder is usually transported in bags. Due to its small density and low transport efficiency over long distances, it mainly reacts with hydrogen and oxygen compounds produced by manual direct decomposition.
Silicon powder is mainly provided in two forms, namely, coarse silicon powder and dense silicon powder.
1. The original ash micro-silica powder, that is, the product directly collected by the dust collector, has a loose volume of about 150-2 bags. Silica powder is poured into the concrete mixer, resulting in large dust in the working environment and low work efficiency.
2. Encrypted silicon powder. In order to solve the problem that the original gray micro-silica powder is not suitable for long-distance transportation and low efficiency, a "silica powder encryption technology" is developed to improve the loose density of silica powder. The technology enables the raw ash micro-silica powder to roll and aggregate into small particles under the action of compressed air flow, and the loose volume of silica powder is increased to 500-700 kg/m3, which is greatly convenient for use. The particle cohesion of the small particles of silicon powder after encryption is weak, and it is easy to disperse in the mixing process of concrete mixer. Therefore, the silica powder particles can be put into the mixer after the aggregate feed to ensure the dispersion and good dispersion of the densified silica powder particles.
3. Quality standard of silica fume
The higher the silica content, the higher the performance of the silica powder, and the lower the content of other non-silica impurities. The content of silica fume is more than 85%, and the carbon of silica fume contains a part of adsorbent entraining agent in concrete. Therefore, the firing loss =7%(carbon and water content control) is again the fineness of silicon powder should be controlled at 45 um, the particle size should be large, and the sieve component should be less than 10%. Some scholars and experts have calculated that when replacing cement with 15% silica powder, the ratio of cement particles to silica powder particles in concrete is 1:200,000. It can be seen that silica fume is a fine powder material. The key to improve the strength of concrete is to improve the bond strength between cement paste and aggregate, reduce fresh water, prevent water accumulation on the surface of aggregate, so as to improve the density of the transition zone of the boundary surface and reduce the thickness of the transition zone of the boundary surface
The particle size of the silica fume is 100 times smaller than that of the cement particles and is filled in between the pores of the cement particles. The effect is the same as that of cement particles filling between aggregates, increasing the compactness of concrete. However, one of the prerequisites for silica powder in these actions is good dispersion in concrete.
Adding a small amount of silica fume to concrete, combined with high efficiency water reducing agent, can improve the physical and mechanical properties of concrete in all aspects, such as significantly reducing the segregation and bleeding of concrete, effectively improving the pumping performance of concrete, significantly improving the early and late strength of concrete, reducing the permeability of chloride ions, and effectively improving the chemical and wear resistance of concrete. Prevent concrete segregation during underwater construction. In short, silica powder has been widely used in high durability and high strength concrete.
In fact, the use of silica powder in concrete can be traced back to Norway in the 1940s. In the late 1970s, Northern Europe and North America also made great progress in the application of silica powder in concrete research. In the early 1980s, China has done a lot of research work on silica powder concrete, and has been widely used in water conservancy projects, and has achieved good results. The Ministry of Water Resources has also promulgated the Interim Provisions on Quality Standards of Silica Powder for Hydraulic Concrete. In addition, when silica powder is applied in concrete, it is strongly promoted by technological progress and social and economic factors, and the durability of concrete is paid more and more attention.
Practice shows that ordinary concrete works may be seriously damaged in a short time under harsh environment, which threatens the quality of the works and greatly reduces the service life of the works. However, the high performance concrete that meets various requirements is formulated by cement, silica ash, fly ash and water reducing agent, and has been successfully applied in various projects, which greatly promotes the progress of shotcrete technology, greatly reduces the rebound of shotcrete, doubles the construction efficiency, and significantly improves the performance of concrete. The flexibility, rapidity and economy of concrete construction have been raised to a new level.
Effect of silica fume on properties of hardened concrete
The transition zone of the interface between cement slurry and aggregate is about 5um thick, which is a weak link in concrete. When wollastonite mortar is added, the microstructure of the transition zone of the aggregate interface is similar to that of the slurry, and it is compact and uniform. The improvement of the performance of the hardened concrete is mainly attributed to the improvement of the interface structure and composition, as well as the improvement of the bond strength between the clean pulp and the aggregate, thus eliminating the "weak connection" problem of different composite components in the concrete, so that the concrete has the characteristics of composite materials, that is, the aggregate particles play a strengthening role in the concrete, rather than just inert filler. Adding silica fume to concrete can improve the impermeability of concrete and the ability to resist chemical corrosion effectively. However, there is also a disadvantage, that is, the concrete with silica fume is easy to absorb water during curing and must be stored in time to prevent cracking.
The above mainly introduces the performance of silica-doped concrete. In the future production and construction, more industries or fields will involve silicon powder.
It can be seen that the importance of micro-silicon powder in the application is reflected in the above content.