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Application of silica fume in steel fiber jet concrete

 In the1970s and the 1980, with the silica fume and concrete mixture standards promulgated by Northern Europe and North America, the research and application of silica fume have rapid developments in worldwide. Silica fume is to filter out the smoke of a furnace gas contains a large number of small amorphous silica (SiO2) particles. It is a by-product of ferrosilicon or silicon metal production process by the electric arc furnace in high purity quartz, coke and wood chips generated by the reduction. Age compressive strength of the accelerating agent is not mixed significant overall improvement, quick-setting agent content increases, the compressive strength of each age decreases. According to the characteristics of the tunneling process arrangements and arch injection rebound slightly larger amount of steel fiber reinforced sprayed concrete side walls and the arch part of the open, which can receive satisfactory results. Doped add a certain amount of silica fume on steel fiber reinforced shotcrete has played the role of the tackifier, thereby reducing the amount of springback and once sprayed layer thickness, and improve the work efficiency. In addition, because the doped Tim silica fume reduced even without the liquid accelerating agent, making the expensive cost of materials is zero in the jet sidewall, and greatly reduces the cost of the project. Silicon powder in China is a relatively new type of additive which has been promoting the use of, used for high strength concrete, but gradually tunnel engineering design and construction in Norway and France. Not limited to the design and construction of the tunnel of Norway and France, but should be widely used in the normal sprayed concrete, especially the initial support, such as not earthquake-prone with or without blasting vibration soft rock tunnel construction can be less or no accelerating agent The use of silica fume replaced. This will not only guarantee the quality of sprayed concrete, as well as lower the cost of the project. Use data from a large number of foreign general to use the robot to jet operations, pumping form of wet spraying machine more doped Tim silica fume concrete pumping strong, therefore, a sprayed layer thickness while the rebound. The amount was very low. On conservation doped Tim silica fume shotcrete important, even if the tunnel should be distinguished from the doped silica fume concrete tunnel and conservation. In other words, the conventional cave for Nature Conservation difficult to achieve the indicators of the jet silica fumes concrete age. Caused by small particles, Silica fume produces much dust. So manufacturers generally made a special densification when taking into account the construction needs and transport. It reduces losses and environmental pollution. Therefore, the densification of silica fume take restitution, dispersed evenly in sprayed concrete. The mixing time is 1 to 2 minutes longer than ordinary shotcrete. China now has a part of metal powder exporters that are in production of ferrosilicon produce the micro-silica fume as a fringe production. The SiO2 content and other indicators of its products are mostly can not meet the international standards. The rigorous tests are necessary to determine the various parameters.Source:http://www.mhcmp.com

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