details on silica fume concrete pdf .
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silica fume concrete pdf
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details on silica fume concrete pdf .
04-04-2017, 12:41 PM
Silica smoke is a byproduct of the production of silicon metal or ferrosilicon alloys. One of the most beneficial uses for silica smoke is concrete. Due to its chemical and physical properties, it is a very reactive pozzolana. Concrete containing silica fume may have a very high strength and can be very durable. Silica fume is available from suppliers of concrete mixtures and, when specified, is simply added during the production of concrete. Placement, finishing and curing of silica-smoke concrete require special attention from the concrete contractor. Metal silicon and alloys are produced in electric furnaces as shown in this photo. The raw materials are quartz, charcoal and wood chips. The smoke that results from the operation of the furnace is collected and sold as silica fume, instead of being poured. Perhaps the most important use of this material is as a particular mineral blend. Silica smoke consists mainly of amorphous (non-crystalline) silicon dioxide (SiO2). The individual particles are extremely small, about 1/100 the size of an average cement particle. Due to its fine particles, large surface area, and high SiO2 content, silica smoke is a highly reactive pozzolan when used in concrete. The quality of the silica fume is specified by ASTM C 1240 and AASHTO M 307.
High-strength concrete is a very economical material for transporting vertical loads in high-rise structures. Until a few years ago, 6,000 psi of concrete was considered high strength. Today, using silica fume, concrete can be easily produced with a compressive strength of more than 15,000 psi. The structure shown on the right above used silica-smoke concrete with a specified compressive strength of 12,000 psi in columns that reach from the ground through the 57th story. The major cause of concrete deterioration in the United States today is thaw-induced corrosion or marine salts. Silica concrete with a low water content is highly resistant to the penetration of chloride ions. More and more transport agencies use silica fumes in their concrete for the construction of new bridges or the rehabilitation of existing structures.
Concrete smoke silica does not just happen. A specifier must make the conscious decision to include it in the concrete to achieve the desired concrete properties. Assistance in specifying silica-smoke concrete for high strength or longer durability can be obtained from the SFA or from major mixing suppliers.
Silica smoke for use in concrete is available in wet or dry forms. It is usually added during the production of concrete in a concrete plant as shown in the photo. Silica-smoke concrete has been successfully produced in both the central blending and drying plants. Assistance is available on all aspects of silica fume management and its use to produce consistent and high quality concrete. The silica-smoke concrete must be transported, placed, finished and cured following the good concreting practices described by the American Concrete Institute. Flat jobs containing silica concrete in general require less finishing effort than conventional concrete. The photo shows the "one-pass" finishing process in which the silica-smoke concrete is placed, consolidated and texturized with little or no waiting time between operations. To obtain the greatest benefits of using silica fume, concrete must be effectively cured. The SFA or your concrete supplier can provide any necessary assistance with respect to construction operations.
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