Silica fume is a byproduct in the carbothermic reduction of highpurity quartz with carbonaceous materials like coal, coke, woodchips, in electric arc furnaces in the production of silicon and ferrosilicon alloys. Silica fume is a pozzolanic material that is used with portland cement to produce portland pozzolana cement. It is a by product from an electric arc furnace used in manufacture of silicon metal or silicon alloy. Apr 08, 2017 effect of fly ash and silica fume on concrete properties. Minimization of cracking in new concrete bridge decks nevada. It has been found experimentally that very high strength silica fume concretes undergo early cracking when deformation. The use of silica fume in concrete shows a tendency for plastic shrinkage2, drying shrinkage3 and cracking resulting in water penetration and corrosion of. This provides architects and engineers with greater design flexibility. Khedr and idriss 1995 studied the effectiveness of silica fume concrete in resisting damage caused by corrosion of embedded steel using an accelerated impressed voltagetesting setup. The ability of high c3a cement to complex with chlorides results in the formation of insoluble compound, able to reduce the mobility of free chloride ion to the reinforcement concrete surface.
Concrete institute disclaims any and all responsibility for the. It is an excellent for use as a portland cement supplement. Cracking can occur in plastic concrete when rapid evaporation of bleedwater from the concrete surface causes the surface to dry out. Used in the right proportion it can also reduce the overall cost of the concrete. The objective of this program was to establish a mix for the production of superior quality concrete using silica fume and type 10 cement at lower quantities. Effect of age on compressive strength of silica fume based geopolymer concrete. For both concrete compressive and tensile strength tests, the scc with silica fume gives the highest values followed by scc with fly ash and then pc concrete for all curing periods and conditions. Test methods for chemical analysis, moisture content and loss on ignition, bulk density, specific surface, air entrainment of mortar, strength acitivity index. The principle physical effect of silica fume in concrete is that of filler, which because of its fineness can fit into space between cement grains in the same way that sand fills the space between particles of coarse aggregates or the cement grains fill the space between the sand grains. This increase is caused primarily by the high surface area of the silica fume. Addition of silica fume to concrete has many advantages like high strength, durability and reduction in cement production.
Fresh concrete containing silica fume is more cohesive and less prone to segregation than concrete without silica fume. Effect of fly ash and silica fume on concrete properties. Silica fume is very high in fineness and in silica content, and a very effective pozzolanic material depending on free lime content of cement use. Under hydrostatic pressure, other forms of waterproofing are required. What are the main effects of adding micro silica silica. Additionally, silica fume reduces bleeding by physically blocking the pores in the fresh concrete. The material shall composed of silica fume, mostly of amorphous silica. What are the main effects of adding micro silica silica fume. Cracking tendency and drying shrinkage of silica fume concrete. Properties of the fumed silica and silica fume have been shown in table 1. Topics will be delivered by concrete industry veterans and subject matter experts with a wide range of experience.
Cracking tendency and drying shrinkage of silica fume concrete for bridge deck applications. In the united states, silica fume is used predominantly to produce concrete with greater resistance to chloride. Evaluation of the installation and initial condition of rosphalt overlays on bridge decks michael m. Silica fume concrete with an hrwr is more cohesive and sticky than conventional concrete. Since the silica fume based geopolymer concrete are subjected to thermal curing for a period of 6 h and kept in a room temperature for a desired period. An experimental program carried out by ravikumar et al. Fresh and hardened properties of silica fume concrete is superior to conventional concrete. Even though silica fume densifies concrete, it is not a waterproofer. Traditionally used in highrise buildings for the benefit of smaller columns increasing the usable space highstrength concrete containing silica fume is often used in precast and prestressed girders allowing longer spans in structural bridge designs.
Silica fume, also known as microsilica, cas number 69012642, einecs number 2737611 is an amorphous noncrystalline polymorph of silicon dioxide, silica. The silica fume association operates under a cooperative agreement with the fhwa to help provide technology transfer on highperformance concretehpc to state and local transportation departments. Fresh concrete containing silica fume is more cohesive and less. Effect of fly ash and silica fume on compressive strength of. Nov 12, 2018 cracking can occur in plastic concrete when rapid evaporation of bleedwater from the concrete surface causes the surface to dry out. The use of silica fume concrete for fulldepth bridge deck. Condensed silica fume pennsylvania state university. Silica fume is defined by the american concrete institute as very fine noncrystalline silica produced in electric arc furnaces as a byproduct of the production. Department of transportation federal highway administration virginia center for transportation innovation and research.
Effect of fly ash and silica fume on compressive strength. Concrete containing silica fume shows substantial reduced bleeding. This study presents an experimental study on selfcompacting concrete scc with two cement content. Silica fume will chemically react with the calcium hydroxide released by the hydration of portland cement to form compounds possessing superior cementitious properties. Although the magnitude of alsf ratio increases by 0.
It may be added directly to concrete as an individual ingredient or in a blend of portland cement and silica fume. A balanced view is presented of the effect of condensed silica fume on the physical, chemical, mechanical, and durability aspects with respect to cement pase, mortar and concrete. The concrete was to exhibit superior durability characteristics when exposed to freezethaw, as well as resistance to other deleterious effects such as scaling, cracking and corrosion. To achieve a maximum improvement in strength and durability, silica fume concrete should contain a high. The work involves three types of mixes, the first consisted of different percentages of fly ash fa, the second uses different percentages of silica fume sf, and the third uses a. Fly ash increases workability when compared with conventional concrete with same water content. This will produce expansive ettringite and cracking of the concrete. Silica fume modified concrete sfmc is a concrete mixture used in rigid overlays to decrease the permeability of the concrete and thus increase the durability of the bridge deck. Its an ultrafine powder recovered from the production of silicon metals and alloys in electricarc furnaces. Silica fume is a very common scm that is frequently used to increase the strength and durability of a concrete structure. This download a contains several papers, technical articles and two instructional videos on finishing, and curing, silica fume concrete an integral step in the producing crack free structures. This area contains information and resources of special interest to anyone involved with producing, or placing silica fume concrete.
Silica fumes behavior in concrete is predictable, but still dictated by the materials composition. Silica fume concrete silica fume for sale, microsilica. Evaluation of alternative materials to control dryingshrinkage. The combustion process creates silicon dioxide molecules, which condense to form particles. The use of good quality fly ash with a high fineness and low carbon content reduces the water demand of concrete. Silica fume is often used in highstrength concrete or highperformance concrete. The causes and prevention of cracking in concrete basf. Silica fume is much cheaper than cement therefore it is very important form economical point of view. Use of silica fume does not signi cantly change the unit. Cracking for highstrength silica fume concrete develops much faster and is signijcantly wider than that of normalstrength concrete. Tony kojundic is a founding board member of the silica fume association, and business manager for elkem materials in pittsburgh, pa. It discusses the nature and types of condensed silica fume, physical characteristics, product variation and problems involved in. These bridge decks were monitored both during construction and after construction to evaluate their constructability and performance.
One disadvantage is low early strength development than portland ceme. These properties indicated silica fume concrete would have a number of advantages when used for the repair of concrete structures. It is a very finely divided material, many hundreds of times finer than cement. The individual particles are extremely small, approximately 1100th the size of an average cement particle. Factors that influence the rate of evaporation of bleed water either separately or collectively include. Silica fume sf is the byproduct of the manufacture of silicon for the computer industry. Silica fume is used in a variety of cementitious concrete, grouts and mortars, refractory, elastomer and polymer applications. It discusses the nature and types of condensed silica fume, physical characteristics, product variation and problems involved in its handling and transportation. Silica fume concrete is composed of cement, silica fume, fine aggregate, coarse aggregate, and water. This specification covers silica fume for use in concrete and other systems containing hydraulic cement. Because of its chemical and physical properties, it is a very reactive pozzolana.
Evaluation of the installation and initial condition of. These combined properties lead to an extended life expectancy in corrosive environments resistance to chlorides, acids and sulphates and improved strength. Four silica fume concrete mixes with silica fume contents of 5%, 10%, 15%, and 20% of the total cementitious material content were prepared along with one plain portland cement concrete mix and. Cracks in concrete can be reduced or often prevented by reducing drying shrinkage. Silica fume improves the characteristics of both fresh and hard concrete.
Pandit3 concluded that addition of micro silica to concrete increases the strength more. In the overlays, five different materials were used. A disadvantage to utilizing silica fume in cement is the cost. Jan 26, 2017 silica fume concrete silica fume is an artificial pozzolona having high pozzolonic activity. This ultrafine material will better fill voids between cement particles and result in a very dense concrete with higher compressive strengths and extremely low permeability. Examples european silica fume committee promotion of. Silica fume concrete transportation research board. Silica fume is not a new product by one company but is a major raw material that has been available over 40 years. Guide to using silica fume in precastprestressed concrete.
The effect of condensed silica fume on the strength development in concrete was studied by replacement of 0, 5, 10, and 20% cement by silica fume. In addition to its pozzolanic properties its is also a very good filler due to its particle size. Astm c1240 20 standard specification for silica fume. Briefly, silica fumea term often used interchangeably with the term microsilica. Low cracking concretes for the closure pours and overlays. Free from the presence of salts that absorbs the moisture from the atmosphere and lead to efflorescence. The rate of increase in compressive strength of silica fume based geopolymer concrete is 1. Silica fume concrete silica fume is an artificial pozzolona having high pozzolonic activity. Microsilica in concrete types, properties, and practical.
Fumed silica is being used in various fields such as pharmaceuticals, paints, adhesives and sealants, plastics, rubber and ink except for concrete. This alternative is a fulldepth silica fume concrete bridge deck. Shrinkagereducing admixtures and the only crackreducing admixture on the market, masterlife cra 007, will reduce drying shrinkage, and minimize time to cracking and width of cracks if cracks do occur, to improve. Our lehigh cement company brand for a fly ash blended cement is intercem, which we produce at our edmonton, canada cement plant today. Reduce and prevent cracks in concrete cracks in concrete can be reduced or often prevented by reducing drying shrinkage. Concrete mix proportioning using micro silica proceedings of 4 th irf international conference on 19 april 2015, cochin, india, isbn. Astm c1240 20 standard specification for silica fume used. This increased durability and resilience can be attributed to decreased permeability and absorption. Many articles have described silica fume sf and its effect on portland cement concrete 24. Silica fume concrete is widely used in concrete and fiber cement industries. Silica fume has become the world standard for chloride corrosion situations and also to improve dramatically the water tightness of concrete structures. It deals with permeability, corrosion, carbonation and resistance against freezingthawing, sulfate, alkaliaggregate. Benefits of using silica fume in concrete civil engineer. It has many advantages and its advantages outweigh its disadvantages.
The condensed silica fumeportland cement mixture must be protected for the first 7 days from drying shrinkage. Department of civil engineering, north eastern regional. Founded in 1904 and headquartered in farmington hills, michigan, usa, the american concrete institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensusbased standards, technical resources, educational programs, and proven expertise for individuals and. Effect of silica fume on concrete properties and advantages for kurdistan region, iraq mezgeen abdulrahman rasol surveying department, zakho technical institute, duhok polytechnic university, duhok, kurdistan region, iraq email. Join master builders solutions for lets talk concrete. Silica fume has been used all over the world for many years in the area where high strength and durable concrete were required.
Concrete made with silica fume can dramatically increase corrosion resistance, decrease alkalisilica reactivity and increase resistance to sulfates. Chapter 3 describes primary uses of silica fume in concrete. To optimize the benefits resulting from the use of condensed silica fume, it must be thoroughly dispersed in the cement mixture. It is an ultrafine powder collected as a byproduct of the silicon and ferrosilicon alloy production and consists of spherical particles with an average particle diameter of 150 nm. The water demand of concrete containing silica fume increases with increasing amounts of silica fume, see carette and malhotra and scali et al. Silica fume consists primarily of amorphous noncrystalline silicon dioxide sio2. Effect of silica fume on concrete properties and advantages. The total length of the three gorges dam is about 2308m, the dam height is 185m, and the normal water storage level is 175 meters, and the investment is rmb 5 billion 200 million yuan. Because of its fine particles, large surface area, and the high sio2 content, silica fume is a very reactive pozzolan when used in concrete. Silica fume in shotcrete pennsylvania state university. It reacts with lime and water in a similar way to fly ash, also known as pulversided fuel ash pfa, to produce a binder.
Founded in 1904 and headquartered in farmington hills, michigan, usa, the american concrete institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensusbased standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design. Silica fume created during silicon alloy production has a higher silica content, while silica fume produced as a result of manufacturing ferrosilicon alloys has a significantly lower silica content. Silicafume microsilica concrete in bridges in the united. Verma7 found that silica fume increases the strength of concrete more 25%. For instance, it has higher compressive and flexural strength. In the wetmix process, the silica fume can be introduced as. Results indicate that the free shrinkage for different concretes does not depend on the unit water content or weight loss and that highstrength silica fume concrete shows higher shrinkage and lower creep. Silica fume, a byproduct of the ferrosilicon industry, is a highly pozzolanic material that is used to enhance mechanical and durability properties of concrete. Compressive strength of silica fume based geopolymer concrete. Silica fume influences the thickness of transition phase in mortars and the degree of the orientation of the ch crystals. If the silica fume concrete contains superplasticizers, both the shear resistance and the cohesiveness of the concrete will be reduced, and improved flow will result. Silica fume is a mineral admixture, a very fine powder of spherical particles that average 0. Mar 28, 2016 silica fume is very high in fineness and in silica content, and a very effective pozzolanic material depending on free lime content of cement use.
The optimum silica fume replacement percentage for obtaining maximum 28 days strength of concrete ranged from 10 to 20 % 45. The condensed silica fume portland cement mixture must be protected for the first 7 days from drying shrinkage. Condensed silica fume in concrete transportation research board. Six fulldepth silica fume concrete bridge decks were constructed in minnesota between 1997 and 1999. Silica fume and kim media kryton international inc.
Cement replacement up to 10% with silica fume leads to increase in compressive. Tests were performed on some 40 mixes made using silica fume as a replacement for cement in quantities of 15, 20, and 30 percent. Making silica fume concrete in the laboratory pdf producing crack free concrete structures. Once again, this cohesiveness is due to its fine particle content. The results for the different ages of silica fume based geopolymer concrete are shown in fig. Silica fume reduces the permeability of the concrete. Silica fume powder is gray to offwhite in color when silica fume is used in concrete, shotcrete and repair products, it performs as a filler, improving the physical structure by occupying the spaces between the cement particles, and as a reacting chemical pozzolanic to create greater strength and durability to concrete. The durability of this type of concrete is superior to conventional concrete. Silica fume concrete included 0%, 10%, 15%, 20%, and 25% silica as equal replacement of ordinary portland cement.
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