What are the disadvantages of silica fume in concrete. These bridge decks were monitored both during construction and after construction to evaluate their constructability and performance. A fractal model of cracking of cement matrix composites. Silica fume concrete may be appr opriate in places where high abrasion resistance and low permeability. Effect of silica fume and rice husk ash on alkalisilica. Guide to using silica fume in precastprestressed concrete. Silica fume is a mineral admixture, a very fine powder of spherical particles that average 0. There are two general recommendations regarding finishing. The construction was funded with 20% virginia department of transportation maintenance funds and 80% special istea section 6005 federal funds specifically allocated to demonstrate overlay technologies. At higher porosities 20 %, transport is dominated by the percolated pathways through the capillary porosity phase. Silica fume is used in a variety of cementitious concrete, grouts and mortars, refractory, elastomer and polymer applications.
Silica fume improves the characteristics of both fresh and hard concrete. Compressive strength of silica fume based geopolymer concrete. Effect of silica fume on mechanical properties of high. Effect of age on compressive strength of silica fume based geopolymer concrete. This video introduces fly ash, slag and silica fume and discusses their properties. Silica fume concrete transportation research board. Mitigation of thermal cracking in massive foundations. Summary of cracks, delaminations, and patches after overlay placements. Silica fume sf is the byproduct of the manufacture of silicon for the computer industry. Panesar, in developments in the formulation and reinforcement of concrete second edition, 2019.
Effects of silica fume on concrete compressive strength. Doublek fracture model dkfm is considered in this paper and the required. Silica fume concrete is widely used in concrete and fiber cement industries. Development of cracking patterns in modified cement matrix. Silica fume is a pozzolanic material that is used with portland cement to produce portland pozzolana cement.
High strength concrete incorporating silica fume is more susceptible to plastic. Silica fume concrete has a gain in flexural strength from 5 th to 20 th days upon filling the voids, silica fume densifies the mix, this increases the tensile strength of concrete and hence there is a increase in flexural strength. Ra and silica fume sf and the crack pattern of a reinforced concrete beam. In the simulation parts geometric nonlinearity and material nonlinearity. 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. From this point of view, cement and concrete industries can be considered to be environmentfriendly since a large amount of waste materials, such as fly ash, blast furnace slag, metakaolin and silica fume in cement and concrete industries is helpful for both manufacturing cementitious products with improved properties and for reducing the. Six fulldepth silica fume concrete bridge decks were constructed in minnesota between 1997 and 1999. Silica fume and metakaolin admixtures are formulated to produce extremely strong and durable concrete.
Note that the itz is seen to extend approximately 15 m into the cement paste, corresponding to the median cement particle diameter. Experimental and computer modeling studies on cement pastes. While for 28 days strength, cement silica fume concrete showed 20% higher splitting tensile strength and flexural. The use of silica fume concrete for bridge decks has become an accepted practice. Strength, permeability and shrinkage cracking of silica fume and metakaolin concretes article pdf available in construction and building materials 34. This increased durability and resilience can be attributed to decreased permeability and absorption. Adds cohesiveness and reduced bleeding improves strength and durability.
Silica fume will increase the autogenous shrinkage of the cement slurry, and the amount of inclusion will exceed 5%, which may increase the risk of cracking. In denser silica fume, concrete the amount of cracking over a period of time is often greater. This alternative is a fulldepth silica fume concrete bridge deck. This area contains information and resources of special interest to anyone involved with producing, or placing silica fume concrete. One disadvantage is low early strength development than portland ceme. This increased densification of the concrete often creates an illusion of waterproofing capability. 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. 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. A mathematical model for prediction of metakaolinsilica. Luther reported the various percentages of silica fume i. This will produce expansive ettringite and cracking of the concrete. The effects of silica fume sf on compressive strength of concrete have been analyzed.
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. This makes silica fume concrete more susceptible than conventional concrete to rapid surface drying and plastic shrinkage cracking. It has many advantages and its advantages outweigh its disadvantages. Concrete made with silica fume can dramatically increase corrosion resistance, decrease alkali silica reactivity and increase resistance to sulfates.
Microsilica, also known as silica fume or condensed silica fume, is a mineral admixture composed of very fine solid glassy spheres of silicon dioxide. The cement silica fume concrete showed 26% higher splitting tensile strength and 22% higher flexural strength than that of cement concrete when 6 to 7. When a micro crack occurs in a silica fume kim mix concrete, and water begins to penetrate the structure, kim will immediately react with the unhydrated cement particles and the water causing crystals to grow throughout the crack. Silica fume is recommended for all types of concrete where improved concrete performance with reduced permeability is required to reduce the effect of corrosive chemicals, such as deicing salts, on structural steel. Silica fume is a byproduct from the production of elemental silicon or alloys containing silicon in electric arc furnaces. Silica fume is an ultrafine material that is approximately 100 times smaller than the average cement particle. Pdf effects of metakaolin and silica fume on properties. Silica fume is a grey superfine powder with a density of 2. To optimize the benefits resulting from the use of condensed silica fume, it must be thoroughly dispersed in the cement mixture. Study of concrete containing silica fume and activated. It may be added directly to concrete as an individual ingredient or in a blend of portland cement and silica fume.
What is fly ash, slag, and silica fume and why do we use. Cracking tendency and drying shrinkage of silica fume concrete for. Ehlen under contract to the life365 consortium ii, which consists of the concrete corrosion inhibitors association, the national ready mix concrete association, the slag cement. The application of mineral additives in concrete mix design for the purpose of obtaining high concrete strength was investigated in this article. Cracking tendency and drying shrinkage of silica fume concrete for bridge deck. Strength, permeability and shrinkage cracking of silica fume. Properties of the fumed silica and silica fume have been shown in table 1. Mockup and model validation in addition to the finite difference model prediction of temperature. Silica fume and microsilica are very important materials in building construction. However, as a further study, the addition of silica fume and metakaolin with fixed cement content, without replacement may also be studied and compared with the findings of this study.
This presentation covers all aspects of using silica fume in concrete and can be viewed directly in your browser. However, experience suggests that the use of silica fume in concrete contributes to high shrinkage levels that can cause deck cracking. The latter evidence is used to support the theory that silica fume strengthens concrete by strengthening the bond between cement paste and aggregate. Life365 service life prediction model and computer.
The seemingly uncracked condition only exists for crack widths below 0. Most civil engineering students will be benefited after seeing this wonderful presentation. The use of good quality fly ash with a high fineness and low carbon content reduces the water demand of concrete. Early age fracture mechanics and cracking of concrete. The condensed silica fume portland cement mixture must be protected for the first 7 days from drying shrinkage.
A fourphase composite model is employed and three functions are chosen. Quality control of silica fume concrete bridge decks youtube. Making silica fume concrete in the laboratory pdf producing crack free concrete structures. The use of silicafume concrete for bridge decks has become an accepted practice. Pdf strength, permeability and shrinkage cracking of silica fume. The use of silica fume concrete for fulldepth bridge deck.
In the united states, silica fume is used predominantly to produce concrete with greater resistance to chloride. Silica fume is used in high performance concrete as a pozzolan to improve its properties. The results of the experiments showed that when the polymerbinder materials ratio increases, the compressive strength of concrete decreases. Most of the cracking is due to the r estraint of contr action induced b y. Produced through a partnership program between the sfa and the federal highway administration. This paper presents research on the restrained shrinkage cracking on several strength levels of concrete. Simulation of the flexural response of ultrahigh performance fiber. The results for the different ages of silica fume based geopolymer concrete are shown in fig. The naturally occurring amorphous silica was activated by first treating it with alkali, after which it was neutralized by acid treatment. Latexmodified and silica fume concrete overlays were placed on six bridges on i95 south of emporia, virginia, in the fall of 1994. Improvement in concrete behavior with fly ash, silicafume. Silica fume concrete included 0%, 10%, 15%, 20%, and 25% silica as equal replacement of ordinary portland cement. Cracking tendency and drying shrinkage of silica fume concrete.
Fumed silica is being used in various fields such as pharmaceuticals, paints, adhesives and sealants, plastics, rubber and ink except for concrete. The tensile cracking of concrete is controlled and. Silica fume, a byproduct of the ferrosilicon industry, is a highly pozzolanic material that is used to enhance mechanical and durability properties of concrete. Thus, the effects of silica fume and metakaolin replacement on the strength, permeability and shrinkage cracking properties of concretes were discussed. Apr 16, 2016 silica fume is a pozzolanic material that is used with portland cement to produce portland pozzolana cement. Silica fume improves the properties of fresh and hardened concrete. 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. Fly ash increases workability when compared with conventional concrete with same water content. It is a by product from an electric arc furnace used in manufacture of silicon metal or silicon alloy. The creep coefficient of concrete with mineral additives silica fume, white ash and metakaolin, obtained by calculation according to the model, can be from 0. Higher strength levels were obtained by partial substitution of cement with silica fume and by reducing the water content. Pdf study of partial replacement of cement by silica fume. Even the most dense silica fume concrete cannot stop water penetration through micro cracks. Second, conduct a trial placement so the finishing crews can perfect their approach to the silica fume concrete.
In the present study, the effect of addition of a mix of silica fume and activated natural silica on the properties of concrete was investigated. Silica fume has been used all over the world for many years in the area where high strength and durable concrete were required. It is a very finely divided material, many hundreds of times finer than cement. In this investigation, this effect has not been considered since the two cements are very close in their particle size distributions and blaine fineness. Plastic shrinkage cracking and bleeding of concrete. Silica fume concrete silica fume for sale, microsilica. Ringtype specimens were used for restrained shrinkage cracking. The least cracking occurred on bridge 6, with the conventional lmc overlay.
Recommendations are given for measuring, mixing, handling, transporting, placing, finishing, and curing concrete with silica fume additives. The combustion process creates silicon dioxide molecules, which condense to form particles. Benefits of using silica fume in concrete civil engineer. Adjustment of cement particle size distribution through addition of finer powder i. Doublek fracture model dkfm is considered in this paper and the required parameters for dkfm are obtained from the model simulated using finite element method fem in abaqus. Silica fume advantages and disadvantages in 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. The lower strength of the concrete with ternary binders led to earlier cracking.
A disadvantage to utilizing silica fume in cement is the cost. Model results for initial cement and silica fume volume fractions vs. It reacts with lime and water in a similar way to fly ash, also known as pulversided fuel ash pfa, to produce a binder. The alkali silica reaction asr, which occurs between the alkaline hydroxides in cement paste and reactive minerals in the aggregate, produces an expansive gel that may cause cracking and displacement in concrete structures. Microsilica in concrete types, properties, and practical. The mechanism, physical characteristics, benefits, and production aspects of concrete made with silica fume are described. This paper presents a new constitutive model describing the mechanical behavior of concrete at early age and beyond. Working with silicafume concrete concrete construction. These combined properties lead to an extended life expectancy in corrosive environments resistance to chlorides, acids and sulphates and improved strength. Effect of supplementary cementitious materials on shrinkage and. In addition to its pozzolanic properties its is also a very good filler due to its particle size. Limiting the maximum crack width allowed requires more reinforcing steel in concrete slabs. The silica fume concrete longterm strength is increased by addition of fly ash. Solidificationmicroprestressmicroplane smm theory for.
The artificial neural network and support vector machine were used to estimate the compressive strength and flexural strength of carbon fiberreinforced lightweight concrete with the silica fume exposed to the high temperature. Currently, pozzolanic materials are used to prevent or minimize this cracking. The compressive strength results of concrete mixed over different waterbinder ratios as well as different replacing percentages of sf were analyzed. This study is designed to explain the contradictory evidence and establish the role played by. The incorporation of fly ash and very fine fly ash decreased the autogenous. Silica fume is often used in highstrength concrete or highperformance concrete. Silica fume effect on fracture parameters and cracking. Measuring, monitoring and modeling concrete properties pp 291296 cite as. Silica fume particles have an average diameter of less than 1 micron. It is easy to cause cracks in mortar and concrete and need concrete maintenance. Life365 service life prediction model and computer program. The best results were obtained with silica fume content of 11. This model, entitled solidificationmicroprestressmicroplane smm model, amalgamates the microplane model and the solidificationmicroprestress theory and takes into account all the most significant aspects of concrete behavior, such as creep, shrinkage, thermal deformation. It is usually found as a byproduct in the industrial manufacture of ferrosilicon and metallic silicon in hightemperature electric arc furnaces.
Jan 26, 2017 silica fume concrete silica fume is an artificial pozzolona having high pozzolonic activity. Plastic shrinkage and settlement cracking in 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. Tony kojundic is a founding board member of the silica fume association, and business manager for elkem materials in pittsburgh, pa. Silica fume and kim media kryton international inc. The length of crack was the greatest for the bridges with the silica fume overlays, bridges 1, 4, and 5. In the wetmix process, the silica fume can be introduced as. A proportion of silica fume, metakaolin, and superplasticizier were add to conventional cementaggregate mix in different proportions and a compressive strength of about 60nmm 2 was targeted. A pozzolan is a material that when in the presence of water has a chemical reaction and forms compounds that possess cementitious properties. The silica fume concrete was slightly darker in color than the latexmodified concrete. It does not contain crystalline water, does not participate in the curing reaction, and does not affect the reaction mechanism. This paper presents the results of experimental work on short and longterm mechanical properties of highstrength concrete containing different levels of silica fume. Cracks are reported in units of length because the bridges are similar in size.
Fresh concrete containing silica fume is more cohesive and less. C3a is seemed to react with acids causing expensive products. As with the silica fume overlay, these cracks, in variable depth overlay areas, did not extend through the entire depth of the overlay and measured 0. 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. The alkalisilica reaction asr, more commonly known as concrete cancer, is a swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive noncrystalline silica found in many common aggregates, given sufficient moisture. Construction products, master builders, and the silica fume association. Influence of active crack width control on the chloride. It is an excellent for use as a portland cement supplement. Silica fume is also recommended where higher density and ultimate strengths are desired.
Effects of metakaolin and silica fume on properties of concrete. Previously, garboczi and bentz have shown that the relative diffusivity of cement paste should be mainly a function of capillary porosity. Because of its extreme fineness and high silica content, silica fume is a very effective pozzolanic material. Tyler, skanska usa civil northeast unless batched, handled, and placed with tight controls and optimal conditions, silica fume decks can suffer wide spread cracking thru. Despite low initial permeability, silica fume is not without limitations. 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. The use of silica fume in concrete shows a tendency for plastic shrinkage2, drying shrinkage3and cracking resulting in water penetration and corrosion of reinforcing steel. Model based interpretation of the influence of silica fume on diffusivity.
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