Silica fume is a byproduct from the production of elemental silicon or alloys containing silicon in electric arc furnaces. Silica fume, a byproduct in the manufacture of ferrosilicon and also of silicon metal, is a very efficient pozzolanic material, though there are some problems associated with its use in concrete. This alternative is a fulldepth silica fume concrete bridge deck. Six fulldepth silica fume concrete bridge decks were constructed in minnesota between 1997 and 1999. It is comparable to silica fume in pozzolanic reactivity, but is lower in price. Rained hard right after concrete pouring aci concrete. Silica fume and kim media kryton international inc. But in defending this approach, you can make two key arguments. Control of plastic shrinkage cracking of concrete has been a subject of several investigations. Concrete that freezes at an early age can lose much of its overall. These measures include fogging during placement, using an evaporation retarder during breaks in the placing sequence, and applying curing compound as soon as the surface texture has been completed.
Drying shrinkage is a very critical factor since the lmc overlays are typically wetcured for two days. As such, ingredients that reduce bleeding in concrete, such as silica fume can lead to plasticshrinkage cracking, unless precautions are taken to protect the surface of the concrete immediately after placing and during early finishing operations. Plastic shrinkage cracking is highly likely to occur when high evapo. Silica fume concrete silica fume for sale, microsilica silica fume concrete is widely used in concrete and fiber cement industries. Early age shrinkage and cracking of nevada concrete. A substitute for cement which reduces shrinkage and retards setting. Suprenant, curing during the pour, concrete con struction, june 1997. Microsilica in concrete types, properties, and practical. When concrete is cured for 7 days under continuously moist conditions, there is no statistically significant effect of silica fume on the tendency of the concrete to exhibit earlyage cracking. Benefits of using silica fume in concrete civil engineer.
Effect of silica fume on the plastic shrinkage and pore water. The exterior concrete walls in this structure are 4. This area contains information and resources of special interest to anyone involved with producing, or placing silica fume concrete. Finishing the biggest difference between conventional concrete and silicafume concrete shows up during finishing. My contractor says that this is normal and will not affect the integrity of the concrete. Combined effect of silica fume and steel fibers on the. This is common in severe situations where rate of evaporation is greater than the concrete bleed rate silica fume mixes come to mind. One disadvantage is low early strength development than portland ceme. Five different watercementitious ratios were used including, 0. Cracking tendency and drying shrinkage of silica fume concrete for. Dry condensed silica fume is typically added after the initial water and aggregates, with premixing prior to the. Farnam created a method for using fly ash, slag and silica fume leftovers from coal furnaces and the smelting process in a new concrete mix that is more durable because it doesnt react with road salt. Properties of the fumed silica and silica fume have been shown in.
The intention with the present investigation was to provide more information about the parameters responsible for this, and which can contribute to the fundamental understanding, of the problem, and in particular of the influence of silica fume. The use of silica fume concrete for fulldepth bridge deck. Pdf strength, permeability and shrinkage cracking of silica fume. Ensure their are good access points for the concrete trucks to the pour 5.
Starting of curing processas soon as possible after finishing. The process of curing concrete becomes more challenging in cold weather since, to properly set and reach maximum strength, fresh concrete must be protected from freezing for at least the first 24 hours, or until it reaches a minimum strength of 500 pounds per square inch psi. Recommendations are given for measuring, mixing, handling, transporting, placing, finishing, and curing concrete with silica fume additives. He recently published his findings in the journal of cement and concrete composites. These bridge decks were monitored both during construction and after construction to evaluate their constructability and performance. 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. Aug 23, 2019 the process of curing concrete becomes more challenging in cold weather since, to properly set and reach maximum strength, fresh concrete must be protected from freezing for at least the first 24 hours, or until it reaches a minimum strength of 500 pounds per square inch psi. Pdf effect of silica fume in concrete researchgate. Silica fume a concrete additive which drastically increases strength and reduces permeability. Published on march 28, 2016 march 28, 2016 39 likes comments. After being collected over the furnace, the silica fume must be transferred, cooled, and physically trapped. Evapre can be used with the meadowpatch and meadowcrete line of repair mortars from w. Silica fume is similar to fly ash, but has a particle size 100 times smaller.
However, no partial sack of dry condensed silica fume shall be used in a batch of sfmc. A recipe for concrete that can withstand road salt. Silica fume is also recommended where higher density and ultimate strengths are desired. It is, therefore, very important that the surface be finished properly. Slab surface prevention repair concrete paving association of. Advantages and disadvantages of silica fume in concrete.
To prevent thermally induced cracking, the designer specified very tight control over the maximum temperature rise allowed in the concrete. They are usually parallel to each other on the order of 1 to 3 feet apart, relatively shallow, and. The development of hydration differs substantially between concrete with and without silica fume 3. Metakaolin is a relatively new mineral admixture for concrete.
Concrete containing silica fume requires particular attention to avoid surface drying during placement. Limiting the amount of finishing greatly reduces the potential for plastic shrinkage cracking and enhances the concretes durability. In the wetmix process, the silica fume can be introduced as. Its small particle size which is 100 times finer than ordinary portland cement complements the finess modulus of concrete and provides a ballbearing effect, which improves thixotropic behavior, in effect modifying concrete viscosity. The practical application of silica fume started in the late seventies. The influence of silica fume on the compressive strength of. It can also be used with condensed silica fume concrete, concrete containing fly ash, and most other cementitous products. Limiting the amount of finishing greatly reduces the potential for plastic shrinkage cracking and enhances the concrete s durability. Guide to using silica fume in precastprestressed concrete. Hooked steel fibers with 60mm length and an aspect ratio of 80, with three volume fractions of 0%, 0. A superplastisizer 1% by weight of cement was added to this slurry which increased infiltration capacity of the slurry. When applying surface hardeners, evapre can be used after screeding and after the first floating operation, if. This study investigated the impact resistance and mechanical properties of steel fiberreinforced concrete with watercement ratios of 0.
Silica fume improves concrete in two ways the basic pozzolanic reaction, and a microfiller effect. Silicafume microsilica concrete in bridges in the united states. Concrete that freezes at an early age can lose much of its overall strength. Types and causes of concrete cracking in bridges 3. The silica fume reacts with the cement paste to form additional strong calcium silicate hydrate csh providing higher strength. In addition to its pozzolanic properties its is also a very good filler due to its particle size. Anyone you share the following link with will be able to read this content. The naturally occurring amorphous silica was activated by first treating it with alkali, after which it was neutralized by acid treatment. In denser silica fume, concrete the amount of cracking over a period of time is often greater. This is the first and foremost step in the repair of hairline cracks in the concrete. Rest with the increase in the content of silica there wont be any effect on durability. Abstract this research describes the importance of the effect of silica fume on concrete properties and the advantages of its use in the kurdistan region, silica fume can either be addition added separately at the concrete mixer or incorporated into a factoryproduced composite cement. Plastic shrinkage cracks appear in the surface of fresh concrete soon after it is placed and while it is still plas.
The mechanism, physical characteristics, benefits, and production aspects of concrete made with silica fume are described. After 20 years exposure to ground water containing 4 gl sulfate and 2. The compressive strengths of silica fume cement paste and mortar were evaluated at various watercementitious ratios. Addition of silica fume improves bonding within the concrete and helps reduce permeability, it also combines with the calcium hydroxide produced in the hydration of portland cement to improve concrete. The tensile creep behavior is extremely important in crack prediction and stress. Although the total porosity of the silica fume concrete is similar to the opc concrete the average pore size is much finer, conducting to a large reduction of permeability. Making silica fume concrete in the laboratory pdf producing crack free concrete structures. This study is designed to explain the contradictory evidence and establish the role played by. My contractor had a representative from the material supplier come out and take a look and he also said that this was normal. This results in a higher surfacetovolume ratio and a much faster pozzolanic reaction. Study of concrete containing silica fume and activated. Reduces thermal cracking caused by the heat of cement hydration. Cracking tendency and drying shrinkage of silica fume concrete for bridge deck applications. Silica fume sf is the byproduct of the manufacture of silicon for the computer industry.
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. Silica fume advantages and disadvantages in concrete. Because of its extreme fineness and high silica content, silica fume is a very effective pozzolanic material. It is a very finely divided material, many hundreds of times finer than cement. Rained hard right after concrete pouring 6080c0ay civil. Concrete containing silica fume requires particular attention to avoid surface drying during placement due to its very low rate of bleeding. Fumed silica is being used in various fields such as pharmaceuticals, paints, adhesives and sealants, plastics, rubber and ink except for concrete. This makes silicafume concrete more susceptible than conventional concrete to rapid surface drying and plastic shrinkage cracking. For example, after construction, strengthening water and sprinkler. Effects of silica fume and fly ash as partial replacement. This presentation covers all aspects of using silica fume in concrete and can be viewed directly in your browser.
Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability. Cip 5 2014 national ready mixed concrete association. Cracks are reported in units of length because the bridges are similar in size. Concretes containing silica fume had higher shrinkages at. Silica fume, a byproduct of the ferrosilicon industry, is a highly pozzolanic material that is used to enhance mechanical and durability properties of concrete. Experimental research on the effect of silica fume on tensile. 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. The results demonstrated that the tendency of concrete to crack is influenced by the addition of silica fume only when the concrete is improperly cured. 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. Shrinkage results in cracks in concrete, so it has been a matter of. Highstrength concrete is more sensitive to cracking before and during setting than normal. It is easy to cause cracks in mortar and concrete and need concrete maintenance. They are usually parallel to each other on the order of 1 to 3 feet apart, relatively shallow, and generally do not intersect the perimeter of the slab. Hairline crack in concrete causes, repair and prevention.
After 5 years in service, the overlays had cracked. I just had a new concrete driveway poured and the very next morning, several cracks showed up in the concrete. On this project silica fume was added primarily to enhance constructability. Due to the inherent nature of concrete, cracking can also be expected after the initial shrinkage has become irrelevant. The combustion process creates silicon dioxide molecules, which condense to form particles. What are the main effects of adding micro silica silica fume. The latter evidence is used to support the theory that silica fume strengthens concrete by strengthening the bond between cement paste and aggregate. Plastic shrinkage cracks appear in the surface of fresh concrete soon after it is placed and while it is still plastic. Aci concrete terminology silica fume, a byproduct of the ferrosilicon industry, is a highly pozzolanic material that is used to enhance mechanical and durability properties of concrete. Produced through a partnership program between the sfa and the federal highway administration. To study the effect of replacement of cement by silica fume on sifcon, slurry was prepared by replacing cement by silica fume at varying percentages like 5%, 10%, 15%, 20%, 25% and 30% by. Although concrete will harden soon after pouring, its still susceptible to damage from weight during the first four weeks.
Silica imparts strength to the concrete as it make it denser by. 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 improves the characteristics of both fresh and hard concrete. Ensure the concrete can be placed as close to its final placement position as possible 6. 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. Jan 16, 2014 a veteran concrete and stone floor polisher, loe learned of the benefits of colloidal silica as a concrete densifier in 2006. Sellevold and nilsen 1987 reported field studies of concretes with and with out 15% silica fume. Free from the presence of salts that absorbs the moisture from the atmosphere and lead to efflorescence. Mar 28, 2016 what are the main effects of adding micro silica silica fume on concrete properties.
The vertical elements are cyclones that are used to remove oversize and other unwanted materials. 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. Plastic shrinkage cracking and bleeding of concrete prepared with. 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. Cracking tendency and drying shrinkage of silica fume. Twentyfive minutes after the addition of water to cement, the. Since then a lot of research has been carried out and the results of many years of practical experience are known. The use of silica fume in concrete should be limited to specialized applications that can take full advantage of its unique properties.
Pdf effects of metakaolin and silica fume on properties. Silica fume is often used in highstrength concrete or highperformance concrete. Department of civil engineering, north eastern regional. Concrete made with silica fume can dramatically increase corrosion resistance, decrease alkali silica reactivity and increase resistance to sulfates. The large pipe on the left is bringing the silica fume from the furnaces. Silica fume can make highly cohesive, sticky concrete, with little bleeding capacity. Adding higher amounts of silica fume reduces bleeding and may eliminate it. This section of the presentation describes the measures that can be taken to prevent plastic shrinkage cracking in silica fume concrete. Improves durability to attack by sulphate and acidic waters. Highstrength concrete is more sensitive to cracking before and during setting than normal concrete is. It has been found experimentally that very high strength silica fume concretes undergo early cracking when deformation is restrained. By the addition of silica fume into concrete can not only.
The steps involved in the repair of hairline cracks in concrete are as follows. Wait at least 24 hours before allowing foot traffic, including pets. Silica fume is a pozzolanic material that is used with portland cement to produce portland pozzolana cement. Fogging the air above the concrete and erecting windshades lessen the risk of plasticshrinkage cracking. It reacts with lime and water in a similar way to fly ash, also known as pulversided fuel ash pfa, to produce a binder. Tony kojundic is a founding board member of the silica fume association, and business manager for elkem materials in pittsburgh, pa. Concrete con taining silica fume requires particular attention to avoid.
Some specifiers may object to the minimal finishing. The effects of metakaolin and silica fume on various properties of concrete were investigated and compared in this study. Cracking tendency and drying shrinkage of silica fume concrete. Silica fume s benefits are already evident in the fresh concrete state before it begins to harden. Silica fume concrete shrinkage rate is large, especially early dry shrinkage, easy to make crack in the application of silica fume concrete, affect the overall strength and using effect. If the free shrinkage has ended and the concrete has not cracked after 91 days it is concluded that it will not.
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. For example, after construction, strengthening water and sprinkler maintenance can decrease this problem, but the cracks are still unavoidable in many. Silicafume concrete sfc has been used in bridges outside the united states since the 1970s 1. Decorative concrete specialist harold spring explains. It has many advantages and its advantages outweigh its disadvantages. The length of crack was the greatest for the bridges with the silica fume overlays, bridges 1. The large building is the bag house where the fume is captured. Working with silicafume concrete concrete construction. At that time and the following years, opinions on the effect of silica fume on reinforcement corrosion varied quite a lot. Silica fume powder due to the inherent nature of concrete, cracking can also be expected after the initial shrinkage has become irrelevant. The effects of utilizing silica fume in portland cement pervious concrete daniel allen mann, candidate for the master of science degree university of missourikansas city, 2014 abstract silica fume has long been used as a supplementary cementing material to provide a high density, high strength, and durable building material. 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. What are the disadvantages of silica fume in concrete. It was observed that drying shrinkage of concrete incorporating silica fume is generally comparable.
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. With little or no bleed water on the surface, silica fume concrete is prone to plastic shrinkage cracking on hot, windy days. Panesar, in developments in the formulation and reinforcement of concrete second edition, 2019. Silica fume has been used all over the world for many years in the area where high strength and durable concrete were required. Properties of the fumed silica and silica fume have been shown in table 1.
This increased durability and resilience can be attributed to decreased permeability and absorption. Cip 5 plastic shrinkage cracking what is plastic shrinkage cracking. What is fly ash, slag, and silica fume and why do we use them in concrete. 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.