1、ACI 234R-06 supersedes ACI 234R-96 (Reapproved 2000) and became effectiveApril 13, 2006.Copyright 2006, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by anymeans, including the making of copies by any photo process, or by electronic ormechani
2、cal device, printed, written, or oral, or recording for sound or visual reproductionor for use in any knowledge or retrieval system or device, unless permission in writingis obtained from the copyright proprietors.ACI Committee Reports, Guides, and Commentaries areintended for guidance in planning,
3、designing, executing, andinspecting construction. This document is intended for the useof individuals who are competent to evaluate the significanceand limitations of its content and recommendations and whowill accept responsibility for the application of the material itcontains. The American Concre
4、te Institute disclaims any andall responsibility for the stated principles. The Institute shallnot be liable for any loss or damage arising therefrom.Reference to this document shall not be made in contractdocuments. If items found in this document are desired by theArchitect/Engineer to be a part o
5、f the contract documents, theyshall be restated in mandatory language for incorporation bythe Architect/Engineer.1Guide for the Use of Silica Fume in ConcreteReported by ACI Committee 234ACI 234R-06(Reapproved 2012)This report describes the physical and chemical properties of silica fume;how silica
6、fume interacts with portland cement; the effects of silica fume onthe properties of fresh and hardened concrete; recent typical applicationsof silica-fume concrete; how silica-fume concrete is proportioned, specified,and handled in the field; and areas where additional research is needed.Keywords: c
7、uring; durability; high-range water-reducing admixture; high-strength concrete; placing; plastic-shrinkage cracking; silica fume; time ofsetting; water-reducing admixture; workability.CONTENTSChapter 1Introduction, p. 21.1General1.2What is silica fume?1.3Silica fume versus other forms of silica1.4Us
8、ing silica fume in concrete1.5Using silica fume in blended cements1.6Worldwide availability of silica fume1.7Types of silica fume products available1.8Health hazards1.9Environmental impactChapter 2Physical properties and chemical composition of silica fume, p. 62.1Color2.2Specific gravity2.3Bulk den
9、sity2.4Fineness, particle shape, and oversize material2.5Chemical composition2.6Crystallinity2.7Variability2.8Relating physical and chemical properties toperformance in concrete2.9Quality controlChapter 3Mechanisms by which silica fume modifies cement paste, mortar, and concrete, p. 93.1General3.2Ph
10、ysical effects3.3Chemical effects3.4Microstructure modifications3.5Self-desiccation and water of hydration3.6Autogenous shrinkage (volume change)3.7Chemical composition of pore fluid3.8Reactions in combination with fly ash or ground-granulated blast-furnace slag3.9Reactions with different types of p
11、ortland cements3.10Heat of hydration3.11Reactions with chemical admixturesChapter 4Effects of silica fume on properties of fresh concrete, p. 174.1Water demand4.2Workability4.3Slump loss4.4Time of setting4.5Segregation4.6Bleeding and plastic shrinkage4.7Color of concrete4.8Air entrainmentJames M. Al
12、dred Terence C. Holland Dudley R. Morgan Della M. RoyMark A. Bury R. Doug Hooton Jan Olek Marco J. ScaliRachel J. Detwiler Tarif M. Jaber H. Celik Ozyildirim Michael D. A. ThomasFouad H. Fouad Kamal H. Khayat Michael F. Pistilli John T. WolsieferWilliam Halczak V. M. Malhotra Jean-Claude Roumain Min
13、-Hong ZhangPer FidjestlChairAnthony N. KojundicSecretary234R-2 ACI COMMITTEE REPORT4.9Bulk density (unit weight) of fresh concrete 4.10Evolution of hydrogen gasChapter 5Effects of silica fume on properties of hardened concrete, p. 234R-185.1General5.2Mechanical properties5.3Durability aspects5.4Misc
14、ellaneous properties5.5Use of silica fume in combination with fibers5.6Use of silica fume in ternary blends5.7Property variations with respect to type, source, andform of delivery of silica fumeChapter 6Applications of silica fume in concrete, p. 234R-356.1Tsing Ma Bridge, Hong Kong6.2311 South Wack
15、er Drive, Chicago6.3Kuala Lumpur City Center, Malaysia6.4Kinzua Dam Stilling Basin, United States6.5Stolma Bridge, Norway6.6Highway bridges, United States6.7Parking structures, United StatesChapter 7Specifications, p. 234R-387.1General7.2Specifying silica fume7.3Specifying silica-fume admixtures7.4S
16、pecifying silica-fume blended cement7.5Specifying silica-fume concrete Chapter 8Proportioning silica-fume concrete mixtures, p. 234R-418.1General8.2Cement and silica fume content8.3Water content8.4Aggregate8.5Chemical admixtures8.6Proportioning8.7Ternary mixturesChapter 9Working with silica fume in
17、field concrete, p. 234R-459.1Transporting and handling silica fume and silica-fume admixture products9.2Producing concrete 9.3Transporting9.4Placing9.5Finishing9.6Curing9.7Accelerated curingChapter 10Research needs, p. 234R-4810.1Frost resistance10.2Scaling resistance10.3Sulfate attack10.4Drying shr
18、inkage and creep10 5Steel corrosion10.6Long-term durability10.7Rheology of fresh concrete 10.8Mechanism of strength development10.9Role of silica fume in special concretes10.10Effect of silica fume on hydration10.11Later-age crackingChapter 11References, p. 234R-4911.1Referenced standards and report
19、s11.2Cited referencesCHAPTER 1INTRODUCTION1.1GeneralSilica fume, a by-product of the ferrosilicon industry, is ahighly pozzolanic material that is used to enhance mechanicaland durability properties of concrete. It may be added directlyto concrete as an individual ingredient or in a blend of portlan
20、dcement and silica fume. ACI Committee 234 estimates thatat least 120,000 metric tons (130,000 tons) of silica fume areused in concrete worldwide annually. Using this figure, morethan 6 million cubic meters (nearly 8 million cubic yards) ofsilica-fume concrete are placed globally each year.Interest
21、in the use of silica fume resulted from the strictenforcement of air-pollution measures designed to stoprelease of the material into the atmosphere. Initial use ofsilica fume in concrete was mostly for cement replacement,along with water-reducing admixtures (WRAs). Eventually,the availability of hig
22、h-range water-reducing admixtures(HRWRAs, often referred to as superplasticizers) allowednew possibilities for the use of silica fume to produce highlevels of performance.This document provides basic information on using silicafume in concrete. The document is organized as follows:Chapter 1 provides
23、 general information on silica fume;Chapter 2 describes the physical properties and chemicalcomposition of silica fume;Chapter 3 describes the mechanisms by which silicafume modifies cement paste, mortar, and concrete;Chapter 4 describes the effects of silica fume on freshconcrete;Chapter 5 describe
24、s the effects of silica fume onhardened concrete;Chapter 6 shows how silica fume has been used onactual projects. This chapter covers only a very smallnumber of applications because ACI Committee 234 iscurrently developing an additional document that willprovide detailed case histories of many more
25、projects;Chapter 7 discusses specifications for silica fume andsilica-fume concrete;Chapter 8 presents a step-by-step methodology for propor-tioning silica-fume concrete for specific applications;Chapter 9 presents recommendations for working withsilica fume in field concrete;Chapter 10 summarizes r
26、esearch needs for using silicafume in concrete; andChapter 11 presents all of the references from the otherchapters.Note that the coverage in Chapters 7, 8, and 9 is somewhatbrief. More details on working with silica-fume concrete inGUIDE FOR THE USE OF SILICA FUME IN CONCRETE 234R-3actual applicati
27、ons may be found in a guide published by theSilica Fume Association (Holland 2005).As with other concrete constituent materials, potentialusers of silica fume should develop their own laboratory datafor the particular type and brand of cement, aggregates, andchemical admixtures to be used with the s
28、ilica fume. Thistesting may be supplemented by field observations ofcompleted silica-fume concrete and by testing of cores takenfrom such concrete.1.2What is silica fume?Silica fume, as defined in ACI 116R, is “very finenoncrystalline silica produced in electric arc furnaces as aby-product of the pr
29、oduction of elemental silicon or alloyscontaining silicon.” The silica fume, which condenses fromthe gases escaping from the furnaces, has a very high contentof amorphous silicon dioxide and consists of very fine sphericalparticles (Fig. 1.1 and 1.2) typically averaging 0.1 to 0.2 m(4 to 8 106in.) i
30、n diameter. Often, several individualspheres can be fused together to form small agglomerates.The first mention of silica fume for use in concrete andmortar is found in a U.S. patent from 1946 (Sharp 1946)where the use of silica fume to improve the properties offresh mortar is the main claim of the
31、patent.Silica fume was first collected in Kristiansand, Norway, in1947. Investigations into the properties of the material andits uses began promptly, with the first paper being publishedby Bernhardt in 1952. Investigations of the performance ofsilica fume in concrete also followed in other Nordic c
32、ountries:Iceland, Denmark, and Sweden. Additional early Scandinavianpapers included those by Fiskaa et al. (1971), Traetteberg(1977), Jahr (1981), Asgeirsson and Gudmundsson (1979),Lland (1981), and Gjrv and Lland (1982). In 1976, aNorwegian standard permitted the use of silica fume inblended cement
33、. Two years later, the direct addition of silicafume into concrete was permitted by a standard in Norway.In South Africa, Oberholster and Westra published researchresults on using silica fume to control alkali-aggregatereaction in 1981.In North America, the first paper was published in 1981 byBuck a
34、nd Burkes of the U.S. Army Corps of EngineersWaterways Experiment Station (WES). Other early researchwas conducted by CANMET (Malhotra and Carette 1983;Carette and Malhotra 1983a), Sherbrooke University (Atcin1983), Norchem (Wolsiefer 1984), and the U.S. Army Corpsof Engineers WES (Holland 1983). In
35、 1978, Norchem didthe first major placement of ready mixed silica-fumeconcrete in the United States for resistance to chemicalattack.*In late 1983, the U.S. Army Corps of Engineers didthe first publicly bid project in the United States using silica-fume concrete (Holland et al. 1986).The SiO2content
36、 of the silica fume is roughly related tothe manufacture of silicon alloys as follows:Typical SiO2Alloy type content of silica fume50% ferrosilicon 74 to 84%75% ferrosilicon 84 to 91%Silicon metal (98%) 87 to 98%Ferrosilicon alloys are usually produced with nominalsilicon contents of 50 to 98%. When
37、 the silicon contentreaches 98%, the product is called silicon metal rather thanferrosilicon. As the silicon content increases in the alloy, theSiO2content increases in the silica fume. The majority ofpublished data and field use of silica fume have been fromalloys of 75% ferrosilicon or higher. Wol
38、siefer et al. (1995)and Morgan and Wolsiefer (1992), however, present infor-mation on using silica fume from production of alloys with*Private communication from committee member.Fig. 1.1Transmission electron microscope micrograph ofsilica fume. (Image courtesy of Elkem ASA materials.)Fig. 1.2Scanni
39、ng electron microscope micrograph of silicafume. (Image courtesy of Elkem ASA materials.)234R-4 ACI COMMITTEE REPORT50% iron in applications such as chemically resistant concrete,shotcrete, blended cement, and oil well cement grouts.Silica fume is also collected as a by-product in the productionof o
40、ther silicon alloys. The use of these fumes should beavoided unless data on their favorable performance inconcrete are available.Silica fume has also been referred to as condensed silicafume, microsilica, and fumed silica (this last term is particularlyincorrectrefer to Section 1.3). The most approp
41、riate termis silica fume. In formal references related to health andsafety regulations, the product is characterized as “ThermallyGenerated Silica Fume.” The Chemical Abstracts Service(CAS) classifies silica fume by the number 69012-64-2. Thecorresponding European Index of Existing ChemicalSubstance
42、s (EINECS) number is 273-761-1. Other forms ofsilicon dioxide, including fumed silica, colloidal silica,diatomaceous earth, and quartz have differing chemical andphysical properties, and thus have other classification numbers.Silica fume is covered by several national and internationalstandards. Cha
43、pter 7 provides a listing of the various standardsin use and a discussion of some of the key provisions. 1.3Silica fume versus other forms of silicaOther products with a high content of amorphous silica aremarketed from time to time to the concrete industry. Thesecan roughly be divided into two grou
44、ps: synthetic silica andnatural silica. None of these products should be confusedwith silica fume as defined in this document.1.3.1 Synthetic silicaSynthetic silicas are amorphousproducts that are occasionally confused with silica fume.Unlike silica fume, they are purposefully made. While theyoffer
45、the potential of performing well in concrete, they aretypically too expensive for such use. These products aremade through three processes:Fumed silica. Fumed silica is produced by a vapor-phase hydrolysis process using chlorosilanes, such assilicon tetrachloride, in a flame of hydrogen and oxygen.F
46、umed silica is supplied as a white, fluffy powder;Precipitated silica. Precipitated silica is produced in afinely divided form by precipitation from aqueousalkali-metal silicate solutions. Precipitated silica issupplied as a white powder or as beads or granules; andGel silica. Gel silica is also pre
47、pared by a wet process inwhich an aqueous alkali-metal silicate solution is reactedwith an acid so that an extensive three-dimensionalhydrated silica structure or gel is formed. It is supplied asgranules, beads, tablets, or as a white powder.Colloidal silica is a stable suspension of discrete partic
48、lesof amorphous silicon dioxide. The source of the silicaparticles may be one of the aforementioned processes.Colloidal silica may also be referred to as silica sol. Silicafume particles are too large to be colloidal.Additional information on these synthetic types of silicamay be found in the work o
49、f Iler (1979), Dunnom (1984),Ulrich (1984), Griffiths (1987), and Larbi and Bijen (1992).ASTM E 1156-87 contains additional descriptions of thesesynthetic amorphous silicas (note that this document hasbeen withdrawn by its committee).1.3.2 Natural silicaNatural silica is typically materialwith amorphous silica, and often reactive alumina, that isdug from the ground and then treated through grinding andclassification. The origin of the raw materials can, forexample, be volcanic as
