1、B ational“ AC1 232.2R-03 Use of Fly Ash in Concrete Reported by AC1 Committee 232 american concrete institute PO. BOX 9094 FARMINGTON HILLS, MICHIGAN 48333-9094 First Printing, March 2004 Use of Fly Ash in Concrete Most AC1 Standards and committee reports are gathered together in the annually revise
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11、ged to assist in enhancing the accuracy and usefulness of AC1 documents. Concrete Construction Inspector-In-Training mation: Concrete Transportation Construction Inspector problem. ISBN 0-87031 -1 37-9 AC1 232.2R-03 Use of Fly Ash in Concrete Reported by AC1 Committee 232 Moms “Skip” Huffman* Chair
12、Michael D. A. Thomas Vice Chair Karen A. Gruber Secretary Gregory S. Barger Alain Bilodeau Mark A. Bury Ramon L. Carrasquillo James E. Cook Douglas W. Deno Barry A. Descheneaux Jonathan E. Dongell Thomas A. Fox Dean M. Golden William Halczak Buffey J. Hauptmann Roy K. Heaps Russell L. Hill* R. Doug
13、Hooton Howard J. Humphrey Jim S. Jensen Steven H. Kosmatka Ronald L. Larsen William J. Lyons, III V. M. Malhotra Bryant Mather+ Tanin R. Naik Robert E. Neal Karthik H. Obla Terry Patzias Sandor Popovics Bruce W. Ramme Dan Ravina D. V. Reddy Anthony G. Reed Harry C. Roof Della M. Roy Caijun Shi Ava S
14、hypula Peter G. Snow Bons Y. Stein Paul J. Tikalsky Orville R. Werner II Min-Hong Zhang *Subcommittee co-chair of this report. +Deceased. Fly ash is used in concrete and other cement-based systems primarily because of its pozzolanic and cementitious properties. These properties contribute to strengt
15、h gain and may improve the performance of fresh and hardened concrete, morta; and grout. The use ofjly ash may result in more economical concrete construction. This report gives an overview of the origin and properties of jly ash, its effect on the properties of hydraulic cement concrete, and the pr
16、oper selection and use ofjy ash in the production of hydraulic cement concrete and concrete products. Information and recommendations concerning the selection and use of Class C and Class Fjy ashes generally conforming to the requirements of ASTM C 618 are provided. Topics covered include a detailed
17、 description of the composition ofjy ash, the physical and chemical effects ofjy ash on pmperiies of concrete, guidance on the handling and use of jly ash in concrete construction, use offly ash in the production of concrete products andspecialty concrete, and recommended procedures for quality cont
18、rol. Relevant documents of standards-making bodies referred to in this document are cited and listed. AC1 Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of
19、 individuais who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and ali responsibility for the stated principles. The Insti
20、tute shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architecangineer to be a part of the contract documents, they shall be restated in mandatory language for incorpor
21、ation by the Architecangineer. Keywords: abrasion resistance; admixture; alkali-aggregate reaction; concrete pavement; controlled low-strength material; drying shrinkage; durability; efflorescence; fineness; fly ash; hydraulic cement; mass concrete; mixture proportion; pozzolan; precast concrete; qu
22、ality control; reinforced concrete; roller-compacted concrete; soil cement; strength; sulfate resistance; workability. CONTENTS Chapter 1-General, p. 232.2R-2 1 .I-Introduction 1.2-Source of fly ash It is the responsibility of the user of this document to establish health and safety practices approp
23、riate to the specific circumstances involved with its use. AC1 does not make any representations with regard to health and safety issues and the use of this document. The user must determine the applicability of all regulatory limitations before applying the document and must comply with all applica
24、ble laws and regulations, including but not limited to, United States Occupational Safety and Health Administration (OSHA) health and safety standards. AC1 232.2R-03 supersedes AC1 232.2R-96 and became effective December 19,2003, Copyright O 2003, American Concrete Institute. All rights reserved inc
25、luding rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless pe
26、rmission in writing is obtained from the copyright proprietors. 232.2R-1 232.2R-2 AC1 COMMITTEE REPORT Chapter 2-Fly ash composition, p. 232.2R-5 2. laeneral 2.2-Chemical composition 2.3-Crystalline constituents 2.4-Glassy constituents 2.5-Physical properties 2.-Chemical activity of fly ash in hydra
27、ulic cement 2.7-Future research needs concrete Chapter 3-Effects of fly ash on concrete, p. 232.2R-11 3.1-Effects on properties of fresh concrete 3.2-Effects on properties of hardened concrete Chapter 4-Concrete mixture proportioning, p. 232.2R-18 4. laeneral 4.2-Considerations in mixture proportion
28、ing Chapter 5-Fly ash specifications, test methods, and quality assurance/control, p. 232.2R-19 5.1-Introduction 5.2-Chemical requirements 5.3-Physical requirements 5.4-General specification provisions 5.5-Methods of sampling and testing 5.6-Source quality control 5.7-Startup, oil, and stack additiv
29、es 5.8-Rapid quality-control tests Chapter 6-Fly ash in concrete construction, p. 232.2R-22 6.1-Ready-mixed concrete 6.2-Concrete pavement 6.3-Mass concrete 6.4-Roller-compacted concrete 6.5-Self-consolidating concrete 6.6-High-volume fly ash concrete 6.7-High-performance concrete 6.8-Bulk handling
30、and storage 6.9-Batching Chapter 7-Fly ash in concrete products, p. 232.2R-26 7.1-Concrete masonry units 7.2-Concrete pipe 7.3-Precast/prestressed concrete products 7.4-No-slump extruded hollow-core slabs Chapter there are both natural and artificial pozzolans.” Fly ash possesses pozzolanic properti
31、es similar to the naturally occurring pozzolans of volcanic or sedimentary origin found in many parts of the world. About 2000 years ago, the Romans mixed volcanic ash with he, aggregate, and water to produce mortar and concrete (Vitnivius 1960). Similarly, fly ash is mixed with portland cement (whi
32、ch releases lime during hydration), aggregate, and water to produce mortar and concrete. All fly ashes exhibit pozzolanic properties to some extent; however, some fly ashes display varying degrees of cementitious value without the addition of calcium hydroxide or hydraulic cement. The cementitious n
33、ature of these fly ashes is attributed to reactive constituents USE OF FLY ASH IN CONCRETE 232.2R-3 that reside within the fly ash, such as crystalline, calcium aluminate phases, and a more highly substituted, and therefore, potentially reactive glass phase. Fly ash in concrete reacts with the hydra
34、ting hydraulic cement in the following ways: 1. Solutions of calcium and alkali hydroxide, which are released into the pore structure of the paste, combine with the pozzolanic particles of fly ash, forming a cementing medium; and 2. Heat generated by hydration of hydraulic cement helps initiate the
35、pozzolanic reaction and contributes to the rate of the reaction. When concrete containing fly ash is properly cured, fly- ash reaction products partially fill in the spaces originally occupied by mixing water that were not filled by the hydration products of the cement, thus lowering the concrete pe
36、rmeability to water and aggressive chemicals (Manmohan and Mehta 1981). The slower reaction rate of fly ash, when compared to hydraulic cement, limits the amount of early heat generation and the detrimental early temperature rise in massive structures. Concrete proportioned with fly ash can have pro
37、perties that are not achievable through the use of hydraulic cement alone. Fly ash from coal-burning electric power plants became readily available in the 1930s. In the U.S., the study of fly ash for use in hydraulic cement concrete began at about that time. In 1937, results of research on concrete
38、containing fly ash were published (Davis et al. 1937). This work served as the foundation for early specifications, methods of testing, and use of fly ash. Initially, fly ash was used as a partial mass or volume replacement of hydraulic cement, typically the most expensive manufactured component of
39、concrete. As fly ash usage increased, researchers recognized that fly ash could impart beneficial properties to concrete. In subsequent research, Davis and colleagues studied the reactivity of fly ash with calcium and alkali hydroxides in portland-cement paste and the ability of fly ash to act as a
40、preventive measure against deleterious alkaii-aggregate reactions. Research (Dunstan 1976, 1980; Tikalsky, Carrasquillo, and Snow 1992; Tikalsky and Carrasquillo 1993) has shown that fly ash often improves the concretes resistance to deterioration from sulfates. Fly ash also increases the workabilit
41、y of fresh concrete and reduces the peak temperature of hydration in mass concrete. The beneficial aspects of fly ash were especially notable in the construction of large concrete dams (Mielenz 1983). Some major projects, including the Thames Barrage in the UK and the Upper Stillwater Dam in the US.
42、, incorporated 30 to 75% mass replacement of hydraulic cement by fly ash to reduce heat generation and decrease permeability. In the US., a new generation of coal-fired power plants was built during the late 1960s and 1970s, at least partially in response to dramatically increased oil prices. These
43、power plants, using efficient coal mills and state-of-the-art pyroprocessing technology, produce finer fly ashes with a lower carbon content. In addition, fly ash containing high levels of calcium oxide became available due to the use of western U.S. coal sources (typically sub-bituminous and lignit
44、ic). Concurrent with this increased availability of fly ash, extensive research has led to a better understanding of the chemical reactions involved when fly ash is used in concrete. Enhanced economics and improved technologies (material- and mechanical-based) have led to a greater use of fly ash, p
45、rincipally in the ready-mix concrete industry. Fly ash is now used in concrete for many reasons, including improvements in workability of fresh concrete, reduction in temperature rise during initial hydration, improved resistance to sulfates, reduced expansion due to alkali-silica reaction, and cont
46、nbutions to the durability and strength of hardened concrete. 1 -2-Source of fly ash Due to the uicreased use of pulverized coal as fuel for electric power generation, fly ash is now available in many areas of the world. Fly ash is a by-product of burning coals that have been crushed and ground to a
47、 fineness of 70 to 80% passing a 75 p (No. 200 0.0030 in.) sieve. Approximately 57,000 Gg (63 million tons) of fly ash is produced annually in the U.S. (American Coal Ash Association 2000). An estimated 18 to 20% of that total is used in the production of concrete and concrete products. ASTM C 618 c
48、ategorizes fly ash by chemical composition, according to the sum of the iron, aluminum, and silicon content (expressed in oxide form). As a group, Class F and C ashes generally show different performance characteristics; however, the performance of a fly ash is not determined solely by its classifca
49、tion. Class F ashes are normally produced from coals with higher heat energy such as bituminous and anthracite, though some sub-bituminous and lignite coals in the western U.S. also produce Class F fly ash. Bituminous and anthracite coal fly ashes rarely contain more than 15% calcium oxide. Sub-bituminous fly ashes usually contain more than 20% calcium oxide and have both cementitious and pozzolanic properties. There are important performance differences between fly ashes from different sources. In general, sulfate-resistant characteristics and the ability of a fly ash to mitigate the
