ACI-211.4R-1993-R1998.pdf

ACI 211.4R-93 (Reapproved 1998) Guide for Selecting Proportions for High-Strength Concrete with Portland Cement and Fly Ash Reported by ACI Committee211 Olga Alonzo* William L Barringer Stanley G. Barton Leonard W. Bell James E. Bennett Mike Boyle* George R.U. Burg Ramon L Carrasquillo* James E. Cook* Russell A. Cook David A. Crocker Guy Detwiler* Gary R. Mass Chairman Calvin L. Dodl Thomas A. Fox* George W. Hollow Tarif M. Jaber* Stephen M. Lane Stanley H. Lee Mark Luther* Richard C. Meininger James S. Pierce Mike Pistilli* Sandor Popovics* Steven E. Ragan Donald E. Dixon l Members of subcommittee who prepared the report. t Subcommittee Chairman. This guide presents a generally applicable method for selecting mixture proportions for high-strength concrete and optimizing these mixture propor- tions on the basis of trial batches. The method is limited to high-stmngth concrete produced using conventional materials and production techniques. Recommendations and tables are based on current practice and infor- mation provided by contractors, concrete suppliers, and engineers who have been involved in projects dealing with high-strength concrete. Keywords: aggregates; capping; chemical admixtures; fine aggregates; fIy ash; high-strength concretes; mixture proportioning; quality control; specimen size; strength requirements; superplasticizers. CONTENTS Chapter 1-Introduction, pg. 211.4R-1 1.1-Purpose 1.2-Scope Chapter 2-Performance requirements, pg. 211.4R-2 2.1-Test age 2.2-Required strength 2.3-Other requirements ACI Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidance in designing, plan- ning, executing, or inspecting construction and in preparing specifications. References to these documents shall not be made in the Project Documents. If items found in these documents are desired to be a part of the Project Docu- ments, they should be phrased in mandatory language and incorporated into the Project Documents. Donald Schlegel James M. Shilstone, Jr.* Paul R. Stodola William X. Sypher Ava Shypula* Jimmie L Thompson* Stanley J. Virgalitte Woodward L Vogt Jack W. Weber Dean J. White, IIt Marshall S. Williams John R. Wilson Chapter 3-Fundamental relationships, pg. 211.4R-3 3.1-Selection of materials 3.2-Water-cementitious materials ratio (w/c +p) 3.3-Workability 3.4-Strength measurements Chapter 4-High-strength concrete mixture proportion- ing, pg. 211.4R-5 4.1-Purpose 4.2-Introduction 4.3-Mixture proportioning procedure Chapter 5-Sample calculations, pg. 21.4R-8 5.1-Introduction 5.2-Example Chapter 6-References, pg. 211.4R-13 6.1-Recommended references CHAPTER l-INTRODUCTION 1.1.Purpose The current ACI 211.1 mixture proportioning proce- ACI 211.4R-93 became effective September 1.1993. Copyright Q 1993, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any elec- tronic 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 permission in writing is obtained from the copyright proprietors. 211.4R-1 211.4R-2 ACI COMMITTEE REPORT dure describes methods for selecting proportions for nor- mal strength concrete in the range of 2000 to 6000 psi. Mixture proportioning is more critical for high-strength concrete than for normal strength concrete. Usually, spe- cially selected pozzolanic and chemical admixtures are employed, and attainment of a low water-to-cementitious material ratio (w/c+p) is considered essential. Many trial mixtures are often required to generate the data neces- sary to identify optimum mixture proportions. The pur- pose of this guide is to present a generally applicable method for selecting mixture proportions for high- strength concrete and for optimizing these mixture pro- portions on the basis of trial batches. 1.2-Scope Discussion in this guide is limited to high-strength concrete produced using conventional materials and production methods. Consideration of silica fume and ground granulated blast furnace slag (GGBFS) is beyond the scope of this document. Information on proportion- ing of silica fume concrete is limited at this time. ACI Committee 234, Silica Fume in Concrete, is developing information on the use of silica fume for a committee report. Proportioning GGBFS concrete is discussed in ACI 226-1R (now ACI Committee 233). When additional data becomes available, it is expected that an ACI guide for proportioning concrete with these materials will be developed. Currently, silica fume and GGBFS suppliers, as well as experienced concrete suppliers, represent the best source of proportioning information for these materials. High-strength concrete is defined as concrete that has a specified compressive strengthf, of 6000 psi or greater. This guide is intended to cover field strengths up to 12,000 psi as a practical working range, although greater strengths may be obtained. Recommendations are based on current practice and information from contractors, concrete suppliers, and engineers who have been involved in projects dealing with high-strength concrete. For a more complete list of references and available publica- tions on the topic, the reader should refer to ACI 363R. CHAPTER 2-PERFORMANCE REQUIREMENTS 2.1-Test age The selection of mixture proportions can be influenced by the testing age. High-strength concretes can gain con- siderable strength after the normally specified 28-day age. To take advantage of this characteristic, many specifica- tions for compressive strength have been modified from the typical 28-day criterion to 56 days, 91 days, or later ages. Proportions of cementitious components usually have been adjusted to produce the desired strength at the test age selected. 2.2-Required strength ACI 318 allows concrete mixtures to be proportioned based on field experience or laboratory trial batches. To meet the specified strength requirements, the concrete must be proportioned in such a manner that the average compressive strength results of field tests exceed the specified design compressive strength f, by an amount sufficiently high to make the probability of low tests small. When the concrete producer chooses to select high-strength concrete mixture proportions based upon field experience, it is recommended that the required average strength fc, used as the basis for selection of concrete proportions be taken as the larger value calcu- lated from the following equations f_ = f, + 1.34s fw = 0.9of, + 2.33s (2-1) (2-2) where s = sample standard deviation in psi. Eq. (2-l) is Eq. (5-l) of the ACI 318 Building Code. Eq. (2-2) is a modified version of Eq. (5-2) qcr = fc + 2.33s - 500) of the modified ACI 318 because, to date, job specifications for high-strength concrete have usually more than 1 in 100 individual tests that will fall below 90 percent of the specified strength. When job specifications cite ACI 318 acceptance criteria, Eq. (5-2) of ACI 318 should be used instead of Eq. (2-2) of this report. When the concrete producer selects high-strength con- crete proportions on the basis of laboratory trial batches, the required average strength f, may be determined from the equation (2-3) Eq. (2-3) gives a higher required average strength value than that required in Table 5.3.2.2 of the ACI Building Code (ACI 318). Experience has shown that strength tested under ideal field conditions attains only 90 percent of the strength measured by tests performed under laboratory conditions. To assume that the average strength of field production concrete will equal the strength of a laboratory trial batch is not realistic, since many factors can influence the variability of strengths and strength measurements in the field. Initial use of a high- strength concrete mixture in the field may require some adjustments in proportions for air content and yield, and for the requirements listed below, as appropriate. Once sufficient data have been generated from the job, mixture proportions should be reevaluated using ACI 214 and ad- justed accordingly. 2.3-Other requirements Considerations other than compressive strength may influence the selection of materials and mixture propor- tions. These include: a) modulus of elasticity, b) flexural and tensile strengths, c) heat of hydration, d) creep and drying shrinkage, e) durability, f) permeability, g) time of HIGH-STRENGTH CONCRETE WITH PORTLAND CEMENT AND FLY ASH 211.4R-3 setting, h) method of placement, and i) workability. CHAPTER 3-FUNDAMENTAL RELATIONSHIPS 3.1-Selection of materials Effective production of high-strength concrete is achieved by carefully selecting, controlling, and pro- portioning all of the ingredients. To achieve higher strength concretes, optimum proportions must be se- lected, considering the cement and fly ash characteristics, aggregate quality, paste proportion, aggregate-paste interaction, admixture type and dosage rate, and mixing. Evaluating cement, fly ash, chemical admixture, and aggregate from various potential sources in varying pro- portions will indicate the optimum combination of mater- ials. The supplier of high-strength concrete should implement a program of uniformity and acceptance tests for all materials used in the production of high-strength concrete. 3.1.1 Portland cement-Proper selection of the type and source of cement is one of the most important steps in the production of high-strength concrete. ASTM C 917 may be useful in considering cement sources. Variations in the chemical composition and physical properties of the cement affect the concrete compressive strength more than variations in any other single material. For any given set of materials, there is an optimum cement con- tent beyond which little or no additional increase in strength is achieved from increasing the cement content. 3.1.2 Other cementitious materials-Finely divided cementitious materials other than portland cement, con- sisting mainly of fly ash, ground blast furnace slag, or silica fume (microsilica), have been considered in the production of high-strength concrete because of the re- quired high cementitious materials content and low w/c+p. These materials can help control the temperature rise in concrete at early ages and may reduce the water demand for a given workability. However, early strength gain of the concrete may be decreased. ASTM C 618 specifies the requirements for Class F and Class C fly ashes, and for raw or calcined natural pozzolans, Class N, for use in concrete. Fly ash proper- ties may vary considerably in different areas and from different sources within the same area. The preferred fly ashes for use in high-strength concrete have a loss on ignition no greater than 3 percent, have a high fineness, and come from a source with a uniformity meeting ASTM C 618 requirements. 3.13 Mixing water-The acceptability of the water for high-strength concrete is not of major concern if potable water is used. Otherwise, the water should be tested for suitability in accordance with ASTM C 94. 3.1.4 Coarse aggregate-In the proportioning of high- strength concrete, the aggregates require special consid- eration since they occupy the largest volume of any ingre- dient in the concrete, and they greatly influence the strength and other properties of the concrete. Usually, high-strength concretes are produced with normal weight aggregates. However, there have been reports of high- strength concrete produced using lightweight aggregates for structural concrete and heavyweight aggregates for high-density concrete. The coarse aggregate will influence significantly the strength and structural properties of the concrete. For this reason, a coarse aggregate should be chosen that is sufficiently hard, free of fissures or weak planes, clean, and free of surface coatings. Coarse aggregate properties also affect aggregate-mortar bond characteristics and mixing water requirements. Smaller size aggregates have been shown to provide higher strength potential. For each concrete strength level, there is an optimum size for the coarse aggregate that will yield the greatest compressive strength per pound of cement. A 1 or 3/4-in. nominal maximum-size aggregate is common for produc- ing concrete strengths up to 9000 psi; and l/z or 3/8-in. above 9000 psi. In general, the smallest size aggregate produces the highest strength for a given w/c+p. How- ever, compressive strengths in excess of 10,000 psi are feasible using a l-in. nominal maximum-size aggregate when the mixture is proportioned with chemical admix- tures. The use of the largest possible coarse aggregate is an important consideration if optimization of modulus of elasticity, creep, and drying shrinkage are important. 3.1.5 Fine aggregate-The grading and particle shape of the fiie aggregate are significant factors in the production of high-strength concrete. Particle shape and surface texture can have as great an effect on mixing water requirements and compressive strength of concrete as do those of coarse aggregate. Fine aggregates of the same grading but with a difference of 1 percent in voids content may result in a 1 gal. per yd3 difference in water demand. More information can be found in ACI 211.1. The quantity of paste required per unit volume of a concrete mixture decreases as the relative volume of coarse aggregate versus fine material increases. Because the amount of cementitious material contained in high- strength concrete is large, the volume of fines tends to be high. Consequently, the volume of sand can be kept to the minimum necessary to achieve workability and com- pactibility. In this manner, it will be possible to produce higher strength concretes for a given cementitious mater- ial content. Fine aggregates with a fineness modulus (FM) in the range of 2.5 to 3.2 are preferable for high-strength con- cretes. Concrete mixtures made with a fine aggregate that has an FM of less than 2.5 may be “sticky” and result in poor workability and a higher water requirement. It is sometimes possible to blend sands from different sources to improve their grading and their capacity to produce higher strengths. If manufactured sands are used, consid- eration should be given to a possible increase in water demand for workability. The particle shape and the in- creased surface area of manufactured sands over natural sands can significantly affect water demand. 3.1.6 Chemical admixtures-In the production of con- crete, decreasing the w/c+p by decreasing the water requirement rather than by increasing the total cementitious materials content, will usually produce higher compressive strengths. For this reason, use of chemical admixtures should be considered when pro- ducing high-strength concrete (see ACI 212.3R and ASTM C 494). In this guide, chemical admixture dosage rates are based on fluid oz per 100 lb of total cementitious mat