ACI 363R-92 (Reapproved 1997)
State-of-the-Art Report on High-Strength Concrete Reported by ACI Committee 363 Henry G. Russell Chairman
Jaime Moreno Secretary
Arthur R. Anderson Jack O. Banning Irwin G. Cantor* Ramon L. Carrasquillo* James E. Cook Gregory C. Frantz Weston T. Hester
Anthony N. Kojundic Brian R. Mastin* William C. Moore Arthur H. Nilson* William F. Perenchio Francis J. Principe
Kenneth L Saucier* Surendra P. Shah* J. Craig Williams* John Wolsiefer, Sr. J. Francis Young Paul Zia
Members responsible for individual chapters
l
ACI Committee 363 Members Balloting 1992 Revisions Kenneth L Saucier Chairman Pierre Claude Aitcin F. David Anderson Claude Bedard Roger W. Black Irwin G. Cantor Ramon L. Carrasquillo Judith A. Castello James E. Cook Kingsley D. Drake Gregory C. Frantz Thomas G. Guennewig
William F. Perenchio Secretary Weston T. Hester + Nathan L Howard Anthony N. Kojundic Mark D. Luther Heshem Marzouk Brian R. Mastin William C. Moore Jaime Moreno Arthur H. Nilson Clifford R. Ohwiler
Currently available information about high-strength concrete is summarized. Topics discussed include selection of materials, concrete mix pro portioning, batching miring, miring, transporting transporting placing, placing, control procedures, procedures, concrete properties, structural design, economics, and applications. applications. A bibliography is included. Keywords: bibliographies; bridges (structures); (structures); buildings; buildings; conveying; economics; high-strength concretes; mechanical properties; mixing; mix proportioning; placing; quality control; raw materials; materials; reviews; structural design.
Reports, Guides, Standard Practices, and Commentaries are intended for guidance in designing, planning, executing, or inspecting construction and in preparing specifications. Reference to these documents shall not be made in the Project Documents. If items found in these documents are desired to be part of the Project Documents, they should be phrased in mandatory language and incorporated into the Project Documents.
ACI Committee
Henry G. Russell Michael T. Russell Surendra P. Shah Bryce P. Simons Ava Szypula Dean J. White, II J. Craig Williams John T. Wolsiefer Francis J. Young Paul Zia
Chapter l-Introduction, pg. 363R-2
1.l-Historical background 1.2-Committee objectives Chapter 2-Selection of materials, pg. 363R-3
2.1-Introduction 2.2-Cements 2.3-Chemical admixtures 2.4-Mineral admixtures and slag cement
c 1992, American Concrete Institute. Copyright O 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 electronic or mechanical device, printed or written or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device,
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2.5-Aggregates 2.6-Water 2.7-Cited references Chapter 3-Concrete mix proportions, pg. 363R-8
3.1-Introduction 3.2-Strength required 3.3-Test age 3.4-Water-cement 3.4-Water-cement ratio or water-cementitious ratio 3.5-Cement content 3.6-Aggregate proportions 3.7-Proportioning with admixtures 3.8-Workability 3.9-Trial batches 3.10-Cited references Chapter 4-Batching, mixing, transporting, placing, curing, and control procedures, pg. 363R-16
4.1-Introduction 4.2-Batching
7.2-Cost studies 7.3-Case histories 7.4-Other studies 7.5-Selection of materials 7.6-Quality control 7.7-Areas of application 7.4-Conclusion 7.9-Cited references Chapter 8-Applications, pg. 363R-44
8.1-Introduction 8.2-Buildings 8.3-Bridges 8.4-Special applications 8.5-Potential applications 8.6-Cited references Chapter 9-Summary, pg. 363R-48 Chapter 10-References, pg. 363R-49
4.3-Mixing
4.4-Transporting 4.5-Placing procedures 4.6-Curing 4.7-Quality assurance 4.8-Quality control procedures 4.9-Strength measurements 4.10-Cited references Chapter 5-P 5-Properti roperties esof high-strength concrete, pg. 363R-22 5.1-Introduction 5.2-Stress-strain behavior in uniaxial compression 5.3-Modulus of elasticity 5.4-Poisso 5.4-Poisson’ n’ s ratio 5.5-Modulus of rupture 5.6-Tensile splitting strength 5.7-Fatigue strength 5.8-Unit weight 5.9-Thermal properties 5.10-Heat evolution due to hydration 5.11-Strength gain with age 5.12-Freeze-thaw 5.12-Freeze-thaw resistance 5.13-Shrinkage 5.14-Creep 5.15-Cited references Chapter 6-Structural design considerations, pg. 363R-
29 6.1-Introduction 6.2-Axially-loaded columns 6.3-Beams and slabs 6.4-Eccentric columns 6.5-Summary 6.6-Cited references Chapter 7--Economic considerations, pg. 363R-41 7.1-Introduction
CHAPTER 1-I 1-INTRODUCTION NTRODUCTION 1.1-Historical 1.1-Historical background
Although high-strength concrete is often considered a relatively new material, its development has been gradual over many years. As the development has continued, the definition of high-strength concrete has changed. In the 1950s, concrete with a compressive strength of 5000 psi (34 MPa) was considered high strength. In the 1960s, concrete with 6000 and 7500 psi (41 and 52 MPa) com pressive strengths were used commercially. commercia lly. In the early 1970s, 9000 psi (62 MPa) concrete was being produced. More recently, compressive strengths approaching 20,000 psi (138 (13 8 MPa) MPa ) have been used u sed in cast-in-place cast-in -place buildings. build ings. For many years, concrete with compressive strength in excess of 6000 psi (41 MPa) was available at only a few locations. However, in recent years, the applications of high-strength concrete have increased, and high-strength concrete has now been used in many parts of the world. The growth has been possible as a result of recent developments in material technology and a demand for higher-strength concrete. The construction of Chicago’s Water Tower Place and 311 South Wacker Drive concrete buildings would not have been possible without the development of high-strength concrete. The use of concrete superstructures in long span cable-stayed bridges such as East Huntington, W.V., bridge over the Ohio River would not have taken place without the availability of high-strength concrete. 1.2-Committee objectives
Since the definition of high-strength concrete has changed over the years, the committee needed to define an applicable range of concrete strengths for its activities. The following working definition definition was adopted: “ The immediate concern of Committee 363 shall be concretes
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2.5-Aggregates 2.6-Water 2.7-Cited references Chapter 3-Concrete mix proportions, pg. 363R-8
3.1-Introduction 3.2-Strength required 3.3-Test age 3.4-Water-cement 3.4-Water-cement ratio or water-cementitious ratio 3.5-Cement content 3.6-Aggregate proportions 3.7-Proportioning with admixtures 3.8-Workability 3.9-Trial batches 3.10-Cited references Chapter 4-Batching, mixing, transporting, placing, curing, and control procedures, pg. 363R-16
4.1-Introduction 4.2-Batching
7.2-Cost studies 7.3-Case histories 7.4-Other studies 7.5-Selection of materials 7.6-Quality control 7.7-Areas of application 7.4-Conclusion 7.9-Cited references Chapter 8-Applications, pg. 363R-44
8.1-Introduction 8.2-Buildings 8.3-Bridges 8.4-Special applications 8.5-Potential applications 8.6-Cited references Chapter 9-Summary, pg. 363R-48 Chapter 10-References, pg. 363R-49
4.3-Mixing
4.4-Transporting 4.5-Placing procedures 4.6-Curing 4.7-Quality assurance 4.8-Quality control procedures 4.9-Strength measurements 4.10-Cited references Chapter 5-P 5-Properti roperties esof high-strength concrete, pg. 363R-22 5.1-Introduction 5.2-Stress-strain behavior in uniaxial compression 5.3-Modulus of elasticity 5.4-Poisso 5.4-Poisson’ n’ s ratio 5.5-Modulus of rupture 5.6-Tensile splitting strength 5.7-Fatigue strength 5.8-Unit weight 5.9-Thermal properties 5.10-Heat evolution due to hydration 5.11-Strength gain with age 5.12-Freeze-thaw 5.12-Freeze-thaw resistance 5.13-Shrinkage 5.14-Creep 5.15-Cited references Chapter 6-Structural design considerations, pg. 363R-
29 6.1-Introduction 6.2-Axially-loaded columns 6.3-Beams and slabs 6.4-Eccentric columns 6.5-Summary 6.6-Cited references Chapter 7--Economic considerations, pg. 363R-41 7.1-Introduction
CHAPTER 1-I 1-INTRODUCTION NTRODUCTION 1.1-Historical 1.1-Historical background
Although high-strength concrete is often considered a relatively new material, its development has been gradual over many years. As the development has continued, the definition of high-strength concrete has changed. In the 1950s, concrete with a compressive strength of 5000 psi (34 MPa) was considered high strength. In the 1960s, concrete with 6000 and 7500 psi (41 and 52 MPa) com pressive strengths were used commercially. commercia lly. In the early 1970s, 9000 psi (62 MPa) concrete was being produced. More recently, compressive strengths approaching 20,000 psi (138 (13 8 MPa) MPa ) have been used u sed in cast-in-place cast-in -place buildings. build ings. For many years, concrete with compressive strength in excess of 6000 psi (41 MPa) was available at only a few locations. However, in recent years, the applications of high-strength concrete have increased, and high-strength concrete has now been used in many parts of the world. The growth has been possible as a result of recent developments in material technology and a demand for higher-strength concrete. The construction of Chicago’s Water Tower Place and 311 South Wacker Drive concrete buildings would not have been possible without the development of high-strength concrete. The use of concrete superstructures in long span cable-stayed bridges such as East Huntington, W.V., bridge over the Ohio River would not have taken place without the availability of high-strength concrete. 1.2-Committee objectives
Since the definition of high-strength concrete has changed over the years, the committee needed to define an applicable range of concrete strengths for its activities. The following working definition definition was adopted: “ The immediate concern of Committee 363 shall be concretes
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have specified compressive strengths for design of 6000 psi (41 MPa) or greater, greate r, but for the present presen t time, considerations shall not include concrete made using exotic materials or techniques.” The word exotic was included in the definition so that the committee would not be concerned with concretes such as polymer-impregnated concrete, epoxy concrete, or concrete with artificial normal and heavy-weight aggregates. Although 6000 psi (41 MPa) was selected as the lower limit, it is not intended to imply that there is a drastic change in material properties or in production techniques that occur at this compressive strength. In reality, all changes that take place above 6000 psi (41 MPa) represent a process which starts with the lowerstrength concretes and continues into high-strength concretes. Many empirical equations used to predict properties of concrete or to design structural members are based on tests using concrete concre te with compressive compre ssive strengths strengt hs less than about 6000 psi (41 MPa). The availability of data for higher-strength concretes requires a reassessment of the equations to determine their applicability with higher-strength concretes. Consequently, caution should be exercised in extrapolating data from lowerstrength to high-strength concretes. If necessary, tests should then be made to develop data for the materials or applications in question. The committee also recognized that the definition of high-strength concrete varies on a geographical basis. In regions where concrete with a compressive strength of 9000 psi (62 MPa) is already being produced commercially, high-strength concrete might be in the range of 12,000 to 15,000 psi (83 to 103 MPa) compressive strength. However, in regions where the upper limit on commercially available material is currently 5000 psi (34 MPa) concrete, 9000 psi (62 MPa) concrete is considered high strength. The committee recognized that material selection, concrete mix proportioning, batching, mixing, trans porting, portin g, placing, placin g, and control contro l procedures proced ures are applicable applic able across a wide range of concrete strengths. However, the committee felt that material properties and structural design considerations given in this report should be concerned with concretes having the highest compressive strengths. The committee has tried to cover both aspects in compiling this state-of-the-art report.
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knowledge regarding material selection and provides a baseline for the subsequent discussion of mix proportions in Chapter 3.
Fig. 2.1-Effects of cement cement on concrete compressive compressive 2.2 strength. 2.2-Cements
The choice of portland cement for high-strength con-
strength is the objective, such as in prestressed concrete, there is no need to use a Type III cement. Furthermore, within a given cement type, different brands will have different strength development characteristics because of the variations in compound composition and fineness that are permitted by ASTM C 150. Initially, silo test certificates should be obtained from potential poten tial suppliers supp liers for the previous previo us 6 to 12 months. mont hs. Not only will this give an indication of strength characteristics from the ASTM C 109 mortar cube test, but also, more importantly, it will provide an indication of cement uniformity. The cement supplier should be required to re port uniformity uniform ity in accordance accorda nce with ASTM C 917. If the tricalcium silicate content varies by more than 4 percent, the ignition loss by more than 0.5 percent, or the fineness 2 by more m ore than th an 375 37 5 cm /g (Blaine), then problems in main2.1 taining a uniform high strength may result. Sulfate (SO,) levels should be maintained at optimum with variaCHAPTER 2-SELECTION OF MATERIALS tions limited to ± 0.20 percent. Although mortar cube tests can give a good indication 2.1-I 2.1-I ntrodu ntroduction of potential strength, tests should be run on trial batches. The production of high-strength concrete that con- These should contain the materials to be used in the job sistently meets requirements for workability and strength and be prepared at the proposed slump, with strengths development places more stringent requirements on determined at 7, 28, 56, and 91 days. The effect of material selection than for lower-strength concretes. cement characteristics on water demand is more noticeQuality materials are needed and specifications require able in high-strength concretes because of the higher enforcement. High-strength concrete has been produced cement contents. using a wide range of quality materials based on the reHigh cement contents can be expected to result in a sults of trial mixtures. This chapter cites the state of high temperature rise within the concrete. For example, I
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the temperature in the 4 ft (1.2 m) square columns used 3 in Water Tower Place which contained 846 lb cement/yd 3 (502 kg/m ), rose to 150 F (66 C) from 75 F (24 C) during hydration.2.2 The heat was dissipated within 6 days without harmful effects. However, when the temperature rise is expected to be a problem, a Type II low-heat-ofhydration cement can be used, provided it meets the strength-producing requirements. A further consideration is the optimization of the cement-admixture system. The exact effect of a waterreducing agent on water requirement, for example, will depend on the cement characteristics. Strength development will depend on both cement characteristics and cement content. 2.3-Chemical admixtures 2.3.1 General-Admixtures are widely used in the pro-
duction of high-strength concretes. These materials include air-entraining agents and chemical and mineral admixtures. Air-entraining agents are generally surfactants that will develop an air-void system appropriate for durability enhancement. Chemical admixtures are generally produced using lignosulfonates, hydroxylated car boxylic boxyli c acids, carbohydrates, carbohy drates, melamine melamin e and naphthalene naphth alene condensates, and organic and inorganic accelerators in various formulations. Selection of type, brand, and dosage rate of all admixtures should be based on performance with the other materials being considered or selected for use on the project. Significant increases in compressive strength, control of rate of hardening, accelerated strength gain, improved workability, and durability are contributions that can be expected from the admixture or admixtures chosen. Reliable performance on previous work should be considered during the selection process.
mixtures with sufficient retarder dosage to give the desirable rate of hardening under the anticipated temperature conditions. Since retarders frequently provide an increase in strength that will be proportional to the dosage rate, mixtures can be designed at different doses if it is expected that significantly different rates will be used. However, there is usually an offsetting effect that minimizes the variations in strengths due to temperature. As temperature increases, later age strengths will decline; however, an increase in retarder dosage to control the rate of hardening will provide some mitigation of the temperature-induced reduction. Conversely, dosages should be decreased as temperatures decline. While providing initial retardation, strengths at 24 hours and later are usually increased by normal dosages. Extended retardation or cool temperatures may affect early (24-hour) strengths adversely. 2.3.4 Normal-setting Normal-setting water reducers reducers (ASTM C 494, Type A Type A-Normal setting ASTM C 494 Type A conven-
tional water-reducing admixtures will provide strength increases without altering rates of hardening. Their selection should be based on strength performance. Increases in dosage above the normal amounts will generally increase strengths, but may extend setting times. When admixtures are used in this fashion to provide retardation, a benefit in strength performance sometimes results. 2.4,2.5
2.3.5 High-range water reducers (ASTM C 494, Types F and G-High-range water reduction provides high-strength performance, particularly at early (24-hour)
ages. Matching the admixture to the cement, both in type and dosage rate, is important. The slump loss characteristics of a high-range water reducer (HRWR) will determine whether it should be added at the plant, at the site, or a combination of each. 2.3.2 Air-entraining admixtures (ASTM C 260)-The 260)-The Use of a HRWR in high-strength concrete may serve use of air entrainment is recommended to enhance dura bility when concrete will be subjected to freezing and the purpose of increasing strength at the slump or inthawing while wet. As compressive strengths increase and creasing slump. The method of addition should distribute water-cement ratios decrease, air-void parameters im- the admixture throughout the concrete. Adequate mixing prove and entrained entrain ed air percentages percen tages can be set at the is critical to uniform performance. Supervision is im porta nt to the successful succes sful use of a HRWR. HRWR . The use of lower limits of the acceptable range as given in ACI 201. portant 2.6 Entrained air has the effect of reducing strength, parti- superplasticizers is discussed further in ACI SP-68. 2.3.6 Accelerators (ASTM C 494, 494, Types C and E)-Accularly in high-strength mixtures, and for that reason it has been used only where there is a concern for durabili- celerators are not normally used in high-strength concrete unless early form removal is critical. High-strength ty. See also Section 5.12. 5.12. 2.3.3 Retarders (ASTM C 494, Types B and D)-HighD)-High- concrete mixtures can provide strengths adequate for verstrength concrete mix designs incorporate high cement tical form removal on walls and columns at an early age. factors that are not common to normal commercial con- Accelerators used to increase the rate of hardening will crete. A retarder is frequently beneficial in controlling normally be counterproductive in long-term strength deearly hydration. The addition of water to retemper the velopment. 2.3.7 Admixture combinations -Combinations of highmixture will result in marked strength reduction. Further, structural design frequently requires heavy reinforcing range water reducers with normal-setting water reducers steel and complicated forming with attendant difficult or retarders have become common to achieve optimum perform ance at lowest cost. Improvements Improv ements in strength placement placeme nt of the concrete. concrete . A retarder can control the performance rate of hardening in the forms to eliminate cold joints gain and control of setting times and workability are posstb le with optimized optimi zed combinations. combin ations. In certain cirand provide more flexibility in placement schedules. Pro- posstble jects have used retarders retarde rs successfully successfu lly by initially initia lly designing designin g cumstances, combinations of normal-setting or retarding
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is 10 to 20 lb/ft3 (160 to 320 kg/m3); however, it is also available in densified or slurry forms for commercial application. Silica fume, because of its extreme fineness and high silica content, is a highly effective pozzolanic material. The silica fume reacts pozzolanically with the lime during the hydration of cement to form the stable cementitious compound calcium silicate hydrate (CSH). The availabili2.4-Mineral admixtures and slag cement ty of high-range water-reducing admixtures has facilitated Finely divided mineral admixtures, consisting mainly the use of silica fume as part of the cementing material of fly ash and silica fume, and slag cement have been in concrete to produce high-strength concretes.2.29 No rwidely used in high-strength concrete. mal silica fume content ranges from 5 to 15 percent of 2.4.1 Fly ash-Fly ash-Fly ash for high-strength concrete is portland cement content. classified into two classes. Class F fly ash is normally proThe use of silica fume to produce high-strength duced from burning anthracite or bituminous coal and concrete increased dramatically in the 1980s. Both laborhas pozzolanic properties, but little or no cementitious atory and field experience indicate that concrete incor properties. properti es. Class C fly ash is normally normall y produced produce d from porating silica fume fu me has an increased in creased tendency to develop de velop 2.29 burning lignite or subbitu s ubbituminous minous coal, and in addition additio n to t o plastic shrinkage cracks. Thus, it is necessary to cracks. having pozzolanic properties, has some autogenous ce- quickly cover the surfaces of freshly placed silica-fume mentitious properties. In general, Class F fly ash is avail- concrete to prevent rapid water evaporation. Since it is able in the eastern United States and Canada, and Class a relatively new material to the concrete industry in the C fly ash is available in the western United States and United States, the user is referred to several recent Canada. symposia and publications for additional information on Specifications for fly ash are covered in ASTM C 618. Methods for sampling and testing are found in 2.4.3 Slag cement - Ground slag cement is produced ASTM C 311. Variations in physical or chemical p roper- only in certain areas of the United States and Canada. ties of mineral admixtures, although within the tolerances Specifications for ground granulated blast furnace slag of these specifications, may cause appreciable variations are given in ASTM C 989. The classes of portland blast in properties of high-strength concrete. Such variations furnace slag cement are covered in ASTM C 595. Slag can be minimized by appropriate testing of shipments appropriate for concrete is a nonmetallic product that is and increasing the frequency of sampling. ACI 212.2R developed in a molten condition simultaneously with iron provides provide s guidelines guidel ines for the th e use of o f admixtures admixt ures in concrete. co ncrete. in a blast furnace. When properly quenched and proIt is extremely important that mineral admixtures be test- cessed, slag will act hydraulically in concrete as a partial ed for acceptance and uniformity and carefully investi- replacement for portland cement. Slag can be intergated for strength-producing properties and compatibility ground with cement or used as an additional cement at with the other materials in the high-strength concrete the batching facility. Blast furnace slag essentially consists mixture before they are used in the work. of silicates and alumino-silicates of calcium and other 2.4.2 Silica fume - Silica fume and admixtures contain bases. Research using ground slag shows much promise 2.8 ing silica fume have been used in high-strength con- for its use in high-strength concrete. 2.9, 2.10 cretes for structural purposes and for surface ap2.4.4 Evaluatio 2.4.4 Evaluation n and selection - Mineral admixtures plications plicati ons and as repair materials material s in situations situati ons where and slag cement, like any material in a high-strength conabrasion resistance and low permeability are advanta- crete mixture, should be evaluated using laboratory trial geous. Silica fume is a by-product resulting from the re- batches batche s to establish establi sh the optimum optim um desirable desirab le qualities. qualit ies. duction of high-purity quartz with coal in electric arc Materials representative of those that will be employed furnaces in the production of silicon and ferrosilicon al- later in the actual construction should be used. Particular loys. The fume, which has a high content of amorphous care should be taken to insure that the mineral admixsilicon dioxide and consists of very fine spherical par- ture comes from bulk supplies and that they are typical. ticles, is collected from the gases escaping from the Generally, several trial batches are made using varying furnaces. cement factors and admixture dosages to establish curves Silica fume consists of very fine vitreous particles with which can be used to select the amount of cement and 2 a surface area on the order of 20,000 m /kg when admixture required to achieve the desired results. 2.29 measured by nitrogen adsorption techniques The When fly ash is to be used, the minimum requirement particle-size particle- size distribution distribu tion of a typical typica l silica fume shows is that it comply with ASTM C 618. Although this specifimost par-titles to be smaller than one micrometer (1 cation permits a higher loss on ignition, an ignition loss 2.11 µm) with an average diameter of about 0.1 µm, which is of 3 percent or less is desirable. High fineness, uniapproximately 100 times smaller than the average cement formity or production, high pozzolanic activity, and com particle. The specific spec ific gravity of silica fume is typically ty pically 2.2, patibility patibili ty with other mixture ingredients ingredie nts are items of pri but may be as high as 2.5. 2 .5. The bulk density as collected c ollected mary importance. water-reducing admixtures plus an accelerating admixture have also been found to be useful. When using a combination of admixtures, they should be dispensed individually individu ally in a manner approved approve d by the manufacturer(s). Air-entraining admixtures should, if used, be dispensed separately from water-reducing admixtures.
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2.5-Aggregates
2.5.1 General - Both fine and coarse aggregates used
for high-strength concrete should, as a minimum, meet the requirements of ASTM C 33; however, the following exceptions may be beneficial.
gregate should be clean, cubical, angular, 100 percent crushed aggregate with a minimum of flat and elongated 2.13 particles. Because, as stated earlier, bond strength is the limiting
factor in the development of high-strength concrete, the 2.5.2 - Grading mineralogy of the aggregates should be such as to promote chemical bonding. Some work has been done with 2.5.2.1 Fine aggregate - Fine aggregates with a rounded particle shape and smooth texture have been artificial material such as portland and aluminous cement 2.14,221 The long-term stability found to require less mixing water in concrete and for clinkers and selected slags. 2.22 2.11 2.12 of the clinkers is in question, however. Harris states this reason are preferable in high-strength concrete ’ The optimum gradation of fine aggregate for high- that Moorehead measured a potential silica-lime bond of strength concrete is determined more by its effect on at least 28,000 psi (193 M Pa). Presumably many siliceous water requirement than on physical packing. One re- minerals would prove to have good bonding potential 2.10 port stated that a sand with a fineness modulus (PM) with portland cement. This would appear to be a promis below 2.5 gave the concrete a sticky consistency, making ing area for further research. it difficult to compact. Sand with an FM of about 3.0 2.5.3 Absorption -Curing is extremely important in the gave the best workability and compressive strength. production of high-strength concrete. To produce a High-strength concretes typically contain such high cement paste with as high a solids content as possible, contents of fine cementitious materials that the grading the concrete must contain the absolute minimum mix of the aggregates used is relatively unimportant com- water. However, after the concrete is in place and the pared to conventional concrete. However, it is sometimes paste structure is established, water should be freely helpful to increase the fineness modulus. A National available, especially during the early stages of hydra2.14,2.23 2.13 During this period, a great deal of water Crushed Stone Association report made several re- tion commendations in the interest of reducing the water re- combines with the cement. All of this water loses approxquirement. The amounts passing the No. 50 and 100 imately ¼ of its volume after the chemical reactions are sieves should be kept low, but still within the require- completed. This creates a small vacuum that is capable of ments of ASTM C 33, and mica or clay contaminants pulling water short distances into the concrete which, at 2.13 should be avoided. Another investigation found that this time, is still relatively permeable. Any extra water the sand gradation had no significant effect on early which can enter the structure will increase the ultimate strengths but that “at later ages and consequently higher amount of hydration and, therefore the percent of solids levels of strength, the gap-graded sand mixes exhibited per unit volume of paste, thereby increasing its strength. lower strengths than the standard mixes.” If the aggregates are capable of absorbing a moderate amount of water, they can act as tiny curing-water reser2.5.2.2 Coarse aggregate voirs distributed throughout the concrete, thereby procompressive strength with high cement content and low viding the added curing water which is beneficial to these water-cement ratios the maximum size of coarse aggre- low water-cement ratio pastes. gate should be kept to a minimum, at ½ in. (12.7 mm) or 2.5.4 Intrinsic aggregate strength-It would seem ob in. (9.5 mm). Maximum sixes of ¾ in. (19.0 mm) and vious that high-strength concrete would require high1 in. (25.4 mm also have been used successfully. Cordon strength aggregates and, to some extent, this is true. 2.24,2.25 2.19 and Gillespie have found that, for felt that the strength increases were However, several investigators caused by the reduction in average bond stress due to the some aggregates, a point is reached beyond which further increased surface area of the individual aggregate. Alex- increases in cement content produce no increase in the 2.20 ander found that the bond to a 3 in. (76 mm) aggre- compressive strength of the concrete. This apparently is gate particle was only about l/10 of that to a ½-in. (13 not due to having fully developed the compressive mm) particle. He also stated that except for very good or strength of the concrete but to having reached the limit very bad aggregates the bond strength was about 50 to 60 of the bonding potential of that cement-aggregate com percent of the paste strength at 7 days. bination. Smaller aggregate sixes are also considered to produce higher concrete strengths because of less severe concen- 2.6-Water trations of stress around the particles, which are caused The requirements for water quality for high-strength by differences between the elastic moduli of the paste concrete are no more stringent than those for convenand the aggregate. tional concrete. Usually, water for concrete is specified to Many studies have shown that crushed stone produces be of potable quality. This is certainly conservative but higher strengths than rounded gravel. The most likely usually does not constitute a problem since most concrete reason for this is the greater mechanical bond which can is produced near a municipal water supply. However, develop with angular particles. However, accentuated an- cases may be encountered where water of a lower quality gularity is to be avoided because of the attendant high must be used. In such cases, test concrete should be water requirement and reduced workability. The ideal ag- made with the water and compared with concrete made
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2.13. “High Strength Concrete,” Manual of Concrete with distilled water, or it may be more convenient to make ASTM C 109 mortar cubes. In either case, speci- Materials-Aggregates, National Crashed Stone Associamens should be tested in compression at 7 and 28 days. tion, Washington, D.C. Jan. 1975, 16 pp. 2.14. Perenchio, W.P., “An Evaluation of Some of the If those made with the water in question are at least equal to 90 percent of the compressive strength of the Factors Involved in Producing Very High-Strength Conspecimens made with distilled water, the water then can crete,” Research and Development Bulletin No. RD014, be considered acceptable to U.S. Army Corps of En- Portland Cement Association, Skokie, 1973, 7 pp. 2.26 gineers’ requirements and ASTM C 94. 2.15. “Methods of Achieving High Strength Concrete,” For more detailed information on specific contamin- ACI J OURNAL , Proceedings V. 64, No. 1, Jan. 1967, pp. ants refer to the literature in References 2.27, 2.28, and 45-48. 2.29. Test methods for water for special situations are 2.16. Fowler, Earl W., and Lewis, D.W., “Flexure and given in AASHTO T26. Compression Tests of High Strength, Air-Entraining Slag Concrete,” ACI JOURNAL, Proceedings V. 60, No. 1, Jan. 2.7-Cited references 1963, pp. 113-128. (See also Chapter 10-References) 2.17. Harris, A.J., “ High-Strength Concrete: Manufac2.1. Hester, Weston, “High Strength Air-Entrained ture and Properties,” The Structural Engineer (London), V. 47, No. 11, Nov. 1969, pp. 441-446. Concrete,” Concrete Construction, V. 22, No. 2, Feb. 1977, pp. 77-82. 2.18. Walker, Stanton, and Bloem, Delmar L., “Effects 2.2. “High Strength Concrete in Chicago High-Rise of Aggregate Size on Properties of Concrete,” ACI Buildings,” Task Force Report No. 5, Chicago Committee J OURNAL, Proceedings V. 57, No. 3, Sept. 1960, pp. 283on High-Rise Buildings, Feb. 1977, 63 pp. 298. 2.3. Freedman, Sydney, “High-Strength Concrete,” 2.19. Cordon, William A, and Gillespie, H. Aldridge, Modern Concrete, V. 34, No. 6, Oct. 1970, pp. 29-36; No. “Variables in Concrete Aggregates and Portland Cement 7, Nov. 1970 pp 28-32; No. 8, Dec. 1970, pp. 21-24; No. Paste Which Influence the Strength of Concrete,” ACI JOURNAL , Proceedings V. 60, No. 8, Aug. 1963, pp. 10299, Jan. 1971, pp. 15-22; and No. 10, Feb. 1971, pp. 16-23. Also, Publication No. IS176T, Portland Cement Associa1052. tion. 2.20. Alexander, K.M., “Factors Controlling the Strength and Shrinkage of Concrete,” Constructional 2.4. “Superplasticizing Admixtures in Concrete,” Publication No. 45.030, Cement and Concrete Association, Review (North Sydney), V. 33, No. 11, Nov. 1960, pp. Wexham Springs, 1976, 32 pp. 19-28. 2.5. Eriksen, Kirsten, and Nepper-Christensen, Palle, 2.21 “Tentative Interim Report of High Strength “Experiences in the Use of Superplasticizers in Some Concrete,” ACI JOURNAL , Proceedings V. 64, No. 9, Sept. Special Fly Ash Concretes,” Developments in the Use of 1967, pp. 556-557. Superplasticizers, SP-68, American Concrete Institute, 2.22. Harris, A.J., “Ultra High Strength Concrete,” Journal, Prestressed Concrete Institute, V. 12, No. 1, Feb. Detroit, 1981, pp. 1-20. 2.6. Developments in the Use of Superplasticizers, SP-68, 1967, pp. 53-59. American Concrete Institute, Detroit, 1981, 572 pp. 2.23. Klieger, Paul, “ Early High Strength Concrete for 2.7. Wolsiefer, John, “Ultra High-Strength Field Place- Prestressing,” Proceedings, World Conference on Prestressed Concrete, San Francisco, 1957, pp. A5-1-A5-14. able Concrete with Silica Fume Admixture,” Concrete In2.24. Burgess. A. James; Ryell, John; and Bunting, ternational Design & Construction, V. 6, No. 4, Apr. 1984, John, “High Strength Concrete for the Willows Bridge,” pp. 25-31. 2.8. Malhotra, V.M., and Carette, G.G., “Silica Fume,” ACI JOURNAL, Proceedings V. 67, No. 8, Aug. 1970, pp. Concrete Construction, V. 27, No. 5, May 1982, pp. 443611-619. 2.25. Gaynor, Richard D., “High Strength Air-En446. 2.9. Fly Ash, Silica Fume, Slag, and other Mineral trained Concrete,” Joint Research Laboratory Publication By-Products in Concrete, SP-79, American Concrete Insti- No. 17, National Sand and Gravel Association/National tute, Detroit, 1983, 1196 pp. Ready Mixed Concrete Association, Silver Spring, Mar. 2.10. Blick, Ronald L., “Some Factors Influencing 1968, 19 pp. High-Strength Concrete,” Modern Concrete, V. 36, No. 12, 2.26. “Requirements for Water for Use in Mixing or Apr. 1973, pp. 38-41. Curing Concrete,” (CRD-C 400-63), Handbook for Con2.11. Wills, Milton H., Jr., “How Aggregate Particle crete and Cement, U.S. Army Engineer Waterways Shape Influences Concrete Mixing Water Requirement Experiment Station, Vicksburg, 2 pp. and Strength,” Journal of Materials, V. 2, No. 4, Dec. 2.27. Concrete Manual, 8th Edition, U.S. Bureau of 1967, pp. 843-865. Reclamation, Denver, 1975, 627 pp. 2.28. McCoy, W.J., “ Mixing and Curing Water for 2.12. Gaynor, R.D., and Meininger, R.C., “ Evaluating Concrete Sands: Five Tests to Estimate Quality,” ConConcrete,” Significance of Tests and Properties of Concrete crete International Design & Construction, V. 5, No. 12, and Concrete-Making Materials, STP-169A, American Dec. 1983, pp. 53-60. Society for Testing and Materials, Philadelphia, 1966, pp.
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515-521.
2.29. “ Silica Fume in Concrete,” preliminary report by ACI Committee 226, Materials Journal, American Concrete Institute, Detroit, V. 84, No. 2, Mar.-Apr. 1987. 2.30 Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, SP-91, American Concrete Institute, Detroit, 1986, 1628 pp. 2.31 Proceedings of the International Workshop on Condensed Silica Fume in Concrete, CANMET, Montreal, Canada, May 1987. 2.32 Proceedings of the Third International Conference on Fly Ash, Silica Fume, and Natural Pozzolans in Concrete, SP-114, American Concrete Institute, Detroit, 1989.
CHAPTER 3 - CONCRETE MIX PROPORTIONS
Concrete mix proportions for high-strength concrete have varied widely depending upon many factors. The strength level required, test age, material characteristics, and type of application have influenced mix proportions. In addition, economics, structural requirements, manufacturing practicality, anticipated curing environment, and even the time of year have affected the selection of mix proportions. Much information on proportioning concrete mixtures is available in ACI 211.1 and ACI 3.1 SP-46. Included in ACI publication SP-46 is the paper “ Proportioning and Controlling High Strength Concrete” (SP-46-9).
High-strength concrete mix proportioning is a more critical process than the design of normal strength concrete mixtures. Usually, specially selected pozzolanic and chemical admixtures are employed, and the attainment of a low water-cementitious ratio is considered essential. Many trial batches are often required to generate the data that enables the researcher to identify optimum mix proportions. 3.2-Strength required 3.2.1 ACI 318- The ACI Building Code Requirements
for Reinforced Concrete (ACI 318) describes concrete strength requirements. Normally the concrete has been proportioned in such a manner that the mean average of compressive strength test results has exceeded the specified strength f c' by an amount sufficiently high to minimize the relative frequency of test results below the specified strength value. An average value can be calculated for any set of measurement data. The amount that individual test values deviate from the average is usually quantified by calculation of the standard deviation. Calculation of standard deviation on concrete test histories can be a valuable aid in predicting future test result variability. Many factors can influence the variability of the test results, including the individual materials, plants, contrac-
tors, inspection agencies, and environmental conditions. All factors which will affect the variability of strengths and strength measurements should be considered when selecting mix proportions and when establishing the standard deviation acceptable for strength results. Materials and proportions used for qualifying the mixture should not be more closely controlled than is planned for the proposed work. Kennedy and Price have identified factors which contribute to the variability of measured com pressive strengths of concretes in lower strength 3.3,3.4 ranges. Hester identified sources of measured strength vari3.5 ations in high-strength concretes. High-strength concrete is recognized to be more difficult to test accurately than normal strength concretes. Testing difficulties may contribute to lower measured values or higher variability. A high variance in test results will dictate a higher required average strength. If variability is predicted to be relatively low, but proves to be higher, the frequency of test results below the specified strength may be unacceptably high. Therefore, when selecting a target standard deviation the concrete producer should submit the most 3.6 appropriate test record. A higher required average strength may be difficult or impossible to attain when producing high-strength concretes because mix proportions may already be optimized. ACI 318 recognizes that some test results are likely to be lower than the specified strength. The most common design approach has been to limit the frequency of tests allowed to fall below the specified strength. The concrete has been judged acceptable if the following requirements are met: a) The average of all sets of three consecutive strength test results shall equal or exceed the required f c'. b) No individual strength test (average of two cylinders) shall fall below f c' by more than 500 psi (3.4 MPa). However, some designers have specified higher or lower overdesign strengths than called for in ACI 318 regardless of established performance. Schmidt and Hoffman3.7 report that they do not automaticalIy order removal of concrete which is represented by cylinders 500 psi (3.4 MPa) below specified strength but do order adjustment of the mixture and correction of the deficiency. This is because the ACI 318 Section 4.7.4 was established for concretes with strengths in the range of 3000 to 5000 psi (21 to 34 MPa). High-strength concretes continue to gain considerable strengths above and beyond design requirements with the passage of time, 3.7 more than lower-strength concretes. While the percentage gain of compressive strength of high-strength concretes from 7 days to 90 days may be equal to or lower than concretes in lower strength ranges, the order of magnitude of strength gain expressed in psi is actually much higher. For example, a mixture which averages 2500 psi (17.2 MPa) in 7 days may average 4200 psi (29 MPa) in 90 days. It would have gained strength equal to 68 percent of the 7-day strength, or 1700 psi (11.7 MPa) at the age of 90 days. A mixture averaging 7300 psi (50.3
HIGH STRENGTH CONCRETE
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MPa) in 7 days could average 10,000 psi (69 MPa) in 90 in lower strength ranges not requiring early strengths or days. That would be an increase of only 37 percent, but early evaluation. High-strength concretes gain considerit would have gained 2700 psi (18.6 MPa), a full 1000 psi able strengths at later ages and, therefore, are evaluated (6.9 MPa) higher total gain than the lower-strength at later ages when construction requirements allow the mixture. concrete more time to develop strengths before loads are ACI 318 allows mix designs to be proportioned based imposed. Proportions, notably cementitious components, on field experience or by laboratory trial batches. When have usually been adjusted depending upon test age. the concrete producer chooses to select high-strength 3.3.3 Later age-- High-strength concretes are frequently concrete mix proportions based upon laboratory trial tested at later ages such as 56 or 90 days. High-strength batches, confirming tests results from concretes placed in concrete has been placed frequently in columns of highthe field should also be established. rise buildings. Therefore, it has been desirable to take 3.2.2 ACI 214-- Once sufficient test data have been advantage of long-term strength gains so that efficient generated from the job, a reevaluation of mix propor- use of construction materials can be achieved. This has tions using “Recommended Practice for Evaluation of often been justified in high-rise buildings where full Compression Test Results of Concrete (ACI 214)” may loadings may not occur until later ages. be appropriate. Analyses affecting reproportioning of In cases where later-age acceptance criteria have been mixtures based upon test histories are described in specified, it may be advantageous for the concrete supSections 4.8.1 and 4.8.2. plier to develop earl -age or accelerated tests to predict 3.8 3.2.3 Other Strength Requirements--In some situations, later-age strengths. The ACI publication SP-56, Accelconsiderations other than compressive strength may in- erated StrengthTesting, provides information on accelerfluence mix proportions. Detailed discussion of material ated testing. 3.9 Of course, historical correlation data must properties including flexural and tensile strengths is given be developed relative to the materials and proportions to in Chapter 5. be used in the work. These tests may not always accurately predict later-age strengths; however, these tests 3.3- Test age could provide an early identification of lower-strength The selection of mix proportions can be influenced by trends before a long history of non-compliance is the testing age. This testing age has varied depending realized. Later-age acceptance criteria can leave suspect upon the construction requirements. Most often the concrete in question for a long time. Test cylinders have been held for testing at ages later testing age has been thought to be the age at which the acceptance criteria are established, for example at 28 than the specified acceptance age. In cases where the days. Testing, however, has been conducted prior to the specified compressive strength f c' was not achieved, subage of acceptance testing, or after that age, depending sequent testing of later-age or “hold” cylinders has someupon the type of information required. times justified the acceptance of the concrete in question. 3.3.1 Early Age-- Prestressed concrete operations may 3.3.4 Test age in relationship to curing- When selecting require high strengths in 12 to 24 hours. Special appli- mix proportions, the type of curing anticipated should be cations for early use of machinery foundations, pavement considered along with the test age, especially when detraffic lanes, or slip formed concrete have required high signing for high early strengths. Concretes gain strength strengths at early ages. Post-tensioned concrete is often as a function of maturity, which is usually defined as a stressed at ages of approximately 3 days and requires function of time and curing temperature. relatively high strengths. Generally concretes which develop high later-age strengths will also produce high 3.4- Water-cement ratio or water-cementitious ratio early-age strengths. However, the optimum materials 3.4.1 Nature of water-cement ratio in high-st rength conselected, and therefore the mix proportions, may vary for crete- The relationship between water-cement ratio and different test ages. For example, Type III cement and no compressive strength, which has been identified in lowfly ash have been used in a high early-strength design, strength concretes, has been found to b e valid for highercompared to Type I or II cement and fly ash for a later- strength concretes also. Higher cement contents and age strength design. Early-age strengths may be more lower water contents have produced higher strengths. variable due to the influence of curing temperature and Proportioning larger amounts of cement into the conthe early-age characteristics of the specific cement. crete mixture, however, has also increased the water Therefore, anticipated mix proportions should be evalu- demand of the mixture. Increases in cement beyond a ated for a higher required average strength or a later test certain point have not always increased compressive age. strengths. Other factors which may limit maximum 3.3.2 Twenty-eight days- A very common test age for cement contents are discussed in Section 3.5.3. When compressive strength of concrete has been 28 days. Per- pozzolanic materials are used in concrete, a water-cement formance of structures has been empirically correlated plus pozzolan ratio by weight has been considered in with moist-cured concrete cylinders, usually 6 x 12 in. place of the traditional water-cement ratio by weight. Fly (152 x 305 mm) prepared according to ASTM C 31 and ash meeting requirements of ASTM C 618 with a loss on C 192. This has produced good results for concretes withignition of less than 3.0 percent and ASTM C 494 types
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A, D, F, and G chemical admixtures have usually been particular pozzolan employed has varied and has gener3.10 ally increased with increasing fineness of the pozzolan. used. Of course the slump of the concrete is related to the Often water requirements for fly ash concrete are lower water-cementitious ratio and the total amount of water than for portland cement. This helps to lower the waterin the concrete. While 0 to 2 in. slump concrete has been cementitious ratio of the mixture. Perenchio 3.15 has reported variable compressive produced in precast operations, special consolidation efstrength results at given water-cement ratios in laboratory forts are required. Specified slumps for cast-in-place concretes not containing high-range water reducers have prepared concretes, depending on the aggregates used. In addition, these results have differed from results achieved ranged from 21/2 to 4 1/4 in. (64 to 114 mm). Field-placed in actual production with materials from the same area. nonplasticized concretes have had measured slumps aver3.10 3 A range of typical strengths reported at given wateraging as high as 4 /4 in. (121 mm). The use of high-range water reducers has provided cementitious ratios is represented in Fig. 3.2. Trial 3.11 batches with materials actually to be used in the work lower water-cementitious ratios and higher slumps. Water-cementitious ratios by weight for high-strength have been found to be necessary. Generally, laboratory concretes typically have ranged from 0.27 to 0.50. The trial batches have produced strengths higher than those quantity of liquid admixtures, particularly high-range strengths which are achievable in production, as seen in 3.2 water reducers, sometimes has been included in the Fig. 3.3 water-cementitious ratio. 3.4.2 Estimating compressive strength-- The compressive
strength that a concrete will develop at a given watercementitious ratio has varied widely depending on the cement, aggregates, and admixtures employed. Principal causes of variations in compressive strengths at a given water-cementitious ratio include the strength producing capabilities of the cement and potential for pozzolanic reactivity of the fly ash or other pozzolan if used. Different types and brands of portland cement have produced different compressive strengths as shown in Fig. 3.1.
3.2,3.12
Compressive
Compressive Strength, MPa
Strength , psi
80 0
Compressive Strength , psi
10000
Water - Cementitious
Ratio
Fig. 3.2-- Strength versus water-cement ratios of various
L
mixtures
3.2,3.10,3.15,3.16
3.5-Cement content
Fig. 3.1-- Effects of variou s brands of cement on concret e 3.2,3.12 compressive strength
Specific information pertaining to the range of values of compressive strengths of cements has been published in ASTM C 917 and Peters.3.13 Fly ashes may vary in pozzolanic activity index from 75 percent to 110 percent of the portland cement control, as defined in ASTM C 618. Proprietary pozzolans containing silica fume have been reported to have activity indexes in excess of 200 percent.3.14 The water requirement of the
The cement quantity proportioned into a high-strength mixture has been determined best by the fabrication of trial batches. Common cement contents in high-strength concrete test programs range from 660 to 940 lb per yd 3 3.2,3.16 In evaluating optimum cement (392 to 557 kg/m3). contents, trial mixes usually are proportioned to equal consistencies, allowing the water content to vary according to the water demand of the mixture. 3.5.1 Strength- For any given set of materials in a concrete mixture, there may be a cement content that produces maximum concrete strength. The maximum strength may not always be increased by the use of
HIGH STRENGTH CONCRETE
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60
. Agg. No. I . Agg. No. 2 . Agg. No.3
r 50
Reduction in Comp. 40 Strength Below Non-A.E. Concrete 30
8000 Compessive
Compressive Strength,
of Some W/C, %
Strength, MPo
psi 6000
40 Points Represent Avg.
of ?-and 28-Day Tests
4000 0
2
4
6
6
IO
Added Air , perce nt 3.26
Fig. 3.4--Strength reduction by air entrainment
2000
the completeness of the testing programs, but particular attention has been given to evaluation of the brand of 90 28 cement to be used with the class and source of pozzolan, Age , days if a pozzolan is to be used. Prior to 1977, Chicago highstrength experience was based on concretes using Class Fig. 3.3--Laboratory-molded concrete strengths versus F fly ash, while other high-strength work has been done 3.2,3.10 ready-mixed field-molded concrete strengths for 9000 psi (62 in Houston using Class C fly ash. Class C fly ash 3.2 MPa) concrete. has been used in Chicago since 1977. The strength efficiency of cement will vary for differcement added to the mixture beyond this optimum ceent maximum size aggregates at different strength levels. ment content. The strength for any given cement content Higher cement efficiencies are achieved at high strength will vary with the water demand of t he mixture and the levels with lower maximum aggregate sixes. Fig. 3.5 strength-producing characteristics of that particular illustrates this principle. For example, a maximum agcement as shown in Fig. 3.1. The “ Standard Method of gregate size of less than in. (9.5 mm) yields the highest Evaluation of Cement Strength Uniformity from a Single cement efficiency for a 7000 psi (48.3 MPa) mixture. Source” (ASTM C 917) may prove useful in considering
cement mill sources.
3.13
Mortar cube compressive
strength data of cements at ages of up to 90 days have been evaluated when proportioning cement in highstrength mixtures.
IO
The strength of the concrete mixture will depend upon the gel-space ratio, which is defined as the “ratio of the volume of hydrated cement paste to the sum of the volumes of the hydrated cement and of the capillary 3.17 6 pores.“ This is particularly true when air-entraining Strength Efficiency, admixtures are employed. Higher cement contents in airpi/lb of cement/cu entrained concrete have not been found to be useful in producing strengths equivalent to, or approaching, strengths attainable with non-air-entrained concretes. Incorporation of entrained air may reduce strength at a ratio of 5 to 7 percent for each percent of air in the mix = 3.8 to 5.8 in. = 28 days, Moist as shown in Fig. 3.4. 3.5.2 Optimization-- A principal consideration in establishing the desired cement content will be the identification of combinations of materials which will produce optimum strengths. Ideally, evaluations of each potential No. 4 3 6 source of cement, fly ash, liquid admixture, and aggregate Maximum Size Aggregate , in. in varying concentrations would indicate the optimum cement content and optimum combination of materials. Fig. 3.5-- Maximum size aggregate for strength efficiency enTesting costs and time requirements usually have limited velop. 3.2
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ACI COMMlTTEE REPORT
requirements even though the net volume of the sand remains the same. The gradation of the fine aggregate plays an important role in properties of the plastic as well as the hardened concrete. For example, if the sand has an overabundance of the No. 50 and No. 100 sieve sixes, the plastic workability will be improved but more paste will be needed to compensate for the increased surface area. This could result in a costlier mixture, or if the paste volume is increased by adding water, a serious loss in strength could result. It is sometimes possible, although not always practical economically, to blend sands from different sources to improve their gradation and their capacity to produce higher-strength concrete. Low fine aggregate contents with high coarse aggregate contents have resulted in a reduction in paste requirements and normally have been more economical. Such proportions also have made it possible to produce higher strengths for a given amount of cementitious materials. However, if the proportion of sand is too low, serious problems in workability become apparent. Consolidation by means of mechanical vibrators may help to overcome the effects of an undersanded mixture, and the use of power finishing equipment can help to offset the lack of trowelability. Particle shape and surface texture of fine aggregate can have as great an effect on mixing water requirements as those of coarse aggregate.“” Tests made by Bloem 3.22 and Gaynor show that concrete-mixing water requirements for each cubic yard of concrete change 1 gal. (3.8 L) for each change of 1 percent in the void content of the sand. Following the work by Bloem and Gaynor, the NSGA-NRMCA Joint Research Laboratory has simplified the procedure for conducting the void content test of sand and a modified gradation is now used. The new procedure is described in Reference 2.12. 3.6.2 Coarse aggregates-The optimum amount and 3.6-Aggregate proportions size of coarse aggregate for a given sand will depend to In the proportioning of high-strength concrete, the aggregates have been a very important consideration a great extent on the characteristics of the sand. Most since they occupy the largest volume of any of the particularly it depends on the fineness modulus (FM) of ingredients in the concrete. Usually, high-strength the sand. This is brought out specifically in Table 3.1, 3.23 sugconcretes have been produced using normal weight ag- which is taken from ACI 211.1. One reference 3.19 3.20 gregates. Shideler and Holm have reported on gests that the proportion of coarse aggregate shown in light-weight high-strength structural concrete. Mather 3.21 Table 3.1 might be increased by up to 4 percent if sands has reported on high-strength high-density concrete using with low void contents are used. If the sand particles are very angular, then it is suggested that the amount of heavyweight aggregate. coarse aggregate should be decreased by up to 4 percent 3.6.1 Fine aggregates-In proportioning a concrete mixture, it is generally agreed that the fine aggregates or from the values in the table. Such adjustments in the sand have considerably more impact on mix proportions proportion of coarse aggregate and sand have been intended to produce concretes of equivalent workability, than the coarse aggregates. The fine aggregates contain a much higher surface although such changes will alter the water demand for a area for a given weight than do the larger coarse ag- given slump. When more or less water is needed in a gregates. Since the surface area of all the aggregate given volume of concrete, to preserve the same consis particles must be coated with a cementitious paste, the tency of paste, it is also necessary to adjust the amount proportion of fine to coarse can have a direct quan- of cement or cementitious materials if a given watertitative effect on paste requirements. Furthermore, the cement ratio is to be maintained. Another possible expedient in the proportioning of shape of these sand particles may be either spherical, subangular, or very angular. This property can alter paste coarse aggregates for high-strength concrete is to alter 3.5.3 Limiting factors-There are several factors which may limit the maximum quantity of cement which may be desirable in a high-strength mixture. The strength of the concrete may decrease if cement is added above and beyond a given optimum content. The maximum desirable quantity of cement may vary considerably depending upon the efficiency of dispersing agents, such as highrange water reducers, in preventing flocculation of cement particles. Stickiness and loss of workability will be increased as higher amounts of cement are incorporated into the mixture. Combinations of cement, pozzolans, and sand should be evaluated for the effect of cementitious content upon mixture placeability. Incorporation of an airentraining admixture may necessitate reevaluation of the effect of the cement upon mixture workability. The maximum temperature desired in the concrete element may limit the quantity or type of cement in the mixture. 3.2,3.18 Modification of the mixture with ice, set retarders, or pozzolans may be helpful. Cement-rich mixtures frequently have very high water demands. Therefore, it is possible that special precautions may be necessary to provide adequate curing water, so that sufficient hydration can occur. It may be preferable to reduce the amount of cement in the mixture and to rely upon more careful selection of aggregates, aggregate proportions, etc., optimizing the use of other constituents. The amount of slump loss experienced, with attendant increase in retempering water, and the setting time of the concrete has varied depending upon the type, brand, and quantity of cement use. Lower cement contents, within limits, are desirable in order to enhance the placement capabilities of the mixture, provided that adequate strengths can be achieved.
HIGH STRENGTH CONCRETE
Table 3.1-Volume of coarse aggregate per unit of volume of concrete* Volume of dry-rodded coarse aggregate’ per unit volume of concrete for different fineness moduli of sand
*Table 3.1 Taken from ACI 211.1. +Volumes are based on aggregates in dry-rodded condition as described in ASTM C 29 for Unit Weight of Aggregate. These volumes are selected from empirical relationships to produce concrete with a degree of workability suitable for usual reinforced construction. For less workable concrete such as required for concrete pavement construction, they may be increased about 10 percent. For more workable concrete see Section 5.3.6.1.
the amount of these aggregates passing certain sieve sixes from the amounts shown in ASTM C 33. This method is described in Reference 3.24 and 3.25 as a means of avoiding “ particle interference,” thus permitting a greater amount of coarse aggregate and less total sand. This has helped to reduce the paste requirements or permit the use of a more viscous paste, resulting in a higher strength. 3.6.3 Proportioning aggregates-The amounts of coarse aggregate suggested in Table 3.1 (which is Table 5.3.6 of ACI 211.1) are recommended for initial proportioning. Considerations should be given to the properties of the sand (FM, angularity, etc.) which may alter the quantity of coarse aggregate. In general, the least sand consistent with necessary workability has given the best strengths for a given paste. Mechanical tools for handling and placing concrete have helped to decrease the proportion of sand needed. As previously stated, the use of the smaller sixes of coarse aggregate are generally beneficial, and crushed aggregates seem to bond best to the cementitious paste.
363R-13
ment content. In those cases where a net increase in the absolute volume of the cementitious materials was experienced due to the addition of a pozzolan, a corresponding decrease in the absolute volume of the sand was usually made. The use of fly ash has often caused a slight reduction in the water demand of the mixture, and that reduction in the volume of water (if any) has been compensated for by the addition of sand. The opposite relationship has been found to be true for other pozzolans. Silica fume, for example, dramatically increases the water demand of the mixture which has made the use of retarding and superplasticizing admixtures a requirement. Proprietary products containing silica fume include carefully balanced chemical admixtures as wel13.14 3.7.2 Chemical admixtures 3.7.2.1 Conventional water-reducers and retarders-
The amount of these admixtures used in high-strength concrete mixtures has varied depending upon the particular admixture and application. Generally speaking, the tendency has been to use larger than normal or maximum quantities of these admixtures. Typical water reductions of 5 to 8 percent may be increased to 10 percent. Corresponding increases in sand content have been made to compensate for the loss of volume due to the reduction of water in the mixture. 3.7.3.2 Superplasticizers or high-range water-reducing admixtures- Adjustments to high-strength concrete made
with high-range water reducers have been similar to those adjustments made when conventional water reducers are used. These adjustments have typically been larger due to the larger amount of water reduction, ap proximately 12 to 25 percent. Corresponding increases in sand content have been made to compensate for the loss of volume from reduction of water in the mixture. Some designers have simply added high-range water reducers to existing mixtures without any adjustments to the mix proportions to improve the workability of that concrete. Sometimes cement or cementitious content has been reduced for reasons of economy or to achieve a reduc3.7-Proportioning with admixtures tion of the heat of hydration. Usually, however, in Nearly all high-strength concretes have contained ad- high-strength concretes high-range water reducers are mixtures. Changes in the quantities and combinations of used to lower the water-cementitious ratio. These adthese admixtures affect the plastic and hardened proper- mixtures have been effective enough to both lower the ties of high-strength concrete. Therefore, special at- water-cementitious ratio and increase the slump. Due the tention has been given to the effects of these admixtures relatively large quantity of liquid that has been added to (described in Sections 2.3 and 2.4). Careful adjustments the mixture in the form of superplasticizing admixture, to mix proportions have been made when changes in ad- the weight of these admixtures has sometimes been inmixture quantities or combinations have been made. Ma- cluded in the calculation of the water-cementitious ratio. terial characteristics have varied extensively, making 3.7.2.3 Air-entraining agents- Although sometimes experimentation with the candidate materials necessary. required, air-entraining agents have been found to be Some of the more common adjustments are described in very undesirable in high-strength concretes due the draSections 3.7.1 and 3.7.2. matic decrease in compressive strength which occurs 3.7.1 Pozzolanic admixtures- Pozzolanic admixtures are when these admixtures are used. Modifications to lower often used as a cement replacement. In high-strength the water-cementitious ratio and adjust the yield of the concretes they have been used to supplement the port- concrete by reduction of sand content have been made. land cement from 10 to 40 percent by weight of the ce- Larger dosage rates of air-entraining admixture have
363R-14
ACI COMMITTEE REPORT
been found to be required in high-strength concretes, especially in very rich low-slump mixtures and mixtures containing large quantities of some fly ashes. 3.7.2.4 Combinations- Most but not all highstrength concretes have contained both mineral and chemical admixtures. It has been common for these mixtures to contain combinations of chemical admixtures as well. High-range water reducers have performed better in high-strength concretes when used in combination with conventional water reducers or retarders. This is because of the reduced rate of slump loss experienced. It is not unusual for portland-pozzolan high-strength concretes to contain both a conventional and high-range water reducer. 3.8-Workability
time placement procedures, vibration techniques, and scheduling have been established since they greatly affect the end product and will influence the apparent placeability of the mixture. 3.8.3 Flow properties and stickiness-Slumps needed for
almost any flow can be designed for the concrete; however, full attention must be given to aggregate selection and proportioning to achieve the optimum slump. Elongated aggregate particles and poorly graded coarse and fine aggregates are examples of characteristics that have affected flow and caused higher water content for placeability with attendant strength reduction. Stickiness is inherent in high-fineness mixtures required for high strengths. Certain cements or cement pozzolan or cement-admixture combinations have been found to cause undue stickiness that impairs flowability. The cementitious content of the mixture normally has been the minimum quantity required for strength development combined with the maximum quantity of coarse aggregate within the requirements for workability. Mixtures that were designed properly but appear to change in character and become more sticky can be considered suspect and quickly checked for proportions, possible false setting of cement, u ndesirable air entrainment, or other changes. A change in the character of a highstrength mixture could be a warning sign for quality control and, while a subjective judgment, may sometimes be more important than quantitative parameters.
Workability is defined in ACI 116R “Cement and Concrete Terminology” as “that property of freshly mixed concrete . . . which determines the ease and homogeneity with which it can be mixed, placed, compacted, and finished.” 3.8.1 Slump- ASTM C 143 describes a standard test method for the slump of portland cement concrete which has been used to quantify the consistency of plastic, cohesive concretes. This test method has not usually been considered applicable to ultra-low and ultra-high slump concretes. Other test methods such as the Vebe consistometer have been used with very stiff mixes and may be a better aid in proportioning some high-strength con3.9- Trial batches cretes. Frequently the development of a high-strength conHigh-strength concrete performance demands a dense, void-free mass with full contact with reinforcing steel. crete pro ram has required a large number of trial Slumps should reflect this need and provide a workable batches. 3.2,3.10 In addition to laboratory trial batches, mixture, easy to vibrate, and mobile enough to pass field-sized trial batches have been used to simulate typthrough closely placed reinforcement. Normally a slump ical production conditions. Care should be taken that all of 4 in. (102 mm) will provide the required workability; material samples are taken from bulk production and are however, details of forms and reinforcing bar spacing typical of the materials which will be used in the work. should be considered prior to development of mix de- To avoid accidental testing bias, some researchers have signs. Slumps of less than 3 in. (76 mm) have made sequenced trial mixtures in a randomized order. 3.9.1 Laboratory trial batch investigations- Laboratory special consolidation equipment and procedures a trial batches have been prepared to achieve several goals. necessity. Without uniform placement, structural integrity may They should be prepared according to “ Standard Method be compromised High-strength mixes tend to lose slump of Making and Curing Concrete Test Specimens in the more rapidly than lower-strength concrete. If slump is to Laboratory” (ASTM C 192). However, whenever possible, be used as a field control, testing should be done at a timing, handling, and environmental conditions similar to prescribed time after mixing. Concrete should be dis- those which are likely to be encountered in the field should be approximated. charged before the mixture becomes unworkable. 3.8.2 Placeability-- High-strength concrete, often Selection of material sources has been facilitated by designed with % in. (12 mm) top size aggregate and with comparative testing, with all variables except the cana high cementitious content, is inherently placeable pro- didate materials being held constant. In nearly every vided attention is given to optimizing the ratio of sand to case, particular combinations of materials have proven to coarse aggregate. Local material characteristics have a be best. By testing for optimum quantities of optimum marked effect on proportions. Cement fineness and par- materials, the investigator is most likely to define the best ticle size distribution influence the character of the combination and proportions of materials to be used. Once a promising mixture has been established, furmixture. Admixtures have been found to improve the ther laboratory trial batches may be required to quantify placeability of the mixture. Placeability has been evaluated in mock-up forms the characteristics of those mixtures. Strength charac prior to final approval of the mix proportions. At that teristics at various test ages may be defined. Water
TH
CONCRETE
363R-15
demand, rate of slump loss, amount of bleeding, seg- Company’s Experience with Class C Fly Ash,” Publication regation, and setting time can be evaluated. The unit No. 163, National Ready-Mixed Concrete Association, weight of the mixture should be defined and has been Silver Spring, Apr. 1981, 11 pp. 3.11. Hester, Weston, T., and Leming, M., “Use of used as a valuable quality control tool. Structural considerations such as shrinkage and elasticity may also Superplasticizing Admixtures in Precast, Prestressed be de te rmined . Wh ile de grees of wo rkab ilit y an d Concrete Operations.” 3.12. “High Strength Concrete,” National Crushed placeability may be difficult to define, at least a Stone Association, Washington, D.C., Jan. 1975, 16 pp. subjective evaluation should be attempted. 3.9.2 Field-production trial batches- Once a desirable 3.13. Peters, Donald J., “Evaluation of Cement mixture has been formulated in the laboratory, field Variability-The First Step,” Publication No. 161, testing with production-sized batches is recommended. National Ready Mixed Concrete Association, Silver Quite often laboratory trial batches have exhibited a Spring, Apr. 1980, 9 pp. 3.14. Wolsiefer, John, “Ultra High-Strength Field strength level significantly higher than that which can be 3.2 reasonably achieved in production as shown in Fig. 3.3 Placeable Concrete with Silica Fume Admixture,” ConActual field water demand, and therefore concrete yield, crete International: Design & Construction, V. 6, No. 4, has varied from laboratory design significantly. Ambient Apr. 1984, pp. 25-31. temperatures and weather conditions have affected the 3.15. Perenchio, William F., and Khieger, Paul, “Some performance of the concrete. Practicality of production Physical Properties of High Strength Concrete,” Research and of quality control procedures have been better eval- and Development Bulletin No. RD056.01T, Portland uated when production-sized trial batches were prepared Cement Association, Skokie, 1978, 7 pp. using the equipment and personnel that were to be used 3.16. Freedman, Sydney, “High-Strength Concrete, in the actual work. Modern Concrete, V. 34, No. 6, Oct. 1970, pp. 29-36; No. 7, Nov. 1970, pp. 28-32; No. 8, Dec. 1970, pp. 21-24; No. 3.10-Cited references 9, Jan. 1971, pp. 15-22; and No. 10, Feb. 1971, pp. 16-23. (See also Chapter l0-References) Also, Publication No. IS176T, Portland Cement Associa3.1. Proportioning Concrete Mixes, SP-46, American tion. Concrete Institute, Detroit, 1974, 240 pp. 3.17. Neville, A.M., Properties of Concrete, 3rd Edition, 3.2. Blick, Ronald L.; Petersen, Charles F.; and Pitman Publishing Limited, London, 1981, 779 pp. Winter, Michael E., “ Proportioning and Controlling High 3.18. Bickley, John A, and Payne, John C., “High Strength Concrete,” Proportioning Concrete Mixes, SP-46, Strength Cast-in-Place Concrete in Major Structures in American Concrete Institute, Detroit, 1974, p. 149. Ontario,” paper presented at the ACI Annual Conven3.3. Kennedy, T.B., “ Making and Curing Concrete tion, Milwaukee, Mar. 1979. Specimens,” Significance of Tests and Properties of 3.19. Shideler, J.J., “ Lightweight-Aggregate Concrete Concrete and Concrete-Making Materials, STP-169A, for Structural Use, ACI JOURNAL , Proceedings V. 54, No. American Society for Testing and Materials, Phila- 4, Oct. 1957, pp. 299-328. delphia, 1966, pp. 90-101. 3.20. Holm, T.A., “Physical Properties of High 3.4. Price, Waller H., “Factors Influencing Concrete Strength Lightweight Aggregate Concretes,” Proceedings, 2nd International Congress on Lightweight Concrete Strength,” ACI JOURNAL, Proceedings V. 47, No. 6, Feb. 1951, pp. 417-432. (London, Apr. 1980), Ci8O, Constructio n Press, 3.5. Hester, Weston T., “Testing High Strength Con- Lancaster, 1980, pp. 187-204. cretes: A Critical Review of the State of the Art,” 3.21. Mather, Katharine, “High Strength, High Density Concrete International Design & Construction, V. 2, No. Concrete,” ACI JOURNAL , Proceedings V. 62, No. 8, Aug. 1965, pp. 951-962. Also, Technical Report No. 6-635, U.S. 12, Dec. 1980, pp. 27-38. 3.6. Gaynor, Richard D., “Mix Design Submission Army Engineer Waterways Experiment Station. Under ACI 318 and ACI 301--(or Which Test Record 3.22. Bloem, Delmar L., and Gaynor, Richard D., Should I Use?),” NRMCA Technical Information Letter “Effects of Aggregate Properties on Strength of Con No. 372, National Ready Mixed Concrete Association, crete,” ACI JOURNAL , Proceedings V. 60, No. 10, Oct. Silver Spring, May 8, 1980, 7 pp. 1963, pp. 1429-1456. 3.23. Tobin, Robert E., “Flow Cone Sand Tests,” ACI 3.7. Schmidt, William, and Hoffman, Edward J., “9000 psi Concrete-Why? Why Not?,” Civil EngineeringJOURNAL, Proceedings V. 75, No. 1, Jan. 1978, pp. l-12. ASCE, V. 45, No. 5, May 1975, pp. 52-55. 3.24. Ehrenburg, D.O., “ An Analytical Approach to 3.8. Gaynor, Richard D., “An Outline on High Gap-Graded Concrete,” Cement, Concrete, and Aggregates, Strength Concrete,” Publication No. 152, National Ready V. 2, No. 1, Summer 1980, pp. 39-42. 3.25. Tuthill, Lewis H., “Better Grading of Concrete Mixed Concrete Association, Silver Spring, May 1975, pp. Aggregates,” Concrete International Design & Construc3, 4, and 10. tion, V. 2, No. 12, Dec. 1980, pp. 49-51. 3.9. Accelerated Strength Testing, SP-56, American 3.26. Gaynor, Richard D., “High Strength Air-EnConcrete Institute, Detroit, 1978, 328 pp. 3.10. Cook, James E., “A Ready-Mixed Concrete trained Concrete,” Joint Research Laboratory Publication
ACI COMMlTTEE REPORT
363R-16
No. 17, National Sand and Gravel Association/National Ready Mixed Concrete Association, Silver Spring, Mar. 1968, 19 pp.
cold miring water effects a moderate reduction in concrete placing temperature. The use of ice is more effective than cold water; however, this will require ice making or chipping equipment at the batch plant. 4.2.3 Charging of materials- Batching procedures have
important effects on the ease of producing thoroughly mixed uniform concrete in both stationary and truck mixers. The uniformity of concrete mixed in central AND CONTROL PROCEDURES mixers is generally enhanced by ribbon loading the aggregate, cement, and water simultaneously. However, if 4.1-Introduction The batching, mixing, transporting, placing, and con- truck mixers are being used, ribbon loading will prevent trol procedures for high-strength concrete are not dif- delayed miring, which is sometimes used to prevent hyferent in principle from those procedures used for con- dration of the cement during long hauls. This procedure ventional concrete. Thus ACI 304 can be followed. Some involves stopping the mixer drum after aggregates and changes, some refinements, and some emphasis on criti- three-quarters of the water are charged and before the cal points are necessary. Maintaining the unit water con- cement is loaded and not starting the drum again until tent as low as possible, consistent with placing require- the job site is reached. Slump loss problems may thus be ments, is good practice for all concrete; for high-strength minimized. High-range water-reducing admixtures are concrete it is critical. Since the production of high- another consideration. These admixtures are very likely strength concrete will normally involve the use of rela- to be used in the production of high-strength concrete. tively large unit cement contents with resulting greater According to the guidelines in the Canadian Standards heat generation, some of the recommendations given in Association’s Preliminary Standard A 266.5-M 1981, tests Chapter 3 on Production and Delivery and Chapter 4 on have shown that high-range water-reducing admixtures Placing and Curing in ACI 305R, “Hot Weather Con- are most effective and produce the most consistent creting,” may also be applicable. results when added at the end of the mixing cycle after In addition, the production and testing of high- all other ingredients have been introduced and thostrength concrete requires well-qualified concrete pro- roughly mired. If there is evidence of improper mixing ducers and testing laboratories, respectively. and nonuniform slump during discharge, procedures used to charge truck and central mixers should be modified to insure uniformity of mixing as required by ASTM C 94. 4.2 - Batching CHAPTER 4- BATCHING, MIXING, TRANSPORTING, PLACING, CURING,
4.2.1 Control, handling and storage of materials- The
control, handling, and storage of materials need not be substantially different from the procedures used for conventional concrete as outlined in ACI 304. Proper stock piling of aggregates, uniformity of moisture in the batching process, and good sampling practice are essential. It may be prudent to place a maximum limit of 170 F (77 C) on the temperature of the cement as batched in warm weather and 150 F (66 C) in hot weather. Where possible, batching facilities should be located at or near the job site to reduce haul time. The temperature of all ingredients should be kept as low as possible prior to batching. Delivery time should be reduced to a minimum and special attention paid to scheduling and placing to avoid having trucks wait to unload. 4.2.2 Measuring and weighing- Materials for production of high-strength concrete may be batched in manual, semiautomatic, or automatic plants. However, since speed and accuracy are required, ACI 304 recommends that cements and pozzolans be weighed with automatic equipment. Automatic weigh batchers or meters are recommended for water measurement. To maintain the proper water-cement ratios necessary to secure highstrength concrete, accurate moisture determination in the fine aggregate is essential. A combination of warm weather and high cement content often requires the cooling of mixing water. ACI 305R notes that the use of
4.3- Mixing
High-strength concrete may be mixed entirely at the batch plant, in a central or truck mixer, or by a combination of the two. In general, mixing follows the recom4.0,4.2 mendations of ACI 304. Experience and tests and standards documents of the Concrete Plant Manufacturers Bureau have indicated that high-strength concrete can be mired in all common types of mixers.4.3,4.4,4.5 It may prove beneficial to reduce the batch size below the rated capacity to insure more efficient mixing. 4.3.2 Mixer performance- The performance of mixers is usually determined by a series of uniformity tests (ASTM C 94) made on samples taken from two to three locations within the concrete batch being mixed for a given time period.4.6 Some work 4.2,4.7 has indicated that due to the relatively low water content and high cement content and the usual absence of large coarse aggregate, the efficient mixing of high-strength concrete is more difficult than conventional concrete. Special precautions or procedures may by required. Thus, it becomes more important for the supplier of high-strength concrete to check mixer performance and efficiency prior to production mixing. 4.3.3 Mixing time- The mixing time required is based upon the ability of the central mixer to produce uniform concrete both within a batch and between batches. Manufacturers’ recommendations, ACI 304, and usual specifi-
HIGH STRENGTH CONCRETE
3
363R-17
3
cations, such as 1 min for 1 yd (0.75 m ) plus min for discharge gate and vibrators mounted on the body are 3 each additional yd of capacity, are used as satisfactory provided at the point of discharge. An apparatus that
guides for establishing mixing time. Otherwise, mixing times can be based on the results of mixer performance tests. The mixing time is measured from the time all ingredients are in the mixer. Prolonged miring may cause 4.8 moisture loss and result in lower workability, which in turn may require retempering to restore slump, thereby reducing strength potential. 4.3.4 Ready-mixed concrete- High strength concrete may be mixed at the job in a truck mixer. However, not all truck mixers can mix high-strength concrete, especially if the concrete has very low slump. Close job control is essential for high-strength ready-mixed concrete operations to avoid causing trucks to wait at the job site due to slow placing operations. (Note Section 4.7.) Retarding admixtures are used to prolong the time the concrete will respond to vibration after it has been placed in the forms. Withholding some of the mixing water until the truck arrives at the job site is sometimes desirable. Then after adding the remaining required water, an additional 30 revolutions at mixing speed are used to incorporate the additional water into the mixture adequately. (See ACI 304.) When loss of slump or workability cannot be offset by these measures, complete batching and miring can be conducted at the job site. If a high-range waterreducer is added at the site, a truck mounted dispenser or an electronic field dispenser is usually required. 4.4-Transporting 4.4.1 General considerations- High-strength concrete
ribbons and blends the concrete as it is unloaded is desirable. However, water is not added to the truck body because adequate mixing cannot be obtained with the agitator. 4.4.4 Pumping- High-strength concrete will in many cases be very suitable for pumping. Pumps are available that can handle low-slump mixtures and provide high pumping pressure. High-strength concrete is likely to have a high cement content and small maximum size aggregate--both factors which facilitate concrete pumping. Chapter 9 of ACI 304 provides guidance for the use of pumps for transporting high-strength concrete. In the field, the pump should be located as near to the placing areas as practicable. Pump lines should be laid out with a minimum of bends, firmly supported, using alternate lines and flexible pipe or hose to permit placing over a large area directly into the forms without rehandling. Direct communication is essential between the pump operator and the concrete placing crew. Continuous pumping is desirable because if the pump is stopped, movement of the concrete in the line may be difficult or impossible to start again. 4.4.5 Belt conveyor- Use of belt conveyors to trans port concrete has become established in concrete construction. Guidance for use of conveyors is given in ACI 304.4R. The conveyors must be adequately supported to obtain smooth, nonvibrating travel along the belt. The angle of incline or decline must be controlled to eliminate the tendency for coarse aggregate to segregate from the mortar fraction. Since the practical slump range for belt transport of concrete is 1 to 4 in. (25 to 100 mm), belts may be used to move high-strength concrete only for relatively short distances of 200 to 300 ft (60 to 90 m). Over longer distances or extended time lapses, 4.9 there will be loss of slump and workability. Enclosures or covers are used for conveyors when protection against rain, wind, sun, or extreme ambient temperatures is needed to prevent significant changes in the slump or temperature of the concrete. As with other methods of transport for high-strength concrete, proper planning, timing, and control are essential.
can be transported by a variety of methods and equipment, such as truck mixers, stationary truck bodies with and without agitators, pipeline or hose, or conveyor belts. Each type of transportation has specific advantages and disadvantages depending on the conditions of use, mixture ingredients, accessibility and location of placing site, required capacity and time for delivery, and weather conditions. 4.4.2 Truck-mixed concrete- Truck miring is a process in which proportioned concrete materials from a batch plant are transferred into the truck mixer where all mixing is performed. The truck is then used to transport the concrete to the job site. Sometimes dry materials are transported to the job site in the truck drum with the 4.5-Placing procedures miring water carried in a separate tank mounted on the 4.5.1 Preparations- Preparations for placing hightruck. Water is added and mixing is completed. This strength concrete should include recognition at the start method, which evolved as a solution to long hauls and of the work that certain abnormal conditions will exist placing delays, is adaptable to the production of high- which will require some items of preparation that cannot strength concrete where it is desirable to retain the be provided readily the last minute before concrete is workability as long as possible. However, free moisture in placed. Since workability time is expected to be reduced, the aggregates, which is part of the mixing water, may preparation must be made to transport, place, consolicause some cement hydration. date, and finish the concrete at the fastest possible rate. This means, first, delivery of concrete to the job site must 4.4.3 Stationary truck body with and without agitatorUnits used in this form of transportation usually consist be scheduled so it will be placed promptly on arrival, parof an open-top body mounted on a truck. The smooth, ticularly the first batch. Equipment for placing the constreamlined metal body is usually designed for discharge crete must have adequate capacity to perform its funcof the concrete at the rear when the body is tilted. A tions efficiently so there will be no delays at distance
363R-18
ACI COMMITTEE REPORT
portions of the work. There should be ample vibration equipment and manpower to consolidate the concrete quickly after placement in difficult areas. All equipment should be in the first class operating condition. Breakdowns or delays that stop or slow the placement can seriously affect the quality of the work. Due to more rapid slump loss, the strain on vibrating equipment will be greater. Accordingly, provision should be made for an ample number of standby vibrators, at least one standby for each three vibrators in use. A high-strength concrete placing operation is in serious trouble, especially in hot weather, when vibration equipment fails and the standby equipment is inadequate. 4.5.3 Equipment- A basic requirement for placing equipment is that the quality of the concrete, in terms of water-cement ratio, slump, air content, and hom ogeneity, must be preserved. Selection of equipment should be based on its capability for efficiently handling concrete of the most advantageous proportions that can be consolidated readily in place with vibration. Concrete should be deposited at or near its final position in the placement. Buggies, chutes, buckets, hoppers, or other means may be used to move the concrete as required. Bottom-dump buckets are particularly useful however, side slopes must be very steep to prevent blockages. High-strength concrete should not be allowed to remain in buckets for extended periods of time, as the delay will cause sticking and difficulty in discharging. 4.5.3 Consolidation- Proper internal vibration is the most effective method of consolidating high-strength concrete. The advantages of vibration in the placement of concrete are well established. The provisions of ACI 309 must be followed. Hi h-strength concrete can be very” 4.1,4.10 indeed, effective consolidation sticky" material. procedures may well start with mix proportioning. Coarse 4.10 sands have been found to provide the best workability. The im ortance of full compaction cannot be overstated. 4.11 Davies has shown that up to 5 percent loss in strength may be sustained from each 1 percent void space in concrete. Thus, vibration almost to the point of excess may be required for high-strength concrete to achieve its full potential. 4.5.4 Special considerations- Where different strength concretes are being used within or between different structural members, special placing considerations are required. To avoid confusion and error in concrete placement in columns, it is recommended that, where practical, all columns and shearwalls in any given story be placed with the same strength concrete. For formwork economy, no changes in column size in the typical highrise buildings are recommended.4.12 In areas where two different concretes are being used in column and floor construction, it is important that the high-strength concrete in and around the column be placed before the floor concrete. With this procedure, if an unforeseen cold joint forms between the two concretes, shear strength will still be available at the column interface.4.13
4.6-Curing 4.5.1 Need for curing- Curing is the process of main-
taining a satisfactory moisture content and a favorable temperature in concrete during the hydration period of the cementitious materials so that desired properties of the concrete can be developed. Curing is essential in the production of quality concrete; it is critical to the production of high-strength concrete. The potential strength and durability of concrete will be fully developed only if it is properly cured for an adequate period prior to being placed in service. Also, high-strength concrete should be water cured at an early age since partial hydration may make the capillaries discontinuous. On renewal of curing, water would not be able to enter the interior of the con4.14 crete and further hydration would be arrested. 4.5.3 Type of curing- Water curing of high-strength concrete is highly recommended4.14 due to the low watercement ratios employed. At water-cement ratios below 0.4, the ultimate degree of hydration is significantly reduced if free water is not provided. Water curing will allow more efficient, although not complete, hydration of 4.15 the cement. Klieger reported that for low watercement ratio concretes it is more advantageous to supply additional water during curing than is the case with higher water-cement ratio concretes. For concretes with water-cement ratio of 0.29, the strength of specimens made with saturated aggregates and cured by ponding water on top of the specimen was 850 to 1000 psi (5.9 to 6.9 M Pa) greater at 28 days than that of comparable specimens made with dry aggregates and cured under damp burlap. He also noted that although early strength is increased by elevated temperatures of mixing and curing, later strengths are reduced by such temperatures. 4.16 has shown that later However, work by Pfieffer strengths may have only minor reductions if the heat is have not applied until after time of set. Others 4.1,4.17 reported that moist curing for 28 days and thereafter in air was highly beneficial in securing high-strength concrete at 90 days. 4.5.3 Methods of curing- As pointed out in ACI 308, the most thorough but seldom used method of water curing consists of total immersion of the finished concrete unit in water. “Ponding” or immersion is an excellent method wherever a pond of water can be created by a ridge or dike of impervious earth or other material at the edge of the structure. Fog spraying or sprinkling with nozzles or sprays provides satisfactory curing when immersion is not feasible. Lawn sprinklers are effective where water runoff is of no concern. Intermittent sprinkling is not acceptable if drying of the concrete surface occurs. Soaker hoses are useful, especially on surfaces that are vertical. Burlap, cotton mats, rugs, and other coverings of absorbent materials will hold water on the surface, whether horizontal or vertical. Liquid mem brane-forming curing compounds retain the original moisture in the concrete but do not provide additional moisture.
HIGH STRENGTH CONCRETE
363R-19
mum elapsed time of 11/2 hr after the cement has entered the drum until completion of discharge is frequently speture has been proportioned, the concrete supplier or cified (See ASTM C 94). Reduction to 45 minutes may sampling and testing program is recommended to assure be necessary under hot weather conditions or where the physical properties required. The use of ASTM severe slump loss is experienced. For extreme job temStandard Method for Evaluation of Cement Strength peratures, field production trial batches are often made. Uniformity from a Single Source (ASTM C 917) with ap propriate limits will provide the proper basis for such 4.8-Quality control procedures uniformity. It is desirable that the aggregates and ad4.8.1 Criteria- The first consideration for selecting mixtures specified in the mixture be uniform and come quality control procedures is determining that the disfrom the same source for the duration of the project. tribution of the compressive strength test results follows 4.18 4.10 a normal distribution curve. It has been suggested that 4.7.2 Control of operations - Effective coordination and control procedures between the supplier and the a skew distribution may prevail due to the mean apcontractor are critical to the operations. The supplier proaching a limit. This may be the case for very-highnormally has full control of high-strength concrete until strength concrete, 15,000 psi (103 MPa) or higher. Howit is placed in the forms. Control of the slump, time on ever available data4.19,4.20 indicate that in the range of job, mixing, and mixture adjustments is under the juris- 6000; to 10,000 psi (41 to 69 MPa) normal distribution is diction of the supplier. The contractor must be prepared achieved. Thus ACI 214 will normally be a convenient to handle, place, and consolidate the concrete promptly tool for quality control procedures for high-strength as received. Cement hydration, temperature rise, slump concrete. Another point which needs consideration both loss, and aggregate grinding during mixing all increase in the quality control and the design phase is the queswith passage of time; thus it is important that the period tion of the age at the time of testing for acceptance for between initial mixing and delivery be kept to an abso- high-strength concrete. Compressive strength tests show lute minimum. The dispatching of trucks is coordinated that a considerable strength gain may be achieved after with the rate of placement to avoid delays in delivery. 28 days in high-strength concrete. To take advantage of When elapsed time from batching to placement is so long this fact, several investigators 4.10,4.13,4.20 have suggested as to result in significant increases in mixing water that the specification for compressive strength should be demand, or in slump loss, mixing in the trucks is delayed modified from the typical 28-day criterion to either 56 or until only sufficient time remains to accomplish mixing 90 days. This extension of test age would then allow, for before the concrete is placed. example, the use of 7000 psi (48 MPa) concrete at 56 4.7.3 Communication equipment- Equipment for direct days in lieu of 6000 psi (41 MPa) at 28 days for design communication between the supply and placement loca- purposes. In this case the same mixture could be used to tions for use by the inspection force is essential. The meet this criterion. High-strength concrete is generally need for other equipment such as signaling and identi- used in high-rise structures; therefore, the extension of fying devices depends on the complexity of the project the time for compressive strength test results is reasonand the number of different concrete mixtures employed. able since the lower portion of the structure will not The project engineer will normally advise the contractor attain full dead load for periods up to one year and of the equipment that is necessary and require him to longer. 4.8.2 Method of evaluation - To satisfy strength perfor present plans or descriptions of the equipment for review well in advance of the start of placement. mance requirements, the average strength of concrete 4.7.4 Laboratoy 4.10-- A competent concrete laboratory must be in excess of f c' , the design strength. The amount must be available for testing the concrete delivered to the of excess strength depends on the expected variability of job site. This laboratory should be inspected regularly by test results as expressed by a coefficient of variation or the Cement and Concrete Reference Laboratory (CCRL) standard deviation and on the allowable proportion of and conform to the requirements of ASTM E 329. A low tests. Available information4.14,4.19,4.20 indicates that minimum of one set of cylinders is normally made for the standard deviation for high-strength concrete be3 3 each 100 yd (76 m ) of concrete placed, with at least comes uniform in the range of 500 to 700 psi (3.5 to 4.8 two cylinders cast for each test age; that is, 7, 28, 56, and MPa), and therefore, the coefficient of variation will actually decrease as the average strength of the concrete 90 days. increases. This, of course, may be the result of increased 4.7.5 Contingency plans- Plans need to be developed to provide for alternate operations in case difficulty is vigilance and quality assurance on the part of the proexperienced in the basic placing concept. Backup equip- ducer. Thus, the method of quality control is closely rement is essential, especially vibrators. Batch sixes are lated to the factors noted in Section 4.7. Assuming that reduced if placing procedures are slowed. For truck- the producer will devote a reasonable effort to proper mixed concrete, rush hour traffic delays can cause serious quality assurance measures, the standard deviation meth problems. It may be desirable to reduce the elapsed time od of evaluation appears to be a logical quality control between contact of the cement and water (mixing and procedure. Consider, for example, that good quality contransporting), especially during warm weather. A maxi- trol may be expected on a job where an f c' of 10,000 psi 4.7-- Quality assurance 4.7.1 Materials- Once the high-strength concrete mix-
ACI COMMlTTEE REPORT
363R-20
(69 MPa) is required. A required average strength f c' of only 11,000 psi (76 MPa) is thus required with a standard deviation of 645 psi (4.4 MPa)
f’
134s = 10,000 + 1.34 x 645 = 10,864 psi (75 MPa) =
+
majority of concrete being placed today. Designers generally assume 6 x 12 in. (152 x 305 mm) specimens as the standard for measured strengths. Recently some 4 x 8 in. (102 x 204 mm) cylinders have been used for determining compressive strength. 4.18,4.19 However, 4 x 8 in. (102 x 204
(4-la)
mm) cylinders exhibit a higher strength and an increase in variability compared to the standard 6 x 12 in. (152 x 305 mm) cylinder.4.23,4.24 Regardless of the specimen size,
or = + 2.33s - 500 = 10,000 + 2.33 x 645 - 500 = 11,000 psi (76 MPa)
(4-lb)
s = standard deviation.
Of course, a close check of the field results and maintenance of records in the form of control charts or other means are necessary to maintain the desired control. Early-age control of concrete strength such as the accelerated curing and testing of compression test specimens according to ASTM C 684 is often used, especially where later-age (56 or 90 days) strength tests are the final acceptance criterion. 4.9 - Strength measurements 4.9.1 Conditions-since much of the interest in high-
strength concrete is limited to strength only in com pression, compressive strength measurements are of primary concern in the testing of high-strength concrete. Standard test methods of the American Society for Testing and Materials (ASTM) are followed except where changes are dictated by the peculiarities of the highstrength concrete. The potential strength and variability of the concrete can be established only by specimens made, used, and tested under standard conditions. Then standard control tests are necessary as a first step in the control and evaluation of the mixture. Curing concrete test specimens at the construction site and under job conditions is sometimes recommended since this is considered more representative of the curing applied to the structure. Tests of job-cured specimens may be highly desirable and are necessary when determining the time of form removal, particularly in cold weather, and when establishing the rate of strength development of structural members. They should never be used for quality control testing. Strength specimens of concrete made or cured under other than standard conditions provide additional information but are analyzed and reported separately. ASTM C 684 requires that a minimum of two cylinders be tested for each age and each test condition. 4.9.2 Specimen size and shape- ASTM standards specify a cylindrical specimen 6 in. (152 mm) in diameter and
12 in. (305 mm) long. This size specimen has evolved over a period of time, apparently from practical considerations. It is about the maximum weight one person can handle with reasonable effort and is large enough to be used for concrete containing 2 in. (50 mm) maximum size aggregate and smaller, which encompasses the
as the compressive stress is transferred through the loading platen-specimen interface, a complex, triaxial distribution of stresses in the specimen end may develop which can radically alter the specimen failure mode and affect results. 4.9.3 Testing apparatus- Testing machine characteristics that may affect the measured compressive strength include calibration accuracy, longitudinal and lateral stiffness, stability, alignment of the machine components, type of platens, and the behavior of the platen spherical seating. Testing machines should meet the requirements of ASTM C 39 when used for testing compressive strength of cylindrical specimens. Overall testing machine design including longitudinal and lateral stiffness and machine stability will affect the behavior of the specimen at its maximum load. The type of platens and behavior of the spherical seating will affect the level of measured 4.23 compressive strength. 4.25 recommended a minimum lateral stiffSigvaldason 4 6 ness of 10 xl0 lb/in. (17.5 x l0 N/m), and a longitudinal stiffness of 10 x l06 lb/in. (17.5 x l06 N/m). He reported that a longitudinally “flexible” machine would contribute to an explosive failure of the specimen at the maximum stress, but that the actual stress achieved was insensitive to machine flexibility. However, he also noted that a machine which is longitudinally stiff but laterally flexible deleteriously influences the measured compressive strengths. Sigvaldason and Cole4.26 reported that use of proper platen size and design is critical if strengths are to be maximized and variations reduced. The upper platen must have a spherical bearing block seating and be able to rotate and achieve full contact with the specimen under the initial load and perform in a fixed mode when approaching the ultimate load. Cole demonstrated that a testing machine with a spherical bearing block seating (able to rotate under load) measured increasingly erroneous results for higher strength concretes, with reductions as high as 16 percent for 10,000 psi (69 MPa) cubes. The diameters of the platen and spherical bearing 4.23 socket are critically important. Ideally, the platen and spherical bearing block diameters should be approximately the same as the bearing surface of the specimen. Bearing surfaces larger than the specimen will be restrained (due to size effects) against lateral expansion will probably not expand as rapidly as the specimen, and will consequently create confining stresses in the specimen end. Bearing surfaces and spherical seating blocks smaller in diameter than those of the specimen may result in portions of the specimens remaining unloaded and bend-
HIGH STRENGTH CONCRETE
ing of the platen around the socket with a consequent nonuniform distribution of stresses. 4.9.4 Type of mold-- The choice of mold materials, and specify construction of the mold regardless of the types of material used, can have a significant effect on measured compressive strengths. A given consolidation effort is more effective with rigidly constructed molds, and sealed waterproofed molds reduce leakage of mortar paste and inhibit the deh ydration of the concrete. 4.15 Blick compared high-strength specimens cast in steel and high-quality paper molds and reported that use of the rigid steel molds increased strengths approximately 13 percent but that use of either mold material did not consistently affect variability of the measured strengths. 4.7 Hester evaluated a number of mold materials used under actual field conditions. Measured compressive strengths achieved with properly prepared specimens were compared. Specimens cast in steel molds achieved approximately 6 percent higher strengths but had a slightly higher coefficient of variation compared to specimens cast in tin molds. Specimens cast in steel molds achieved approximately 16 percent higher strength than specimens cast in plastic molds. 4.9.5 Specimen preparation- For many years concrete technologists have recognized the need to cap or grind the ends of cast concrete test specimens prior to testing for compressive strength. The detrimental effects of non planeness, irregulari din and grease, etc., have been 4.23 well documented. For high-strength concrete the strength of the cap, if used, is another consideration. 4.27 4.28 Troxell, Wemer, and other have compared the relative merits of sulfur mortars, gypsum plaster, highalumina cements, and other capping materials. If the compressive strength or modulus of elasticity of the capping material is less than that of the specimen, loads applied through the cap will not be transmitted uniformly. Sulfur mortar is the most widely used capping material. Most commercially available sulfur mortar capping compounds are combinations of sulfur with inert minerals and fillers and, when properly prepared, are economical, convenient to apply, and develop a relatively high strength in a short period of time. However, these materials are sensitive to the material formulations and handling practices. Kennedy4.29 and Werner investigated the effect of the thickness of sulfur mortar caps on com pressive strengths of moderate strength concretes. Cap thicknesses in the range of 1/16 to in. (1.5 to 3 mm) are desirable for use on high-strength concrete. However, caps consistently thinner than in. (3 mm) are difficult 4.23 to obtain. Kennedy4.26 and Hester note that the principal problems with thin caps are air voids at the specimen-cap interface and cracking of the specimen cap under load. Caps with a thickness of in. (6 mm) are apparently satisfactory. Low-strength thick caps may creep laterally under load and therefore contribute to increased tensile stresses in the specimen ends and consequently substantially reduce measured compressive
363R-21
4.30
strengths for the concrete specimen. Gaynor and 4.31 Saucier indicate that concrete strengths up to 10,000 psi (69 MPa) may be determined using high-strength cap ping materials, including sulfur mortar, which hav e strengths in the range of 7000 to 8000 psi (50 to 60 MPa), if the cap thickness is maintained at approximately in. (6 mm). For expected compressive strengths above 10,000 psi (69 MPa), the ends are usually formed or 4.29.4.30 ground to tolerance. 4.10- Cited References
(See also Chapter l0-- References) 4.1. Saucier, K.L.; Tynes, W.O.; and Smith, E.F., “High-Compressive-Strength Concrete-Report 3, Summary Report,” Miscellaneous Paper No. 6-520, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Sept. 1965, 87 pp. 4.2. Saucier, K.L., “Evaluation of Spiral-Blade Concrete Mixer, Shelbyville Reservoir Project, Shelbyville, Illinois,” Miscellaneous Paper No. 6-975, U.S. Army Engineer, Waterways Experiment Station, Vicksburg, Mar. 1968, 17 pp. 4.3. Strehlow. Robert W., “Concrete Plant Production,” Concrete Plant Manufacturers Bureau, Silver Spring, 1973, 112 pp.
4.4. “Concrete Plant Standards of the Concrete Plant Manufacturers Bureau,” 7th Revision, Concrete Plant Manufacturers Bureau, Silver Spring, Jan. 1, 1983, 11 pp. 4.5. “Concrete Plant Mixer Standards of the Plant Mixer Manufacturers Division, Concrete Plant Manufacturers Bureau,” 5th Revision, Concrete Manufacturers Bureau, Silver Spring, July 18, 1977, 4 pp. 4.6. Concrete Manual, 8th Edition, U.S. Bureau of Reclamation, Denver, 1975. 627 pp. 4.7. Saucier, K.L., “Evaluation of a 16-cu-ft Laboratory Concrete Mixer,” Miscellaneous Paper No. 6-692, U.S. Army Engineer Waterways Experiment Section, Vicksburg, Jan. 1965. 4.8. Bloem, Delmar L., “High-Energy Mixing,” Technical Information Letter No. 169. National Ready Mixed Concrete Association, Silver Spring, Aug. 1961, pp. 3-8. 4.9. Saucier Kenneth L., “Use of Belt Conveyors to Transport Mass Concrete,” Technical Report No. C-74-4, U.S. Army Engineer Waterways Experiment Station, Vicksburg, 1974, 42 pp. 4.10. Blick, Ronald L., “Some Factors Influencing High-Strength concrete,” Modern Concrete, V. 36, No. 12, Apr. 1973, pp. 38-41. 4.11. Davies, R.D., “Some Experiments on the Com paction of Concrete by Vibration,” Magazine of Concrete Research (London), V. 3, No. 8, Dec. 1951, pp. 71-78. 4.12. Schmidt, William, and Hoffman, Edward J., “9000-psi ConcreteWhy?-Why Not?,” Civil Engineering -ASCE, V. 45, No. 5, May 1975, pp. 52-55. 4.13. “High-Strength Concrete in Chicago High-Rise Buildings,” Task Force Report No. 5, Chicago Committee on High-Rise Buildings, 1977, 63 pp. 4.14. Neville, A.M., Properties of Concrete, 2nd Edition,
363R-22
ACI COMMITTEE REPORT
periment Station, Vicksburg, Apr. 1972, 51 pp. John Wiley and Sons, New York, 1973, 686 pp. 4.15. Klieger. Paul, “Early High Strength Concrete for Prestressing,” Proceedings, World Conference on Prestressed Concrete, San Francisco, 1957, pp. A5-l-A5-14. CHAPTER 5-PROPERTIES OF 4.16. Pfieffer, D.W., and Ladgren, J.R., “Energy EfHIGH-STRENGTH CONCRETE ficient Accelerated Curing of Concrete-A Laboratory Study for Plant-Produced Prestressed Concrete,” Tech5.1-Introduction nical Report No. 1, Prestressed Concrete Institute, Concrete properties such as stress-strain relationship, Chicago, Dec. 1981. 4.17. Price, Walter H., “Factor Influencing Concrete modulus of elasticity, tensile strength, shear strength, and bond strength are frequently expressed in terms of the Strength,” ACI JOURNAL, Proceedings V. 47, No. 6, Feb uniaxial compressive strength of 6 x 12-m. (152 x 3051951, pp. 417-432. mm) cylinders. Generally, the expressions have been 4.18. Mather, Brant, “Stronger Concrete,” Highway Research Record No. 210, Highway Research Board, 1967, based on experimental data of concrete with compressive strengths less than 6000 psi (41 MPa). Various properties pp. l-28. 4.19. Day, K.W., “Quality Control of 55 MPa Concrete of high-strength concrete are reviewed in this chapter. The applicability of current and proposed expressions for for Collins Place Project, Melbourne, Australia,” Concrete predic ting pro perties of hig h-strength con crete are International Design & Construction, V. 3, No. 3, Mar. examined. 1981, pp. 17-24. 4.20. Cook, James E., “Research and Application of 5.2-Stress-strain behavior in uniaxial compression High-Strength Concrete Using Class C Fly Ash,” Concrete Axial-stress versus strain curves for concrete of com International: Design & Construction, V. 4, No. 7, July pressive strength up to 12,000 psi (83 MPa) are shown in 1982, pp. 72-80. 4.21. Fortie, Douglas A, and Schnoreier, P.E., “Four- Fig. 5.1. The shape of the ascending part of the stressstrain curve is more linear and steeper for high-strength by-Eight Test Cylinder Are Big Enough,” Concrete Conconcrete, and the strain at the maximum stress is slightly struction, V. 24, No. 11, Nov. 1979, pp. 751-753. 5.5-5.6 4.22. Wolsiefer, John, private communication with higher for high-strength concrete. The slope of the descending part becomes steeper for high-strength conACI Committee 363, 1982. 4.23. Hester, Weston T., “Field Testing High-Strength crete. To obtain the descending part of the stress-strain curve, it is generally necessary to avoid the specimenConcretes: A Critical Review of the State-of-the-Art,” testing system interaction; this is more difficult to do for Concrete International Design & Construction, V. 2, No . high-strength concrete. 5.3,5.5,5.8 12, Dec. 1980, pp. 27-38. A simple method of obtaining a stable descending part 4.24. Carrasquillo, Ramon L.; Nilson, Arthur H.; and of the stress-strain curve is described in References 5.3 Slate, Floyd O., “Properties of High-Strength Concrete Subject to Short-Term Loads,” ACI JOURNAL , Proceedings V. 78, No. 3, May-June 1981, pp. 171-178. 4.25. Sigvaldason, O.T., “The Influence of Testing Machine Characteristics Upon the Cube and Cylinder Strength of Concrete, Magazine of Concrete Research (London), V. 18, No; 57, Dec. 1966, pp. 197-206. Stress, 4.26. Cole, D.G., “Some Mechanical Aspects of Comksi pression Testing Machines,” Magazine of Concrete Research (London), V. 19, No. 61, Dec. 1967, pp. 247251.
4.27. Troxell, G.E., “The Effect of Capping Methods and End Conditions Before Capping Upon the Compressive Strength of Concrete Test Cylinder,” Proceedings, ASTM, V. 41, 1941, pp. 1038-1052. 4.28. Werner, George, “The Effect of Type of Capping Material on the Compressive Strength of Concrete Cylinder,” Proceedings, ASTM V. 58, 1958, pp. 1166-1186.
4.29. Holland, Terrence C., “Testing High Strength Concrete,” Concrete Construction, June 1987, pp. 534-536.
4.30. Godfrey, K.A., Jr.,"Concrete Strength record Jumps 36%,” Civil Engineering, Oct. 1987, pp. 84-88. 4.31. Saucier, K.L., “Effect of Method of Preparation of Ends of Concrete Cylinders for Testing," Miscellaneous Paper No. C-72-12, U.S. Army Engineer Waterways Ex-
Strain, percent
Fig. 5.1 -Complete compressive stress-strain curves
5.I
363R-23
HIGH STRENGTH CONCRETE
and 5.7. Concrete cylinders were loaded in parallel with a hardened steel tube with a thickness such that the total load exerted by the testing machine was always increasing. This approach can be employed with most conventional testing machines. An alternate approach is to use a closed-loop testing machine.‘.’ In a closed-loop testing machine, specimens can be loaded so as to maintain a constant rate of strain increase and avoid unstable failure. High-strength concrete exhibits less internal microcracking than lower-strength concrete for a given im posed axial strain. 5.9 As a result, the relative increase in lateral strains is less for high-strength concrete (Fig. 5.10 5.2). The lower relative lateral expansion during the inelastic range may mean that the effects of triaxial stresses will be proportionally different for high-strength concrete. For example, the influence of hoop reinforcement is observed to be different for high-strength concrete.5.11 It was reported that the effectiveness of spiral 5.11 reinforcement is less for high-strength concrete.
(see Fig. 5.3) was reported in Reference 5.19 as E c
6
= 40,000 + 1.0 x l0 p si for 3000 psi < < 12,000 psi
(E C = 3320
+ 6900 M P a
for 21 MPa
< 83 MPa)
(5-l)
Other empirical equations for predicting elastic modulus have been proposed.5.17,5.18 Deviation from predicted values are highly dependent on the properties and pro portions of the coarse aggregate. For example, higher values than predicted by Eq. (5-l) were reported by 5.20 5.21 5.22 Russell, Saucier, and Pfeiffer. 5.4-Poisson’ s ratio
Experimental data on values of Poisson’s ratio for 5.23 high-strength concrete are very limited. Shideler and 5.2 Carrasquillo et al reported values for Poisson’s ratio of lightweight-aggregate high-strength concrete having uniaxial compressive strengths up to 10,570 psi (73 M Pa) at 28 days to be 0.20 regardless of compressive strength, age, and moisture content. Values determined by the dynamic method were slightly higher. 5.24 On the other hand, Perenchio and Klieger reported values for Poisson’s ratio of normal weight high-strength concretes with compressive strengths ranging from 8000 to 11,600 psi (55 to 80 MPa) between 0.20 and 0.28. They concluded that Poisson’s ratio tends to decrease with increasing water-cement ratio. Kaplan5.25 found values for Poisson’s ratio of concrete determined using dynamic measurements to be from 0.23 to 0.32 regardless of com pressive strength, coarse aggregate, and test age for concretes having compressive strengths ranging from 2500 to Fig. 5.2-- Axial stress versus axial strain and lateral strain 11,500 psi (17 to 79 MPa). 5.10 for plain normal weight concrete Based on the available information, Poisson’s ratio of high-strength concrete in the elastic range seems compar5.3-Modulus of elasticity able to the expected range of values for lower-strength 5.12 reported values for concretes. In 1934, Thoman and Raede the modulus of elasticity determined as the slope of the tangent to the stress-strain curve in uniaxial compression 5.5-Modulus of rupture 5.23,5.26-5.28 at 25 percent of maximum stress from 4.2 x l06 to 5.2 x The values reported by various investigators 6 l0 psi (29 to 36 GPa) for concretes having compressive for the modulus of rupture of both lightweight and norstrengths ranging from 10,000 (69 MPa to 11,000 psi (76 mal weight high-strength concretes fall in the range of 7.5 5.4,5.13-5.18 MPa). Many other investigators have reported to 12 where both the modulus of rupture and values for the modulus of elasticity of high-strength con6 the compressive strength are expressed in psi. The folcretes of the order of 4.5 to 6.5 x l0 psi (31 to 45 GPa) 5.2 depending mostly on the method of determining the lowing equation was recommended for the prediction 5-19 modulus. A comparison of experimentally determined of the tensile strength of normal weight concrete, as values for the modulus of elasticity with those predicted measured by the modulus of rupture from the com by the expression given in ACI 318, Section 8.5 for pressive strength as shown in Fig. 5.4 lower-strength concrete, based on a dry unit weight of 3 3 145 lb/ft (2346 kg/m ) is given in Fig. 5.3. The ACI 318 = 11.7 psi expression overestimates the modulus of elasticity for for 3000 psi < < 12,000 psi concretes with compressive strengths over 6000 psi (41 MPa) for the data given in Fig. 5.3. = 0.94 MPa A correlation between the modulus of elasticity E c and for 21 MPa < < 83 MPa) the compressive strength f c' for normal weight concretes (5-2)
C
0
363R-25
HIGH STRENGTH CONCRETE
0 I
2 I
4
6
8
0 I
1O
I
1200
4
2
20
0
8
6
MPa 40
60
80
1000 Splitting Tensile
Strength
Modulus
Modulus of
Rupture
Rupture
, psi
800
, MPa
psi
600 400
2000 6000 Cylinder Strength I
I
0
20
40
10000 . psi
8o 1 00
14000
120
5.2
Fig. 5.5-Tensile strength based on split cylinder test
jected to repeated load varied between 66 and 71 percent of the static strength for a minimum stress level of 1250 Fig. 5.4-- Tensile strength based on modulus of rupture 5.2 psi (8.6 MPa). The lower values were found for the test higher-strength concretes and for concrete made with the smaller-size coarse aggregate, but the actual magnitude 5.6-Tensile splitting strength 5.27 Dewar studied the relationship between the indirect of the difference was small. To the extent that is known, tensile strength (cylinder splitting strength) and the com- the fatigue strength of high-strength concrete is the same pressive stre ngth of concretes hav ing compressive as that for concretes of lower strengths. strengths of up to 12,105 psi (83.79 MPa) at 28 days. He concluded that at low strengths, the indirect tensile 5.8-Unit Weight The measured values of the unit weight of highstrength may be as high as 10 percent of the compressive strength but at higher strengths it may reduce to 5 per- strength concrete are slightly higher than lower-strength cent. He observed that the tensile splitting strength was concrete made with the same materials. about 8 percent higher for crushed-rock-aggregate concrete than for gravel-aggregate concrete- In addition, he 5.9-Thermal properties The thermal properties of high-strength concretes fall found that the indirect tensile strength was about 70 percent of the flexural strength at 28 days. Carrasquillo, within the a proximate range for lower-strength con5.21,5.26 5.2 Quantities that have been measured are Nilson, and Slate reported that the splitting strength cretes. did not vary much from the usual range shown in Fig. specific heat, diffusivity, thermal conductivity, and co5.5, although as the compressive strength increases, the efficient of thermal expansion. values for the splitting strength fall in the upper limit of the expected range. The following equation for the pre- 5.10-Heat evolution due to hydration The temperature rise within concrete due to hydration diction of the tensile splitting strength of normal 5.2 depends on the cement content, water-cement ratio, size weight concrete was recommended of the member, ambient temperature, environment, etc. 5.15 Freedman has concluded from data of Saucier et al. = 7.4 psi f ' in Fig. 5.6 that the heat rise of high-strength concretes for 3000 psi c < 12,000 psi 3 will be approximately 11 to 15 F/l00 lb of cement/yd (6 3 = 0.59 MPa to 8 C per 59 kg/m of cement). Values for temperature rise of the order of 100 F (56 C) in high-strength confor 21 MPa < < 83 MPa) (5-3) 3 crete members containing 846 lb of cement/yd (502 3 kg/m ) were measured in a building in Chicago as shown 5.7-Fatigue strength 5.16 The available data on the fatigue behavior of high- in Fig. 5.7. strength concrete is very limited. Bennett and Muir.5.29
studied the fatigue strength in axial compression of highstrength concrete with a 4-in. (102-mm) cube compressive strength of up to 11,155 psi (76.9 MPa) and found that after one million cycles, the strength of specimens sub-
5.11-Strength gain with age
High-strength concrete shows a higher rate of strength gain at earl a es as compared to lower-strength concrete5.1,5.2,5.13,5.15 but at later ages the difference is not
ACI
363R-26
COMMITTEE
REPORT
strength concrete and 0.7 to 0.75 for lower-strength c o n 5.2,5.9
Temp. , F
40 0 0
20
40
60
80
100
Time, hours
5.12-Freeze thaw resistance
Information about air content requirement for highstrength concrete to produce adequate durability is contradictory. For example, Saucier, Tynes, and Smith 5.21 concluded from accelerated laboratory freeze-thaw tests that, if high-strength concrete is to be frozen under wet conditions, air-entrained concrete should be considered despite the loss of strength due to air entrainment. In contrast, Perenchio and Klieger 5.24 obtained excellent resistance to freezing and thawing of all of the highstrength concretes used in their study, whether air entrained or non-air-entrained. They attributed this to the greatly reduced freezable water contents and the increased tensile strength of high-strength concrete.
Fig. 5.6-Temperature rise of high-strength field-cast 10 x
20 x 5-ft (3 x 6 x 1.5-m) blocks
5.21
20 0
Column
150
50
0
5
15
10
20
Age, days
Fig. 5.7-- Measured concrete temperatures at Water Tower 5.16 Place.
100
Compressive Strength Compressive
crete, while Carrasquillo, Nilson, and Slate found typical ratios of 7-day to 95-day strength of 0.60 for low-strength, 0.65 for medium-strength, and 0.73 for high-strength concrete. It seems likely that the higher rate of strength development of high-strength concrete at early ages is caused by (1) an increase in the internal curing temperature in the concrete cylinders due to a higher heat of hydration and (2) shorter distance between hydrated particles in high-strength concrete due to low water-cement ratio.
Strength
at 95 days
Little information is available on the shrinkage behavior of high-strength concrete. A relatively high initial 5.26,5.30 but after rate of shrinkage has been reported, drying for 180 days there is little difference between the shrinkage of high-strength and lower-strength concrete made with dolomite or limestone. Reducing the curing period from 28 to 7 days caused a slight increase in the 5.26 Shrinkage was unaffected by changes in shrinkage. water-cement ratio 5.15 but is approximately proportional to the percentage of water by volume in the concrete. 5.31 5.16,5.22,5.28 Other laboratory studies and field studies have shown that shrinkage of high-strength concrete is similar to that of lower-strength concrete. Nagataki and Yonekuras 5.32 reported that the shrinkage of highstrength concrete containing high-range water reducers was less than for lower-strength concrete. 5.14-- Creep
5.26
0
7
95
28
Age, days
Fig. 5.8-- Normalized strength gain with age for moist-cured 5.2 limestone concretes 5.26
significant (see Fig. 5.8). Parrott reported typical ratios of 7-day to 28-day strengths of 0.8 to 0.9 for high-
Parrott reported that the total strain observed in sealed high-strength concrete under a sustained loading of 30 percent of the ultimate strength was the same as that of lower-strength concrete when expressed as a ratio of the short-term strain. Under drying conditions, this ratio was 25 percent lower than that of lower-strength concrete. The total long-term strains of drying and sealed high-strength concrete were 15 and 65 percent higher, respectively, than for a corresponding lower-strength con5.31 crete at a similar relative stress level. Ngab et a1. found little difference between the creep of high-strength concrete under drying and sealed conditions. The creep
HIGH STRENGTH CONCRETE
363R-27
of high-strength concrete made with high-range water “Stress-Strain Curves of Normal and Lightweight 5.32 to be decreased significantly. The Concrete in Compression,” ACI JOURNAL , Proceedings V. reducers is reported maximum specific creep was less for high-strength con- 75, No. 10, Nov. 1978, pp. 603-611. 5.4. Kaar, P.H.; Hanson, N.W.; and Capell, H.T., crete than for lower-strength concrete loaded at the same 5.16,5.20,5.31 5.28 age. “Stress-Strain Characteristics of High-Strength Concrete,” An example is shown in Fig. 5.9. However, high-strength concretes are subjected to higher Douglas McHenry International Symposium on Concrete stresses. Therefore, the total creep will be about the and Concrete Structures, SP-55, American Concrete Instisame for any strength h concrete. No problems due to tute, Detroit, 1978, pp. 161-185. Also, Research and creep were found 5.22 in columns cast with high-strength Development Bulletin No. 051.01D, Portland Cement concrete. As is found with lower-strength concrete, creep Association. 5.31 decreases as the age at loading increases, specific 5.5. Shah, S.P.; Gokoz, U.; and Ansari, F., “An 5.24 creep increases with increased water-cement ratio, and Experimental Technique for Obtaining Complete Stress5.31 Strain Curves for High Strength Concrete,” Cement, there is a linear relationship with the applied stress. This linearity extends to a higher stress-strain ratio than Concrete and Aggregates, V. 3, No. 1, Summer 1981, pp. for lower-strength concrete. 21-27. 5.6. Shah, S.P., “High Strength Concrete-A WorkSome additional information on properties of highstrength concrete can be obtained from References 5.33 shop Summary,” Concrete International Design & Conto 5.42. struction, V. 3, No. 5, May 1981, pp. 94-98. 5.7. Shah, S.P.; Naaman, A.E.; and Moreno, J., “Effect 1.75 of Confinement on the Ductility of Lightweight ConUnsealed crete,” International Journal of Cement Composites and Sealed Lightweight Concrete (Harlow, Essex), V. 5, No. 1, Feb. 1.50
1983, pp. 15-25. 5.8. Holm, T.A., “Physical Properties of High Strength Lightweight Aggregate Concrete,” Proceedings, 2nd Inter-
psi
1.25
national Congress on Lightweight Concrete (London, Apr. 1980) Ci80, Construction Press, Lancaster, 1980,
Creep Coefficient,
pp. 187-204.
5.9. Carrasquillo, Ramon L.; Slate, Floyd 0.; and Nilson, Arthur H., “ Microcracking and Behavior of HighStrength Concrete Subject to Short-Term Loading,” ACI JOURNAL, Proceedings V. 78, No. 3, May-June 1981, pp.
075
179-186.
5.10. Ahmad, Schuaib, and Shah, Surendra P., “Complete Triaxial Stress-Strain Curves for Concrete,” Proceedings, ASCE, V. 108, ST4, Apr. 1982, pp. 728-742. 5.11. Ahmad, S.H., and Shah, S.P., “Stress-Strain Curves Of Concrete Confined by Spiral Reinforcement, ACI JOURNAL , Proceedings V. 79, No. 6, Nov.-Dec. 1982,
0.50 1000 psi = 6.895 M PO 0.45 in All Cases
0.25
Age at Loadi ng 2 Days Af te r 28 Day s Cu rin g 0
,
0
15
I
I
I
30
45
60
75
Time After Loading, days
pp. 484-490. 5.12. Thoman, William H., and Raeder, Warren, “Ulti-
mate Strength and Modulus of Elasticity of High Strength Portland Cement Concrete,” ACI J OURNAL , Proceedings V. 30, No. 3, Jan-Feb. 1934, pp. 231-238. 5.13. Smith, E.F.; Tynes, W.O.; and Saucier, K.L., 5.15-Cited references “ High-Compressive-Strength Concrete, Development of (See also Chapter 10-References) Concrete Mixtures,” Technical Documentary Report No. 5.1 Wischers, Gerd, “Applications and Effects of RTD TDR-63-3114, U.S. Army Engineer Waterways ExCompressive Loads on Concrete,” Bet ontechnisc he periment Station, Vicksburg, Feb. 1964, 44 pp. Berichte 1978, Betone Verlag GmbH, Dusseldorf, 1979, 5.14. Nedderman, Howard, “Flexural Stress Distri pp. 31-56. (in German) bution in Very-High-Strength Concrete,” MSc thesis, 5.2. Carrasquiho, Ramon L.; Nilson, Arthur H.; and University of Texas at Arlington, Dec. 1973, 182 pp. Slate, Floyd O., “Properties of High Strength Concrete 5.15. Freedman, Sydney, High-Strength Concrete,” Subjected to Short-Term Loads,” ACI JOURNAL , Proceed Modern Concrete, V. 34, No. 6, Oct. 1970, pp. 29-36; No. ings V. 78, No. 3, May-June 1981, pp. 171-178, and 7, Nov. 1970, pp. 28-32; No. 8, Dec. 1970, pp. 21-24; No. Discussion, Proceedings V. 79, No. 2, Mar.-Apr. 1982, pp. 9, Jan. 1971, pp. 15-22; and No. 10, Feb. 1971, pp. 16-23. 162-163. Also, Publication No. lS176T, Portland Cement Associ5.3. Wang, P.T.; Shah, S.P.; and Naaman, A.E., ation.
Fig. 5.9-- Relationship between creep coefficient and time 5.31 for sealed and unsealed concrete specimens
363R-28
ACI COMMlTTEE REPORT
5.16. “High-Strength Concrete in Chicago High-Rise pression,” Magazine of Concrete Research (London), V. 19, No. 59, June 1967, pp. 113-117. Buildings,” Task Force Report No. 5, Chicago Committee 5.30. Swamy, R.N., and Anand, K.L., “Shrinkage and on High-Rise Buildings, Feb. 1977, 63 pp. 5.17. Teychenne, D.C.; Parrott, L.J.; and Pomeroy, Creep of High Strength Concrete,” Civil Engineering and C.D., “The Estimation of the Elastic Modulus of Con- Public Works Review (London), V. 68, No. 807, Oct. 1973, crete for the Design of Structures,” Current Paper No. pp. 859-865, 867-868. CP23/78, Building Research Establishment, Garston, 5.31. Ngab, A.S.; Slate, F.O.; and Nilson, A.H., Watford, 1978, 11 pp. “Behavior of High-Strength Concrete Under Sustained 5.18. Ahmad, S.H., “Properties of Confined Concrete Compressive Stress,” Research Report No. 80-2, DepartSubjected to Static and Dynamic Loading,” PhD thesis, ment of Structural Engineering, Cornell University, University of IIIinois at Chicago Circle, Mar. 1981. Ithaca, Feb. 1980, 201 pp. Also, PhD dissertation, Cornell 5.19. Martinez, S.; NiIson, AH.; and Slate, F.O., University, 1980, and “Shrinkage and Creep of High “Spirally-Reinforced High-Strength Concrete Columns,” Strength Concrete,” ACI JOURNAL , Proceedings V. 78, Research Report No. 82-10, Department of Structural No. 4, July-Aug. 1981, pp. 255-261. 5.32. Nagataki, S., and Yonekura, A., “Studies of the Engineering, Cornell University, Ithaca, Aug. 1982. 5.20. Russell, H.G., and Corley, W.G., “Time- Volume Changes of High Strength Concretes with SuperDependent Behavior of Columns in Water Tower Place, pla sti ciz er,” Journal, Japan Prestressed Concrete Engineering Association (Tokyo), V. 20, 1978, pp. 26-33. Douglas McHenry International Symposium on Concrete 5.33. Ahmad, S.H. and Shah, S.P. “Behavior of Hoop and Concrete Structures, SP-55, American Concrete Institute, Detroit, 1978, pp. 347-373, Also, Research and Confined Concrete Under High Strain Rates,” ACI Development Bulletin No. RD052.01B, Portland Cement JOURNAL , Proceedings V. 82, No. 5. Sept.-Oct. 1985, pp. Association. 634-647. 5.21. Saucier, K.L.; Tynes, W.O.; and Smith, E.F., 5.34. “Research Needs for High-Strength Concrete,” “High Compressive-Strength Concrete-Report 3, Sum- reported by ACI Committee 363, ACI Materials Journal, mary Report,” Miscellaneous Paper No. 6-520, U.S. Army Proceedings V. 84, No. 6, Nov.-Dec. 1987, pp. 559-561. Engineer Waterways Experiment Station, Vicksburg, 5.35. Proceedings of Symposium on Utilization of HighSept. 1965, 87 pp. Strength Concrete, Stavanger, Norway, June 15-18, 1987, 5.22. Pfeifer, Donald W.; Magura, Donald D.; Russell, Tapir, Publishers, N-7034 Trondheim-N7H, Norway, 688 Henry G.;, and Corley, W.G., “Time Dependent Defor- PP. 5.36. Yogendram, Langan, Hagne and Ward, “Silica mations in a 70 Story Structure,” Designing for Effects of Creep, Shrinkage, Temperature in Concrete Structures, Fume in High Strength Concrete,” ACI Materials Journal, SP-37, American Concrete Institute, Detroit, 1971, pp. V. 84, No. 2, Mar.-Apr. 1987, pp. 124-129. 159-185. 5.37. Carrasquillo, P., and Carrasquillo, R., “Current 5.23. Shideler, J J., “Lightweight-Aggregate Concrete Practice in Evaluation of High Strength Concrete,” for Structural Use,” ACI JOURNAL , Proceedings V. 54, ACI Materials Journal, V. 85, No. 1, Jan.-Feb., 1988, pp. No. 4, Oct. 1957, pp. 299-328. 49-54. 5.24. Perenchio, William F., and Khieger, Paul, “Some 5.38. Smadi, M.M., Slate, F.O., and Nilson, A.H., “Shrinkage and Creep of High, Medium, and Low Physical Properties of High Strength Concrete,” Research and Development Bulletin No. RD056.01T, Portland Strength Concretes Including Overloads,” ACI Materials Cement Association, Skokie, 1978, 7 pp. Journal, Proceedings V. 84, No. 3, May-June 1987, pp. 5.25. Kaplan, M.F., “Ultrasonic Pulse Velocity, 224-234. Dynamic Modulus of Elasticity, Poisson’s Ratio and the 5.39. Smadi, M.M., Slate, F.O., and Nilson, AH., Strength of Concrete Made with Thirteen Different “ High, Medium, and Low Strength Concrete Subject to Coarse Aggregates,” RILEM Bulletin (Paris), New Series Sustained Loads-Strains, Strengths and Failure Mechanisms,” ACI JOURNAL , Proceedings V. 82, No. 5, No. 1, Mar. 1959, pp. 58-73. 5.26. Parrot, LJ., “The Properties of High-Strength Sept.-Oct. 1985, pp. 657-664. Concrete,” Technical Report No. 42.417, Cement and 5.40. Ahmad, S.H., and Shah, S.P., “Structural Properties of High Strength Concrete and Its ImpliConcrete Association, Wexham Springs, 1969, 12 pp. 5.27. Dewar, J.D., “The Indirect Tensile Strength of cations on Precast and Prestressed Concrete,” Journal of Concretes of High Compressive Strength,” Technical Prestressed Concrete Institute, Nov.-Dec. 1985. 5.41. Ahmad, S.H., and Shah, S.P., “High Strength Report No. 42.377, Cement and Concrete Association, Concrete-A Review,” Proceedings of International SymWexham Springs, Mar. 1964, 12 pp. 5.28. Kaplan, M.F., “ Flexural and Compressive posium on Utilization of High Strength Concrete, Strength of Concrete as Affected by the Properties of the Stavanger, Norway, June 15-18, 1987. 5.42. Shirley, T. Scott, Burg, G. Ronald, and Fiorato, Coarse Aggregates, ACI JOURNAL , Proceedings V. 55, E. Anthony, “Fire Endurance of High Strength Concrete No. 11, May 1959, pp. 1193-1208. 5.29. Bennett, E.W., and Muir, S.E. St. J., “Some Slabs,” ACI Materials Journal, Mar.-Apr. 1988, pp. 102Fatigue Tests of High-Strength Concrete in Axial Com- 108.
HIGH STRENGTH CONCRETE
363R-29
CHAPTER 6-STRUCTURAL DESIGN CONSIDERATIONS
High-strength concretes have some characteristics and engineering properties that are different from those of lower-strength concretes. Internal changes resulting from short-term and sustained loads and environmental factors are known to be different. Directly related to these internal differences are distinctions in mechanical properties that must be recognized by design engineers in predicting the performance and safety of structures. These distinctions are increasingly important as strengths increase. Tests of unreinforced high-strength concrete have shown, for example, that such material in many cases may be closely characterized as linearly elastic up to stress levels approaching the maximum stress. Thereafter, the stress06 0 02 04 strain curve of high-strength concrete decreases at a 6.1-6.10 Strain, percent much greater rate than lower-strength concretes. Extensive experimentation at several research centers Fig. 6.1-- Concrete and steel stress-strain curves has provided a fundamental understanding of the behavior of high-strength concrete. While substantial infor- The steel reaches its yield point at about the same strain mation is now available on many aspects, some final re- in this case; thus, concrete is at its maximum stress, steel commendations must await the results of current and is at f y , and the strength of the column is predicted by future work. In this chapter, the emphasis will be placed on design P = 0.85 f c' Ac + f y A s (6-l) 6.11 Where recommendations of members and structures. are made, they are based on the best current experi- where f c' = cylinder compressive strength of the conmental information and in most cases must be considered crete tentative. f y = yield strength of steel Ac = area of concrete section A s 6.2-Axially-loaded columns = area of steel Few columns in practice are subjected to truly axial loads. Bending moments, due to eccentric application of The factor 0.85 is used to account for the observed difload or associated with rigid frame action, are usually ference in strength of concrete in columns compared with superimposed on axial loads. ACI 318-83 requirements concrete of the same mix in standard compression-test for design and ACI 318R-83 reflect this. However, it is cylinders. useful to look first at the behavior of columns carrying A similar analysis holds for high-strength concrete axial load only. columns, except the steel will yield before the concrete 6.2.1 Strength contribution of steel and concrete-The reaches its peak strength. However, the steel will conattribute of main interest is the ultimate strength. Present tinue to yield at essentially constant stress until the design practice, in calculating the nominal strength of an concrete is fully stressed. Prediction of strength may axially loaded member, is to assume a direct addition law therefore still be based on Eq. (6-l). Experimental summing the strength of the concrete and that of the documentation also supports use of the factor 0.85 for steel. The justification for this is seen in Fig. 6.1, which high-strength concrete.6.12-6.13 superimposes typical stress-strain curves in compression 6.2.2 Effects of confinement steel-Lateral steel in for three concretes with that for reinforcing steel having columns, preferably in the form of continuous spirals, has 60,000 psi (414 MPa) yield strength (the last curve is two beneficial effects on column behavior: (a) it greatly drawn to a different vertical scale for convenience). The increases the strength of the core concrete inside the usual assumption is made that steel and concrete strains spiral by confining the core against lateral expansion are identical at any load stage. under load, and (b) it increases the axial strain capacity For lower-strength concrete, when the concrete of the concrete, permitting a more gradual and ductile 6.12-6.16 reaches the range of significant nonlinearity (about 0.001 failure, i.e., a tougher column. strain), the steel is still in the elastic range and conThe basis for design of spiral steel under the 1977 and sequently starts to pick up a larger share of the load. later versions of ACI 318 is that the strengthening effect When the strain is close to 0.002, the slope of the con- of the spiral must be at least equal to the column crete curve is nearly zero and it can be thought of as de- strength lost when the concrete shell outside of the spiral forming plastically, with little or no increase in stress. spalls off under load. The ACI 318 equation for mini-
363R-30
ACI COMMITTEE REPORT
mum volumetric ratio of spiral is =
where
0.45
associated with increasing spacing of the spiral wires. 6.13,6.17 Thus an improved version of Eq. (6-3a) is
f '
=
= ratio of volume of spiral reinforcement to volume of concrete core = gross area of concrete section = area of concrete core = cylinder compressive strength of concrete = yield strength of spiral steel
The increase in compressive strength of columns provided by spiral steel is based on an experimentally derived relationship for strength gain
= where
(6-3a)
= compressive strength of spirally reinforced concrete column = compressive strength of unconfined concrete column concrete confinement stress produced by spiral =
This relationship can be shown to lead directly to Eq. (6-2). The concrete confinement stress produced by spiral f 2' is calculated on the basis that the spiral steel has yielded, using the familiar hoop tension equation.
(1 -
(6-3b)
Fig. 6.2 shows the results of the Cornell tests on columns using different strength concretes. It is clear that the strength gain predicted by Eq. (6-3b) is valid for normal weight concrete of all strengths for confinement stress up to at least 3000 psi (21 MPa). A similar plot based on Eq. (6-3a) shows a somewhat unconservative prediction for higher confinement stresses, but it can be shown that typical confinement stresses for practical column spirals are seldom more than about 1000 psi (7 MPa). For this range Eq. (6-3a) gives good results. From the strength viewpoint, the present ACI 318 equ ation for minimum spiral steel ratio can be used safely for highstrength normal weight columns as well as for lowerstrength concrete columns. Fig. 6.2 also shows that a spiral has much less confining effect in lightweight concrete columns. The lightweight concrete tends to crush under the spirals at heavy 6.13 For lightweight loads, relieving the confining pressure. spirally reinforced columns, Martinez has suggested that Eq. (6-3a) be replaced by =
(6-4a)
and Eq. (6-3b) be replaced by = 1.8
(1 -
(6-4b)
This important difference in behavior means that Eq. (6-2) found in ACI 318 must be reexamined. It appears that lightweight concrete columns would require about or 2.5 times more spiral steel than corresponding normal weight columns to satisfy strength requirements after the f cover spalls off, a requirement that is not reflected in = ACI 318. Whether or not such heavy spirals are practical where = area of spiral steel may be questioned. = diameter of concrete core There is not yet general agreement on the effective= pitch of spiral ness of spiral steel for improving the ductility of highS strength concrete columns, that is, for increasing the and other terms are as already defined. strain limit and flattening the negative slope of the 6.14 has shown that stress-strain curve past the point of peak stress. A paper Recent work by Ahmad and Shah spiral reinforcement is less effective for columns of by Ahmad and Shah 6.14 indicates that confining spirals higher-strength concrete and for lightweight concrete are about as effective in flattening the negative slope of columns. They found also that the stress in the steel the stress-strain curve for high-strength concrete columns spiral at peak load for high-strength concrete columns as for lower-strength concrete columns. However, the 6.13 and lightweight concrete columns is often significantly Cornell work showed significant differences. Fig. 6.3 less than the yield strength assumed in the development shows experimental stress-strain curves for different strengths of normal weight concrete columns with varying of Eq. (6-2). spiral reinforcement. Three groups of curves are identiThese conclusions are consistent with results of experimental research at Cornell University. 6.13 In the Cornell fied by the three concrete strength levels studied. Each research, an “effective” confinement stress f 2 (1 - s/dc) of these groups consists of three sets of curves correswas used in evaluating results, where f 2 is the confine- ponding to three different amounts of lateral reinforcement stress in the concrete, calculated using the actual ment. Indicated in each set of curves with a short horistress in the spiral steel, often less than f y . The term (1 - zontal line is the average unconfined column strength corresponding to that particular set of confined columns. s/dc) reflects the reduction in effectiveness of spirals
363R-31
HIGH STRENGTH CONCRETE
Effective Confinement Stress 0
5
t
12
10
Normal Weight Concrete A High- Strength . Medium - Strength l
, MPa 20
15 I
IO I
I
80
Low- Strength
Lightweight Concrete
A High- Strength
60
a Medium - Strength
Strength
Strength Increment
Low- Strength
Incrememt
, ksi
6 -
MPa
- 2 0 4 x 16 - in. (102 x 406 -mm) Cylinder Stroke Rote: 12,000 p-in (0.30 mm)/min. 2000 Effective Confinement Stress
3000
0
, psi
Fig. 6.2-Strength increment provided by spiral reinforcement action on 4 x 16-in. columns
Normal Weight Spiral Columns 4 x 16 - in. (102 x 406 -mm) Cylinder
Stroke Rate: 12.000 = Unconfined Column Strength (2500) = Effective Ccnfinement stress
Axial
Axial Stress , M Pa
Stress, ksi
Axial
Strain , in. / in.
Fig. 6.3-Experimental stress-strain curves of 4 x 16-in. normal weight spiral columns
Referring to Fig. 6.3, the curves for high-strength predicted well by present equations, but that their proconcrete columns NC167 that had an effective confine- perties past peak stress may be deficient compared with ment stress of 767 psi (5 MPa) are compared with the lower-strength columns. The design of lightweight concurves for lower-strength concrete columns NC163 with crete columns with spiral steel should be approached very 6.13,6.17 an effective confinement stress of 800 psi (6 MPa). Dif- carefully. Another interesting and important observation relating ferent behavior for comparable confinement stress is evident. Not only is the strain at peak stress much less to spirally reinforced columns generally is that the level for high-strength concrete, but the stress falls off sharply of confinement stress corresponding to spirals designed just past the peak value. This last fact is seen to be true by ACI 318 is rather low for all columns. The confineeven for columns NC169 with a very high confinement ment stress becomes significantly lower for larger diastress of 2500 psi (17 MPa) (probably not attainable in meter columns, assuming that the cover requirements remain constant. This follows directly from Eq. (6-2). For practical columns). Based on the available evidence, one may conclude larger columns, the ratio A g /Ac becomes much smaller; that normal density high-strength concrete columns with consequently the required spiral steel ratio becomes spiral steel show strength gain due to the spirals that is smaller and the effective confinement stress becomes
ACI COMMITTEE REPORT
363R-32
proportionately smaller. Confinement stress produced by spirals designed to ACI 318 for lower-and high-strength concrete, for 15 and 50 in. column core diameters are compared in Table 6.1. Table 6.1-Confinement stress produced by spirals designed by ACI 318
(1 -
psi (MPa)
in. (mm)
in. (mm)
strains associated with these stresses have a profound effect on the structural behavior. Such strains are directly related to long-term deflection, losses in prestress force, and cracking. Column strength may be reduced due to sustained loading of high intensity. It may also be increased because of the capability of a concrete structure to adjust itself to local high over-stresses through creep. Creep may be described either in terms of the creep coefficient
= 3000 psi (21 MPa) (#3 spiral bar) 0.0099 0.0028
15(38) 50( 172)
238 (1.64) 83 (0.57)
2.96 (75) 3.17 (81)
= 10,000 psi (69 MPa) (#5 spiral bar) 5 0 ( 1 2 7 )
0.0330 0.0093
825(5.69) 263(1.81)
2.50(64) 2.67(68)
*Ratio of volume of spiral reinforcement to total volume of core (out-to-out of spirals).
C c =
creep strain initial elastic strain
(6-5)
or by the coefficient of specific creep (unit creep coefficient) = creep strain per unit stress
(6-6)
The two can be related through the modulus of elasticity Tests show that for lower-strength concrete even the reduction in confinement stress from 238 to 83 psi (1.64 = (6-7) to 0.57 MPa) obtained under ACI 318 wilI produce a column with very large strain capacity without significant There is general agreement that creep of high-strength loss of resistance. For high-strength concrete, the concrete is significantly less than that of a lower-strength reduction of confinement stress from 825 to 263 psi (5.69 concrete6.7,6.24-6.27 The most recent information, for conto 1.81 MPa) produces a column with virtually no post- cretes with strength up to about 10,000 psi (69-MPa), in peak strain capacity. Even the higher confinement stress dicates that high-strength concrete has a specific creep of 825 psi (5.69 MPa) produces a column with the unde- only about 20 percent that of lower-strength concrete and 6.27 sirable characteristic of a sharp drop-off of resistance a creep coefficient about 30 percent as high. 6.13 immediately after peak stress. As a result, for axially loaded high-strength concrete While some experimental data are available at this columns, creep shortening at a given stress level will be time for high-strength concrete columns using lateral ties less than that of lower-strength columns, a fact of pos6.18,6.19 rather than spirals, more work must be done for sible significance in high-rise concrete structures. 6.30 In such members. addition, the distribution of load between concrete and 6.2.3 Repeated loading-High-strength concrete is relasteel of high-strength concrete columns will be less subtively free of internal microcracking, even close to ulti- ject to change with the passage of time. Elastic distri6.1 On the other bution of stresses may be more nearly maintained. Loss mate load, when loaded monotonically. hand, high-strength concrete is reported to be more of stress in a prestressed member due to creep shorten brittle than lower-strength concrete,6.2 lacking much of ing will be much less at a given concrete stress level, but the ductility that accompanies progressive crack growth. this advantage may be largely canceled if higher sustained Some experimental research indicates that fatigue load stresses are permitted. strength is essentially independent of compressive strength.6.20 Recent research indicates that failure of 6.3-Beams and slabs concrete subject to repeated loading can be approximateThe material properties described in Chapter 5 and in ly predicted by the concept of the envelope curve, di- Section 6.2 may effect the characteristic behavior of highrectly related to the short-term monotonic stress-strain strength concrete beams.6.31-6.34 In some cases, improvecurve. 6.21 For high-strength concrete, each load appli- ments are seen; in other cases less satisfactory behavior cation causes relatively less incremental damage. How- will result. In many ways, high-strength beams may beever, the number of cycles to failure may not be neces- have according to essentially the same rules that have sarily larger because of the greater negative slope of the been used to describe behavior of beams made of lower post-peak envelope curve. strength concrete. However, some questions remain to be While important work has been done,6.20,6.22,6.23 it is answered. 6.3.1 Compressive stress distribution-The compressive clear that additional research is needed on all aspects of high-strength concrete, with and without confinement stress distribution in beams is directly related to the steel, subject to various repeated load regimens, before shape of the stress-strain curve in uniaxial compression. Consequently, for high-strength concrete, which displays design recommendations can be made. differences in that shape, as shown in Fig. 6.1, it is 6.2.4 Sustained loading-In most structures, concrete reasonable to expect differences in flexural compressive is subjected to sustained loads. The time-dependent
HIGH STRENGTH CONCRETE
363R-33
For ordinary design purposes, it is convenient to work stress distribution, particularly at loads approaching with an equivalent rectangular compressive stress distriultimate. In present U.S. practice as in ACI 318 and ACI 318R, bution, shown in Fig. 6.4(b), with magnitude of compres proportioning of beam sections is generally based on con- sive resultant and line of action the same as before. Such an equivalent distribution is specifically referenced and ditions at a hypothetical state of incipient collapse at factored loads. Fig. 6.4(a) shows the generally parabolic permitted in ACI 318 and its Commentary, ACI 318R. shape of the compressive stress distribution in a beam With the uniform value of concrete compression assumed equal to 0.85f c', a single parameter is sufficient to made of lower-strength concrete. The nominal resisting moment may be calculated knowing the internal forces T define both magnitude and line of action. and C and the internal lever arm between them. The actFor high-strength concrete, the stress-strain curve is more linear than parabolic. Therefore, there is reason to ual shape of the compressive stress distribution at insuspect that the stress block parameters may be different. cipient failure, always highly variable even within a given Experimental research has confirmed that differences do range of concrete strengths, may be considered irrelevant exist, and alternatives to the rectangular stress block have if one knows (a) the magnitude of the compressive resul6.34 tant C, and (b) the level in the beam at which it acts. been proposed, such as in Fig. 6.4(c). However, differences in calculated strength values for beams and eccenThese may be established in terms of three parameters tric columns depend on steel ratios and other factors. characteristic of a given stress distribution [see Fig. ACI 318R suggests, based on an equivalent rectangu6.4(a)]. lar stress block, that the nominal flexural strength of a k 1 = ratio of average to maximum compressive stress singly reinforced beam that is under-reinforced can be calculated by in beam k 2 = ratio of depth to compressive resultant to neutral axis depth k 3 = ratio of maximum stress in beam to maximum stress in corresponding axially loaded cylinder w h e r e M n = nominal moment strength at section, in-lb = area of tension reinforcement, in. 2 = specified yield strength of reinforcement, psi = distance from extreme compression fiber d to centroid of tension reinforcement, in. = ratio of tension reinforcement = specified compressive strength of concrete, psi > T = Asf s The coefficient 0.59 can be shown to be equivalent to k 2 /k 1k 3. The experimental variation of k 2 /k 1k 3 with concrete compressive strength based on research at several centers is shown in Fig. 6.5. 6.6,6.31-6.35 While a detailed study of the separate k values indicates that significant differences in the separate values exist depending on C-O.85 concrete strength, it is clear from Fig. 6.5 that the differences are compensative and that the combined coefficient is well-represented by the constant value 0.59. This statement is reinforced by the results shown in Fig. 6.6, which compares flexural strength predictions obtained using the usual rectangular stress block, a triangular stress block, and a distribution based on experimentally derived stress-strain curves with test data for beams of varying reinforcement ratios and concrete strengths to 11,000 psi (76 MPa). Test values were best predicted using actual stress-strain curves, but either the rectangular or triangular distributions gave acceptable lower bounds to the experimental and theoretical values. 6.36 Based on these and similar studies, it appears that, for under-reinforced beams, the present ACI 318 methods can be used without change, at least for concrete strengths up to 12,000 psi (83 MPa). For over-reinforced Fig. 6.4-Concrete stress distributions for rectangular beams
-
ACI COMMITTEE REPORT
363R-34
Pa
Concrete Strength ,
Concrete Strength , 0.005
0
20
40
I
I
60
80
l00
120
I
I
.
08
0. 6 -
&
-
-
-
-
A
.. -
-
-
-
-
-
Rectangular
. 0. 4
0. 2 4
8
12
16
20
Concrete Strength , ksi 0 0
4
8
I2
20
16
Concrete Strength , ksi
Fig. 6.7-- Ultimate concrete flexural strain
versus con-
crete compressive strength
Fig. 6.5-- Stress block parameter k 2 /k 1k 3 versus concrete strength 140 Test ACI Cods Triangular Stress Block
Theoretical
Mu,
energy release from the testing equipment. Fig. 6.7 6.5 shows the variation of concrete strain at failure at the extreme compression face of singly reinforced concrete beams or eccentrically loaded columns without lateral confinement steel. The constant value of strain at extreme concrete compression fiber of 0.003 prescribed by ACI 318 is seen to represent satisfactorily the experimental results for high-strength as well as lower-strength concrete, although it is not as conservative for highstrength concrete. 6.3.3 Influence of confinement steel and compression Steel-Considering the more limited strain capacity of
kip-ft 80
high-strength concrete in compression, it is necessary to evaluate the ductility of beams made of high-strength concrete. Deflection ductility index will be defined here as
60
4 0
20 0.5
I
2
3
Reinforcement Ratio
Fig. 6.6-- Comparison of flexural strength M u , of beams for several compressive stress distributions
beam s, which are not allowed by ACI 318, or for members combining axial compression and bending, 6.33 important differences may occur. 6.2.3 Limiting compressive strain-While high-strength concrete reaches its peak stress at a compressive strain slightly higher than that for lower-strength concrete, the ultimate strain is lower for high-strength concrete, both in uniaxial compression tests and in beam tests. 6.13,6.34 It has been suggested that this result apparently is due to
where = beam deflection at failure load = beam deflection at the load producing yielding of tensile steel 6.34 of beams made of relatively highTests by Pastor et al strength concrete are summarized in Table 6.2 (Series A) and Table 6.3 (Series B). Beams of Series A were singly reinforced with no compression steel and no confinement steel. The series includes beams with concrete strengths from 3700 to 9265 psi (26 to 64 MPa). For the highstrength beams, tensile steel ratio varied from 0.29 to 1.11 where = reinforcement ratio for balanced strain conditions. The results show a lower ductility for the beams with
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HIGH STRENGTH CONCRETE
the higher concrete strengths. Based on these results, the second series summarized in Table 6.3 was performed. These beams included varying amounts of compression steel (50 to 100 percent of tensile steel area) and lateral confinement steel in the form of closed hoops at spacing of 3, 6, and 12 in. (7.6, 15.2, and 30.5 mm). All beams were of high-strength concrete and comparable to Beam A4 of the first series, which had no ties and no com pression steel. Table 6.2-Deflection ductility index for Series A beams 6.34 Ductility
index
for
in psi
for
in MPa
Y
(6.10)
Y
is derived on the basis that the resisting moment of the cracked section should be at least as great as the moment that caused the member to crack, based on the modulus of rupture. Since the latter is known to be greater for high-strength concrete than for lower-strength concrete, 6.2,6.12 it is evident that the strength of concrete should be included in a revised version of Eq. (6.10). With modulus of rupture taken at 7.5 (0.62 it can be shown that (6.11)
*Ratio of tension reinforcement divided by reinforcement ratio producing balanced strain conditions.
Table 6.3-Deflection ductility index for Series B b e a m s 6.34 Ductility
Beam
psi
B6
8534 8605 8578 8478 8516 8466
index 0.57 0.55 0.57 0.59 0.56 0.58
2.36 2.64 4.88 8.32 5.61 6.14
From Beams Bl and B2, compared with Beam A4, it can be concluded that ties at 12 in. (30.5 mm) increased the ductility index, but not significantly. Ductility index increased markedly when the tie spacing was reduced to 6 in. (15.2 mm) in Beams B3 and B4, but showed no upward trend when the spacing was further reduced to 3 in. (7.6 mm).
A comparison between Beams B3 and B4 indicates a beneficial effect in adding more compression steel, although this trend is not clearly reflected in a comparison of Beams B5 and B6. 6.3.4 Minimum tensile steel ratios- ACI 318 sets an upper limit on the tensile steel ratio for beams at 75 percent of the balanced ratio to insure that failure, should it occur, will be a gradual, yielding type. A lower limit of tensile steel ratio is set to guard against sudden failure of very lightly reinforced beams upon concrete cracking, when the tension formerly carried by the concrete is transferred to the steel reinforcement. The present ACI 318 expression for minimum steel ratio
would be an appropriate equation for all concrete strengths from 3000 to 12,000 psi (21 to 83 MPa).6.28 6.3.5 Shear and diagonal tension- In current US. practice, design for shear is based on conditions at factored loads. The total shear resistance is made up of two parts: V s provided by the stirrups and V c , nominally the “concrete contribution.” The nominal concrete contribution includes, in an undefined way, the contributions of the still uncracked concrete at the head of a hypothetical diagonal crack, the resistance provided by aggregate interlock along the diagonal crack face, and the dowel resistance provided by the main reinforcing steel. High-strength concrete loaded in uniaxial compression fractures suddenly and, in so doing, may form a failure surface that is smooth and nearly a plane. 6.1-6.3 This is in contrast to the rugged failure surface characteristic of lower-strength concrete. In beams controlled by shear strength, the state of stress is biaxial, combining diagonal compression in the direction from the load point to the support with diagonal tension in the perpendicular direction. Diagonal tension cracks in high-strength concrete beams can be expected to have a smooth surface, likely to be deficient in aggregate interlock. Tests confirm that aggregate interlock decreases as concrete strength increases. Thus, a shear strength deficiency may be produced which is not accounted for by present design equations. Data from Frantz 6.38,6.39 at the University of Connecticut have indicated that the calculated concrete contribution V c is ade uate for highstrength concrete. Data byNilson 6.40,6.41 at Cornell University indicates that current design methods are not conservative for high strength concrete. Experimental re6.42,6.43 search by Ahmad et al. indicates that the shear strength contribution of the concrete is conservatively predicted by ACI 318-83 Eq. (11-3) for shear-span ratios of 2.5 or less, but for higher ratios, more typical in ordinary construction, and for relatively low steel ratios, the ACI equation may be unconservative. It was further
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ACI COMMlTTEE REPORT
shown by their research that the more complex ACI 318Chapter 5 may be used unless actual values of modulus 83 Eq. (11-6) is unconservative for high-strength concrete are known. beams with low steel ratios. Recent research by Russell and Roller 6.37 indicates that, for beams with high flexural E c = 40,000 + 1.0 x 10 6 psi steel ratios, the current AC I Code equations are safe. The beneficial effects of high-strength concrete for pre(6-12) + 6900 MPa) ( E c = 3320 stressed beams was demonstrated, using an analysis based on truss models, by Kaufman and Ramirez.6.44 Higher Eq. (6.12) should be modified by the correction factor strength concrete increases the strength of the diagonal (w/c/145)1.5 [for SI units (wc/2300)1.5 for concrete densities truss members, resulting in increased efficiency of the other than 145 lb/ft3 (2320 kg/m 3). 6.2,6.13,6.46 web reinforcement through the mobilization of more stirThe modulus of rupture has been discussed in Section rups as well as increased load-carrying capacity of the 6.3.7. For prediction of deflections a value of 7.5 struts themselves. Currently, no research data are availmay be used to calculate the flexural cracking moment of able regarding the minimum requirement of web reinforthe beam. The eauation for effective moment of inertia cement to prevent brittle failure resulting from the I e included in the ACI 318 is formation of a critical diagonal crack. 6.3.6 Bond, anchorage, and development lengthPresent AC I 318 methods of design for development length and anchorage of tensile steel are based on tests, (6-13) generally using concretes with compressive strengths not greater than about 4000 psi (28 MPa). Although some information has recently become available for high-strength where M cr cracking moment concrete, not enough data have been obtained to permit M maximum moment recommendations. = gross moment of inertia of section I g 6.3.7 Cracking-The modulus of rupture, which is the I cr = moment of inertia of cracked transformed appropriate measure of concrete tensile strength for use section in predicting flexural cracking load, has been reported in =
a
Chapter 5 to be 11.7 for normal weight concretes with strengths in the range from 3000 to 12,000 psi (21 to 83 MPa). It thus appears that the ACI 318 value of 7.5 is too low. However, for curing conditions such as seven days moist curing followed by air drying, a value of
=
This provides a basis for beam deflection calculation that appears valid for high-strength concrete as well as normal concrete beams, based on information currently availablee 6.34,6.47,6.48
6.3.9 Time-dependent deflections-Time-dependent deflections of beams due to creep and shrinkage are 7.5 is probably fairly close for the full strength range. It may, therefore, be recommended with no presently calculated by applying multipliers to computed change. The assumption of a modulus of rupture lower elastic deflections. This procedure is generally valid for than the actual value for a flexural member is neither high-strength concrete members, but experimental data indicates that the multipliers may be significantly less conservative nor unconservative but simply results in an inaccurate prediction of cracking load. This will result in because of the lower creep coefficient typical of highstrength concrete. According to ACI 318, additional longinaccurate estimation of both elastic and creep deflecterm deflections are obtained using the following multitions. The direct tensile strength is seldom measured but is plier of interest in studying web-shear cracking in prestressed concrete members, for one example. Both modulus of rupture and tensile splitting strength of high-strength 1 + concrete are well above the corresponding values for lower-strength concrete. In this respect, at least, emwhere pirically derived equations for flexural shear and torsional = reinforcement ratio for nonprestressed shear strength could be used for high-strength concrete compression reinforcement calculations based on the lower-strength material. How= time-dependent factor ever, other aspects of concern are discussed in Section 6.3.5. The time-dependent factor is given by Fig. 6.8, taken 6.3.8 Elastic deflections--The main uncertainties in from ACI 318R. predicting elastic deflections of reinforced concrete Research in progress,6.47,6.48 providing an indication of beams are (a) elastic modulus E c; (b) modulus of rupture long-term multipliers and their variation with time, is f r ; and (c) effective moment of inertia, which depends on summarized in Fig. 6.9. Results are currently available up
HIGH STRENGTH CONCRETE
0 1 3 6
12
24
18
30
36
48
60
Duration of Load , months
Fig. 6.8-ACI 318R Commentary multiplier for long-time deflections of beams
Multiplier
0 0
l00
30 0
200
Duration of Load, days
Multiplier
psi I
100
200
30 0
Duration of Load, days
Multiplier
I
l00
200
30 0
Duration of Load, days
Fig. 6.9-- Multipliers for long-term deflections for different strength concrete beams
a. For 3600 psi (2.5 MPa) concrete beams, l-year multipliers of 0.85, 0.60, and 0.50 for beams with p’ /p, respectively, equal to 0, 0.5, and 1.0 are less than the ACI 318 l-year values of 1.40, 1.10, and 0.80, which were determined for lower-concrete strengths. b. For high-strength concrete beams, deflection multi pliers are still lower than the ACI 318 values. For ex-
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ample, for high-strength beams with no compression steel, the value of 0.55 at 1 year is only 40 percent of the ACI 318 value and 65 percent of the experimental value for lower-strength concrete. c. The influence of compression steel may be less im portant for high-strength concrete beams than for lowerstrength beams. For beams of lower-strength concrete, addition of compression steel having an area equal to that of the tensile steel reduces l-year deflections by 41 percent. For high-strength concrete, the beam with com pression steel shows about 35 percent reduction. This could be expected because the role of compression steel is mainly to reduce the creep of the concrete in the com pression zone under sustained loads, the high-strength concrete with lower creep coefficient needs less help in this respect. Deflection measurements are continuing in the research described. Results over a longer period of time will be available as well as information for beams with compressive strengths f c' to 12,000 psi (83 MPa). Concrete strength should appear as a parameter in equations to predict long-term deflections. Concrete strength not only influences long-term deflections directly because of the lower creep coefficient but also influences the effectiveness of compression steel. 6.3.10 Repeated Loading-With reference to Section 6.2.3, it appears that high-strength concrete, because of its relative freedom from internal microcracking at service loads, would be more resistant to repeated loading consisting of a large number of cycles at relatively low stress ranges such as in bridges. If ductility is an im portant consideration, as is the case in seismic resistant design, it would be important to include lateral confinement steel in the form of closed hoop stirrups as well as compression reinforcement. While the subject has been thoroughly studied for lower-strength concrete,6.20,6.22,6.23 little information on high-strength concrete beams subject to repeated loads is available at this time. 6.3.11 Prestressed concrete beams-Characteristics of high-strength concrete, discussed previously in this chapter in the context of axially loaded members and reinforced concrete beams, affect the behavior of prestressed concrete beams in corresponding ways. Special mention must be made, however, of the effects of a very low creep coefficient. At the same concrete stress levels, time-dependent deflection of high-strength beams will be less. On the other hand, low concrete creep may have little effect on prestressed beam deflections because upward creep deflection due to prestress is, in many cases, canceled by downward creep deflection due to sustained loads. This results in only very small net d eflections associated with all sustained loads. For a given level of concrete stress, loss of prestress force due to creep could be expected to be much smaller for prestressed beams using high-strength concrete. Higher sustained concrete stress would negate this advantage.
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ACI COMMITTEE REPORT
6.4-Eccentric columns 6.4.1 Compressive stress distribution-It was pointed out
in discussing beams in Section 6.3.1 that the shape of the
3000
compressive stress distribution in high-strength concrete beams is apt to be different from that in lower-strength concrete beams, reflecting the different shape of the compressive stress-strain curve as shown in Fig. 6.1. For under-reinforced concrete beams, with strength con2000 Nominal Axial trolled by the yield strength of the reinforcement, the Load Strength actual shape of the compressive stress block used in calat given culation of the nominal flexural strength is of little Eccentricity P kips importance so long as the internal lever arm to the com pressive resultant is close to the true value. The con1000 ventional rectangular stress block and equations for determining nominal flexural strength based on the rectangular stress block will normally be satisfactory. Overreinforced beams are not permitted according to ACI 318, and so one concludes that present procedures will 0 produce adequate results for all beams designed under provisions of ACI 318, whether lower- or high-strength Moment concrete is used. Fig. 6.10-- Comparative interaction diagrams for highIn the case of combined bending and axial load, i.e., eccentric columns, members failing in flexural compres- strength concrete column sion cannot be avoided. For members with relatively low strain limit in compression of 0.003. It has been shown in eccentricity, failure will be initiated by the concrete Section 6.3.2 that this is less conservative for highreaching its limiting strain, while the steel on the far side of the column may be well below tensile yielding or may strength concrete than for lower-strength concrete. In the n,
remain in compression at the failure load. For such cases, a more accurate representation of the concrete compressive stress block could be important. 6.4.2 Interaction diagram for strength of short columns-
presence of effective lateral confinement, such as provided by continuous spirals in normal weight concrete columns, the effective strain limit is larger than this value, and strain compatibility analysis can be based on 0.003 strain. However, there is no apparent justification for increasing limiting strain assumptions above present values. 6.4.3 Slenderness effects-The moment magnification method for dealing with slenderness effects in reducing the strength of reinforced concrete columns appears to be generally valid for high-strength concrete. An exception may be in the equations for calculating effective flexural rigidity. Two alternative equations are given in ACI 318 for flexural rigidity, both of which include factors to account for the effect of concrete creep in an approximate way. The validity of these equations for high-strength concrete may at least be questioned, recognixing the significantly lower creep coefficient for highstrength concrete. No experimental information is available at this time. In addition, calculations should incorporate estimates of E c as given by Eq. (6-12).
Limited analytical studies have been made of eccentric columns comparing the predictions of the current ACI 318R Commentary approach based on the equivalent rectangular stress block, with a trapezoidal concrete stress 6.49 distribution. The general shape of the trapezoid would vary, ranging from nearly rectangular for lower-strength concrete to nearly triangular for very-high-strength as discussed in Section 6.3.1. Fig. 6.10 shows a comparison of the strength interaction diagram relating axial load capacity P n and flexural capacity M n for a 14 x 14 in. column made of 12,000 psi (83 MPa) strength concrete. Reinforcement is provided by four No. 11 comer bars having yield strength f y = 60,000 psi (414 MPa). Strength under combined axial load and bending was computed first using the conventional rectangular stress block (solid line), then using a variable-proportioned trapezoid (dashed line). For relatively large eccentricities, when moment dom- 6.5-Summary 6.5.1 Review-A brief summary has been given of the inates and failure is initiated by tensile reinforcement yielding, the two curves are almost indistinguishable. For special characteristics of high-strength concrete as they intermediate to small eccentricities, ACI 318 results in bear upon the behavior and design of reinforced concrete members and structures. larger values for both moment and axial force at a given For axially loaded columns, the direct addition of coneccentricity at failure than those obtained by the more exact calculation. Differences of up to 15 percent in the crete and steel strength contributions is generally valid, as for lower-strength concrete members. Lateral steel interaction diagram relating moment to axial load have 6.49 plays a particularly important role in that it is necessary been found based on comparative calculations. to improve ductility and toughness. Of special concern is ACI 318 procedures in corporate an assumed concrete
HIGH STRENGTH CONCRETE
the sharp drop-off of load after peak stress and the apparent diminished effectiveness of lateral steel in increasing ductility compared with lower-strength concrete columns. Further studies are needed. High-strength concrete columns will exhibit less shortening under load than lower-strength concrete columns because of the higher elastic modulus and lower creep coefficient. For beams, use of the conventional equivalent rectangular stress block appears to give satisfactory results for under-reinforced members required by ACI 318 procedures. The compressive strain limit is less than found for lower-strength concrete but still may be taken at 0.003. Confinement steel and compressive steel should be used in designing concrete beams where ductility is im portant as for seismic resistant structures. Changes have been recommended for ACI 318 values for minimum tensile steel ratio to reflect the influence of concrete strength, as well as in the modulus of elasticity to be used in deflection calculations. Significant changes should also be considered in the calculation of long-term beam deflections to reflect the much lower creep coefficient and reduced effectiveness of compression steel in the case of high-strength concrete beams. The calculation of eccentric column strength may be influenced by the shape of the compressive stress block used, particularly for columns with relatively small eccentricity with neutral axis at failure close to an edge. Limited trial calculations comparing rectangular stress block with trapezoidal stress block indicate only small differences. In determining slenderness effects, special consideration should be given to the lower creep coefficient for high-strength concrete, as it affects the effective flexural rigidity used in the calculations, and to improved values of modulus of elasticity. 6.5.2 Research needs-The material of Chapter 6 should be considered to be subject to revision based on future research results. Areas in which information is lacking include shear, diagonal tension, torsion, bond, anchorage, development length, and the effects of re peated loading. Research programs are now in progress in several centers that are aimed at filling some of these gaps. In this way, the research base will be expanded so that the many advantages of high-strength concrete may be used safely and with confidence based on thorough documentation of material properties and behavioral characteristics of members. 6.6-Cited references
(See also Chapter l0--References) 6.1. Carrasquillo, Ramon L.; Nilson, Arthur H.; and Slate, Floyd O., “Microcracking and Engineering Pro perties of High-Strength Concrete,” Research Report No. 80-1, Department of Structural Engineering, Cornell University, Ithaca, Feb. 1980, 254 pp. 6.2. Carrasquillo, Ramon L.; Nilson, Arthur H.; and Slate, Floyd O., “Properties of High Strength Concrete Subject to Short-Term Loads,” ACI JOURNAL , Proceedings V. 78, No. 3, May-June 1981, pp. 171-178.
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6.3. Carrasquillo, Ramon L.; Slate, Floyd 0.; and Nilson, Arthur H., “ Microcracking and Behavior of High Strength Concrete Subject to Short-Term Loading,” ACI JOURNAL, Proceedings V. 78, No. 3, May-June 1981, pp. 179-186.
6.4. “High Strength Concrete in Chicago High-Rise Buildings,” Task Force Report No. 5, Chicago Committee on High-Rise Buildings, 1977, 63 pp. 6.5. Kaar, P.H.; Hanson, N.W.; and Capell, H.T., “Stress-Strain Characteristics of High-Strength Concrete,” Douglas McHenry International Symposium on Concrete and Concrete Structures, SP-55, American Concrete Institute, Detroit, 1978, pp. 161-185. Also, Research and Development Bulletin No. RD051.01D, Portland Cement
Association. 6.6 Perenchio, William F., and Klieger, Paul, “Some Physical Properties of High Strength Concrete,” Research and Development Bulletin No. RD056.01T, Portland Cement Association, Skokie, 1978, 7 pp. 6.7. Shah, S.P., Editor, Proceedings, National Science Foundation Workshop on High Strength Concrete, University of Illinois at Chicago Circle, Dec. 1979, 226 pp. 6.8. Wang, P.T.; Shah, S.P.; and Naaman, A.E., “Stress-Strain Curves of Normal and Lightweight Concrete in Compression,” ACI JOURNAL , Proceedings V. 75, No. 11, Nov. 1978, pp. 603-611. 6.9. “Research Needs for High-Strength Concrete,” reported by ACI Committee 363, ACI Materials Journal, Proceedings V. 84, No. 6, Nov.-Dec. 1987, pp. 559-561. 6.10. Proceedings of Symposium on Utilization of HighStrength Concrete, Stavanger, Norway, June 15-18, 1987, Tapir Publishers, N-7034 Trondheim-NTH, Norway, 688 pp. 6.11. Nilson, A.H., “Design Implications of Current Research on High-Strength Concrete,” High-Strength Concrete, SP-87, American Concrete Institute, Detroit, 1985, pp. 85-118. 6.12. Martinez, S., Nilson, AH., and Slate, F.O., “Spirally-Reinforced High-Strength Concrete Columns,” Research Report No. 82-10, Department of Structural Engineering, Cornell University, Ithaca, Aug. 1982. 6.13. Martinez, S., Nilson, AH., and Slate, F.O., “Spirally-Reinforced High-Strength Concrete Columns, ACI JOURNAL , Proceedings V. 81, No. 5, Sept.-Oct. 1984, pp. 431-442. 6.14. Ahmad, S.H., and Shah, S.P., “Stress-Strain Curves of Concrete Confined by Spiral Reinforcement,” ACI JOURNAL , Proceedings V. 79, No. 6, Nov.-Dec. 1982, pp. 484-490. 6.15. Fafitis, A., and Shah, S.P., “Lateral Reinforcement for High-Strength Concrete columns,” HighStrength Concrete, SP-87, American Concrete Institute, Detroit, 1985, pp. 213-232. 6.16. Yong, Y.K., Nour, M.G., and Nawy, E.G., “Behavior of Laterally-Confined High-Strength Concrete Under Axial Loads,” Journal of Structural Engineering, V. 114, No. 2, Feb. 1988, pp. 332-351. 6.17. Slate, F.O., Nilson, A.H., and Martinez, S.,
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“ Mechanical Properties of High-Strength Lightweight Dependent Behavior of Columns in Water Tower Place,” Douglas McHenry International Symposium on Concrete Concrete,” ACI JOURNAL , Proceedings V. 83, No. 4, Julyand Concrete Structures, SP-55, American Concrete InstiAug. 1986, pp. 606-613. 6.18. Vallenas, J.; Bertero, V.V.; and Popov, E.P., tute, Detroit, 1978, pp. 347-373. Also, Research and “ Concrete Confined by Rectangular Hoops and Subjected Development Bulletin No. RD052.01B, Portland Cement to Axial Loads,” Report No. UCB/EERC-77/13, Earth- Association. 6.31. Leslie, Keith E.; Rajagopalan, K.S.; and Everard, quake Engineering Research Center, University of Cali Noel J., “ Flexural Behavior of High-Strength Concrete fornia, Berkeley, 1977. 6.19. Sheikh, S.A. and Uzumeri, S.M., “Strength and Beams,” ACI JOURNAL , Proceedings V. 73, No. 9, Sept. 1976, pp. 517-521. Ductility of Tied Concrete Columns,” Journal of Structur6.32. Nedderman, H., “Flexural Stress Distribution in al Division, ASCE, V. 106, No. ST5, May 1980, pp. 1079Very-High Strength Concrete,” MSc thesis, University of 1102. Texas at Arlington, Dec. 1973, 182 pp. 6.20. Bennett, E.W., and Muir, S.E. St. J., “Some 6.33. Zia, Paul, “Structural Design with High Strength Fatigue Tests on High Strength Concrete in Uniaxial Concrete,” Report No. PZIA-77-01, Civil Engineering Compression,” Magazine of Concrete Research (London), Department, North Carolina State University, Raleigh, V. 19, No. 59, June 1967, pp. 113-117. 6.21. Ahmad, S.H., “Properties of Confined Concrete Mar. 1977, 65 pp. 6.34. Pastor, J.A.; NiIson, A.H.; and Slate, F.O., Subject to Static and Dynamic Loading,” PhD thesis, “ Behavior of High Strength Concrete Beams,” Research University of Illinois at Chicago Circle, Mar. 1981. 6.22. Bertero, V.V.; Bresler, B.; and Liao, H., Report No. 84-3, Department of Structural Engineering, “Stiffness Degradation of Reinforced Concrete Members Cornell University, Ithaca, Feb. 1984. 6.35. Wang, Pao-Tsan; Shah, Surendra P.; and Subject to Cyclic Flexural Moments,” Report No. EERC69/12, University of California, Berkeley, Dec. 1969. Naaman, Antoine E., “ High Strength Concrete in Ulti6.23. Bresler, B., and Bertero, V.V., “Influence of High mate Strength Design,” Proceedings, ASCE, V. 104, ST11, Strain Rate and Cyclic Loading Behavior of Unconfined Nov. 1978, pp. 1761-1773. 6.36. Discussion of “Flexural Behavior of Highand Confined Concrete in Compression,” Proceedings, 2nd Canadian Conference on Earthquake Engineering, Strength Concrete Beams” by Keith E. Leslie, K.S. Department of Civil Engineering, McMaster University, Rajagopalan, and Noel J. Everard, ACI JOURNAL , Proceedings V. 74, No. 3, Mar. 1977, pp. 140-145. Hamilton, June 1975, pp. 15-1 - 15-38. 6.37. Russell, H., and Roller, J.J., “Shear Strength of 6.24. Ngab, AS.; Slate, F.O.; and NiIson, A.H., “Behavior of High-Strength Concrete Under Sustained High-Strength Concrete Beams,” accepted for publication in ACI Structural Journal. Compressive Stress,” Research Report No. 80-2, Depart6.38. Mphonde, A.G., and Frantz G.C., “Shear Tests ment of Structural Engineering, Cornell University, of High and Low Strength Concrete Beams Without Ithaca, Feb. 1980, 201 pp. 6.25. Ngab, Ali S.; NiIson, Arthur H.; and Slate, Floyd Stirrups,” ACI JOURNAL, Proceedings V. 81 No. 4, JulyO., “Shrinkage and Creep of High Strength Concrete, Aug. 1984. 6.39. Mphonde, A.G., and Frantz G.C., “Shear Tests ACI JOURNAL, Proceedings V. 78, No. 4, July-Aug. 1981, of High- and Low-Strength Concrete Beams with Stir pp. 255-261. 6.26. Ngab, Ali S.; Slate, Floyd 0.; and Nilson, Arthur rups,” High-Strength Concrete, SP-87, American Concrete H., “Microcracking and Time-Dependent Strains in High- Institute, Detroit, 1985, pp. 179-196. 6.40. El-Zanaty, AH., Nilson, AH., and Slate, F.O., Strength Concrete, ACI JOURNAL , Proceedings V. 78, No. “Shear Capacity of Prestressed Concrete Beams Using 4, JuIy-Aug. 1981, pp. 262-268. 6.27. Smadi, M.M.; Slate, F.O.; and NiIson, A.H., High-Strength Concrete,” ACI JOURNAL, Proceedings V. “Time-Dependent Behavior of High-Strength Concrete 83, No. 3, May-June 1986, pp. 359-368. 6.41. El-Zanaty, A.H., Nilson, A.H., and Slate, F.O., Under High Sustained Compressive Stresses,” Research “Shear Capacity of Reinforced Concrete Beams Using Report No. 82-16, Department of Structural Engineering, High-Strength Concrete,” ACI JOURNAL, Proceedings V. Cornell University, Ithaca, Nov. 1982. 6.28. Smadi, M.M., Slate, F.O., and Nilson, A.H., 83, No. 2, Mar.-Apr. 1986, pp. 290-296. 6.42. Ahmad, S.H., Khaloo, A.R., and Poveda, A., “Shrinkage and Creep of High-, Medium-, and LowStrength Concretes, Including Overloads,” ACI Materials “Shear Capacity of Reinforced High-Strength Concrete Beams,” ACI JOURNAL , Proceedings, V. 83, No. 2, Mar.Journal Proceedings V. 84, No. 3, May-June 1987, pp. Apr. 1986, pp. 297-305. 224-234. 6.43. Ahmad, S.H., and Lue, D.M., “Flexure-Shear 6.29. Smadi, M.M., Slate, F.O., and Nilson, A.H., “High-, Medium-, and Low-Strength Concrete Subject to Interaction of Reinforced High-Strength Concrete Sustained Overloads--Strains, Strengths, and Failure Beams,” ACI Structural Journal, V. 84, No. 4, July-Aug. 1987, pp. 330-341. Mechanisms,” ACI JOURNAL , Proceedings V. 82, No. 5, 6.44. Kaufman, M.K., and Ramirez, J.A., “Re-evalSept.-Oct. 1985, pp. 657-664. 6.30. Russell, H.G., and Corley, W.G., “Time- uation of the Ultimate Shear Behavior of High-Strength
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Concrete Prestressed I-Beams,” ACI Structural Journal, Proceedings V. 85, No. 3, May-June 1988, pp. 295-303.
amount of reinforcing steel equal to 4 percent of the column area for a given load, whereas the same column in 9,000 psi would require only 1 percent steel-the minimum allowed by code." 7.3
6.45. Treece, R.A., and Jima, J.O., “ Bond Strength of Epoxy-Coated Reinforcing Bars,” ACI Materials Journal, V. 86, No. 2, Mar.-Apr. 1989. 6.46. Pauw, Adrian, “ Static Modulus of Elasticity of 7.2-Cost studies The Material Service Corporation 7.4 conducted a Concrete as Affected by Density,” ACI J OURNAL , Pro pricing study that dramatically demonstrated the cost ceedings V. 57, No. 6, Dec. 1960, pp. 679-688. 6.47. Leubkeman, C.H., Nilson, A.H., and Slate, F.O., advantage of replacing percentages of steel with high“ Sustained Load Deflection of High-Strength Concrete strength concrete in short tied columns. This 1983 study was made for a column supporting a design load (1.4D Beams,” Research Report No. 85-2. Department of Struc+ 1.7L) of 1000 kips (4.45 MN) and based on the followtural Engineering, Cornell University, Ithaca, Feb. 1985, ing prices: 164 PP. 6.48. Paulson, K.A., and Nilson, A.H., “Deflections of $760/ton in place Reinforcing steel High-Strength Concrete bea ms Un der Sus tai ned $80/yd 3 in place 7000 psi concrete Loading,” Research Report (in preparation), Department $85/yd 3 in place 9000 psi concrete of Structural Engineering, Cornell University, Ithaca. 3 $104/yd in place 11,000 psi concrete 6.49. Garcia, D.T., and Nilson, AH., “ A Comparative $129/yd 3 in place 14,000 psi concrete Study of Eccentrically Loaded High-Strength Concrete $280/yd 3 in place Formwork Columns,” Research Report (in preparation), Department of Structural Engineering, Cornell University, Ithaca. As Fig. 7.1 shows, using high-strength concrete with a minimum of steel is the most economical solution. CHAPTER 7-- ECONOMIC CONSIDERATIONS Compressive Strength , MPa 30
60 I
80
I As earlier chapters have demonstrated, high-strength concrete is a state-of-the-art material, and like most Cost of 40 x 40 in. state-of-the-art materials, it commands a premium price. Column per Foot of 20 In some instances, the benefits are well worth the addiLength per 1000 tional effort and expense; in others they are not. Before kips of Design Load the cost/benefit trade-offs in specific applications are 10 $ discussed, the economic considerations regarding the use of high-strength concrete generally will be examined. In many areas and for many uses, the benefits of highI I 14 12 6 IO strength concrete more than compensate for the in8 creased costs of raw materials and quality control. Compressive Strength , ksi Basically, high-strength concrete will carry a compression 7. 1 Fig. 7.1-- Cost of columns load at less cost than any lower-strength concrete. Chicago-based structural engineers William Schmidt and 7.3-Case histories Edward S. Hoffman compiled charts indicating the cost Two examples might help translate this savings into of supporting 100,000 lb (445 kN) of service load comes actual dollars. to $5.02 per story with 6000 psi (41 MPa) concrete, $4.21 7.3.1 Case history No. 1-In 1968, Philadelphia’s first with 7500 psi (52 MPa), and drops to $3.65 with 9000 psi high-rise office building using 6000 psi (41 MPa) concrete (62 MPa) concrete (which the authors report they had no 7.2 was designed. To meet the span requirements [approxidifficulty obtaining in the Chicago area). mately 30 ft (9m) square bays] while avoiding unacceptWhile the figures reflect 1975 costs, the ratio should able oversized columns on the lower floors, the columns remain similar. The reason for these economies is that, of the first three floors were built of structural steel. although the concrete itself is more costly than lowerHowever, a comparison study made by the designing enstrength mixtures, the cost differential is offset by siggineers for 8000 psi (55 MPa) concrete showed that nificant reduction in the given member size. This capa7.3.1.1- With the same column sixes as the original bility is particularly attractive for use in columns. unacceptable sixes, a 60 percent reduction in reinforcing Since column size is so important for architectural and rental reasons, the ability to limit the sixes for taller steel with the 8000 psi (55 MPa) concrete would have structures often allows the use of a concrete solution in been made. This would also have resulted in 24 fewer splices per column, a side benefit in labor and time cost lieu of one of structural steel. In 1976, Architectural Record noted that ". . . a 30 x savings. 7.3.12- With the same amount of reinforcing used 30-in. column of 6,000 psi concrete might require an
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as in the original column, the column size could have been reduced from 36 x 46 in. (915 x 1170 mm) to 30 x 30 in. (760 x 760 mm). This size would have been acceptable to the architect and owner and would have eliminated the need for an additional trade-structural steel-on the job. Rough calculations show that 8000 psi (55 MPa) concrete for the lower-floor columns with a stepped strength reduction, as the building reached the upper floors, to 3000 psi (21 MPa) concrete at the top would have resulted in a column size that met the demands of the architect, owner, and rental agent. This would have saved close to $530,000 in 1968 dollars. 7.3.2 Case history No. 2-- The economies of highstrength concrete were more dramatically demonstrated in the construction of New York City’s first building using 8000 psi (55 MPa) concrete, The Palace Hotel built in 1979. The building was originally conceived using structural steel for the lower floors, designated for ballroom and restaurant functions, with a reinforced concrete superstructure for the hotel facilities. However, the engineers were able to convert the entire design, except for two columns on the lowest four levels, to reinforced concrete through the use of 8000 psi (55 MPa) concrete. These ballroom and restaurant areas required large column spacing. The common limitations of 6000 psi (41 MPa) concrete would have made the columns prohibitively large and uneconomical. A presentation to the New York City Building Department about the values of high-strength concrete, together with the proposed controls to insure quality, resulted in its acceptance for use in New York. Concrete with compressive strengths of 8000 and 7000 psi (55 and 48 MPa) was used in the columns of the building only. Lightweight concrete with compressive strength of 3500 psi (24 MPa) was used for floor slabs, and 5000 to 6000 psi (34 to 41 MPa) concrete was used in wall construction. On the lower five levels of the hotel, column sixes were reduced by approximately 25 percent. Approximately 10 percent less reinforcing steel was used because of the strength of the concrete. In addition, No. 11 reinforcing bars remained a viable size, avoiding the need for mechanical connections between the reinforcing bars, thus considerably reducing the floor-framing time requirements. Further economies were realized by minimixing changes in column sixes and reducing column reinforcement on the upper floors. The ability to reduce the amount of costly reinforcing steel without sacrificing strength is an attractive benefit to owners, builders, and engineers, but the use of highstrength concrete in building columns has a corollary economic benefit. It enables the lower floors of high-rise buildings to maintain an acceptable column size, while at the same time increasing the number of possible stories 7.1 This is a case of a relatively new material meeting the needs of market economics. The Chicago Committee 7. 5 noted “The potential number of stories in study
high-rise buildings is limited by the required large columns if they were to be built with ordinary lowstrength concrete. Real estate properties in prime locations had to be developed with maximum rental floor area. Architectural layout of apartment or condominium units demanded flexibility, which is restricted by large columns. High-strength concrete satisfied this condition by allowing column sixes to be reduced to a minimum.” 7.4-Other studies
In Ontario, Canada, the Richmond-Adelaide Center’s use of high-strength concrete columns enabled the architect to increase the use of the underground parking 7.6 garage by approximately 30 percent. In times when all building construction is difficult to capitalize, a material that both reduces construction costs and substantially increases the amount of revenue-gathering space within a building can be a tremendous factor in the decision to build. 7.5-Selection of materials
The economic consequences of requiring fly ash may vary. On The Royal Bank Plaza Project in Ontario, Canada, a 43-story building constructed from 1973-1976 (one of the first to use fly ash in high-strength concrete), all of the various strength concrete mixtures on the project were converted to local fly ash. This resulted in a saving of approximately $100,000 over the contract and produced concretes with extremely good fresh and hardened 7.6 pro perties. The Scotia Plaza-A 68-story building in Toronto, Canada, constructed in 1988--is one of the first buildings to employ the use of silica fume in concrete as an element in increasing strength. Strengths of up to 10,000 psi have been achieved. Two Union Square in Seattle em ploys 19,000-psi concrete containing silica fume-the highest strength used to date in a conventional building. 7.6-Quality control
While selection of materials will influence costs, another factor, and one more exclusively the result of the use of high-strength concrete, is the cost of the increased testing, quality control, and inspection that the use of high-strength concrete requires. The quality and consistency of the concrete is crucial, and additional steps must be taken to insure that quality and consistency. In the Royal Bank Plaza Project, a number of precautions were necessary. The supplier had to have a quality control person at the site to control both the scheduling of trucks and the consistency of the concrete at the time it was delivered. For this central plant project, the supplier agreed that there would be no water added to the trucks after they had come onto the site and that any minor adjustments would be made prior to sending the truck to the site. Regular visits were made to the batch plant to check batching procedures and to obtain the test samples. Furthermore, a full-time technician was employed to carry out sampling and testing on site. This was
HIGH STRENGTH CONCRETE
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found to be an essential feature of quality control. premium material such as high-strength concrete for On a later project, Richmond-Adelaide Center, Phase slabs or beams. II, Ontario, Canada, 1977-1979, by the same engineers, Long-span bridges are another area where the qualinot only did the supplier maintain full-time inspection on ties of high-strength concrete are proving themselves economically attractive. High-strength concrete’s comthe site to insure that the delivered material met requirements but the engineers employed by the owner also paratively greater compressive strength per unit weight maintained full-time inspection and regularly inspected and unit volume allows lighter, more slender bridge piers. This provides improved horizontal clearances. In addithe batch plant. Often this type of stringent quality tion, the increased stiffness of high-strength concrete is control is required by regulation. For The Palace Hotel, advantageous when deflections or stability govern the the New York City Building Department stipulated that at least two suppliers of concrete prequalify the concrete bridge design. Increased tensile strength of high-strength concrete is helpful in service load design in prestressed mixtures to strengths up to 8000 psi (55 MPa). The pre7. 9 concrete. qualification was to be performed by an independent In bidding to build a cable-stayed bridge across the testing laboratory, and a full-time professional engineer would be required to continuously inspect the progress of Ohio River, a concrete deck proposal beat steel by 29 the work, performing no other work during the construc- percent-roughly $10 million. The two-lane crossing between Huntington, West Virginia, and Proctorville, Ohio, tion.7.7 For hot weather concreting, the engineers required mixing water limited to no more than 50 F (10 C) includes the first major asymmetrical stayed-girder structure in the United States. The bridge has a main span of and the truck drums to be hosed down if standing in 3 direct sunlight. Further, all trucks were limited to 10 yd 900 feet over one pier. The three bids to construct the 3 3 3 (7.6 m ) loads, despite capacities of 16 yd (12.2 m ). bridge using concrete ranged from $23.5 million to $29.7 million, all well below the lowest steel bid ($33.3 million). While the professional inspection does add to cost, the The designer, Arvid Grant Associates, specified box gircontinuing education of the suppliers and concrete subders only 5 ft (1.5 m) deep cast of 8000 psi (55 MPa) contractors in the areas of quality control should ulhigh-strength concrete. 7.8 timately create better concretes of all strengths and result in better and more economical use of materials. 7.8-Conclusion
The economic benefits of high-strength concrete are In general, the economic advantages of high-strength just now becoming fully apparent. Certainly as the use of concrete are most readily realized when the concrete is high-strength concrete increases, additional and possibly used in the columns of high-rise buildings. In this applieven greater benefits will be realized. In any case, those cation, engineers may take full advantage of its increased projects that have led the way in the use of high-strength compressive strength: reducing the amount of steel, reconcrete have clearly demonstrated its economic advantages. For now, it allows the profession to engineer most ducing column size to increase usable floor space, or allowing additional stories without detracting from lower cost effectively and space effectively. In the future, those floors. These benefits overshadow the increased quality considerations may tip the balance on whether certain control costs and possible higher cost of raw materials projects are constructed at all. discussed earlier. Yet the use of high-strength concrete 7.9-Citedreferences has also spread to other applications, primarily slabs, beams, and long-span bridges. The economic considera(See also Chapter 10--References) tions of these uses should also be examined. 7.1. “High Strength Concrete--Costs More in the Parking garages, bridge decks, and other installations Truck, Costs Less in the Structure,” PCA Concrete Techrequiring improved density, lower permeability, and in- nology Today, No. 4, Dec. 1980, p. 3. creased resistance to freeze-thaw and corrosion have 7.2. Schmidt, William, and Hoffman, Edward S., become prime candidates for consideration of the use of “9,000-psi Concrete-Why?, Why Not?,” Civil Engineering high-strength materials. -ASCE, V. 45, No. 5, May 1975, pp. 52-55. The primary advantage of high-strength concrete in 7.3. “High-Strength Concrete Allows Bigger Loads on slabs is the resulting reduction in dead load. 7.8 However, Smaller Columns,” Architectural Record, V. 159, No. 7, as Schmidt and Hoffman point out, significant economies June 1976, pp. 133-135. can be achieved only by reducing the thickness that is 7.4. Private correspondence from J. Moreno of required for stiffness; the additional reinforcement Material Service Corp. to Irwin G. Cantor, May 12, 1983. required may offset the concrete savings. Used for rec7.5. “High-Strength Concrete in Chicago High-Rise tangular beams, T-beams, and one-way slabs, high- Buildings,” Task Force Report No. 5, Chicago Committee strength concrete yields reduced section width or thickon High-Rise Buildings, Feb. 1977, 63 pp. ness and allows for longer spans, but (as with slabs) less 7.6. Bickley, John A., and Payne, John C., “High expensive lightweight concrete continues to perform this Strength Cast-in-Place Concrete in Major Structures in job satisfactorily. Presently, there is no economic justiOntario,” paper presented at the ACI Annual Convenfication, under normal circumstances, for the use of a tion, Milwaukee, Mar. 1979. 7.7-Areas of application
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7.7. Private correspondence from J. T. Walsh, Department of Buildings, New York, to Irwin G. Cantor, Aug. 11, 1977.
7.8. “Concrete Beats Steel by 29%,” Eng ineering News-Record, V. 206, May 14, 1981, p. 16. 7.9. Carpenter, James E., “Applications of High Strength Concrete for Highway Bridges,” Public Roads, V. 44, No. 2, Sept. 1980, pp. 76-83. CHAPTER 8-APPLICATIONS
Some specific applications of high-strength concrete are described in this chapter. Separate sections describe applications in buildings, bridges, and special structures. The applications are not all-inclusive but demonstrate a range of applications of high-strength concrete. Some potential applications for high-strength concrete are also discussed.
8.2-Buildings
The largest application of high-strength concrete in buildings has been for columns of high-rise structures. The history of high-strength concrete columns in the Chicago area has been described in Task Force Report No.58.1 of the Chicago Committee on High-Rise Build-
ings. Since 1972, more than 30 buildings in the Chicago area have been constructed with columns having a design compressive strength of 9000 psi (62 MPa). The development of concrete for use in two buildings in Toronto has 8.2 Other applica been reported by Bickley and Payne. 8.3 8.4,8.5 tions have been reported in New York, Houston, Minneaplis, 8. 6 Melbourne, Australia,8.7 Dallas, 8.25 and 8.26 Seattle. Information obtained from these and other sources is summarized in Table 8.1. 8.3-Bridges
There have been many applications of high-strength concrete in precast prestressed bridge girders. However, published information on actual structures is limited.
Table 8.1-- Buildings with high-strength concrete
Total Building
Location
S.E. Financial center Petrocanada Building Lake Point Tower 1130 S. Michigan Ave. Texas Commerce Tower Helmsley Palace Hotel Trump Tower City Center Project Collins Place Larimer Place Condominium 499 Park Avenue Royal Bank Plaza Richmond-Adelaide Center Midcontinental Plaza Water Tower Place River Plaza Chicago Mercantile Exchange Columbia Center Interfirst Plaza Eugene Terrace 311 S. Wacker Drive 900 N. Michigan Annex Two Union Square 225 W. Wacker Drive
Miami Calgary Chicago Chicago Houston New York New York Minneapolis Melbourne Denver New York Toronto Toronto Chicago Chicago Chicago
Scotia Plaza
Toronto
Chicago
Seattle Dallas Chicago Chicago Chicago
Seattle Chicago
Year*
1982 1982 1965
53 34 70
1981 1978
75 53 68 52 44 31 27 43 33 50 79 56 40 76 72 44 70
1981 1980 1975 1978 1972 1975 1976 1982 1983 1983 1987 1988 1986 1987 1988 1988
* Year in which high-strength concrete was cast. experimental columns of 11,000 psi strength were included. Two experimental columns of 14,000 psi strength were included. l
* 19,000 psi indirectly specified to achieve a high modulus of elasticity.
15
62 30 68
Maximum design concrete strength, psi 7000 7250 7500 7500 7500 8000 8000 8000 8000 8000 8500 8800 8800 9000 9000
9500 10,000 11,000 12,000 ss 14,000 14,000** 14,000 10,000
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Table 8.2-- Bridges with high-strength concrete
Year
San Diego to Coronado 8.13 Linn Cove Viaduct
Pasco-Kennewick Intercity
Coweman River Bridges 8.14
Huntington to Proctorville Annicis Bridge Nitta Highway Bridge Kaminoshima Highway Bridge Tower Road Fukamitsu Highway Bridge Ootanabe Railway Bridge Akkagawa Railway Bridge
California I North Carolina
Washington Washington W. Va. to Ohio British Columbia Japan
Japan Washington Japan Japan Japan
Maximum span, ft 158 750 140
1967 1981 1969 1979 1978
981
1984
146 900
1986
1968 1970 1987 1974 1973 1976
180
1526 98 282 161 85 79
150
Maximum design concrete strength, psi 6,000 6,000 6,000 L* 6,000 6,000 7,000 8,000 8,000 8,500 8,500 9,000 10,000 11,400 11,400
* Lightweight concrete Metric equivalent: 100 psi = 6.895 MPa
The effect of using high-strength concrete in four different solid-section girders has been described by Carpenter. 8.8 For integral deck bulb tees, span capability for closely spaced girders increased with increase in concrete strength. For wider spaced girders, capability increased when concrete strength was increased up to 8000 psi (55 MPa). Above 8000 psi (55 MPa) compressive strength, span capability did not increase because sufficient prestress forces could not be provided. Similar results were obtained for other cross sections. For post-tensioned box girder bridges, Carpenter re ported that high-strength concrete can be used to increase span capability. However, for higher-strength concretes, maximum available prestress force again limited maximum spans. For segmental box girder bridges, he showed that high-strength concrete is feasible in regions where member thickness is controlled by stress. However, where thickness is controlled by other factors, highstrength concrete may not be beneficial. Some actual bridges in which the use of high-strength concrete has been reported are listed in Table 8.2. Perhaps the most significant application in the United States is the Huntington, West Virginia, to Proctorville, Ohio, crossing for which a compressive strength of 8000 psi (55 8.9 MPa) was specified. The bridge consists of an asymmetrical stayed-girder superstructure with a main span of 900 ft (274 m). The use of concrete with compressive strengths up to 11,000 psi (76 MPa) in railway bridges in Japan has also been reported. 8.10,8.11 Nagataki 8.11 reports that strengths of 11,400 psi (79 MPa) can be easily obtained in the field in Japan. 8.4-Special applications
In 1948, concrete with a specified compressive strength of 9000 psi (62 MPa) was used for precast panels for a powerhouse at Fort Peck Dam, Montana. High-strength concrete was specified to provide an extremely dense
concrete that would withstand the harsh exposure. Actual 8.15 compressive strengths of concrete were reported to be considerably higher than 9000 psi (62 MPa). The use of 10,000 psi (69 MPa) concrete for prestressed concrete poles produced by spinning has been 8.16 m 1970. High-strength concrete described by Skrastins was selected to reduce the size of the poles. Copen 8.17 has indicated that the use of 10,000 psi (69 MPa) concrete in thin arch dams would usually result in greater economy through reduced volume of concrete. High-strength concrete would tend to reduce deflections in a dam and may improve strength of construction joints and permit earlier removal of formwork. Disadvantages of high-strength concrete listed by Copen include development of stress concentrations, particularly in the foundation for the dam; tendency toward more cracking in concrete; increased temperature control problems; and complications involved with openings through the dam and railways over the dam. The application of high-strength concrete in two 8.18 grandstand roofs has been described by Bobrowski 3 Lightweight concrete with a density of 118 lb/ft (1.89 Mg/m 3) and a minimum cube strength of 7500 psi (52 MPa) at 28 days was used in the roof beams at Doncaster racecourse, England. Roof beams at Leopardstown racecourse, Ireland, had 28 day cube compressive strengths between 7200 and 8850 psi (50 and 61 MPa) and an average density of 115 lb/ft3 (1.84 Mg/m3). Anderson has reported8.19 the use of high-strength concrete in piles for marine foundations in northwestern United States. Measured 28 day compressive strengths ranged between 7900 and 9900 psi (55 to 68 MPa). Highstrength concretes with compressive strengths up to 9400 psi (65 MPa) have also been used for decks of dock structures in the northwestern United States. In 1984, the Glomar Beaufort Sea I8.27 was placed in the arctic, This exploratory drilling structure contains about 12,000 yd3 (9200 m3) of high-strength lightweight
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Table 8.3-- Corrosion resistance data for selected high-strength concrete (data from reference 8.29) Strength (mpa) (psi) 5,160 7,360 8,580 9,290 12,120
35.6 50.8 59.2 64.1 83.6
(wt.
Chloride Permeability* (Coulombs)
Electrical Resistivity (ohm.cm)
3,663 198 98 132 75
8 95
0 15 15 8 15
18 month Corrosion Data (mv) -456 -26
11 8
-53
( 22 4 4
74
-3
1
16 1
+53
4
By weight of portland cement.
* Measured by AASHTO-T-227 rapid chloride permeability tat at 28 days age. Corrosion potential measured with respect to a copper sulfate reference electrode. is the polarization current; its reciprocal is a measure of the rate of corrosion.
3
concrete with unit weights of about 112 lb/ft (1794 3 kg/m ) with 56-day compressive strength of 9000 psi (62 3 3 MPa) and about 6500 yd (5000 m ) of high-strength nor3 mal-weight concrete with unit weights of about 145 lb/ft 3 (2323 kg/m ) and 56-day compressive strengths of about 10,000 psi (69 MPa). Field placements of high-strength, low-permeability, and chemical-resistant concretes for industrial manufac8.20 turing applications were reported by Wolsiefer. Special applications have included several modular bank vaults placed at slumps of 9 in. (230 mm) with measured compressive strengths of 12,000 psi (83 MPa) at 45 days. The protection of reinforcing steel from corrosion can be expected to be enhanced when high-strength concrete is used. The resultant low porosity should increase the electrical resistivity and reduce the rate at which oxygen reaches the steel, both of which will reduce corrosion rates. Moreover, the ease with which chloride ions from deicing salts can reach the steel and initiate corrosion is also reduced. Although there are many studies evaluating the corrosion of steel embedded in regular strength concrete, no systematic studies in the influence of concrete strength appear to have been reported. Published data for highstrength concrete can be extracted from studies investigating other factors, particularly the influence of silica fume. The conclusions obtained with regular concretes are also applicable to high-strength concrete: namely, 8.28,8.29 and a there is an increase in electrical resistivity 8.29,8.30 reduction in chloride permeability with increased strength. Data linking these parameters with laboratory corrosion data are given in Table 8.3. The corrosion behavior of a very high-strength mortar has also been re8.31 port ed . Useful discussions regarding the factors affecting the corrosion of steel in concretes with silica fume 8.31,8.32,8.33 are to be found in references. 8.5-- Potential applications
Most applications of high-strength concrete have used the strength property of the material. However, highstrength concrete may possess other characteristics that could be used advantageously in concrete structures.
8.21
LeMessurier proposed the use of high-strength concrete to satisfy the need for a high modulus of elasticity. Similarly, high-strength concrete can be used in slabs to 8.22 allow early removal of formwork and avoid reshoring. This takes advantage of both the high modulus of elasticity and lower creep of high-strength concrete. Ander8.19 son had suggested that the low creep of high-strength concrete should be taken into account when considering prestress losses. Since most of the prestress loss is attributable to creep and shrinkage, prestress losses for high-strength concrete members should be less than for lower-strength concrete members. 8.23 Rabbat and Russell have reported that the maximum span capability of solid-section girders can be increased by 15 percent when the concrete compressive strength is increased from 5000 to 7000 psi (34 to 48 8.24 MPa). Finally, Manning has suggested that the relationship between high-strength concrete and high-quality concrete may make high-strength concrete attractive not for its strength but for its long-term service performance. More recently, high-strength concrete has been specified for applications in warehouses, foundries, parking garages, bridge deck overlays, dam spillways, and heavy duty industrial floors. In these applications, high-strength concrete is being used to provide a concrete with im proved resistance to chemical attack, better abrasion resistance, improved freeze-thaw durability, and reduced permeability. 8.6-Cited references
(See also Chapter 10-References) 8.1. “High-Strength Concrete in Chicago High-Rise Buildings,” Task Force Report No. 5, Chicago Committee on High-Rise Buildings, Feb. 1977, 63 pp. 8.2. Bickley, John A., and Payne, John C., “HighStrength Cast-in-Place Concrete in Major Structures in Ontario,” paper presented at the ACI Annual Convention, Milwaukee, Mar. 1979. 8.3. “New York City Gets Its First High-Strength Concrete Tower,” Engineering News-Record, V. 202, Nov. 2, 1978, p. 22. 8.4. Pickard, Scott S., “Ruptured Composite Tube
HIGH STRENGTH CONCRETE
Design for Houston’s Texas Commerce Tower,” Concrete International: Design & Construction, V. 3, No. 7, July 1981, pp. 13-19. 8.5. Cook, James E., “Research and Application of High-Strength Concrete Using Class C Fly Ash,” Concrete International Design & Construction, V. 4, No. 7, July 1982, pp. 72-80. 8.6. Venema, T.P., and Regnier, H.J., “Placement, Batching, and Tests of High Strength Concrete for Minneapolis City Center Project,” submitted to ACI for publication. 8.7. Day, K.W., “Quality Control of 55 MPa Concrete for Collins Place Project, Melbourne, Australia,” Concrete International Design & Construction, V. 3, No. 3, Mar. 1981, pp. 17-24. 8.8. Carpenter, James E., “Applications of High Strength Concrete for Highway Bridges,” Public Roads, V. 44, No. 2, Sept. 1980, pp. 76-83. 8.9. “Concrete Beats Steel by 29%,” Eng ine ering News-Record, V. 206, May 14, 1981, p. 16. 8.10. “Stronger Concrete,” EngineeringNews-Record, V. 189, June 8, 1982, p. 12. 8.11. Nagataki, Shigeyoshi, “On the Use of Superplasticizers,” Seminar on Special Concretes, 8th FIP Congress (London, 1978), Federation Intenationale de la Precontrainte, Wexham Springs, 1978, 15 pp. 8.12. “Concrete Box Girder Span Establishes U.S. Record,” Engineering News-Record, V. 208, No. 1, Jan. 7, 1982, pp. 22-25. 8.13. Pfeifer, Donald W., “Development of the Concrete Technology for a Precast Prestressed Concrete Segmental Bridge,” Journal, Prestressed Concrete Institute, V. 27, No. 5, Sept.-Oct. 1982, pp. 78-99. 8.14. Hurlbut, Roger, “146-ft Long Precast Prestressed Bridge Girders in Washington State, “Journal, Prestressed Concrete Institute, V. 24, No. 1, Jan.-Feb. 1979, pp. 8892. 8.15. “Unusual Strengths Attained in Precast Slabs Used for Facing Power House Walls,” Concrete, V. 57, No. 5, May 10, 1949, pp. 9-10. 8.16. Skrastins, Janis I., ‘Toward High-Strength Concrete,” Modern Concrete, V. 34, No. 1, May 1970, pp. 4448. 8.17. Copen, Merlin D., “Problems Attending Use of Higher Strength Concrete in Thin Arch Dams,” ACI JOURNAL , Proceedings V. 72, No. 4, Apr. 1975, pp. 138 140. 8.18. Bobrowski, J., and Bardham-Roy, B.K., “Structural Assessment of Lightweight Aggregate Concrete,” Concrete (London), V. 5, No. 7, July 1971, pp. 229-234. 8.19. Anderson, Arthur R., “Research Answers Needed for Greater Utilization of High Strength Concrete,” Journal, Prestressed Concrete Institute, V. 25, No. 4, July-Aug. 1960, pp. 162-164. 8.20. Wolsiefer, John, “Ultra High-Strength Field Placeable Concrete with Silica Fume Admixtures,” Con-
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crete International Design & Construction, V. 6, No. 4, Apr. 1984, pp. 25-31. 8.21. Fischer, R.E., “Round Table--Concrete in Architecture: A Current Assessment,” Architectural Record, Nov. 1982. 8.22. Nilson, AH., “Structural Design Considerations for High Strength Concrete,” Proceedings, Na ti on al Science Foundation Workshop on High Strength Concrete, University of Illinois at Chicago Circle, Dec. 1979. 8.23. Rabbat, Basile G., and Russell, Henry G., “Optimized Sections for Precast, Prestressed Bridge Girders,” Journal, Prestressed Concrete Institute, V. 27, No. 4, July-Aug. 1982, pp. 88-104. 8.24. Young, F.J., and Russell, H.G., “Session V-Summary of Floor Discussion,” Proceedings, National Science Foundation Workshop on High Strength Concrete, University of Illinois at Chicago Circle, Dec. 1979. 8.25. “Tower Touches Few Bases,” Engineering News Record, V. 210, No. 24, June 16, 1983, pp. 24-25. 8.26 Godfey, K.A., Jr., “ Concrete Strength Record Jumps 36%,” Civil Engineering, V. 57, No. 10, Oct. 1987, pp. 84-88. 8.27. Fiorato, A.E., Person, A, and Pfeifer, D.W., “ The First Large-Scale Use of High Strength Lightweight Concrete in the Arctic Environment,” Second Symposium on Artic Offshore Drilling Platforms, Houston, Texas, Apr. 1984.
8.28. Vennesland. O., and Gjorv, O.E., “Silica Concrete-- Protection Against Corrosion of Embedded Steel,” Fly Ash, Silica Fume and Other Mineral By-Products in Concrete, ACI SP-79, V. 2, 1983, pp. 719-730.
8.29. Burke, N.S., and Weil, T.G., “Corrosion Protection Through the Use of Concrete Admixtures,” Supplementary Paper, Proceedings, 2nd International Conference on Performance of Concrete in the Marine Environment, St. Andrews-by-the-Sea, New Brunswick, Aug. 1988.
8.30. Preece, C.M., Frolund, T., and Bager, D.H., “Chloride Ion Diffusion in Low Porosity Silica Cement Paste,” Condensed Silica Fume in Concrete, Report BML 82.610, Norwegian Institute of Technology, Trondheim, 1982, pp. 51-58. 8.31. Preece, C.M., Frolund, T., and Bager, D.H., “Electrochemical Behavior of Steel in Dense SilicaCement Mortar,” Fly Ash, Silica Fume and Other Mineral By-Products in Concrete, ACI SP-79, V. 2, 1983, pp. 785796.
8.32. Fidjestol, P., “Reinforcement Corrosion and the Use of CSF-Based Additives,” Concrete Durability, ACI SP-100, V. 2, 1987, pp. 1445-1458. 8.33. Scali, M.J., Chin, D., and Burke, N.S., “ Effect of Microsilica and Fly Ash Upon the Microstructure and Permeability of Concrete,” Proceedings, Ninth International Conference on Cement Microscopy, International Cement Microscopy Association, Texas, 1987, pp. 375397.
ACI COMMlTTEE REPORT
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CHAPTER 9-- SUMMARY
The objective of this report was to present state-ofthe-art information on concrete with strengths in excess of about 6000 psi (41 MPa) but not including concrete made using exotic materials or techniques. This section of the report presents a summary of the material contained in the previous chapters. All materials for use in high-strength concrete must be carefully selected using all available techniques to insure uniform success. Items to be considered in selecting materials include cement characteristics, aggregate size, aggregate strength, particle shape and texture, and the effects of set-controlling admixtures, water reducers, silica fume, and pozzolans. Trial mixtures are essential to insure that required concrete strengths will be obtained and that all constituent materials are compatible. Mix proportions for high-strength concrete generally have been based on achieving a required compressive strength at a specified age. Depending on the appropriate application, a specified age other than 28 days has been used. Factors included in selecting concrete mix proportions have included availability of materials, desired workability, and effects of temperature rise. All materials must be optimized in concrete mix proportioning to achieve maximum strength. High-strength concrete mixes have usually used high cement contents, low watercement ratios, normal weight aggregate, and chemical and pozzolanic admixtures. Required strength, specified age, material characteristics, and type of application have strongly influenced mix design. High-strength concrete mix proportioning has been found to be a more critical process than the proportioning of lower-strength concrete mixes. Laboratory trial batches have been required in order to generate necessary data on mix design. In many cases, laboratory mixes have been followed by field production trial batches. Batching, mixing, transporting, placing, and control procedures for high-strength concrete are not essentially different from procedures used for lower-strength concretes. However, special attention is required to insure a high-strength uniform material. Special consideration should be given to minimizing the length of time between concrete batching and final placement in the forms. Delay in concrete placement can result in a subsequent loss of long-term strength or difficulties in concrete placement. Special attention should also be p aid to the testing of high-strength concrete cylinders since any deficiency will result in an apparent lower strength than that actually achieved by the concrete. Items deserving specific attention include manufacture, curing, and capping of control specimens for compressive strength measurements; characteristics of testing machines; type of mold used to produce specimens; and age of testing. In many instances, strength measurements at early ages have been made even though the compressive strength has not been specified until 56 or 90 days. Some research data have indicated that the modulus
of elasticity of high-strength concrete is lower than would have been predicted from data on lower-strength concretes. However, values of Poisson’s ratio appear to be in the expected range, based on lower-strength concretes. The modulus of rupture for high-strength concretes is higher than would have been anticipated. However, the tensile splitting strength values appear to be consistent with lower-strength concretes. Unit weight, specific heat, diffusivity, thermal conductivity, and coefficient of thermal expansion have been found to fall generally within the usual range for lower-strength concretes. Highstrength concrete has shown a higher rate of strength gain at early ages as compared to lower-strength concrete, but at later ages the difference is not significant. Information on creep and shrinkage of high-strength concrete has indicated that the shrinkage is similar to that for lower-strength concrete. However, specific creep is much less for high-strength concretes than for lowerstrength concretes. In the area of structural design, it has been found that axially loaded columns with high-strength concrete can be designed in the same way as lower-strength columns. It has also been identified that high-strength concrete columns exhibit less shortening under load than lowerstrength columns because of the higher modulus of elasticity and lower creep coefficients. For beams, use of the conventional equivalent rectangular stress block appears to give satisfactory results for under-reinforced concrete members. The compressive strain limit of 0.003 appears to be acceptable. However, changes have been recommended for present code values for minimum tensile steel ratio, modulus of rupture, modulus of elasticity, shear strength, and development length. Changes are also needed in the area of calculating long-term beam deflections. The economic advantages of using high-strength concrete in the columns of high-rise buildings have been clearly demonstrated by applications in many cities. The ability to reduce the amount of reinforcing steel in columns without sacrificing strength and to keep, the columns to an acceptable size has been an economic benefit to owners of high-rise buildings. Consequently, concrete with compressive strengths in excess of 6000 psi (41 MPa) has been used in the columns of high-rise buildings in cities throughout North America. Studies have also indicated advantages in the use of high-strength concrete in long-span concrete bridges. However, this ap plication has yet to be fully implemented. There have also been applications where high-compressive-strength concrete has been needed to satisfy special local requirements. These have included dams, prestressed concrete poles, grandstand roofs, marine foundations, parking garages, bridge deck overlays, heavy duty industrial floors, and industrial manufacturing applications. Although high-strength concrete is often considered a relatively new material, it is becoming accepted in more parts of North America as shown by the many examples of its usage. At the same time, material producers are
HIGH STRENGTH CONCRETE
responding to the demands for the material and are learning production techniques. As with many developments of new materials, research data supporting the growth has also increased. However, the need for additional research has been documented in ACI 363.1R. Some research projects are underway to satisfy these needs. However, further work is needed to fully use the advantages of high-strength concrete and to affirm its capabilities. This report has documented existing knowledge of high-strength concrete so that the direction for future development may be ascertained.
C 150 C 192 C 260 C 311 C 494 C 595 C 618
CHAPTER 10-REFERENCES
C 684 10.1-Recommended references
The documents of the various standards-producing organizations referred to in this document are listed below with their serial designation.
C 917
C 989 American Association of State Highway and Transportation Officials Quality of Water to be Used in Concrete T-26
E 329
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Standard Specification for Portland Cement Standard Method of Making and Curing Concrete Test Specimens in the Laboratory Standard Specification for Air-Entraining Admixtures for Concrete Standard Methods of Sampling and Testing Fly Ash or Natural Pozzolans for Use as a Mineral Admixture in Portland Cement Concrete Standard Specification for Chemical Admixtures for Concrete Standard Specification for Blended Hydraulic Cements Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete Standard Method of Making, Accelerated Curing, and Testing of Concrete Compression Test Specimens Standard Method for Evaluation of Cement Strength Uniformity from a Single Source Standard Specification for Ground Iron BlastFurnace Slag for use in Cement and Mortars Standard Recommended Practice for Inspection and Testing Agencies for Concrete, Steel, and Bituminous Materials as Used in Construction
American Concrete Institute 116R Cement and Concrete Terminology
20l.lR
Guide for Making a Condition Survey of Concrete in Service Standard Practice for Selecting Proportions for 211.1 Normal, Heavyweight, and Mass Concrete 212.2R Guide for Use of Admixtures in Concrete Recommended Practice for Evaluation of 214 Strength Test Results of Concrete Guide for Measuring, Mixing, Transporting, and 304 Placing Concrete 304.4R Placing Concrete with Belt Conveyors 305R Hot Weather Concreting Standard Practice for Curing Concrete 308 Guide for Consolidation of Concrete 309 Building Code Requirements for Reinforced 318 Concrete 318R Commentary on Building Code Requirements for Reinforced Concrete American Society for Testing and Materials Standard Method of Making and Curing ConC 31 C 33 C 39
C 94 C 109
C 143
crete Test Specimens in the Field Standard Specification for Concrete Aggregates Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens Standard Specification for Ready-Mixed Concrete Standard Test Method for Compressive Strength of Hydraulic Cement, Mortars (using 2 in. or 50 mm cube specimens) Standard Test Method for Slump of Portland Cement Concrete
Canadian Standards Association
A 266.5-M1981 Guidelines for the Use of Super plasticizing Admixtures in Concrete Concrete Plant Manufacturers Bureau
Concrete Plant Manufacturers Standards of the Plant Mixer Manufacturers Division The above publications may be obtained from the following organizations: American Association of State Highway and Transportation Officials 333 N Capitol St. N.W. Suite 225 Washington, D.C. 20001 American Concrete Institute P.O. Box 19150 Detroit, MI 48219 American Society for Testing and Materials 1916 Race Street Philadelphia, PA 19103 Canadian Standards Association 178 Rexdale Blvd. Rexdale, Ont. Canada M9W 1R3
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ACI COMMlTTEE
Concrete Plant Manufacturers Bureau 900 spring St. Silver Spring, Md. 20910 10.2-- Cited references
Cited references are provided at the end of each chapter. 10.3-- Bibliography
The purpose of this bibliography is to call attention to literature on high-strength concrete in addition to that listed at the ends of chapters in this report. The entries are organized alphabetically by author. Anonymous references are listed alphabetically according to their titles. 10.1. Abeles Paul W., “Experience with High-Strength Concrete in Combination with High-Strength Steel in Precast Reinforced and Prestressed Concrete,” Materials
REPORT
Proceedings V. 77, No. 2, Mar.-Apr. 1980, pp. 59-73.
10.12. Bertero, Vitelmo V., “Inelastic Behavior of Structural Elements and Structures,” Proceedings, National Science Foundation Workshop on High Strength Concrete, University of Illinois at Chicago Circle, 1979, Report E-l, 70 pp. 10.13. Bickley, J.A., “Concrete Optimization,” Concrete International: Design & Construction, V. 4, No. 6, June 1982, pp. 38-41. 10.14. Billington, C.J., “ Underwater Repair of Concrete Offshore Structures,” Proceedings, 11th Annual Offshore Technology Conference (Houston, 1979), Offshore Technology Conference, Dallas, 1979, V. 2, pp. 927-937.
10.15. Bloss, D.R.; Hubbard, S.J.; and Gray, B.H., “Development and Evaluation of a High-Strength Polyester Synthetic Concrete,” Technical Report No. M-2, U.S. Army Construction Engineering Research Laboratory, Champaign, Mar. 1970, 70 pp. 10.16. Bremer, F., “Prestressed Concrete Pressure Vessels for Nuclear Reactors,” Technical Session on Design and Construction of Nuclear Power Plants, 7th FIP Congress (New York, 1974), Federation Internationale de la Precontrainte, Wexham Springs, 1975, pp. 34-40. 10.17. Bromham, S.B., “Superplasticizing Admixtures in High Strength Concrete,” Symposium on Concrete in Engineering: Engineering for Concrete (Brisbane, Aug. 1977), National Conference Publication No. 77/8, Institution of Engineers, Australia, Brisbane, 1977, pp. 17-22. 10.18. Brooks, J.J., and Neville, AM., “Predicting Long-Term Creep and Shrinkage from Short-Term Tests,” Magazine of Concrete Research (London), V. 30, No. 103, June 1978, pp. 51-61. 10.19. Brown, Colin B., “ A Discussion on the Micromechanics of Achieving High Strength and Other Superior Properties,” National Science Foundation Workshop on High Strength Concrete, University of Illinois at Chicago Circle, Dec. 1979, Report No. B-l, 5 pp. 10.20. Carrasquillo, R.L.; Nilson, A.H.; and Slate, F.O., “High-Strength Concrete: An Annotated Biblio-
and Structures, Research and Testing (RILEM Paris) V. 6, No. 36, Nov.-Dec. 1973, pp. 464-472. 10.2. Ahmad, S.H., and Shah, S.P., “ Complete StressStrain Curve of Concrete and Nonlinear Design,” Progress Report, National Science Foundation Grant PFR 78 22878, University of Illinois at Chicago Circle, Aug. 1979, 29 pp. Also, Nonlinear Design of Concrete Structures, University of Waterloo Press, 1980, pp. 61-81. 10.3. Aitcin, Pierre-Claude, “How to Produce High Strength Concrete,” Concrete Construction, V. 25, No. 3, Mar. 1980, pp. 222-230. 10.4. Albinger, John, and Moreno, Jaime, “HighStrength Concrete, Chicago Style,” Concrete Construction, V. 26, No. 3, Mar. 1981, pp. 241-245. 10.5. Alexander, K.M.; Bruere, G.M.; and Ivanusec, I., “The Creep and Related Properties of Very HighStrength Superplasticized Concrete,” Cement and Concrete Research, V. 10, No. 2, Mar. 1980, pp. 131-137. 10.6. Anderson, Arthur R., “Some Examples of Energy and Resource Conservation Utilizing High-Strength Concrete,” presented at the ACI Annual Convention, Milwaukee, Mar. 1979. graphy 1930-1979,” Cement, Concrete, and Aggregates, V. 10.7. Bache, H.H., “Compression Failure in Brittle 2, No. 1, Summer 1980, pp. 3-19. Materials. Fracture Hardening (Trykbrud I Skore Materi10.21. Carrasquillo, R.L.; Nilson, A.H.; and Slate, aler),” Nordisk Betong (Stockholm), No. 1, 1977, pp. 7-10. (in Swedish) F.O., “The Prediction of High-Strength Concrete,” Report 10.8. Bazant, Z.P., “High Strength Concrete: Discus- No. 78-1, Department of Structural Engineering, Cornell sion on Material Behavior Under Various Types of Load- University, Ithaca, May 1978, 91 pp. Also, MSc thesis, ing,” Proceedings, National Science Foundation Workshop Cornell University, Ithaca, May 1978, 90 pp. 10.22. Carrasquillo, R.L.; Nilson, A.H.; and Slate, on High Strength Concrete, University of Illinois at Chicago Circle, 1979, Report D-l, 13 pp. F.O., “Very High-Strength Concrete-An Annotated Bib10.9 Bennett, E.W., “Fatigue in Concrete,” Concrete liography 1930-1976,” Report No. 367, Department of Structural Engineering, Cornell University, Ithaca, Apr. (London), May 1974, pp. 43-45. 10.10. Berntsson, L.; Hedberg, B.; and Malinowski, R., 1977, 46 pp. “ Triaxial Deformations by Uniaxial Load on Heat-Cured 10.23. Carrasquillo, Ramon L., and Slate, Floyd O., and High-Strength Concrete (Triaxiala Deformationer “Micro-cracking and Definition of Failure of High- and Till Foljd av Enaxlig Tryckbelastning pa Varmerhardad, Normal-Strength Concretes,” Cement, Concrete, and Ag gregates, V. 5, No. 1, Summer 1983, pp. 54-61. hoghallfast betong),” Cement-och-Betonginstitutet, V. 45, 10.24. Chernobaev, V.I., “Investigation of the Carrying No. 2, May 1970, pp. 205-224. (in Swedish) 10.11. Berry, E.E., and Malhotra, V.M., “Fly Ash for Capacity of High Strength Concrete Flexible Columns (Issledovanie Nesush-ehei Sposobnosti Gibkikh Kolonn Use in Concrete-A Critical Review,” ACI J OURNAL ,
HIGH STRENGTH CONCRETE
353R-51
Iz Vysokoprochnykh Betonov),” Beton i Zhelezobeton “Consistency, Setting, and Strength Gain Characteristics (Moscow), No. 4, Apr. 1975, pp. 9-11. (in Russian) of a ‘Low Porosity’ Portland Cement Paste,” Cement and 10.25. Chung, H.; Hayashi, S; and Kokusho, S., Concrete Research, V. 8, No. 5, Sept. 1978, pp. 613-621. “Experimental Study on the Shear Strength of High 10.39. Dikeou, J.T.; Kukacka, L.E.; Backstrom, J.E.; Strength Concrete Beams,” Transactions, Japan Concrete and Steinberg, M., “Polymerization Makes Tougher ConInstitute, Tokyo, V. 2, 1980, pp. 233-240. crete,” ACI JOURNAL , Proceedings V. 66, No. 10, Oct. 10.26. Chung, H.; Hayashi, S.; and Kokusho, S., 1969, pp. 829-839. “Reinforced High Strength Concrete Columns Subjected 10.40. Erntroy, H.C., and Shacklock, B.W., “Design of to Axial Forces, Bending Moments and Shear Forces,” High Strength Concrete Mixes,” Reprint No. 32, Cement Transactions, Japan Concrete Institute, Tokyo, V. 2, 1980, and Concrete Association, London, 1954. 10.41. “Federal Complex Strikes Low-Key Note,” pp. 335-342. Building Design and Construction, V. 22, No. 11, Nov. 10.27. Colaco, Joseph P.; Ames, Jay B.; and Dubinsky, Eli, “Concrete Shear Walls and Spandrel Beam Moment 1981, pp. 92-94. Frame Brace New York Office Tower,” Concrete Interna10.42. FIP 7th Congress (New York, 1974), Proceedtional Design & Construction, V. 3, No. 6, June 1981, pp. ings, V. 2, Lectures and General Reports, Federation Internationale de la Wexham Springs, 23-28. 10.28. Collepardi, Mario, and Corradi, Mario, “Influ- 1975, 137 pp. ence of Naphthalene-Sulfonated Polymer Based Super10.43. Fintel, Mark, “Creep, Shrinkage and Tempera plasticizers on the Strength of Ordinary and Lightweight ture Effects in Tall Buildings,” Concrete Industry Bulletin, Concretes,” Superplasticizers in Concrete, SP-62, American V. 14, No. 3, Mar. 1974, pp. 4-11. Concrete Institute, Detroit, 1979, pp. 315-336. 10.44. French, P.J.; Montgomery, R.G.J.; and Robson, 10.29. Collins, A.R., “ The Principles of Making High- T.D., “High Concrete Strength Within the Hour,” ConStrength Concrete,” Civil Engineers Review, V. 4, Maycrete (London), V. 5, No. 8, Aug. 1971, pp. 253-258. 10.45. Fukuchi, Toshio, and Ohama, Yoshihiko, ‘ProJune 1954, pp. 172-176, 203-206. Also, Civil Engineering 2 and Public Works Review (London), V. 45, No. 524, Feb. cess Technology and Properties of 2500 kg/cm --Strength 1950, pp. 110-112, and No. 525, Mar. 1950, pp. 170-171, Polymer-Impregnated Concrete,” Proceedings, 2nd Inter180. national Congress on Polymers in Concrete (Austin, Oct. 10.30. “Concrete Strength Secret: Dry Mix,” En1978), University of Texas at Austin, 1979, pp. 45-56. gineering News-Record, V. 189, June 15, 1972, p. 3. 10.46. Fukuchi, Toshio, et al., “Effect of Course 10.31. Coppetti, G.; Cambini, F.; and Tognon, G., Aggregate on Compressive Strength of Polymer-Impreg“Use of Very High-Strength Concrete for the Manufac- nated Autoclaved Concrete,” Proceedings, 22nd Japan ture of Centrifuged Piles (Impiego Di Calcestruzzi Ad Congress on Materials Research (Kyoto, Sept. 1978), Altissime Resistenze Per la Producione De Pali Centri- Society of Materials Science, Kyoto, 1979, pp. 373-376. fugati),” Industria Italiana del Cemento (Rome), V. 50, 10.47. Funakoshi, M., and Okamoto, T., “The Shear No. 2, Feb. 1980, pp. 121-130. (in Italian) Strength of Prestressed Beams for which Very High 10.32. Craven, M.A., “ High-Strength and Lightweight Strength Concrete is Employed,” Transactions, Japan Concrete Institute, Tokyo, V. 2, 1980, pp. 271-278. Concretes for Prestressing,” New Zealand Concrete Con struction (Wellington), V. 11, No. 3, Mar. 1967, pp. 40-41. 10.48. Gallagher, J.E., “Acrylic-Latex Additives Create 10.33. Cross, Hardy, “Design of Reinforced Concrete Extra Strength New Concretes,” Architectural Record, Columns Subject to Flexure,” ACI JOURNAL , Proceedings Mar. 1967, pp. 199-200. 10.49. Galwey, AK., et al., “ Relatively High Strength V. 26, No. 2, Dec. 1929, pp. 157-169. 10.34. Crow, L.J., and Bates, R.C., “Strengths of Sul- of a Chalk-Aggregate Concrete,” Journal of Applied Chemistry, May 1966, pp. 159-162. fur-Basalt Concretes,” Report Investigations No. 7349, U.S. Bureau of Mines, Washington, D.C., 1970, 21 pp. 10.50. Garas, F.K., “Research and Development in Support of the Design of a Prestressed Concrete Pressure 10.35. Dawson, P., “Design and Construction of a Pre2 stressed Concrete Pressure Vessel for a Working Pres- Vessel for a Working Pressure of 69 N/mm (10,000 psi),” 2 sure of 69 N/mm (10,000 psi),” Transactions, 4th Inter- International Journal of Pressure Vessels Piping, V. 8, No. national Conference on Structural Mechanics in Reactor 3, May-June 1980, pp. 233-244. 10.51. Gaynor, R.D., “Producing High Strength AirTechnology (San Francisco, Aug. 1977) Committee of the European Communities, Luxemburg, 1977, Volume H, Entrained Concrete,” unpublished discussion paper. For Paper H l/5, 13 pp. detailed information of the test data, see Gaynor, Richard D., “High Strength Air-Entrained Concrete,” 10.36. Desov, A.E., “Basic Principles of High Strength Concrete,” Transportation Research Record No. 504, Joint Research Laboratory Publication No. 17, National Transportation Research Board, 1974, pp. 37-42. Sand and Gravel Association/National Ready Mixed Con10.37. “Development of Prestressed Concrete High crete Association, Silver Spring, Mar. 1968, 19 pp. 10.52. Ghosh, R.S., and Malhotra, V.M., “Use of Strength Concrete,” Concrete and Constructional EnSuper-plasticizers as Water Reducers,” Cement, Concrete, gineering (London), V. 57, No. 7, July 1962, p. 268. and Aggregates, V. 1, No. 2, 1979, pp. 56-63. 10.38. Diamond, Sidney, and Gomez-Toledo, Carlos,
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Site Concrete Preventing from Cracking Due to Shrink10.53. Givens, J.J., Jr., and Carter, G., “Rehabilitation age and Creep,” Transactions, Architectural Institute of of Offshore Platforms,” Civil Engineering-- ASCE, V. 40, Japan (Tokyo), V. 215, Jan. 1974, pp. 13-30. (in Japanese No. 4, Apr. 1970, pp. 47-49. 10.54. Golikov, A.E., “The Effect of High-Strength with English abstract) 10.70. “Innovation in Concrete,” Progressive ArchConcrete Moulding Technology on the Physico-Mechanical Properties,” Beton i Zhelezobeton (Moscow), No. 9, itecture, V. 59, No. 5, May 1978, pp. 100-109. 10.71. “In Sub-Freezing Weather: Bridge Deck 1967, pp. 34-35. (in Russian) 10.55. Green, Arthur N., “Low Dosage Super Water Repaired with Quick-Set Gunned Concrete,” Bet ter Reducer,” presented at the International Symposium on Roads, V. 45, No. 5, May 1975, p. 44. 10.72. James, Robert M., “High-Strength Concrete Superplasticizers in Concrete, Ottawa, May 1978. 10.56. Gupchup, V.N.; Jayaram, S.; and Kulkarni, J.A., Does Have Its Problems,” ACI JOURNAL , Proceedings, V. “Effect of Admixtures on Properties of High-Strength 75, No. 2, Feb. 1978, p. N8. 10.73. Johnston, Colin D., “Fifty-Year Developments Concrete Mixes,” Indian Concrete Journal (Bombay), V. in High Strength Concrete,” Proceedings, ASCE, V. 101, 53, No. 12, Dec. 1979, pp. 331-335. 10.57. Guy, I.N., Editor, Advances in Concrete (SymC04, Dec. 1975, pp. 801-818. 10.74. Kageyama, H.; Nakagawa, K.; and Nagafuchi, posium Proceedings, University of Birmingham, Sept. T., “High-Strength Concrete Made With Special Cement 1971), The Concrete Society, London, 1972. 10.58. Hanson, J.A, “Shear Strength of Lightweight Admixture,” Zairyo, V. 29, No. 318, Mar. 1980, pp. 220225. Also, abstract in Chemical Abstracts, V. 93, No. 3, Reinforced Concrete Beams,” ACI JOURNAL , Proceedings V. 55, No. 3, Sept. 1958, pp. 387-403. Aug. 11, 1980, p. 371. 10.59. Harris, Alan, “Optimization of Concrete Hulls,” 10.75. Kar, Anil K., “Underwater Structures,” Bulletin, International Association for Shell and Spatial Structures Proceedings, Conference on Concrete Ships and Floating Structures (Berkeley, Sept. 1975), University of Califor- (Madrid), No. 50, Dec. 1972, pp. 49-56. 10.76. Karlsson, Inge, “High-Strength Concrete (Hognia, Berkeley, 1976, pp. 270-273. 10.60. Hattori, Kenichi, ‘Experiences with Mighty hallfast Betong),” Nordisk Betong (Stockholm), No. 4, Superplasticizer in Japan,” Superplasticizers in Concrete, 1977, pp. 19-22. (in Swedish) 10.77. Kemi, Toroa, et al., ‘Experiment of Grouting by SP-62, American Concrete Institute, Detroit, 1979, pp. Special Super High Early Strength Cement Paste,” Review 37-66. 10.61. Hattori, K., “Properties of Admixtures for High of the 31st General Meeting-Technical Session, Cement Strength Concrete and Their Water Reducing Meehan- Association of Japan, Tokyo, May 1977, pp. 218-221. 10.78. Kennedy, Henry, “High Strength Concrete,” Proism,” Concrete Journal (Tokyo), V. 14, No. 3, 1976, pp. 12-19. (in Japanese) ceedings, 1st United States Conference on Prestressed Concrete, Massachusetts Institute of Technology, Cam10.62. Hester, Weston T., “High Strength, Superplasticized Concrete: The Significance of Mix Water-Cement bridge, 1951, pp. 126-135. Ratio, Mortar-Aggregate Bond and Cement Efficiency, 10.79. Klieger, Paul, “High Strength Concrete,” pre presented at the ACI Annual Convention, Atlanta, Jan. sented at the 3rd Symposium on Modern Concrete Tech1982. nology, Caracas, Nov. 1976, 29 pp. 10.80. Kobayashi, Masaki, and Tanaka, Hiroshi, “On 10.63. “High-Strength Concrete,” Building (London), V. 211, No. 6436, 1966, pp. 129-130. Frost Resistance of High-Strength Concrete,” Review of 10.64. “ High-Strength Concrete-Crushed Stone Ag- the 28th General Meeting- Technical Session, Cement Assogregate Makes the Difference,” National Crushed Stone ciation of Japan, Tokyo, 1974, pp. 173-174. Association, Washington, D.C., Nov. 1974, 31 pp. 10.81. Krishna, Raju N., “Compressibility and Modulus 10.65. Hognestad, E., and Perenchio, W.F., “Devel- of Rupture of High-Strength Concrete,” Journal of the Inopments in High-Strength Concrete,” Proceedings, 7th stitute of Engineering (India), Civil Engineering Division, FIP Congress (New York, 1974), Federation Inter- V. 52, No. 3, Part C12, Nov. 1971, pp. 98-101. nationale de la Wexham Springs, 1975, V. 10.82. Law, Sheldon M., and Rasoulian, Masood, “De2, Lectures and General Reports, pp. 21-24. sign and Evaluation of High Strength Concrete for Gir10.66. Hollister, S.C., “Urgent Need for Research in ders,” Report No. FHWA/LA-80/138, Louisiana DepartHigh-Strength Concrete,” ACI JOURNAL, Proceedings V. ment of Transportation, Baton Rouge, 1980, 50 pp. Also, 73, No. 3, Mar. 1976, pp. 136-137. PB81-151 623, National Technical Information Service. 10.83. Lawrence, C.D., “The Properties of Cement 10.67. “How Super are Superplasticizers?,” Concrete Construction, V. 27, No. 5, May 1982, pp. 409-415. Paste Compacted Under High Pressure,” Research Report 10.68. Hughes, B.P., “Temperature Rises in Low-Heat No. 19, Cement and Concrete Association, Wexham Springs, June 1969, pp. 1-20. Cement Concrete,” Proceedings, ASCE, V. 97, ST12, Dec. 10.84. Lobanov, A.T., et al., “Practice of Prefabrication 1971, pp. 2807-2823. 10.69. Ikenaga, Hirotake, and Oshima, Hisaji, “Study of High-Strength Concrete Columns for Buildings (Opyt on the Relation between an Age of Concrete and Shrink- Izgotovleniya Kolonn Iz Vysokoprochnyky Betonov Dlya age, Creep, and Strength--Study of Mixing Design of Zhilykh Domov),” Beton i Zhelezobeton (MOSCOW ), No.
HIGH STRENGTH CONCRETE
12, Dec. 1976, pp. 14-15. (in Russian) 10.85. Machida, F.; Nakahara, S.; Hirose, T.; Kumonda, T.; Miyasaka, T.; and Ishikawa, H., “Design and Execution of Prestressed Concrete Girder Using High Strength Concrete,” Journal, Japan Prestressed Concrete Engineering Association (Tokyo), V. 16, No. 4, 1974, pp. 30-36, and No. 5, 1974, pp. 36-45. (in Japanese) 10.86. MacInnis, Cameron, and Kosteniuk, Paul W., “Effectiveness of Revibration and High-Speed Slurry Mixing for Producing High-Strength Concrete,” ACI J OURNAL , Proceedings V. 76, No. 12, Dec. 1979, pp. 1255-1265.
10.87. MacInnis, Cameron, and Thomas, Donald V., “Special Techniques for Producing High Strength Concrete,” ACI JOURNAL , Proceedings V. 67, No. 12, Dec. 1970, pp. 996-1002. 10.88. Malhotra, V.M., “Development of Sulphur-lnfiltrated High-Strength Concrete,” ACI JOURNAL , Proceedings V. 72, No. 9, Sept. 1975, pp. 466-473. 10.89. V.M., “Superplasticizers in Concrete,” Modern Concrete, V. 41, No. 12, Apr. 1978, pp. 38-43. 10.90. Malhotra, V.M.; Painter, K.E.; and Soles, J.A., “ Development of High-Strength Concrete at Early States Using a Sulphur Infiltration Technique,” Mines Branch Internal Report No. MPI (A) 74-4, CANMET, Department of Energy, Mines and Resources, Ottawa, July 1974, 13 pp. 10.91. Mather, Bryant, “High-Compressive-Strength Concrete, A Review of the State of the Art,” Technical Documentary Report No. AFSWC-TDR-62-56, Air Force Special Weapons Center, Kirtland Air Force Base, Aug. 1962, 90 pp. 10.92. Mather, Bryant, “ High Strength Concrete,” Seminar on Control of Quality of Concrete and Construction Practice, ACI Canadian Capital Chapter, Ottawa,
1968, 56 pp. 10.93. Mather, Bryant, “Tests of High-Range WaterReducing Admixtures,” Superplasticizers in Concrete, SP-62, American Concrete Institute, Detroit, 1979, pp. 157-166. 10.94. Mather, Katharine, “High Strength, High Density Concrete,” ACI JOURNAL, Proceedings V. 62, No. 8, Aug. 1965, pp. 951-962. 10.95. Matsumoto, Y., et al., “Precast Prestressed Concrete Truss Railway Bridge Using Extremely High Strength Concrete,” Final Report, 10th IABSE Congress (Tokyo, 1976), International Association for Bridge and Structural Engineering, Zurich, 1976, pp. 433-438. 10.96. Matsushita, H., “Studies on High-Strength Concrete with Superplasticizer,” Abstract of 31st General Meeting, Cement Association of Japan, Tokyo, 1977, pp. 191-192. (in Japanese) 10.97. Mattison, E.N., and Beresford, F.D., “Studies of the Production of High Strength Concrete,” 4th Symposium on Concrete Research and Development 1970-1973, National Conference Publication No. 73/6, Institution of Engineers, Australia, Sydney, 1973, pp. 5-10. 10.98. Maxson, Orwin G., and Achenbach, Gary D.,
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“Properties of Concrete with Pressured Hydrocarbons and Seawater,” Proceedings, 8th Annual Offshore Technology Conference, Houston, May 1976, paper OTC2662, V. 3, pp. 507-512. 10.99. McBee, William C., and Sullivan, Thomas A., “ Development of Specialized Sulphur Concretes,” Report No. 8346, U.S. Bureau of Mines, Washington, D.C., 1979, 21 pp. 10.100. Melnik, R.A., and Patsula, A.Y., “Investigation of the Nonlinear Creep of High Strength Concrete (Issledovanie Nelineinoi Polzuchesti Vysokoprochnykh Betonov),” Beton i Zehelzobeton (Moscow), No. 3, Mar. 1973, pp. 39-40. (in Russian) 10.101. “Mix Design for Pre-Mixed Concrete 50-55 MPa,” Boral Resources (Vic) Pty Limited, Boral Concrete, Abbotsford, Australia, 11 pp. 10.102. Moe, Johannes, “Feasibility Study of Prestressed Concrete Tanker Ships,” ACI JOURNAL , Proceedings V. 71, No. 12, Dec. 1974, pp. 617-626. 10.103. Moreno, Jaime, “Sixteen Years of HighStrength Concrete in the Chicago Area,” presented at the ACI Annual Convention, Atlanta, Jan. 1982. 10.104. Morgan, Austin H., “High-Strength ReadyMixed Concrete,” National Ready Mixed Concrete Association, Silver Spring, Jan. 1971, 18 pp. 10.105. Morin, A.L.; Tkachuk, V.M.; and Korytnyuk, Y.V., “Investigation of the Eccentrically Compressed Structural Components Built by Using High-Strength Concrete (Issledovaniya Vnetsen-trenno Szhatykh Elementov Iz Betonov Vysokikh),” Beton i Zhelezobeton (Moscow), No. 1, Jan. 1974, pp. 39-41. (in Russian) 10.106. Muguruma, Hiroshi, and Tanaka, Shinzo, “Mechanical Properties of High-Strength Concrete,” Review of the 27th General Meeting-Technical Session,
Cement Association of Japan, Tokyo, May 1973, pp. 140143.
10.107. Nagataki, S., “The Properties of High-Strength Concrete,” Concrete Journal (Tokyo), V. 14, No. 3, 1976, pp. 38-41. (in Japanese) 10.108. Nagataki, S., and Imai, M., “Some Experiments on High-Strength Concrete,” 27th Annual Meeting, Japan Society of Civil Engineers, Tokyo, 1972, pp. V-187-190. (in Japanese) 10.109. Nasser, George D., “ Are We Headed Towards Very High-Strength Concretes?"Concrete Products, V. 70, Oct. 1967, pp. 53-54. 10.110. Nasser, George D., “Bibliography on High Strength Concretes,” ACI JOURNAL , Proceedings V. 64, No. 10, Oct. 1967, pp. 690-691. 10.111. Nilson, A.H., and Slate, F.O., “Properties of High Strength Concrete,” presented at the Session on Inelastic Response of Normal, Lightweight, and High-S trength Concrete, ASCE Fall Convention, Chicago, Oct. 1978.
10.112. Nilson, A.H., and Slate, F.O., “Structural Properties of High-Strength Concrete,” presented at the ACI Annual Convention, Milwaukee, Mar. 1979. 10.113. Nishi, H.: -Ohshio, A.: and Fukuzawa, K.,
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COMMlTTEE REPORT
“Autoclave-Cured High Strength Concrete and Piles,” Cement and Concrete, No. 299, Cement Association of Japan, Tokyo, 1972, pp. 23-29. (in Japanese) 10.114. Okada, Kiyoshi, and Azimi, M. Azam, “ Strength and Ductility of Reinforced High Strength Concrete Beams,” Memoirs, Faculty of Engineering, Kyoto University, V. 43, Part 2, Apr. 1981, pp. 304-318. 10.115. Okada, Kiyoshi, and Kobayashi, Kazuo, “Effects of Addition of Gypsum and Super Water-Reducing Agent on Mechanical Properties of Blast-Furnace Slag Cement Mortar,” Proceedings, 21st Japan Congress on Materials Research (Tokyo, Oct. 1977), Society of Materials Science, Kyoto, 1978, pp. 209-213. 10.116. Parrot, L.J., “High-Strength Concrete,” Concrete (London), V. 4, No. 2, Feb. 1970, pp. 83-84. 10.117. Parrot, L.J., “The Production and Properties of High-Strength Concrete,” Concrete (London), V. 3, No. 11, Nov. 1969, pp. 443-448. 10.118. Parrott, L.J., “The Selection of Constituents and Proportions for Producing Workable Concrete with 2 a Compressive Cube Strength of 80 to 110 n/mm (11,600 2 to 15,900 lbf/in ),” Technical Report No. 416, Cement and Concrete Association, Wexham Springs, 1969, 12 pp. 10.119. Pastor, J.A.; Nilson, A.H.; and Slate, F.O., “Strength and Deformation of High Strength Reinforced Concrete Beams,” Research Report, Department of Structural Engineering, Cornell University, Ithaca (in pre paration). 10.120. Perenchio, W.F.; Whiting, D.A.; and Kantro, D.L., “Water Reduction, Slump Loss, and Entrained Air Void Systems as Influenced by Superplasticizers,” Super plasticizers in Concrete, SP-62, American Concrete Institute, Detroit, 1979, pp. 137-155. 10.121. Pollet, Henri M., “Attainment of Very High Strength Concrete-eater than 1000 kg/cm2 (Realisation de Betons a Tres Haute Resistance-Supreiure a 1000 kg/cm2),” Annales, Institut Technique du Batiment et des Travaux Publics (Paris), No. 214, Oct. 1965, pp. 1425-1426. (in French) 10.122. Popovics, Sandor, “Strength Relationships for Fly Ash Concrete,” ACI, JOURNAL, Proceedings V. 79, No. 1, Jan.-Feb. 1982, pp. 43-49. 10.123. “Precasting Efficiency Pays Off on Long Bridge," Construction Equipment, V. 64, No. 1, Aug. 1981. 10.124. P’yachev, V.A.; P’yachev, G.E.; and Kokhaev, N.F., “ Raw Materials in Cement Manufacture for Produc-
ing High-Strength Concrete (Tsementy Dlya Vysokoprochniykh Betonov),” Tsement (Leningrad), No. 1, Jan. 1974, pp. 21-22. (in Russian) 10.125. Rayner, Johnathan, “Floating Docks in Vancouver Need Continuous Pour of New High-Strength Concrete,” Engineering and Contract Record (Don Mills), V. 89, No. 9, Sept. 1976, pp. 22-24. 10.126. Reigstad, Gordon H., “Energy Conservation in Buildings: A Prestressed Concrete System,” Professional Engineer, V. 47, No. 4, Apr. 1977, pp. 27-28.
10.127. Richart, F.E., “A Study of the Economics of High Strength Concrete in Building Construction,” ACI
JOURNAL , Proceedings V. 32, No. 4, Mar.-Apr. 1936, pp. 459-472.
10.128. Roy, Della M., and Gouda, G.R., “High Strength Generation in Cement Pastes,” Cement and Concrete Research, V. 3, No. 6, Nov.-Dec. 1973, pp. 807-820.
10.129. Roy, D.M.; Gouda, G.R.; and Bobrowsky, A., “Very High Strength Cement Pastes Prepared by Hot Pressing and Other High Pressure Techniques,” Cement and Concrete Research, V. 2, No. 3, May-June 1972, pp. 349-366. 10.130. Ryaboshapko, Y.I.; Vaslavskii, V.F.; and Olginskii, A.G., “ Experience in the Application of HighStrength Concrete with Acid FIy Ash Admixture (Opyt Primeneniya Vysokomarochnogo Betona S Prisadkoi Kisloi Zoly-Unosa),” Beton i Zhelezobeton (Moscow), No. 5, May 1974, pp. 12-13. (in Russian) 10.131. Ryell, John, “High Strength Concrete,” Tenth Annual School of Concrete Technology, Ready Mixed Concrete Association of Ontario, Toronto, Apr. 1969, 19 pp.
10.132. Ryell John, “High Strength Concrete,” Canadian Pit and Quarry (Don Mills), Jan. 1970, pp. 16-19, and Feb. 1970, pp. 26-28. 10.133. Saito, T.; Ohshio, A.; Goto, Y.; and Omori, Y.,
“High Strength Concrete. Part 2, Strength Properties, Durability, and Thermal Characteristics,” Journal of Research, Onoda Cement Co., V. 28, 1976, pp. 12-27. (in Japanese) 10.134. Saucier, Kenneth L., “High-Strength Concrete, Past, Present, Future: Concrete International Design & Construction, V. 2, No. 6, June 1980, pp. 46-50. 10.135. Saucier, Kenneth L., “Determination of Practical Ultimate Strength of Concrete,” Miscellaneous Paper No. C-72-16, U.S. Army Engineer Waterways Experiment Station, Vicksburg, June 1972, 29 pp. 10.136. Savage, E.S., “Deep-Bed Filtration Lengthens Filter Runs, Lowers Backwash Water Needs,” American City, V. 88, No. 1, Jan. 1973, p. 44. 10.137. Schrader, Ernest K., and Munch, Anthony V., “ Fibrous Concrete Repair of Cavitation Damage,” Proceedings, V. 102, C02, June 1976, pp. 385-399. 10.138. Shah, S.P., and Ahmad, S.H., “Effective Confinement on High-Strength Concrete,” presented at the ACI Annual Convention, Atlanta, Jan. 1982. 10.139. Shah, S.P.; Gokoz, UIker; and Ansari, Farhad, “Experimental Technique for Obtaining Complete StressStrain Curves for High Strength Concrete,” Cement, Concrete, and Aggregates, V. 3, No. 1, Summer 1981, pp. 21-27. 10.140. Schukla, S.N., and Mittal, M.K., “Short-Term
Deflection in Two-Way Reinforced Concrete Slabs After Cracking,” ACI JOURNAL , Proceedings V. 73, No. 7, July 1976, pp. 416-419.
10.141. Slate, F.O., and Nilson, A.H., “High-Strength Concrete-Preliminary Results on Microcracking and Creep,” presented at the ACI Annual Convention, Milwaukee, Mar. 1979.