Chap3 - HOME PAGE CHAPTER 3 Fly Ash, Slag, Silica Fume, and...

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Unformatted text preview: HOME PAGE CHAPTER 3 Fly Ash, Slag, Silica Fume, and Natural Pozzolans conservation standpoint but also for the technical benefits they provide concrete. Supplementary cementitious materials are added to concrete as part of the total cementitious system. They may be used in addition to or as a partial replacement of portland cement or blended cement in concrete, depending on the properties of the materials and the desired effect on concrete. Supplementary cementitious materials are used to improve a particular concrete property, such as resistance to alkali-aggregate reactivity. The optimum amount to use should be established by testing to determine (1) whether the material is indeed improving the property, and (2) the correct dosage rate, as an overdose or underdose can be harmful or not achieve the desired effect. Supplementary cementitious materials also react differently with different cements. Traditionally, fly ash, slag, calcined clay, calcined shale, and silica fume were used in concrete individually. Today, due to improved access to these materials, concrete producers can combine two or more of these materials to optimize concrete properties. Mixtures using three cementitious materials, called ternary mixtures, are becoming more Fig. 3-1. Supplementary cementitious materials. From left to right, fly ash (Class C), metakaolin (calcined clay), silica fume, fly ash (Class F), slag, and calcined shale. (69794) Fly ash, ground granulated blast-furnace slag, silica fume, and natural pozzolans, such as calcined shale, calcined clay or metakaolin, are materials that, when used in conjunction with portland or blended cement, contribute to the properties of the hardened concrete through hydraulic or pozzolanic activity or both (Fig. 3-1). A pozzolan is a siliceous or aluminosiliceous material that, in finely divided form and in the presence of moisture, chemically reacts with the calcium hydroxide released by the hydration of portland cement to form calcium silicate hydrate and other cementitious compounds. Pozzolans and slags are generally catergorized as supplementary cementitious materials or mineral admixtures. Table 3-1 lists the applicable specifications these materials meet. The use of these materials in blended cements is discussed in Chapter 2 and by Detwiler, Bhatty, and Bhattacharja (1996). The practice of using supplementary cementitious materials in concrete mixtures has been growing in North America since the 1970s. There are similarities between many of these materials in that most are byproducts of other industrial processes; their judicious use is desirable not only from the national environmental and energy 57 Fig. 3-2. Scanning electron microscope (SEM) micrograph of fly ash particles at 1000X. Although most fly ash spheres are solid, some particles, called cenospheres, are hollow (as shown in the micrograph). (54048) Design and Control of Concrete Mixtures N EB001 Table 3-1. Specifications and Classes of Supplementary Cementitious Materials Ground granulated iron blast-furnace slags--ASTM C 989 (AASHTO M 302) Grade 80 Slags with a low activity index Grade 100 Slags with a moderate activity index Grade 120 Slags with a high activity index Fly ash and natural pozzolans--ASTM C 618 (AASHTO M 295) Class N Raw or calcined natural pozzolans including: Diatomaceous earths Opaline cherts and shales Tuffs and volcanic ashes or pumicites Calcined clays, including metakaolin, and shales Class F Fly ash with pozzolanic properties Class C Fly ash with pozzolanic and cementitious properties Silica fume--ASTM C 1240 Fig. 3-3. Fly ash, a powder resembling cement, has been used in concrete since the 1930s. (69799) common. Supplementary cementitious materials are used in at least 60% of ready mixed concrete (PCA 2000). ASTM C 311 provides test methods for fly ash and natural pozzolans for use as supplementary cementitious material in concrete. FLY ASH Fly ash, the most widely used supplementary cementitious material in concrete, is a byproduct of the combustion of pulverized coal in electric power generating plants. Upon ignition in the furnace, most of the volatile matter and carbon in the coal are burned off. During combustion, the coal's mineral impurities (such as clay, feldspar, quartz, and shale) fuse in suspension and are carried away from the combustion chamber by the exhaust gases. In the process, the fused material cools and solidifies into spherical glassy particles called fly ash (Fig. 3-2). The fly ash is then collected from the exhaust gases by electrostatic precipitators or bag filters. Fly ash is a finely divided powder resembling portland cement (Fig. 3-3). Most of the fly ash particles are solid spheres and some are hollow cenospheres. Also present are plerospheres, which are spheres containing smaller spheres. Ground materials, such as portland cement, have solid angular particles. The particle sizes in fly ash vary from less than 1 m (micrometer) to more than 100 m with the typical particle size measuring under 20 m. Only 10% to 30% of the particles by mass are larger than 45 m. The surface area is typically 300 to 500 m 2/kg, although some fly ashes can have surface areas as low as 200 m 2/kg and as high as 700 m2/kg. For fly ash without close compaction, the bulk density (mass per unit volume including air between particles) can vary from 540 to 860 kg/m3 (34 to 54 lb/ft 3), whereas with close packed storage or vibration, the range can be 1120 to 1500 kg/m3 (70 to 94 lb/ft 3). Fly ash is primarily silicate glass containing silica, alumina, iron, and calcium. Minor constituents are magnesium, sulfur, sodium, potassium, and carbon. Crystalline compounds are present in small amounts. The relative density (specific gravity) of fly ash generally ranges between 1.9 and 2.8 and the color is generally gray or tan. ASTM C 618 (AASHTO M 295) Class F and Class C fly ashes are commonly used as pozzolanic admixtures for general purpose concrete (Fig. 3-4). Class F materials are generally low-calcium (less than 10% CaO) fly ashes with Fig. 3-4. Fly ash, slag, and calcined clay or calcined shale are used in general purpose construction, such as (left to right) walls for residential buildings, pavements, high-rise towers, and dams. (67279, 48177, 69554, 69555) 58 Chapter 3 N Fly Ash, Slag, Silica Fume, and Natural Pozzolans Fig. 3-5. Ground granulated blast-furnace slag. (69800) Fig. 3-7. Silica fume powder. (69801) carbon contents usually less than 5%, but some may be as high as 10%. Class C materials are often high-calcium (10% to 30% CaO) fly ashes with carbon contents less than 2%. Many Class C ashes when exposed to water will hydrate and harden in less than 45 minutes. Some fly ashes meet both Class F and Class C classifications. Fly ash is used in about 50% of ready mixed concrete (PCA 2000). Class F fly ash is often used at dosages of 15% to 25% by mass of cementitious material and Class C fly ash is used at dosages of 15% to 40% by mass of cementitious material. Dosage varies with the reactivity of the ash and the desired effects on the concrete (Helmuth 1987 and ACI 232 1996). SLAG Ground granulated blast-furnace slag (Fig. 3-5), also called slag cement, is made from iron blast-furnace slag; it is a nonmetallic hydraulic cement consisting essentially of silicates and aluminosilicates of calcium developed in a molten condition simultaneously with iron in a blast furnace. The molten slag at a temperature of about 1500C (2730F) is rapidly chilled by quenching in water to form a glassy sandlike granulated material. The granulated material, which is ground to less than 45 microns, has a surface area fineness of about 400 to 600 m2/kg Blaine. The relative density (specific gravity) for ground granulated blastfurnace slag is in the range of 2.85 to 2.95. The bulk density varies from 1050 to 1375 kg/m3 (66 to 86 lb/ft 3). The rough and angular-shaped ground slag (Fig. 3-6) in the presence of water and an activator, NaOH or CaOH, both supplied by portland cement, hydrates and sets in a manner similar to portland cement. However, air-cooled slag does not have the hydraulic properties of watercooled slag. Granulated blast furnace slag was first developed in Germany in 1853 (Malhotra 1996). Ground slag has been used as a cementitious material in concrete since the beginning of the 1900s (Abrams 1925). Ground granulated blastfurnace slag, when used in general purpose concrete in North America, commonly constitutes between 30% and 45% of the cementing material in the mix (Fig. 3-4) (PCA 2000). Some slag concretes have a slag component of 70% or more of the cementitious material. ASTM C 989 (AASHTO M 302) classifies slag by its increasing level of reactivity as Grade 80, 100, or 120 (Table 3-1). ASTM C 1073 covers a rapid determination of hydraulic activity of Fig. 3-6. Scanning electron microscope micrograph of slag particles at 2100X. (69541) 59 Fig. 3-8. Scanning electron microscope micrograph of silicafume particles at 20,000X. (54095) Design and Control of Concrete Mixtures N EB001 Fig. 3-9. Although they can be used in general construction, silica fume and metakaolin are often used in applications such as (left) bridges and (right) parking garages to minimize chloride penetration into concrete. (68681, 69542) ground granulated blast furnace slag and ACI 233 (1995) provides an extensive review of slag. NATURAL POZZOLANS Natural pozzolans have been used for centuries. The term "pozzolan" comes from a volcanic ash mined at Pozzuoli, a village near Naples, Italy, following the 79 AD eruption of Mount Vesuvius. However, the use of volcanic ash and calcined clay dates back to 2000 BC and earlier in other cultures. Many of the Roman, Greek, Indian, and Egyptian pozzolan concrete structures can still be seen today, attesting to the durability of these materials. The North American experience with natural pozzolans dates back to early 20th century public works projects, such as dams, where they were used to control temperature rise in mass concrete and provide cementitious material. In addition to controlling heat rise, natural pozzolans were used to improve resistance to sulfate attack and were among the first materials to be found to mitigate alkali-silica reaction. The most common natural pozzolans used today are processed materials, which are heat treated in a kiln and then ground to a fine powder (Figs. 3-10, 3-11, and 3-12); they include calcined clay, calcined shale, and metakaolin. SILICA FUME Silica fume, also referred to as microsilica or condensed silica fume, is a byproduct material that is used as a pozzolan (Fig. 3-7). This byproduct is a result of the reduction of high-purity quartz with coal in an electric arc furnace in the manufacture of silicon or ferrosilicon alloy. Silica fume rises as an oxidized vapor from the 2000C (3630F) furnaces. When it cools it condenses and is collected in huge cloth bags. The condensed silica fume is then processed to remove impurities and to control particle size. Condensed silica fume is essentially silicon dioxide (usually more than 85%) in noncrystalline (amorphorous) form. Since it is an airborne material like fly ash, it has a spherical shape (Fig. 3-8). It is extremely fine with particles less than 1 m in diameter and with an average diameter of about 0.1 m, about 100 times smaller than average cement particles. Condensed silica fume has a surface area of about 20,000 m2/kg (nitrogen adsorption method). For comparison, tobacco smoke's surface area is about 10,000 m2/ kg. Type I and Type III cements have surface areas of about 300 to 400 m2/kg and 500 to 600 m2/kg (Blaine), respectively. The relative density of silica fume is generally in the range of 2.20 to 2.5. Portland cement has a relative density of about 3.15. The bulk density (uncompacted unit weight) of silica fume varies from 130 to 430 kg/m3 (8 to 27 lb/ft 3). Silica fume is sold in powder form but is more commonly available in a liquid. Silica fume is used in amounts between 5% and 10% by mass of the total cementitious material. It is used in applications where a high degree of impermeability is needed (Fig. 3-9) and in highstrength concrete. Silica fume must meet ASTM C 1240. ACI 234 (1994) and SFA (2000) provide an extensive review of silica fume. 60 Fig. 3-10. Scanning electron microscope micrograph of calcined shale particles at 5000X. (69543) Chapter 3 N Fly Ash, Slag, Silica Fume, and Natural Pozzolans Fig. 3-11. Metakaolin, a calcined clay. (69803) Fig. 3-12. Scanning electron microscope micrograph of calcined clay particles at 2000X. (69544) Calcined clays are used in general purpose concrete construction much the same as other pozzolans (Fig. 3-4). They can be used as a partial replacement for the cement, typically in the range of 15% to 35%, and to enhance resistance to sulfate attack, control alkali-silica reactivity, and reduce permeability. Calcined clays have a relative density of between 2.40 and 2.61 with Blaine fineness ranging from 650 m2/kg to 1350 m2/kg. Calcined shale may contain on the order of 5% to 10% calcium, which results in the material having some cementing or hydraulic properties on its own. Because of the amount of residual calcite that is not fully calcined, and the bound water molecules in the clay minerals, calcined shale will have a loss on ignition (LOI) of perhaps 1% to 5%. The LOI value for calcined shale is not a measure or indication of carbon content as would be the case in fly ash. Metakaolin, a special calcined clay, is produced by lowtemperature calcination of high purity kaolin clay. The product is ground to an average particle size of about 1 to 2 micrometers. Metakaolin is used in special applications where very low permeability or very high strength is required. In these applications, metakaolin is used more as an additive to the concrete rather than a replacement of cement; typical additions are around 10% of the cement mass. Natural pozzolans are classified by ASTM C 618 (AASHTO M 295) as Class N pozzolans (Table 3-1). ACI 232 (2000) provides a review of natural pozzolans. Table 3-2 illustrates typical chemical analysis and selected properties of pozzolans. EFFECTS ON FRESHLY MIXED CONCRETE This section provides a brief understanding of the freshly mixed concrete properties that supplementary cementitious materials affect and their degree of influence. First it should be noted that these materials vary considerably in their effect on concrete mixtures. The attributes of these materials when added separately to a concrete mixture can also be found in Table 3-2. Chemical Analysis and Selected Properties of Typical Fly Ash, Slag, blended cements using Silica Fume, Calcined Clay, Calcined Shale, and Metakaolin supplementary cementitious materials. Class F Class C Ground Silica Calcined Calcined fly ash SiO 2, % Al 2O 3, % Fe 2O 3, % CaO, % SO 3, % Na 2O, % K 2O, % Total Na eq. alk, % Loss on ignition, % Blaine fineness, m2/kg Relative density 52 23 11 5 0.8 1.0 2.0 2.2 2.8 420 2.38 fly ash 35 18 6 21 4.1 5.8 0.7 6.3 0.5 420 2.65 slag 35 12 1 40 9 0.3 0.4 0.6 1.0 400 2.94 fume 90 0.4 0.4 1.6 0.4 0.5 2.2 1.9 3.0 20,000 2.40 clay 58 29 4 1 0.5 0.2 2 1.5 1.5 990 2.50 shale 50 20 8 8 0.4 -- -- -- 3.0 730 2.63 Metakaolin 53 43 0.5 0.1 0.1 0.05 0.4 0.3 0.7 19,000 2.50 Water Requirements Concrete mixtures containing fly ash generally require less water (about 1% to 10% less at normal dosages) for a given slump than concrete containing only portland cement. Higher dosages can result in greater water reduction (Table 3-3). However, some fly ashes can in- 61 Design and Control of Concrete Mixtures N EB001 bleed water is primarily due to the reduced water demand in fly ash concretes. Gebler and Klieger (1986) correlate reduced bleeding of concrete to the reduced water requirement of fly ash mortar. Concretes containing ground slags of comparable fineness to that of the cement tend to show an increased rate and amount of bleeding than plain concretes, but this appears to have no adverse effect on segregation. Slags ground finer than cement reduce bleeding. Silica fume is very effective in reducing both bleeding and segregation; as a result, higher slumps may be used. Calcined clays, calcined shales, and metakaolin have little effect on bleeding. Table 3-3. Effect of Fly Ash on Mixing Water Requirements for Air-Entrained Concrete Fly ash mix identification C1A C1D C1E C1F C1G C1J C2A C2D C2E C2F C2G C2J Class of fly ash C F F C C F C F F C C F Fly ash content, % by mass of cementitious material 25 25 25 25 25 25 50 50 50 50 50 50 Change in mixing water requirement compared to control, % -6 -2 -6 -8 -6 -6 -18 -6 -14 -16 -12 -10 All mixtures had cementitious materials contents of 335 kg/m3 (564 lb/yd3), a slump of 125 25 mm (5 1 in.), and an air content of 6 1%. Water to cement plus fly ash ratios varied from 0.40 to 0.48 (Whiting 1989). Air Content crease water demand up to 5% (Gebler and Klieger 1986). Fly ash reduces water demand in a manner similar to liquid chemical water reducers (Helmuth 1987). Ground slag usually decreases water demand by 1% to 10%, depending on dosage. The water demand of concrete containing silica fume increases with increasing amounts of silica fume, unless a water reducer or plasticizer is used. Some lean mixes may not experience an increase in water demand when only a small amount (less than 5%) of silica fume is present. Calcined clays and calcined shales generally have little effect on water demand at normal dosages; however, other Table 3-4. Effect of Fly Ash on Bleeding of Concrete natural pozzolans can significantly in(ASTM C 232, AASHTO T 158)* crease or decrease water demand. The amount of air-entraining admixture required to obtain a specified air content is normally greater when fly ash is used. Class C ash requires less air-entraining admixture than Class F ash and tends to lose less air during mixing (Table 3-5). Ground slags have variable effects on the required dosage rate of air-entraining admixtures. Silica fume has a marked influence on the air-entraining admixture requirement, which in most cases rapidly increases with an increase in the amount of silica fume used in the concrete. The inclusion of both fly ash and silica fume in non-air-entrained concrete will generally reduce the amount of entrapped air. Workability Fly ash, slag, and calcined clay and shale generally improve the workability of concretes of equal slump. Silica fume may contribute to stickiness of a concrete mixture; adjustments, including the use of high-range water reducers, may be required to maintain workability and permit proper compaction and finishing. Bleeding and Segregation Concretes using fly ash generally exhibit less bleeding and segregation than plain concretes (Table 3-4). This effect makes the use of fly ash particularly valuable in concrete mixtures made with aggregates that are deficient in fines. The reduction in Fly ash mixtures Identification Class of fly ash A C B F C F D F E F F C G C H F I C J F Average of: Class C Class F Control mixture Bleeding Percent mL/cm2** 0.22 0.007 1.11 0.036 1.61 0.053 1.88 0.067 1.18 0.035 0.13 0.004 0.89 0.028 0.58 0.022 0.12 0.004 1.48 0.051 0.34 1.31 1.75 0.011 0.044 0.059 * All mixtures had cementitious materials contents of 307 kg/m 3 (517 lb/yd3), a slump of 75 25 mm (3 1 in.), and an air content of 6 1%. Fly ash mixtures contained 25% ash by mass of cementitious material (Gebler and Klieger 1986). ** Volume of bleed water per surface area. 62 Chapter 3 N Fly Ash, Slag, Silica Fume, and Natural Pozzolans Table 3-5. Effect of Fly Ash on Air-Entraining Admixture Dosage and Air Retention Percent of air-entraining admixture relative to control Fly ash mixtures Identification Class of fly ash A C B F C F D F E F F C G C H F I C J F Control mixture Fly ash, natural pozzolans, and ground slag have a lower heat of hydration than portland cement; consequently their use will reduce the amount of heat built up in a concrete structure (Fig. 3-13). Calcined clay imparts a heat of hyConcretes had a cementitious materials content of 307 kg/m3 (517 lb/yd3) and a slump of 75 25 mm dration similar to mod(3 1 in.). Fly ash mixtures contained 25% ash by mass of cementitious material (Gebler and Klieger 1983). erate heat cement (Barger and others 1997). Some The amount of air-entraining admixture required for a pozzolans have a heat of hydration of only 40% that of Type I portland cement. This reduction in temperature rise certain air content in the concrete is a function of the fineis especially beneficial in concrete used for massive strucness, carbon content, alkali content, organic material tures. Silica fume may or may not reduce the heat of hydracontent, loss on ignition, and presence of impurities in the tion. Detwiler and others (1996) provide a review of the fly ash. Increases in alkalies decrease air-entraining agent effect of pozzolans and slags on heat generation. dosages, while increases in the other properties increase dosage requirements. The Foam Index test provides an indication of the required dosage of air-entraining admixSetting Time ture for various fly ashes relative to non-ash mixtures; it can also be used to anticipate the need to increase or decrease The use of fly ash and ground granulated blast-furnace the dosage based on changes in the foam index (Gebler and slag will generally retard the setting time of concrete (Table Klieger 1983). 3-6). The degree of set retardation depends on factors such 126 209 553 239 190 173 158 170 149 434 100 Air content, % Minutes after initial mixing 0 30 60 90 7.2 6.0 6.0 5.8 5.3 4.1 3.4 3.1 7.0 4.7 3.8 2.9 6.6 5.4 4.2 4.1 5.6 4.6 4.3 3.8 6.8 6.5 6.3 6.4 5.5 4.8 4.5 4.2 7.6 6.9 6.5 6.6 6.6 6.5 6.5 6.8 5.5 4.2 3.8 3.4 6.6 6.0 5.6 5.3 The air-entraining dosage and air retention characteristics of concretes containing ground slag or natural pozzolans are similar to mixtures made only with portland cement. Heat of Hydration Table 3-6. Effect of Fly Ash on Setting Time of Concrete Fly ash test mixtures Identification Class of fly ash A C B F C F D F E F F C G C H F I C J F Average of: Class C Class F Control mixture Setting time, hr:min Initial Final 4:30 5:35 4:40 6:15 4:25 6:15 5:05 7:15 4:25 5:50 4:25 6:00 4:55 6:30 5:10 7:10 5:00 6:50 5:10 7:40 4:40 4:50 4:15 6:15 6:45 5:30 Retardation relative to control, hr:min Initial Final 0:15 0:05 0:25 0:45 0:10 0:45 0:50 1:45 0:10 0:20 0:10 0:30 0:40 1:00 0:55 1:40 0:45 1:20 0:55 2:10 0:30 0:35 -- 0:45 1:15 -- Concretes had a cementitious materials content of 307 kg/m3 (517 lb/yd3). Fly ash mixtures contained 25% ash by mass of cementitious material. Water to cement plus fly ash ratio = 0.40 to 0.45. Tested at 23C (73F) (Gebler and Klieger 1986). 63 Design and Control of Concrete Mixtures Heat, percent of Type I cement at 28 days 120 100 80 60 40 20 0 0 5 10 15 Time, days N EB001 containing supplementary cementing materials are similar to the effects on concrete made with only portland cement; however, the curing time may need to be longer for certain materials with slow-early-strength gain. High dosages of silica fume can make concrete highly cohesive with very little aggregate segregation or bleeding. With little or no bleed water available at the concrete surface for evaporation, plastic cracking can readily develop, especially on hot, windy days if special precautions are not taken. Proper curing of all concrete, especially concrete containing supplementary cementing materials, should commence immediately after finishing. A seven-day moist cure or membrane cure should be adequate for concretes with normal dosages of most supplementary cementitious materials. As with portland cement concrete, low curing temperatures can reduce early-strength gain (Gebler and Klieger 1986). ASTM Type I cement 70% slag 20 25 30 Fig. 3-13. Effect of a slag on heat of hydration at 20C (68F) compared to a Type I cement. as the amount of portland cement, water requirement, the type and reactivity of the slag or pozzolan dosage, and the temperature of the concrete. Set retardation is an advantage during hot weather, allowing more time to place and finish the concrete. However, during cold weather, pronounced retardation can occur with some materials, significantly delaying finishing operations. Accelerating admixtures can be used to decrease the setting time. Calcined shale and clay have little effect on setting time. EFFECTS ON HARDENED CONCRETE Strength Fly ash, ground granulated blast-furnace slag, calcined clay, metakaolin, calcined shale, and silica fume contribute to the strength gain of concrete. However, the strength of concrete containing these materials can be higher or lower than the strength of concrete using portland cement as the only cementing material. Fig. 3-14 illustrates this for various fly ashes. Tensile, flexural, torsional, and bond strength are affected in the same manner as compressive strength. Finishability Concrete containing supplementary cementing materials will generally have equal or improved finishability compared to similar concrete mixes without them. Mixes that contain high dosages of cementitious materials--and especially silica fume--can be sticky and difficult to finish. 42 6 Pumpability Compressive strength, 1000 psi Compressive strength, MPa The use of supplementary cementing materials generally aids the pumpability of concrete. Silica fume is the most effective, especially in lean mixtures. 35 5 Plastic Shrinkage Cracking Because of its low bleeding characteristics, concrete containing silica fume may exhibit an increase in plastic shrinkage cracking. The problem may be avoided by ensuring that such concrete is protected against drying, both during and after finishing. Other pozzolans and slag generally have little effect on plastic shrinkage cracking. Supplementary cementing materials that significantly increase set time can increase the risk of plastic shrinkage cracking. 28 4 21 14 None Fly ash A Fly ash D Fly ash E Fly ash F Fly ash G Fly ash J 3 2 7 1 1 10 Age, days 100 Curing The effects of temperature and moisture conditions on setting properties and strength development of concretes 64 Fig. 3-14. Compressive strength development at 1, 3, 7, 28, and 90 days of concrete mixtures containing 307 kg/m3 (517 lb/yd3) of cementitious materials with a fly ash dosage of 25% of the cementitious materials (Whiting 1989). Chapter 3 N Fly Ash, Slag, Silica Fume, and Natural Pozzolans Because of the slow pozzolanic reaction of some supplementary cementing materials, continuous wet curing and favorable curing temperatures may need to be provided for longer periods than normally required. However, concrete containing silica fume is less affected by this and generally equals or exceeds the one-day strength of a cement-only control mixture. Silica fume contributes to strength development primarily between 3 and 28 days, during which time a silica fume concrete exceeds the strength of a cement-only control concrete. Silica fume also aids the early strength gain of fly ash-cement concretes. The strength development of concrete with fly ash, ground slag, calcined clay, or calcined shale, is similar to normal concrete when cured around 23C (73F). Fig. 3-15 illustrates that the rate of strength gain of concrete with fly ash, relative to its 28-day strength, is similar to concrete without fly ash. Concretes made with certain highly reactive fly ashes (especially high-calcium Class C ashes) or ground slags can equal or exceed the control strength in 1 to 28 days. Some fly ashes and natural pozzolans require 28 to 90 days to exceed a 28-day control strength, depending on the mixture proportions. Concretes containing Class C ashes generally develop higher early-age strength than concretes with Class F ashes. Strength gain can be increased by: (1) increasing the amount of cementitious material in the concrete; (2) adding high-early strength cementitious materials; (3) decreasing the water-cementing materials ratio; (4) increasing the curing temperature; or (5) using an accelerating admixture. Fig. 3-16 illustrates the benefit of using fly ash as an addition instead of a cement replacement to improve strength development in cold weather. Mass concrete design often takes advantage of the delayed strength gain of pozzolans as these structures are often not put into full service immediately. Slow early strength gain resulting from the use of some supplementary cementitious materials is an advantage in hot weather construction as it allows more time to place and finish the concrete. With appropriate mixture adjustments, all supplementary cementitious materials can be used in all seasons. 60 55 Cold weather cure: First 24 hrs at 23C (73F) Remainder at 4C (39F) 8500 7800 Compressive strength, MPa 45 40 35 Control 30 25 20 0 10 20 30 40 50 60 70 80 90 Age, days Fly Ash A 20% S Fly Ash A 20% P Fly Ash A 20% A 6400 5700 5000 4300 3600 2900 Fig. 3-16. Compressive strengths for concretes cured at 23C (73F) for the first 24 hours and 4C (40F) for the remaining time. Control had a cement content of 332 kg/m3 (560 lb/yd3) and w/c of 0.45. The fly ash curves show substitution for cement (S), partial (equal) substitution for cement and sand (P), and addition of fly ash by mass of cement (A). The use of partial cement substitution or addition of fly ash increases strength development comparable to the cement-only control, even in cold weather (Detwiler 2000). Supplementary cementing materials are often essential to the production of high-strength concrete. Fly ash, especially, has been used in production of concrete with strengths up to 100 MPa (15,000 psi). With silica fume, ready mix producers now have the ability to make concrete with strengths up to 140 MPa (20,000 psi), when used with high-range water reducers and appropriate aggregates (Burg and Ost 1994). Impact and Abrasion Resistance The impact resistance and abrasion resistance of concrete are related to compressive strength and aggregate type. Supplementary cementing materials generally do not affect these properties beyond their influence on strength. Concretes containing fly ash are just as abrasion resistant as portland cement concretes without fly ash (Gebler and Klieger 1986). Fig. 3-17 illustrates that abrasion resistance of fly ash concrete is related to strength. Compressive strength, percent of 28-day strength 180 160 140 120 100 80 60 40 20 0 1 10 100 Age, days 1000 10000 With fly ash Without fly ash 28 days Freeze-Thaw Resistance It is imperative for development of resistance to deterioration from cycles of freezing and thawing that a concrete have adequate strength and entrained air. For concrete containing supplementary cementing materials to provide the same resistance to freezing and thawing cycles as a concrete made using only portland cement as a binder, four conditions for both concretes must be met: 65 Fig. 3-15. Compressive strength gain as a percentage of 28-day strength of concretes with and without fly ash (Lange 1994). Compressive strength, psi 50 7100 Design and Control of Concrete Mixtures N EB001 4. They must be air-dried for one month prior to exposure to saturated freezing conditions. Table 3-7 shows equal frost resistance for concrete with and without fly ash. Fig. 3-18 illustrates the long term durability of concretes with fly ash, slag, or shale. 2.2 3 28-Day moist-cured compressive strength, 1000 psi 4 5 6 2.0 1.8 Depth of wear, mm Deicer-Scaling Resistance Decades of field experience have demonstrated that airentrained concretes containing normal dosages of fly ash, slag, silica fume, calcined clay, or calcined shale are resistant to scaling caused by the application of deicing salts in a freeze-thaw environment. Laboratory tests also indicate that the deicer-scaling resistance of concrete made with supplementary cementing materials is often equal to concrete made without supplementary cementing materials. Scaling resistance can decrease as the amount of certain supplementary cementing materials increases. However, concretes that are properly designed, placed, and cured, have demonstrated good scaling resistance even when made with high dosages of some of these materials. Deicer-scaling resistance of all concrete is significantly improved with the use of a low water-cement ratio, a moderate portland cement content, adequate air entrainment, proper finishing and curing, and an air-drying period prior to exposure of the concrete to salts and freezing temperatures. Lean concrete with only about 240 kg/m3 (405 lb/yd3) or less of cementitious material can be especially vulnerable to deicer scaling. A minimum of 335 kg/m3 1.6 1.4 1.2 1.0 20 25 30 35 40 28-Day moist-cured compressive strength, MPa Fig. 3-17. Comparison of abrasion resistance and compressive strength of various concretes with 25% fly ash. Abrasion resistance increases with strength (Gebler and Klieger 1986). 1. They must have the same compressive strength. 2. They must have an adequate entrained air content with proper air-void characteristics. 3. They must be properly cured. A C B D Fig. 3-18. View of concrete slabs in PCA outdoor test plot (Skokie, Illinois) containing (A) fly ash, (B) slag, (C) calcined shale, and (D) portland cement after 30 years of deicer and frost exposure. These samples demonstrate the durability of concretes containing various cementitious materials. Source: RX 157, LTS Cement No. 51, slabs with 335 kg/m3 (564 lb/yd3) of cementing material and air entrainment. (69714, 69716, 69715, 69717) 66 Chapter 3 N Fly Ash, Slag, Silica Fume, and Natural Pozzolans Table 3-7. Frost and Deicer-Scaling Resistance of Fly Ash Concrete Results at 300 cycles Frost resistance in water, Deicer scaling resistance, ASTM C 666 Method A (AASHTO T 161) ASTM C 672** Expansion, Mass loss, Durability Water Curing % % factor cure compound 0.010 1.8 105 3 2 0.001 1.2 107 2 2 0.005 1.0 104 3 3 0.006 1.3 98 3 3 0.003 4.8 99 3 2 0.004 1.8 99 2 2 0.008 1.0 102 2 2 0.006 1.2 104 3 2 0.004 1.7 99 3 2 0.004 1.0 100 3 2 0.006 0.004 0.002 1.6 1.8 2.5 101 102 101 3 3 2 2 2 2 Fly ash mixtures* Class of Identification fly ash A C B F C F D F E F F C G C H F I C J F Average of: Class C Class F Control mixture * Concrete mixtures had a cementitious materials content of 307 kg/m3 (517 lbs/yd3), a water to cementitious materials ratio of 0.40 to 0.45, a target air content of 5% to 7%, and a slump of 75 mm to 100 mm (3 in. to 4 in.). Fly ash dosage was 25% by mass of cementitious material. Gebler and Klieger 1986a. ** Scale rating (see at right) 0 = No scaling 1 = Slight scaling 2 = Slight to moderate scaling 3 = Moderate scaling 4 = Moderate to severe scaling 5 = Severe scaling (2718) (564 lb/yd3) of cementitious material and a maximum water to cementitious materials ratio of 0.45 is recommended. A satisfactory air-void system is also critical. The importance of using a low water-cement ratio for scale resistance is demonstrated in Fig. 3-19. The effect of high fly ash dosages and low cementing material contents is demonstrated in Fig. 3-20. The performance of scaleresistant concretes containing fly ash at a dosage of 25% of 5 Scale rating at 50 cycles ASTM C 672 4 3 2 1 0 0.4 0.5 Moist cure 0.6 0.7 0.8 0.9 1 Water to portland cement ratio 1.1 1.2 cementing material by mass is presented in Table 3-7. The table demonstrates that well designed, placed and cured concretes with and without fly ash can be equally resistant to deicer scaling. The ACI 318 building code states that the maximum dosage of fly ash, slag, and silica fume should be 25%, 50%, and 10% by mass of cementing materials, respectively for deicer exposures. Total supplementary cementing materials should not exceed 50% of the cementitious material. Dosages less than or higher than these limits have been shown to be durable in some cases and not in others. Different materials respond differently in different environments. The selection of materials and dosages should be based on local experience and the durability should be demonstrated by field or laboratory performance. Drying Shrinkage and Creep When used in low to moderate amounts, the effect of fly ash, ground granulated blast-furnace slag, calcined clay, calcined shale, and silica fume on the drying shrinkage and creep of concrete is generally small and of little practical significance. Some studies indicate that silica fume may reduce creep (Burg and Ost 1994). 67 Fig. 3-19. Relationship between deicer-scaling resistance and water to portland cement ratio for several air-entrained concretes with and without fly ash. A scale rating of 0 is no scaling and 5 is severe scaling (Whiting 1989). Design and Control of Concrete Mixtures Scale rating at 150 cycles (ASTM C 672) N EB001 Scale rating at 150 cycles (ASTM C 672) 5 4 3 2 1 0 None A D E Fly ash F G J 25% replacement Moist cure Cementitious material 250 kg/m3 (417 lb/yd3) 305 kg/m3 (508 lb/yd3) 335 kg/m3 (588 lb/yd3) 5 4 3 2 1 0 None A D E Fly ash F G J 50% replacement Moist cure Cementitious material 250 kg/m3 (417 lb/yd3) 305 kg/m3 (508 lb/yd3) 335 kg/m3 (588 lb/yd3) Fig. 3-20. Relationship between deicer-scaling resistance and dosage of fly ash for air-entrained concretes made with moderate to high water-cementitious materials ratios. Replacement of portland cement with fly ash: (left) 25% and (right) 50%. A scale rating of 0 is no scaling and 5 is severe scaling (Whiting 1989). Permeability and Absorption With adequate curing, fly ash, ground slag, and natural pozzolans generally reduce the permeability and absorption of concrete. Silica fume and metakaolin are especially effective in this regard. Silica fume and calcined clay can provide concrete with a chloride resistance of under 1000 coulombs using the ASTM C 1202 rapid chloride permeability test (Barger and others 1997). Tests show that the permeability of concrete decreases as the quantity of hydrated cementing materials increases and the water-cementitious materials ratio decreases. The absorption of fly-ash concrete is about the same as concrete without ash, although some ashes can reduce absorption by 20% or more. 0.25 Alkali-Aggregate Reactivity Alkali-silica reactivity can be controlled through the use of certain supplementary cementitious materials. Silica fume, fly ash, ground granulated blast-furnace slag, calcined clay, calcined shale, and other pozzolans have been reported to significantly reduce alkali-silica reactivity (Figs. 3-21 and 3-22). Low calcium Class F ashes have reduced reactivity 0.7 No pozzolan 0.6 ASTM C 1260 expansion at 14 days, percent 0.5 0.20 Expansion, percent 0.4 ASTM C 441 Cement: 0.92% alkali Pyrex glass 0.15 0.10 0.3 0.05 0.2 20% Calcined shale 15% 25% Low-CaO fly ash 15% 25% 15% 25% Medium-CaO High-CaO fly ash fly ash 35% 50% Slag Control 0 0.1 20% Calcined clay Fig. 3-21. Effect of different fly ashes and slag on alkali-silica reactivity. Note that some ashes are more effective than others in controlling the reaction and that dosage of the ash or slag is critical. A highly reactive natural aggregate was used in this test. A less reactive aggregate would require less ash or slag to control the reaction. A common limit for evaluating the effectiveness of pozzolans or slags is 0.10% expansion using this rapid mortar bar test (Detwiler 2002). 68 0 0 2 4 6 Age, months 8 10 12 Fig. 3-22. Reduction of alkali-silica reactivity by calcined clay and calcined shale (Lerch 1950). Chapter 3 N Fly Ash, Slag, Silica Fume, and Natural Pozzolans expansion up to 70% or more in some cases. At optimum dosage, Class C ashes can also reduce reactivity but to a lesser degree than most Class F ashes. Supplementary cementing materials provide additional calcium silicate hydrate to chemically tie up the alkalies in the concrete (Bhatty 1985, and Bhatty and Greening 1986). Determination of optimum supplementary cementing materials dosage is important to maximize the reduction in reactivity and to avoid dosages and materials that can aggravate reactivity. Dosage rates should be verified by tests, such as ASTM C 1260 (AASHTO T 303) or ASTM C 1293. Supplementary cementing materials that reduce alkali-silica reactions will not reduce alkali-carbonate reactions, a type of reaction involving cement alkalies and certain dolomitic limestones. Descriptions of aggregate testing and preventive measures to be taken to prevent deleterious alkali-aggregate reaction are discussed in Farny and Kosmatka (1997), PCA (1998), and AASHTO (2000). Corrosion of Embedded Steel Some supplementary cementing materials reduce steel corrosion by reducing the permeability of properly cured concrete to water, air, and chloride ions. Fly ash can significantly reduce chloride-ion ingress. Silica fume greatly decreases permeability and chloride-ion ingress and also significantly increases electrical resistivity, thereby reducing the electrochemical reaction of corrosion. Concrete containing silica fume or metakaolin is often used in overlays and full-depth slab placements on bridges and parking garages; these structures are particularly vulnerable to corrosion due to chloride-ion ingress. Carbonation Carbonation of concrete is a process by which carbon dioxide from the air penetrates the concrete and reacts with the hydroxides, such as calcium hydroxide, to form carbonates. In the reaction with calcium hydroxide, calcium carbonate is formed. Carbonation lowers the alkalinity of concrete. High alkalinity is needed to protect embedded steel from corrosion; consequently, concrete should be resistant to carbonation to help prevent steel corrosion. The amount of carbonation is significantly increased in concretes with a high water-cementing materials ratio, low cement content, short curing period, low strength, and a highly permeable or porous paste. The depth of carbonation of good quality concrete is generally of little practical significance. At normal dosages, fly ash is reported to slightly increase carbonation, but usually not to a significant amount in concrete with short (normal) moist-curing periods (Campbell, Sturm, and Kosmatka 1991). Sulfate Resistance With proper proportioning and material selection, silica fume, fly ash, calcined shale, and ground slag can improve the resistance of concrete to sulfate or seawater attack. This is done primarily by reducing permeability and by reducing the amount of reactive elements (such as calcium) needed for expansive sulfate reactions. For improved sulfate resistance of lean concrete, one study showed that for a particular Class F ash, an adequate amount was approximately 20% of the cement plus fly ash; this illustrates the need to determine optimum ash contents, as higher ash contents were detrimental (Stark 1989). The sulfate resistance of high-cement-content, low water-cement ratio concrete made with a sulfate resistant cement is so great that fly ash has little opportunity to improve resistance. Concretes with Class F ashes are generally more sulfate resistant than those made with Class C ashes. Some Class C ashes have been shown to reduce sulfate resistance at normal dosage rates. Ground slag is generally considered beneficial in sulfate environments. However, one long-term study in a very severe environment showed a slight reduction in sulfate resistance in concrete containing ground slag compared to concrete containing only portland cement as the cementing material (Stark 1986 and 1989). One reason for decreased performance with slag in this study is that the mixtures may not have been optimized for sulfate resistance. Other studies indicate that concrete with ground slag has a sulfate resistance equal to or greater than concrete made with Type V sulfate-resistant portland cement (ACI 233 and Detwiler, Bhatty, and Bhattacharja 1996). Calcined clay has been demonstrated to provide sulfate resistance greater than high-sulfate resistant Type V cement (Barger and others 1997). 69 Chemical Resistance Supplementary cementing materials often reduce chemical attack by reducing the permeability of concrete. Although many of these materials may improve chemical resistance, they do not make concrete totally immune to attack. Concrete in severe chemical exposure should be protected using barrier systems. Kerkhoff (2001) provides a discussion of methods and materials to protect concrete from aggressive chemicals and exposures. Soundness Normal dosages of fly ash, slag, silica fume and natural pozzolans do not affect the soundness of concrete. Concrete soundness is protected by soundness requirements, such as autoclave expansion limits, on the materials. Dosages in concrete should not exceed dosages deemed safe in the autoclave test. Concrete Color Supplementary cementitious materials may slightly alter the color of hardened concrete. Color effects are related to Design and Control of Concrete Mixtures N EB001 the color and amount of the material used in concrete. Many supplementary cementing materials resemble the color of portland cement and therefore have little effect on color of the hardened concrete. Some silica fumes may give concrete a slightly bluish or dark gray tint and tan fly ash may impart a tan color to concrete when used in large quantities. Ground slag and metakaolin can make concrete whiter. Ground slag can initially impart a bluish or greenish undertone. STORAGE In most cases, moisture will not affect the physical performance of supplementary cementing materials. These materials should, however, be kept dry to avoid difficulties in handling and discharge. Class C fly ash and calcined shale must be kept dry as they will set and harden when exposed to moisture. Equipment for handling and storing these materials is similar to that required for cement. Additional modifications may be required where using silica fume, which does not have the same flowing characteristics as other supplementary cementing materials (and may be supplied as a liquid). These materials are usually kept in bulk storage facilities or silos, although some products are available in bags. Because the materials may resemble portland cement in color and fineness, the storage facilities should be clearly marked to avoid the possibility of misuse and contamination with other materials at the batch plant. All valves and piping should also be clearly marked and properly sealed to avoid leakage and contamination. Fly ash, slag, and natural pozzolans should be weighed after the portland or blended cement in the batching sequence to avoid overdosing in case valves stick. CONCRETE MIX PROPORTIONS The optimum amounts of supplementary cementing materials used with portland cement or blended cement are determined by testing, by the relative cost and availability of the materials, and by the specified properties of the concrete. Several test mixtures are required to determine the optimum amount of pozzolan or slag. These mixtures should cover a range of blends to establish the relationship between strength and water to cementing materials ratio. These mixtures should be established according to ACI Standard 211.1 or 211.2, taking into account the relative densities of the supplementary cementing materials. These are usually different from the relative density of portland cement. The results of these tests will be a family of strength curves for each age at which the concrete is required to meet certain specified requirements. The dosage of a cementitious material is usually stated as a mass percentage of all the cementitious materials in a concrete mixture. Typical practice in the United States uses fly ash, slag, silica fume, calcined clay, or calcined shale as an addition to portland cement or as a partial replacement for some of the portland cement. Blended cements, which already contain pozzolans or slag, are designed to be used with or without additional supplementary cementitious materials. Concrete mixtures with more than one supplementary cementitious material are also used. For example, a concrete mixture may contain portland cement, fly ash, and silica fume. Such mixes are called ternary concretes. When fly ash, slag, silica fume, or natural pozzolans are used in combination with portland or blended cement, the proportioned concrete mixture should be tested to demonstrate that it meets the required concrete properties for the project. REFERENCES AASHTO, Guide Specification on Alkali-Silica Reaction, Section 56, http://leadstates.tamu.edu/ASR/library/ gspec.stm, 2000. Abrams, Duff A., "Effect of Hydrated Lime and Other Powdered Admixtures in Concrete," Proceedings of the American Society for Testing Materials, Vol. 20, Part 2, 1920. Reprinted with revisions as Bulletin 8, Structural Materials Research Laboratory, Lewis Institute, June 1925, 78 pages. Available through PCA as LS08. ACAA, http://www.acaa-usa.org, American Coal Ash Association, Alexandria, Virginia, 2001. ACI, Concrete Durability, Katherine and Bryant Mather International Conference, SP100, American Concrete Institute, Farmington Hills, Michigan, 1987. ACI Committee 211, Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete, ACI 211.1-91, American Concrete Institute, Farmington Hills, Michigan, 1991, 38 pages. ACI Committee 211, Standard Practice for Selecting Proportions for Structural Lightweight Concrete, ACI 211.2-98, American Concrete Institute, Farmington Hills, Michigan, 1998, 14 pages. ACI Committee 211, Guide for Selecting Proportions for High Strength Concrete with Portland Cement and Fly Ash, ACI 211.4R-93, American Concrete Institute, Farmington Hills, Michigan, 1993, 13 pages. 70 AVAILABILITY All supplementary cementitious materials may not be available in all areas. Consult local material suppliers on available materials. Class F fly ashes are usually available in the Eastern United States, while Class C ashes are available in the Midwest and West. Silica fume is available in most locations because only small dosages are used. Calcined clays and shales are available in select areas. Ground granulated slags are available in most regions. Chapter 3 N Fly Ash, Slag, Silica Fume, and Natural Pozzolans ACI Committee 232, Use of Fly Ash in Concrete, ACI 232.2R96, American Concrete Institute, Farmington Hills, Michigan, 1996, 34 pages. ACI Committee 232, Use of Raw or Processed Natural Pozzolans in Concrete, ACI 232.1R-00, American Concrete Institute, Farmington Hills, Michigan, 2000, 24 pages. ACI Committee 233, Ground Granulated Blast-Furnace Slag as a Cementitious Constituent in Concrete, ACI 233R-95, American Concrete Institute, Farmington Hills, Michigan, 1995, 18 pages. ACI Committee 234, Guide for the Use of Silica Fume in Concrete, ACI 234R-96, American Concrete Institute, Farmington Hill, Michigan, 1996, 51 pages. Barger, Gregory S.; Lukkarila, Mark R.; Martin, David L.; Lane, Steven B.; Hansen, Eric R.; Ross, Matt W.; and Thompson, Jimmie L., "Evaluation of a Blended Cement and a Mineral Admixture Containing Calcined Clay Natural Pozzolan for High-Performance Concrete," Proceedings of the Sixth International Purdue Conference on Concrete Pavement Design and Materials for High Performance, Purdue University, West Lafayette, Indiana, 1997, 21 pages. Bhatty, M. S. Y., "Mechanism of Pozzolanic Reactions and Control of Alkali-Aggregate Expansion," Cement, Concrete, and Aggregates, American Society for Testing and Materials, West Conshohocken, Pennsylvania. Winter 1985, pages 69 to 77. Bhatty, M. S. Y., and Greening, N. R., "Some Long Time Studies of Blended Cements with Emphasis on AlkaliAggregate Reaction," 7th International Conference on AlkaliAggregate Reaction, 1986. Buck, Alan D., and Mather, Katharine, Methods for Controlling Effects of Alkali-Silica Reaction, Technical Report SL-87-6, Waterways Experiment Station, U.S. Army Corps of Engineers, Vicksburg, Mississippi, 1987. Burg, R. G., and Ost, B. W., Engineering Properties of Commercially Available High-Strength Concretes (Including Three-Year Data), Research and Development Bulletin RD104, Portland Cement Association, 1994, 62 pages. Campbell, D. H.; Sturm, R. D.; and Kosmatka, S. H., "Detecting Carbonation," Concrete Technology Today, PL911; Portland Cement Association, http://www.portcement. org/pdf_files/PL911.pdf, March 1991, pages 1 to 5. Carette, G. G., and Malhotra, V. M., "Mechanical Properties, Durability, and Drying Shrinkage of Portland Cement Concrete Incorporating Silica Fume," Cement, Concrete, and Aggregates, American Society for Testing and Materials, West Conshohocken, Pennsylvania, Summer 1983. Cohen, Menashi, D., and Bentur, Arnon, "Durability of Portland Cement-Silica Fume Pastes in Magnesium Sulfate and Sodium Sulfate Solutions," ACI Materials Journal, American Concrete Institute, Farmington Hills, Michigan, May-June 1988, pages 148 to 157. Detwiler, Rachel J., "Controlling the Strength Gain of Fly Ash Concrete at Low Temperature," Concrete Technology Today, CT003, Portland Cement Association, http://www. portcement.org/pdf_files/CT003.pdf, 2000, pages 3 to 5. Detwiler, Rachel J., Documentation of Procedures for PCA's ASR Guide Specification, SN 2407, Portland Cement Association, 2002. Detwiler, Rachel J.; Bhatty, Javed I.; and Bhattacharja, Sankar, Supplementary Cementing Materials for Use in Blended Cements, Research and Development Bulletin RD112, Portland Cement Association, 1996, 108 pages. Farny, J. A., and Kosmatka, S. H., Diagnosis and Control of Alkali-Aggregate Reactivity, IS413, Portland Cement Association, 1997, 24 pages. Gaynor, R. D., and Mullarky, J. I., "Survey: Use of Fly Ash in Ready-Mixed Concrete," NRMCA Technical Information Letter No. 426, National Ready Mixed Concrete Association, Silver Spring, Maryland, June 1985. Gebler, S. H., and Klieger, P., Effect of Fly Ash on the Air-Void Stability of Concrete, Research and Development Bulletin RD085, Portland Cement Association, http://www.port cement.org/pdf_files/RD085.pdf, 1983, 40 pages. Gebler, Steven H., and Klieger, Paul, Effect of Fly Ash on Some of the Physical Properties of Concrete, Research and Development Bulletin RD089, Portland Cement Association, http://www.portcement.org/pdf_files/RD089.pdf, 1986, 48 pages. Gebler, Steven H., and Klieger, Paul, Effect of Fly Ash on the Durability of Air-Entrained Concrete, Research and Development Bulletin RD090, Portland Cement Association, http:// www.portcement.org/pdf_files/RD090.pdf, 1986a, 44 pages. Helmuth, Richard A., Fly Ash in Cement and Concrete, SP040T, Portland Cement Association, 1987, 203 pages. Hogan, F. J., and Meusel, J. W., "Evaluation for Durability and Strength Development of a Ground Granulated Blast Furnace Slag," Cement, Concrete, and Aggregates, Vol. 3, No. 1, American Society for Testing and Materials, West Conshohocken, Pennsylvania, Summer 1981, pages 40 to 52. Kerkhoff, Beatrix, Effect of Substances on Concrete and Guide to Protective Treatments, IS001, Portland Cement Association, 2001, 36 pages. Klieger, Paul, and Isberner, Albert W., Laboratory Studies of Blended Cements--Portland Blast-Furnace Slag Cements, Research Department Bulletin RX218, Portland Cement Association, http://www.portcement.org/pdf_files/ RX218.pdf, 1967. Klieger, Paul, and Perenchio, William F., Laboratory Studies of Blended Cement: Portland-Pozzolan Cements, Research and 71 Design and Control of Concrete Mixtures x EB001 Stark, David, Longtime Study of Concrete Durability in Sulfate Soils, Research and Development Bulletin RD086, Portland Cement Association, http://www.portcement.org/pdf_ files/RD086.pdf, 1982. Stark, David, Durability of Concrete in Sulfate-Rich Soils, Research and Development Bulletin RD097, Portland Cement Association, http://www.portcement.org/pdf_ files/RD097.pdf, 1989, 14 pages. Tikalsky, P. J., and Carrasquillo, R. L., Effect of Fly Ash on the Sulfate Resistance of Concrete Containing Fly Ash, Research Report 481-1, Center for Transportation Research, Austin, Texas, 1988, 92 pages. Tikalsky, P. J., and Carrasquillo, R. L., The Effect of Fly Ash on the Sulfate Resistance of Concrete, Research Report 481-5, Center for Transportation Research, Austin, Texas, 1989, 317 pages. Whiting, D., Strength and Durability of Residential Concretes Containing Fly Ash, Research and Development Bulletin RD099, Portland Cement Association, http://www.port cement.org/pdf_files/RD099.pdf, 1989, 42 pages. Development Bulletin RD013, Portland Cement Association, http://www.portcement.org/pdf_files/RD013.pdf, 1972. Lange, David A., Long-Term Strength Development of Concrete, RP326, Portland Cement Association, 1994. Lerch, William, Studies of Some Methods of Avoiding the Expansion and Pattern Cracking Associated with the AlkaliAggregate Reaction, Research Department Bulletin RX031, Portland Cement Association, http://www.portcement.org /pdf_files/RX031.pdf, 1950. Malhotra, V. M., Pozzolanic and Cementitious Materials, Gordon and Breach Publishers, Amsterdam, 1996, 208 pages. PCA, Survey of Mineral Admixtures and Blended Cements in Ready Mixed Concrete, Portland Cement Association, 2000, 16 pages. PCA Durability Subcommittee, Guide Specification to Control Alkali-Silica Reactions, IS415, Portland Cement Association, 1998, 8 pages. SFA, http://www.silicafume.org, Silica Fume Association, Fairfax, Virginia, 2000. 72 ...
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