HtMk0>}Vv=6v*az8G%/Tu "Fly Ash in Roadway Construction," Proceedings of the First Ash Utilization Symposium. 0000012109 00000 n <> 87 0 obj<]/Info 73 0 R/Filter/FlateDecode/W[1 2 1]/Index[74 22]/DecodeParms<>/Size 96/Prev 132005/Type/XRef>>stream (8) There should be no more tendency for fly ash concrete to scale in freezing and thawing exposures than conventional concrete, provided the fly ash concrete has achieved its design strength and has the proper air void system. 202-366-4000, Federal Highway Administration Research and TechnologyCoordinating, Developing, and Delivering Highway Transportation Innovations. xZYo8~7/ @qlvI!vi9VIIlv7:b.zu{zu|zi{qXuy[=\^2Y+.$[//?2[m5+^/44x(o j[qyq!w';mS1r`8DH J3S55Lo)K^Zp%66sKv1c]c}|H+&pEyv|%I:s:>n)>Az0o|$7+ 3`. 197 0 obj<>stream 0000001037 00000 n stream HS[o0~WGsyH[U5jqRW6]1w9'&iARVTSBYK$Ij!{RB>C508Zz0RYx661B;iT@iBhM3HCxo6};][N+]HN8:^xAQ6++Z;GqIp_BQvoo h}F{(J\I4V 0000008336 00000 n Most specifying agencies refer to ASTM C618(2) when citing acceptance criteria for the use of fly ash in concrete. (9) Both Class F and Class C fly ashes are beneficial in the production of high-strength concrete.

Some Class C fly ashes are as effective as Portland cement in developing 28-day strength. Structural design procedures for concrete pavements containing fly ash are no different than design procedures for conventional concrete pavements. Hester, J. When used as a raw feed material for the production of Portland cement, either dry or conditioned ash can be used. x]%5r}8/^3J~,m2nq)I[sPRz+%~|qyhIb=zvQ]WE/9_EY}Ucw(q>8uYeQpYLj~.4\GT]Sme7(y4*mFW#GJh_~{Kkh_5EMUOTjn]9g\9kWt,Uq=`i(s9$uHTE;j>f2G/2b@MeyVu15SGr`jn$}#epT?R:??fSS]>%{7|2t;W$ZNv_"ua$3Bzew]=ve_kQfo%J QWh5u~|h^v[0[S5>V?1pXB5>C!a3^xDS0xnesx'&/{[kje uZmat_B_pOy%.0* &Rj~Yur: 0000010846 00000 n ASTM C618 requires that the pozzolanic activity index with Portland cement, as determined in accordance with ASTM C311,(6) be a minimum of 75 percent of the average 28-day compressive strength of control mixes made with Portland cement. 4{((Pb0gf MQLf`,20pfd`ar 1P~f zT The ACI mix proportioning guidelines recommend a separate trial mix for each 5-percent increment in the replacement of Portland cement by fly ash. (5) This percentage usually ranges from 20 to 35 percent when Class C fly ash is used. endstream endobj 210 0 obj<>stream There is less of a concern with the use of Class C fly ash in cold weather than Class F fly ash. Once fly ash concrete has developed adequate strength, no significant differences in concrete durability have usually been observed. As a consequence of the Clean Air Act, many coal-fired power plants are being equipped with low NOx burners. (17) For pavement concrete, the design strength may be either the tensile or flexural strength, or possibly the unconfined compressive strength. To ensure that such is the case, air content testing of fly ash concrete mixes may initially need to be done at a greater frequency than with normal PCC mixes. FHWA-SA-94-081, Washington, DC, December, 1995. U.S. Department of Transportation endstream endobj 78 0 obj<>stream The use of Class F fly ash usually results in slower early strength development, but the use of Class C fly ash does not and may even enhance early strength development. ACI 211.1. Fly Ash Facts for Highway Engineers. Slump testing of fly ash concrete can be done at the same frequency as for normal PCC mixes. A2)IIijVs]z,~x>Y3f6$UA= Portland Cement Association, Publication No. endstream endobj 211 0 obj<>stream ASTM C204. 0000011847 00000 n Helmuth, Richard. The air content of the concrete must be carefully checked and adjusted during production to ensure that it remains within those limits. Procedures for proportioning fly ash concrete mixes differ slightly from those for conventional concrete mixes. 3 0 obj

However, because of differences in the specific gravity values of Portland cement and fly ash, the volume of cementitious material will vary with each trial mixture.(10). endobj endobj Fly Ash in Cement and Concrete. National Cooperative Highway Research Program Synthesis of Highway Practice No. A. The design of any concrete mix, including fly ash concrete mixes, is based on proportioning the mix at varying water-cementitious ratios to meet or exceed requirements for compressive strength (at various ages), entrained air content, and slump or workability needs. Sulfate Resistance: Class F fly ash will generally improve the sulfate resistance of any concrete mixture in which it is included. (2) This is because carbon contents (reflected by LOI) higher than 3 to 4 percent have an adverse effect on air entrainment. %PDF-1.5 0000005767 00000 n 0000009260 00000 n :YbTJpq't. Current specifications include a requirement for the maximum allowable percentage retained on a 0.045 mm (No. However, because some fly ashes (including some Class C fly ashes) may have appreciable amounts of soluble alkalis, it is necessary to test materials to be used in the field to ensure that expansion due to alkali-silica reactivity will be reduced to safe levels.(8). 1200 New Jersey Avenue, SEWashington, DC 20590 (19) Trial usage of high percentage fly ash concrete mixes is needed in order to be able to evaluate the field performance of these mixes. Scheduling of pavement construction should allow adequate time for the desired or specified strength gain prior to the placement of traffic loads, the onset of freeze-thaw cycles, and the application of deicing salts because of the detrimental effect of cold weather on strength gain. ASTM C618 specifies a maximum of 34 percent retained on a 0.045 mm (No. %PDF-1.6 % Ash from plants burning different coals or blends of coal. Ash from plants using precipitator additives, such as ammonia. Halstead, Woodrow J. In a concrete mix design, the water-cement (w/c) ratio is a key design parameter, with a typical range being from 0.37 to 0.50. 2 0 obj 0000002125 00000 n endstream endobj 212 0 obj<>stream Class F fly ash may have cementitious ability when blended with other by-products such as cement kiln dust prior to being introduced into a concrete mix. Transportation Research Board, Washington, DC, 1994. American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken, Pennsylvania, 1994. The mix design procedures stipulated in ACI 211.1 provide detailed, step-by-step directions regarding trial mix proportioning of the water, cement (or cement plus fly ash), and aggregate materials. 0000009852 00000 n "Use of High-Volume Class F Fly Ash for Structural-Grade Concrete,". (4), The principal benefits ascribed to the use of fly ash in concrete include enhanced workability due to spherical fly ash particles, reduced bleeding and less water demand, increased ultimate strength, reduced permeability and chloride ion penetration, lower heat of hydration, greater resistance to sulfate attack, greater resistance to alkali-aggregate reactivity, and reduced drying shrinkage. 0000011696 00000 n (8) The increased volume of fines and reduced water content also play a role. 8VSXNILaV;ZX%h"$HF.@eMX4nf5!j.U$|]vH64L2Y uM GYIgMYjZb}+)cHg)PyjlI L (5) Normal procedures for screeding, finishing, edging, and jointing of conventional PCC are also applicable to fly ash concrete. However, some Class C fly ashes may have little effect on, or possibly even decrease, the time of setting. Certain fly ashes will reduce the effectiveness of air entraining agents, requiring a higher dosage to meet specifications.

74 0 obj <> endobj

Another important quality control consideration in freshly mixed PCC is its workability, as determined by performing slump tests. ASTM C311-92. Ash from start-up or shut-down phases of operation. Class C fly ash is usually substituted at a 1:1 ratio. National Ready-Mix Concrete Association, Publication No.

4 0 obj (8), Time of Setting: When replacing up to 25 percent of the Portland cement in concrete, all Class F fly ashes and most Class C fly ashes increase the time of setting. ASTM C595(1) defines two blended cement products in which fly ash has been added: 1) Portland-pozzolan cement (Type IP), containing 15 to 40 percent pozzolan, or 2) Pozzolan modified Portland cement (Type I-PM), containing less than 15 percent pozzolan. When fly ash is used, the absolute volume of cement plus fly ash usually exceeds that of cement in conventional concrete mixes. Federal Highway Administration, Report No. 0000007213 00000 n

endstream endobj 196 0 obj<> endobj 198 0 obj<>/Font<>>>/DA(/Helv 0 Tf 0 g )>> endobj 199 0 obj<> endobj 200 0 obj<> endobj 201 0 obj<>/ProcSet[/PDF/Text]/ExtGState<>>> endobj 202 0 obj<> endobj 203 0 obj<> endobj 204 0 obj<> endobj 205 0 obj<> endobj 206 0 obj<> endobj 207 0 obj<> endobj 208 0 obj<> endobj 209 0 obj<>stream Ash that is handled and stored using a wet system. ]5 @!4@(&ePi% AT1 199. (5) There are some states that require that fly ash be added in certain mixes with no reduction in cement content. xbbd``b`:$f $M@+HA% 3Hbx4&H/#n?c/ : As a result, finishing operations may have to be delayed, possibly by 1 to 2 hours, depending on the temperature. 0000005539 00000 n HtTNA+8#w"AdoQYG)TDd=0g}fLkL0LW. Fly ash, especially Class F fly ash, is effective in three ways in substantially reducing alkali-silica expansion: 1) it produces a denser, less permeable concrete; 2) when used as a cement replacement it reduces total alkali content by reducing the Portland cement; and 3) alkalis react with fly ash instead of reactive silica aggregates. Federal Highway Administration stream (8) Class F fly ashes are generally more effective than Class C fly ashes in reducing the heat of hydration. 163, Silver Spring, Maryland, April, 1981. American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken, Pennsylvania, 1994. ASTM C441. As the fineness increases, the pozzolanic activity can be expected to increase. Users of Class C fly ash are cautioned to carefully evaluate the long-term volume stability of concrete mixes in the laboratory prior to field use, with ASTM C441(15) as a suggested method of test. \"Tr9(l Cold-Weather Concreting. American Coal Ash Association. The proper application of a curing compound should retain moisture in the concrete for a sufficient period of time to permit strength development. However, the American Concrete Institute (ACI) recommends that Class F fly ash replace from 15 to 25 percent of the Portland cement and Class C fly ash replace from 20 to 35 percent.(10). Ash from a peaking plant instead of a base loaded plant. A number of states also did not permit the use of fly ash in white concrete items, such as curbs, sidewalks, and median barriers, and two states (Arkansas and New Mexico) reported questionable performance experience: Arkansas had temporarily discontinued the use of fly ash in bridge deck concrete, and New Mexico had a temporary moratorium on the use of Class C fly ash in concrete, pending further investigation.

"Standard Methods of Sampling and Testing Fly Ash or Natural Pozzolans for Use as a Mineral Admixture in Portland Cement Concrete." 0000011978 00000 n

pA*~Jv0s:Lv2}|m|6@Mkw.XuHM(UE(B%(B*K:;|\/HIdmgG"[ <>>> 199, Transportation Research Board, Washington, DC, 1994. ASTM C39. 195 0 obj <> endobj Heat of Hydration: The initial impetus for using fly ash in concrete stemmed from the fact that the more slowly reacting fly ash generates less heat per unit of time than the hydration of the faster reacting Portland cement. (14) Class F fly ashes are probably more effective than Class C fly ashes because of their higher silica content, which can react with alkalis. The coal ash industry is developing comparative information on the characteristics and engineering properties of ASTM C618 sources of fly ash before and after installation of low NOx burners. Mid-Atlantic Regional Technical Committee of the National Ready-Mix Concrete Association, Silver Spring, Maryland, 1993. Concrete mixes are designed by selecting the proportions of the mix components that will develop the required strength, produce a workable consistency concrete that can be handled and placed easily, attain sufficient durability under exposure to in-service environmental conditions, and be economical. Thus, the temperature rise in large masses of concrete (such as dams) can be significantly reduced if fly ash is substituted for cement, since more of the heat can be dissipated as it develops. 0000008734 00000 n endstream endobj 75 0 obj<> endobj 76 0 obj<> endobj 77 0 obj<>stream x@,g 5PHII"llwXRDFaL PLi iFbh(AT208P' A)u@ZMi3100L-w8,=%Td ##\3 1>=5~ #-Ce%f#Lp_LOT$Hv77x/x^MWuaamsD;kD,4:"+7=>, 46-oQLqopVq>tjDJH Z5Bsr&e4DG A_8LnU}h8LG)},'j{WQ)O j@ (3), At the time of this survey, at least eight states did not permit the use of fly ash in either bridge deck or structural concrete. H|Mk@+ABVz&\*48Ac{Gu}! _wWo!lGpaoEy2TdfQ b^eQ'9-S#Sly`j-JENa9FLvdVrMo< Fly ash used in concrete should be as consistent and uniform as possible. As with any concrete, excessive vibration should be avoided because it may reduce the air content of the in-place concrete.(5). Loss on Ignition: Many state transportation departments specify a maximum LOI value that does not exceed 3 or 4 percent, even though the ASTM criteria is a maximum LOI content of 6percent.

xUmO0+4u~I Uj)IU$*>J~>NH|\r4BXBx Lb8c4Y\5%zT&7\V\kd: u>RrGPmy]-^]{uLI}4aoqwm%9Ng|+uYmr\cCxZzJR2-uO&YR8b x4N~dzF1k3fx80p@g6F&}IsNU5"_u!(tL; |XyMV-URfpAW_wQ"3g,iWMN0GCQY]lw:{.".SCv5[=|nL>cL?d~>">Vr0$v8qm]qHW8!tx0=%lnMWr9I*Vq^&-#' IB7m? Basic mix design guidelines for normal concrete (16) and high-strength concrete are provided by ACI.(10).

0000004437 00000 n SP040.01T, Skokie, Illinois, 1987. Fly ashes must have a low enough LOI (usually less than 3.0 percent) to satisfy ready-mix concrete producers, who are concerned about product quality and the control of air-entraining admixtures. Portland Cement Association, Publication No. 0000011599 00000 n "Guide for Selecting Properties for High-Strength Concrete with Portland Cement and Fly Ash," ACI Manual of Concrete Practice, Part 1. Furthermore, consistent LOI values are almost as important as low LOI values to ready-mix producers, who are most concerned with consistent and predictable quality. The percentage of Class F fly ash used as a percent of total cementitious material in typical highway pavement or structural concrete mixes usually ranges from 15 to 25 percent by weight. 325) sieve when wet sieved. <> endstream endobj 230 0 obj<>/W[1 1 1]/Type/XRef/Index[168 27]>>stream "Standard Test Method for Effectiveness of Mineral Admixtures or Ground Blast-Furnace Slag in Preventing Excessive Expansion of Concrete Due to the Alkali-Silica Reaction." This same survey indicated that 44 states had specifications for the use of fly ash as a partial replacement for Portland cement in concrete. (5) The pozzolanic reaction consumes calcium hydroxide (Ca(OH)2), which is leachable, replacing it with insoluble calcium silicate hydrates (CSH). <>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 595.32 841.92] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> endstream endobj 214 0 obj<>stream The most important quality control consideration concerning the use of fly ash in PCC mixes is to ensure that the air content of the freshly mixed concrete is within specified limits and does not fluctuate to any greater extent than a normal PCC mix. endobj The procedures are based to a great extent on the design strength of the concrete mix, usually determined by testing after moist curing for 28 days.

Collins, Robert J. and Stanley K. Ciesielski. Prequalification of fly ashes from different sources provides an agency with a certain level of confidence in the event fly ashes from different sources are to be used in the same project. "Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan For Use as Mineral Admixture in Portland Cement Concrete," American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken, Pennsylvania, 1994. 1, American Society for Testing and Materials, West Conshohocken, Pennsylvania, 1980. 0000001955 00000 n H|TM0W=JT%V]{ 6mJ!cg4 KdoJR W@{tSZ~o4G.8lfD-p@m P^jQ@ys)JM@E\Hc,"1CFI/ e@S*t9]~{W6"--H.4lB@j:7#/o+fnmwze (4g+aKy)jd0&|}Do~z}w'wGJEFd6Vti=_[ooeMb^O\Gw`_05 a2fQe ~`L[ Ni9K;ItR/]o Ses|65Uuwzp=8s x When fly ash is used as a mineral admixture, the ready-mix producer typically handles fly ash in the same manner as Portland cement, except that fly ash must be stored in a separate silo from the Portland cement. One mix design approach commonly used in proportioning fly ash concrete mixes is to use a mix design with all Portland cement, remove some of the Portland cement, and then add fly ash to compensate for the cement that is removed. Recycling and Use of Waste Materials and By-Products in Highway Construction, National Cooperative Highway Research Program Synthesis of Highway Practice No. 0000006481 00000 n Hn@E)=#aV vA )3jJi| %1(!,Xub (U)S%:;8}6Xe:]GF:C(UE(BN~0 Recycling and Use of Waste Materials and By-Products in Highway Construction - Volume 2. Placement and handling of fly ash concrete is in most respects similar to that of normal concrete. Fineness: Fineness is the primary physical characteristic of fly ash that relates to pozzolanic activity. xb```b`` a`e``vcc@ >'E&B4^TQ^ofoRaai>O73wG}:`e^5&Ik5;(8eTGOEBmsJKn*]zGb@iXtH^0$2o,qur6 YX{SS4Nm.0qE3 XqeTr+S4zJ,(dJ!15`x endstream endobj 213 0 obj<>stream 195 36 0000011529 00000 n

When used in blended cement or as a partial replacement for Portland cement in ready-mix concrete, fly ash must be in a dry form and as such requires no processing. 8348, Washington, DC, 1967, pp. xbbH` Q0 The short-term effect of burning coal in a low NOx burner appears to be an increase in the LOI of the fly ash. In theory, the reaction between the very small particles of amorphous silica glass in the fly ash and the alkalis in the Portland cement, as well as the fly ash, ties up the alkalis in a nonexpansive calcium-alkali-silica gel, preventing them from reacting with silica in aggregates, which can result in expansive reactions.

}")E` L? %PDF-1.3 <<11afc172887ded458feca726ca04124f>]>> 0000011766 00000 n Not only is the risk of thermal cracking reduced, but greater ultimate strength is attained in concrete with fly ash because of the pozzolanic reaction. (11) Some Class C fly ashes may improve sulfate resistance, while others may actually reduce sulfate resistance(12) and accelerate deterioration. Special attention must be given to attaining the proper amount of entrained air and air void distribution. 95 0 obj<>stream There are considerable laboratory and limited field data that indicate that high percentage (50 to 70 percent) Class F or Class C fly ash, in combination with a high range water reducing admixture, produces concrete with exceptional compressive strength. Cook, James E. A Ready-Mixed Concrete Company's Experience with Class C Ash. HdSM0W1JPj7U=Pp6T PpMC?S,$n~. 5xJOhP`>h$s^xRH)WAJk2"y^nweBIuF The increased ratio of solids volume to water volume produces a paste with improved plasticity and more cohesiveness. (10), Mix design procedures for normal, as well as high-strength, concrete involve a determination of the total weight of cementitious materials (cement plus fly ash) for each trial mixture that is being investigated in the laboratory. National Cooperative Highway Research Program Technical Appendix to Synthesis of Highway Practice No. Class C fly ashes often exhibit a higher rate of reaction at early ages than Class F fly ashes. ACI 211.4R-93. A 1992 survey of all 50 state transportation agencies indicated that 40 states have had experience in the use of fly ash as a mineral admixture in concrete, usually as a partial replacement for Portland cement, although a number of states have also used blended Portland-pozzolan cement. Moisture Content: ASTM C618 specifies a maximum allowable moisture content of 3.0 percent. xb```f``e`a``b`@ r4@"%xZ~?uO;um)[{d_aA`&Gq0Jtppe,&>@Z `O1fS6/&D?3003YU00@{K1"h` *30 Fineness can also be assessed by methods that estimate specific surface area, such as the Blaine air permeability test(7) commonly used for Portland cement. 0000005869 00000 n (13) Class C fly ashes should be individually tested before use in a sulfate environment. Ash from plants using oil as a supplementary fuel. There is no need to add more fly ash to a concrete mix in which blended cement is being used, and it is recommended that no fly ash be added in such cases. The blended cement can be used in the mix design process in essentially the same way as a Type I Portland cement. endstream endobj

Class F fly ash may also be substituted at a 1:1 ratio, but is sometimes specified at a 1.25:1 ratio, and in some cases may even be substituted at a 1.5:1 ratio. When fly ash is used as a separately batched material, trial mixes should be made using a water-cement plus fly ash (w/c+f) ratio, sometimes referred to as the water-cementitious ratio, instead of the conventional w/c ratio.(16). Use of Fly Ash in Concrete. Many state transportation agencies, through their own program of sampling and testing, have been able to prequalify sources of fly ash within their own state (or from nearby states) for acceptance in ready-mixed concrete. (8), Pumpability: Pumpability is increased by the same characteristics affecting workability, specifically, the lubricating effect of the spherical fly ash particles and the increased ratio of solids to liquid that makes the concrete less prone to segregation.(8). 87-100. "Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens," American Society for Testing and Materials, Annual Book of ASTM Standards, Volume 04.02, West Conshohocken, Pennsylvania, 1994.

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