Fly Ash Types and Benefits

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The American Society for Testing and Materials (ASTM) definespozzolan as a siliceous or siliceous and aluminous material, whichin itself possesses little or no cementitious value, but will, in finely

divided form and in the presence of moisture, chemically react with calciumhydroxide at ordinary temperatures to form compounds possessingcementitious properties.

Class F and Class C fly ash are products of the combustion of coal in largepower plants. Fly ash is collected in electrostatic precipitators or baghouses,then transferred to large silos for shipment. When needed, fly ash isclassified by precise particle size requirements, thus assuring a uniform,quality product.

Class F fly ash is available in the largest quantities. Class F is generally low in

lime, usually under 15 percent, and contains a greater combination of silica,alumina and iron (greater than 70 percent) than Class C fly ash.

Class C fly ash normally comes from coals which may produce an ash withhigher lime content generally more than 15 percent often as highas 30 percent. Elevated CaO may give Class C unique self-hardeningcharacteristics.

Although both types of fly ash impart a wide range of qualities to many typesof concrete, they differ chiefly in the following ways:

Class F

1. Most effectively moderates heat gain during concrete curing and istherefore considered an ideal cementitious material in mass concreteand high strength mixes. For the same reason, Class F is the solutionto a wide range of summer concreting problems.

2. Provides sulfide and sulfate resistance equal or superior to Type Vcement. Class F is often recommended for use where concrete may beexposed to sulfate ions in soil and ground water.

Class C

1. Most useful in performance mixes, prestressed applications, andother situations where higher early strengths are important.

2. Especially useful in soil stabilization since Class C may not require theaddition of lime.

Concrete manufacturers, engineers, architects, developers and contractorsall have an interest in specifying or using fly ash on a routine basis toimprove the quality of their project and to increase their cost effectiveness.

Ready Mix Producers.A ready mix producer has several reasons for usingfly ash in concrete.

1. Fly ash can compensate for fines not found in some sands and therebyenhance pumpability and concrete finishing.

2. Fly ash will result in a more predictable and consistent finishedproduct that will ensure customer acceptance.

3. Fly ash offers flexibility in mix design providing a greater range omixes from liquid soil at 100 psi to high strength (8,000 plus psconcrete) produced by the same batch plant without exoticequipment.

4. Fly ash improves the flowability of the concrete, which translates intoless wear and tear on all the producers equipment, from batchingfacilities to trucks.

5. Fly ash enables the producer to customize designs to each

customers needs, thus providing the producer a competitiveadvantage.

Engineers and Architects. Engineers and architects will find that fly ashprovides the following benefits:

1. It enables engineers and architects to provide the client with a superioand more durable finished concrete.

2. Fly ash produces a high strength concrete that accommodates thedesign of thinner sections.

3. Fly ash permits design flexibility accommodating curves, arches andother pleasing architectural effects.

4. The addition of fly ash to the mix is a built-in insurance fo

later-age strength gain in concrete.

5. Fly ash ensures that the concrete will qualify as a durablebuilding material.

6. Fly ash contributes to the aesthetic appearance of the concrete.

Developers, Contractors, Owners. Fly ash concrete provides thefollowing advantages to developers, contractors and owners:

1. The workability of fly ash concrete generally ensures that the speed oconstruction is faster, which translates into a quicker return oninvestment.

2. Fly ash in the mix accommodates more creative designs.

3. Since fly ash concrete is not as vulnerable to deterioration or

disintegration as rapidly as concrete without fly ash, it ensures low-maintenance buildings that will retain their value over the long-term.

Fly Ash Types and Benefits

Fly ash is the best known, pozzolan in the worldand one of the most commonly used.

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For more information or answers to specific questions about the use of fly ash,

contact your nearest Headwaters Resources technical representative,

call 1-888-236-6236, or visit us online at www.flyash.com.

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The table below shows typical compound analyses for twofly ashes and a natural pozzolan (Class F fly ash, Class Cfly ash and Class N - Natural) and ordinary portland cement. A

glance at the table reveals:

1. The same compounds exist in fly ash and portland cement. Those of flyash are amorphous (glassy) due to rapid cooling; those of cement arecrystalline, formed by slower cooling.

2. The major difference between fly ash and portland cement is the relativequantity of each of the different compounds. Portland cement is rich in lime(CaO) while fly ash is low. Fly ash is high in reactive silicates while portlandcement has smaller amounts.

TYPICAL CHEMICAL COMPOUNDS

IN POZZOIANS AND PORTLAND CEMENT

The table illustrates the basic chemical difference. Portland cement ismanufactured with CaO, some of which is released in a free state duringhydration. As much as 20 pounds of free lime is released during hydrationof 100 pounds of cement. This liberated lime forms the necessaryingredient for reaction with fly ash silicates to form strong and durablecementing compounds no different from those formed during hydration ofordinary portland cement.

A review of the chemistry of both materials makes it apparent that a blendof the two will enhance the concrete product and efficiently utilize theproperties of both.

HYDRATION PRODUCTS OF CEMENTING BINDERS

Through pozzolanic activity, fly ash combines with free lime to produce thesame cementious compounds formed by the hydration of portland cement

Chemical Comparison of Fly Ash and Portland CementNUMBER

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The chemical composition of fly ash is very similar to that of portland cement.

SiO

A12O3

Fe2O3

CaO

MgOSO3

Na2O & K2O

54.90

25.80

6.90

8.70

1.800.60

0.60

39.90

16.70

5.80

24.30

4.603.30

1.30

58.20

18.40

9.30

3.30

3.901.10

1.10

22.60

4.30

2.40

64.40

2.102.30

0.60

CLASS F CLASS C CLASS N

CHEMICALCOMPOUND

POZZOLAN TYPE CEMENT

PORTLAND CEMENT

PORTLAND + WATER (H20)CEMENT(PC)

CalciumSilicateHydrate

Free Lime (CaOH)

(CSH)

Water

Soluable

Durable Binder

NonDurable By-Product

PORTLAND CEMENT + FLY ASH

PORTLAND + FLY + WATERCEMENT ASH (H20)

(PC) (FA)

CalciumSilicateHydrate

(CSHDurable Binder

FREE LIME + FLY ASH(CaOH) (FA)




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Compressive Strength. Strength gain contributed by portlandcement occurs very rapidly at early ages up to about seven days, after

which it slows markedly. Strength development contributed by flyash occurs through chemical combination of reactive fly ash glass withcalcium hydroxide generated by hydration of portland cement. This processis called pozzolanic activity.

A fly ash concrete mix, designed for equivalent performance to conventionalconcrete at normal ages, will generally gain strength more slowly at earlyages. After about seven days, the rate of strength gain of fly ash concreteexceeds that of conventional concrete, enabling equivalence at the desiredage. This higher rate of strength gain continues over time, enabling fly ashconcrete to produce significantly higher ultimate strength than can be

achieved with conventional concrete.

Fly ash concrete designed for equivalent performance at seven days orearlier will yield practically the same strength gain prior to the design age.

At all ages thereafter, fly ash concrete will exhibit much higher strength gainthan conventional concrete.

Concrete made with Class C fly ash (as opposed to Class F) hashigher early strengths because it contains its own lime. This allowspozzolanic activity to begin earlier. At later ages, Class C behaves very muchlike Class F, yielding higher strengths than conventional concrete at 56 and90 days.

Uniformity. Statistical analyses of compression tests have shown that theuse of fly ash often lowers the variability of strengths (lower

coefficient of variation). This can result in a reduction in overdesign,yielding a direct cost savings to the concrete producer.

Flexural Strength. In general, a relationship exists between the compres-sive and flexural strengths of concrete. Concrete which has a highercompressive strength will have a correspondingly higher flexural strength.This holds true for fly ash concrete. However, in many cases, fly ashconcrete has demonstrated flexural strength exceeding that of conventionaconcrete when compressive strengths were roughly equal.

High Strength Concrete. In instances where high strength concrete hasbeen specified (above 7,000 psi), fly ash has consistently proven its use-fulness. After a certain amount of cement has been added to a mix (usuallyabout 700 pounds), the addition of fly ash usually results in higher strengths

than an equal amount of added cement. This is especially true for 56 and 90day strengths. Production of high strength concrete requires the use of highquality fly ash at a minimum of 15 percent by weight of total cementitiousmaterials.

Strength of Fly Ash ConcreteNUMBER

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Fly ash concrete can be designed to achieve any level of strength obtainable by concrete containing only

portland cement.

Compre

ssiveStrength

Fly Ash Concrete

PlainConcrete

7 28Age (Days)




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ACI 211 gives the proportioner a series of steps through which values are selected for:

These ingredients are converted into solid volumes. The difference between the sum ofthe total volumes and 27 cubic feet will determine the necessary volume of sand. Sandweight is then calculated to complete the trial mix proportions. The accuracy of this mixmust be checked by physically preparing a sample of the proportioned ingredients andtesting the mixture for yield.

While fly ash is a cementitious material that greatly benefits concrete, the proportioningof concrete containing fly ash requires adjustments because of the physical properties ofthe ash. Viewed microscopically, fly ash particles are spherical in shape. Because of thisand other physical attributes of fly ash, one can expect the following:

The ball bearing shape significantly aids the workability of concrete. This allows forlower sand content than conventional mixes while handling remains similar. As the

proportion of sand is reduced, all performance aspects of the concrete are enhanced.

Again, because of fly ashs spherical particle shape, less water is required to achievethe same level of slump as in the control concrete. The addition of fly ash inconventional mixtures typically reduces the water needed by 5% to 10% over plainconcrete (depending upon the quantity of fly ash), and this reduction can be furtherincreased where high levels of fly ash are used.

The specific gravity of fly ash is much lower than that of portland cement; therefore,100# of fly ash has a much greater solid volume than the same weight of portlandcement. Past practice has dictated a cement reduction when water-reducingadmixtures are used; however, in fly ash concrete, the cementitious materials (cementand fly ash) volume is higher, not lower. This higher quantity of cementitiousmaterials greatly assists in the finishing process.

Air entrainment is not affected adversely with high quality fly ash supplied byHeadwaters. Headwaters has developed a proprietary foam index test that allows us

to control fly ash quality with respect to air entrainment in concrete. A slight increasein admixture dosage can be expected because of the increased solid volume ofcementitious fines, but performance should be uniform. This increase in dosagetypically amounts to less than 0.25 ounces per 100# of cementitious materials.

The use of water-reducing admixtures is encouraged with fly ash concretemixtures; however, certain factors must be considered:

1. During warm temperatures, a normal dosage of water-reducing admixture is cal-culated on the combined weight of cement plus fly ash.

2. During periods of low temperatures, it is advisable to use a conservative dosage ofnormal set time water-reducing admixture calculating the dosage based only onthe weight of cement. Under cool temperatures, normal setting water-reducingadmixtures may cause retarded concrete set. Reducing the dosage utilized duringcool conditions can help maintain proper concrete set times.

DETERMINATION OF FLY ASH CONTENT

Several methods exist for the selection of the fly ash content in a mixture.

Specification. The specifications for a particular project may define a required fly ashcontent. The percentage of fly ash required may range from as little as 10% to as high as50% or 60%, depending upon the intention of the engineer. Failure to adhere to thespecified level of fly ash may result in concrete of substandard properties and may not besuitable for the intended purpose.

Optimum Ash Curves. In this method, a control curve is first generated bytesting mixes with cement contents which vary from a low of 300# to a high of 700#per cubic yard in increments of 100#. All mixes should be of identical lump and yieldPlot cement contents on the abscissa (X axis), plot comprehensive strength on theordinate (Y axis). A separate curve will be generated for each age of test. A family ofoptimum ash curves will be generated for each age of test. A family of optimum ashcurves is then derived in the following manner:

For each point on the control curve, a series of mixes should be tested with fly ashcontents varying between 10% and 30% of total cementitious material(by weight) in increments of 10%. Plot these results on the same charts as thecontrol mixture. These curves can then be utilized to choose the appropriateproportions of cementitious materials for any requirements.

Water/Cementitious Materials Ratio Curves. In this method, the Abrams law owater to cement ratio is utiliz ed. As this law is applic able to plain cemenconcrete, so is it applicable to fly ash concrete. The objective is to construct afamily of curves which are plotted together, with each curve indicating a specificpercentage of fly ash by weight of total cementitious materials (typically 0%, 10%, 20%30%, etc.). This method is particularly useful where specifications require a maximumwater/cementitious materials ratio.*

Do not be surprised to find that for a fly ash mixture to be equivalent in strength to plain cement mixture, the W/(C+FA) must be lower than the W/C. This is acceptabledue to the fact that fly ash acts like a water reducer. Where cement is replaced by an

equivalent weight of fly ash and the strengths are equal, they both have the same weighof cementitious materials but the fly ash mix will have a lower water demand.

Replacement Method.Another successful method of designing fly ash concrete is byreplacement. This involves selecting a conventional mix which has demonstrated anadequate performance level. Replacement tests should be run on a series of mixecontaining fly ash in amounts ranging from 10% to 30% or more. To obtain 28-daystrengths equal to the straight cement mix, it may be necessary to replace cement at aratio exceeding 1:1. This can be determined by experimenting with mixes designed withreplacement ratios of 1:1, 1:1.1, 1:1.2, etc. As in the other methods, specification factorwill influence the selection of the optimum replacement percentage and ratio.

Proportioning Fly Ash Concrete MixesNUMBER

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For detailed explanations of the testing programs mentioned above, the followingreferences are available:1. Cannon, R. W., Proportioning Fly Ash Concrete Mixes For Strength And Economy

Journal of The American Concrete Institute; V. 65; No. 11; November 1968.2. Lovewell, C. E. and Hyland, Edward J., Proportioning Concrete Mixes - A Method o

Proportioning Structural Concrete Mixtures With Fly Ash And Other PozzolansAmerican Concrete Institute Publications SP-46-8.

3. Lovewell, C. E. and Washa, G. W., Proportioning Concrete Mixes Using Fly Ash,Journal of The American Concrete Institute; V. 54; No. 12; June 1958.

*Note - The American Concrete Institute now defines that water to cement ratio is equivalent towater to cementitious materials ratio. This means that fly ash is counted by weight the same asportland cement in this calculation. The importance of this to the concrete designer is the waterreducing capability of fly ash. Where plain cement concrete may require 300# of water toprovide the necessary degree of workability, fly ash concrete will use significantly less water, andmay only require 90% of this, or 270# of water. If a max W/C of 0.5 is specified, the plain mixwould need 600# of cement, while the fly ash mix would only need 540# of cementitious ma-terials. The economic benefits are obvious.

Proportioning fly ash concrete mixtures is only slightly more complicated than proportioning plain cement concrete

mixtures. The same solid volume proportioning techniques described in ACI 211 are employed as are used with

conventional concrete mixtures.

cementitious materials content air content water content coarse aggregate size and content




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Blemishes in concrete, typically called rock pockets, are indicative ofconcrete without suitable workability, even though the slump may be

judged to be acceptable. Rock pockets indicate a separation of thepaste from the coarse aggregate in the concrete mix. Concrete must becohesive even at high slumps to maintain its homogeneous character andavoid segregation and costly rock pockets. Fly ash offers this feature withoutextra cost.

Reduced Water of Convenience. Approximately 25 pounds (threegallons) of water are normally required to hydrate 100 pounds of cement1.

A normal concrete mix will generally contain twice the required amount of

water to hydrate the cement enough to facilitate handling and placing ofthe concrete. This additional water, called water of convenience, increasesslump but at the cost of decreased cohesiveness. Water of convenience isreduced when fly ash is added to the mix because the plasticizing actionresults in a 2% to 10% water reduction in the plastic concrete to producethe same level of slump as plain concrete. Reduced water of convenience atthe same level of slump makes for more cohesive concrete and decreases theoccurrence of costly segregation.

Greater Consolidation. Fly ash concrete is actually more workable thanplain cement concrete at equivalent slump. The VEBE test measures thetime and energy necessary for consolidation of concrete under vibration.Figure 1 shows the remarkable difference in time and energy required forconsolidation of plain and fly ash concretes.

Great benefits can be obtained when using more completely consolidatingfly ash concrete in areas of difficult placement where rock pockets and otherplacing defects often occur. Engineers understand the effectiveness of usingfly ash concrete in tall thin walls, such as those used in water tanks. Theyknow they have a better chance of getting the dense, void free concrete theyhave specified when fly ash is included in the mix.

Paste Volume Increases. The specific gravity of fly ash is lighter thancement. When replacing fly ash on a pound for pound basis, the result is agreater solid volume of cementitious fines. Proportioning concrete mixtures

with only water-reducing admixtures results in a greatly diminished volume

of cementitious fines. In effect, this amounts to taking cement out of themix and replacing it with sand and gravel. The strengths may be acceptablebut the workability may not be. Proportioning performance concrete withfly ash virtually guarantees a greater solid volume of cementitious materials

which in itself helps promote cohesiveness and workability.

Cementitious fines are very important to the contractor who finishesflatwork. These fines are necessary to allow proper leveling, sealing, anddensification of the surface. Fly ash spheres help ease the contractors jobby lubricating the surface, making it much easier and faster to finish the job

In lean mixes, or where aggregates are deficient in fines, an increase in thevolume of paste and an improvement in consistency will be advantageous forworkability and may also increase strength by allowing more complete

compaction.2

Economical Mixture. Pound for pound, no other solid material improvethe workability, strength, and other properties of a concrete mix like fly ashcan, resulting in the most economical of mixtures.

Placing and finishing concrete becomes easier because of the improvedworkability from the spherically shaped fly ash particles. Lower slumpconcrete can be placed more easily (and at lower water content) because othe plasticity provided by fly ash spheres. Segregation and bleeding arereduced because of to the increased cohesiveness of fly ashconcrete, so form finish and sharpness of detail are enhanced. And coarseclean sands can be used in concretes utilizing fly ash and still have good

workability.

Fly Ash Improves WorkabilityNUMBER

5BULLETIN

1. Highway Research Board, Bulletin 284, Fly Ash in Concrete, January 1960,p. 27.

2. Central Electricity Generating Board, Application of PFA in Concrete and Cement,RIBA Products Data, Lonon, March 1982.

Though it is never specified, workability is one of the most critical characteristics of concrete. Workability refers to

the ease of handling, placing and finishing of fresh or plastic concrete. Slump is the general indicator of

workability, yet different concretes can have greatly different levels of workability with the same slump measurement.

Use of fly ash in concrete can greatly enhance workability.

25

20

15

10

5

0

VEBETIMEsec.

SLUMP - in.

0 1 2 3 4 5

PLAIN CEMENT

20% FLY ASH

TYPICAL VEBE TIME vs SLUMP




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Permeability is defined as the coefficient representing the rate at

which water is transmitted through a saturated specimen of concreteunder an externally maintained hydraulic gradient.1 Permeability is

inversely linked to durability in that the lower the permeability, the higherthe durability of concrete.

Permeability is most frequently described by the chloride-ion permeabilitytest, which measures the passage of electrical current through a concretespecimen exposed to a batch of sodium chloride.2 Limits of acceptability areas shown in the table below.3

CHLORIDE PERMEABILITY BASED ON CHARGE PASSED

Recent testing has shown that properly proportioned concretes using acombination of fly ash, normal or high-range water reducing admixtures,and air entraining admixtures have the ability to produce the same low levelsof permeability as latex modified and silica-fume concretes.

Fly ash increases the cementitious compounds, minimizes water demand,and reduces bleed channels all of which increase concrete density. Thesefactors yield concrete of low permeability with low internal voids. Durabilityis increased with regard to freeze-thaw damage and disintegration fromattack by acids, salts or sulfates.

FLY ASH HELPS FIVE WAYS

Using fly ash in the concrete mix greatly aids permeability and durability infive ways:

1. Through pozzolanic activity, fly ash chemically combines with waterand calcium hydroxide forming additional cementitious compound

which result in denser, higher strength concrete. The calciumhydroxide chemically combined with fly ash is not subject to leachingthereby helping to maintain high density.

2. The conversion of soluble calcium hydroxide to cementitioucompounds decreases bleed channels, capillary channels and voidspaces and thereby reduces permeability.

3. At the same time, the above chemical reaction reduces the amount o

calcium hydroxide susceptible to attack by weak acids, salts or othersulfates.4

4. Concrete density is also increased by the small, finely divided particleof fly ash which act like micro-aggregates to help fill in the tiniest voidsin the concrete.

5. Fly ash provides a dramatic lubricating effect which greatly reduceswater demand (2% to 10%). This water reduction reduces internavoids and bleed channels and keeps harmful compounds out of theconcrete.

Fly Ash Decreases the Permeability of ConcreteNUMBER

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1. Admixtures for Concrete, American Concrete Institute, Journal of ACI Proceedings, Vol.60, No. 11, November 1963, p. 1512.

2. Standard Method of Test for Rapid Determination of the Chloride Permeability ofConcrete, American Association of State Highway and Transportation Officials, AASHTOT277-89, Washington, DC.

3. Suprenant, Bruce A., Testing for Chloride Permeability of Concrete, ConcreteConstruction, July 1991.

4. Fly Ash Increases Resistance to Sulfate Attack, U.S. Department of the Interior, Bureauof Reclamation, Research Report No. 23, 1970, p.5.

Permeability of concrete and the resulting level of durability are matters of great concern to designers of concrete

structures. Fly ash can be a valuable tool in reducing permeability.

Charge Passed(coulombs)

>4,000

2,000 - 4,000

1,000 - 2,000

100 - 1,000

0.6), PCC

Moderate water/cement ratio(0.4 to 0.5), PCC

Low water/cement ratio(


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Sulfate attack is a two-phased process. Sulfates combine with calcium

hydroxide generated during cement hydration to form calcium sulfate (gyp-sum). The volume of this gypsum is greater than the sum of its componentscausing internal pressure and expansion, which fractures the concrete. Thenaluminate compounds from portland cement react chemically with sulfates andcalcium to form a compound called ettringite (calcium sulphoaluminate). Ettringiteformation destroys the concrete in the same manner as gypsum formation.

Fly ash effectively reduces this sulfate deterioration in three important ways:1) Fly ash chemically binds free lime in cementitious compounds, rendering it

unavailable for sulfate reaction.2) Fly ash activity reduces concrete permeability, keeping sulfates from

penetrating concrete.3) Replacing a portion of portland cement with fly ash reduces the amount of

reactive aluminates (tricalcium aluminate) available for sulfate reaction.

Studies by the United States Bureau of Reclamation (USBR) show that properlyproportioned concrete utilizing up to 35 percent Class F fly ash will withstandsulfate attack far better than conventional portland cement. Plain and fly ashconcrete mixes using Type I, moderate sulfate resisting Type II, and sulfate resistingType V cements were compared under standardized conditions of exposure tosodium sulfate. In all instances, Class F fly ash concrete dramatically outperformedconventional portland cement concrete.4,5 These tests clearly demonstrate that TypeII cement with Class F fly ash was more resistant to sulfate attack than Type Vcement alone.

Further USBR work correlates the chemistry of a given fly ash with its ability toresist sulfate attack through a mathematical equation called the R factor, formulatedbelow:2,3

As CaO calcium oxide increases and Fe2O3 decreases, sulfate resistance decreases

due to fly ash chemistry.

R factor requirements are currently used in USBR concrete specifications. Thelimits established by the USBR requiring progressively lower R values as sulfateattack severity increases are as follows:

The Portland Cement Association (PCA) reports the use of Class F fly ash improvessulfate resistance, while Class C fly ash is less effective and may even acceleratedeterioration.4

ACI 232.2R-96 (Use of Fly Ash in Concrete) reports that fly ash with CaO contenless than 15% will generally improve sulfate resistance. Fly ash with greater CaOcontent should be evaluated for use per ASTM C1012 or USBR test 4908.

To ensure the most durable concrete possible, Class F fly ash is an essentialingredient when the project will be vulnerable to attack by sulfates or otheraggressive compounds.

Class F Fly Ash Increases Resistance to Sulfate AttackNUMBER

7BULLETIN

1. Dikeou, J.T., Fly Ash Increases Resistance of Concrete to Sulfate Attack, United

States Department of the Interior, Bureau of Reclamation, Research Report No. 23,

US Government Printing Office, 1975.

2. Dunstan, E. R., A Spec Odyssey-Sulfate Resistant Concrete for the 80s, United

States Department of the Interior, Water and Power Resources Service, March 1980.

3. Dunstan, E. R., Fly Ash and Fly Ash Concrete, US Bureau of Reclamation, U.S.

Government Printing Office, May 1984.

4. Helmuth, R. Fly Ash in Cement and Concrete, Portland Cement Association, Skokie, IL,

1987.

Soluble sulfates in soils, ground waters, and sewage can destroy portland cement concrete unless it is produced with fly ash

to provide sulfate resistance commensurate with the severity of the attack.

AverageExpansionat10,0

00Days,pct

(valuesextrapolatedfrome

xpansionsobtainedtodate)

Expansion to failure

Type V+ Fly Ash

Type VCement

Type IICement

Type II+ Fly Ash

Type ICement

Type I+ Fly Ash

Type V+ Fly Ash

Type VCement

Type IICement

Type II+ Fly Ash

Type ICement

Type I+ Fly Ash

25

20

15

10

5

0

* R = (CaO-5)/ Fe2O3 percentage from fly ash oxide analysis; for very severe cyclicconditions of wetting and drying or for MgSO4 reduce the R value by 0.50.

** Slightly improved to slightly reduced.*** Compared to a Type II cement control at 0.45 w/c2.

PercentExpansion

0.005

0.004

0.003

0.002

0.001

0

-0.001

200 400 600 800 1000 1200

High C

Low C

Class F

Control

R Limits* Sulfate Resistance***

3.0

Greatly improved

Moderately improved

No significant change**

Reduced

Reduced expansion of concrete containing 30 percent fly ash illustrates improved sulfateresistance afforded by fly ash use.1

Von Fay, Kurt and Pierce,James S., Sulfate Resistanceof Concrete with VariousFly Ashes, ASTMStandardization News,Dec. 1989.

For more information or answers to specific questions about the use of fly ash

for resistance to sulfate attack, contact your nearest Headwaters Resources technical

representative, call 1-888-236-6236, or visit us online at www.flyash.com.

CaO-5

Fe2O3R =

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Under certain conditions and in certain areas, reactive silica inaggregates will react with soluble alkalis from any available source,causing excessive and deleterious expansion.1A volume change will

occur over a period of time which causes the concrete to spall at thesurface. In addition to resulting surface ruptures, interior stresses may occur

which cause cracking and seriously impair structural integrity of theconcrete.

The use of low alkali (LA) cement (


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Freeze/thaw deterioration begins when water enters voids inconcrete. Leaching of calcium hydroxide, producing thehydration of portland cement, provides greater voids for wa-

ter to occupy, thereby aggravating the rate of deterioration. Uponfreezing, this water expands in volume 9%, generating pressures of30,000 psi.

This tremendous pressure greatly exceeds the capacity ofconcrete to resist it, and the concrete is forced apart fromwithin. Deterioration provides ever easier paths for water topenetrate into the concrete, resulting in greater disintegration asfreeze/thaw cycles continue.

Entrained air voids have been found to be particularly useful inresisting the destructive action of freeze/thaw cycles. Theory has itthat each of the microscopic air voids purposefully put into theconcrete acts as a pressure release vessel. The pressure exerted aswater turns to ice finds a point of release in these numerous smallair voids.

ACI RECOMMENDATIONS

Even though entrained air is put into concrete, certainconditions must accompany it in order for the concrete to

successfully resist deterioration. The American Concrete Institute(ACI) recommends that the concrete producer take steps to:

1. Introduce the proper percentage of suitably sized and spaced airbubbles into the concrete.

2. Provide a minimum level of compressive strength (typically4,000 psi).

3. Proportion the mix for low concrete absorption.

4. Design the concrete for high density and low permeability.

5. Assure that the concrete be properly cured, thendehydrated, prior to exposure to freeze/thaw.

FLY ASH VALUABLE AID

High quality fly ash can be a concrete producers most valuable assetin achieving all five objectives stated. High quality fly ash works asfollows:

1. Fly ash combines with calcium hydroxide to produceadditional cementitious materials, thereby reducing the amountof calcium hydroxide that may be leached out of the concreteLeaching of the calcium hydroxide increases concrete voidswhich can accelerate freeze/thaw damage. As a resul tpermeability and porosity are reduced.

2. Fly ash fills the minute voids that no other part of the mix can fillthus creating a more dense and less absorptive concrete.

3. Fly ash reduces the amount of water required in the mixby approximately 2% to 10%, because the spherical shape of thefly ash particles reduces bleed channels and void spaces. Reducingbleed channels limits the entrance of water; fewer void spacesmean less space for water to accumulate.

4. Fly ash helps maintain an even distribution of entrained airthrough the plasticizing effect that fly ash particles have on theconcrete mix. High quality fly ash also produces more cohesiveconcrete which holds entrained air inside the concrete.

5. Fly ash helps produce higher compressive strengths long termthat provide a strong concrete which resists the forces generatedduring the freezing of water in the voids.

Fly ash concrete is more stable, uniform, dense, less absorptive andless permeableall factors which improve freeze/thaw durability.

Fly Ash Increases Resistance to Freezing and ThawingNUMBER

9BULLETIN

Concrete deterioration from freeze/thaw cycles has been and continues to be a major problem in cooler areas of the

country. Use of fly ash concrete mixes can help reduce exposure to damage.

For more information or answers to specific questions about the use of fly ash to increase

resistance to freezing and thawing, contact your nearest Headwaters Resources technical


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Compressive Strength. Specifications for normal strength concretegenerally require a given level of strength in 28 days. Fly ash concrete is easilyproportioned to meet strength requirements at this age or any other age

desired.

Fly ash concrete designed to be equivalent in strength to ordinary concrete at 28 dayswill normally exhibit slightly lower strength at early ages. This slight early age strengthreduction does not adversely affect job sequencing due to construction loading. (Seestrength gain curves in Fig. 1).

Fly ash concrete can be easily proportioned to meet strength specifications at earlyages (3 to 7 days). Economics, although still attractive, will not be as great as whenproportioning for 28 days of age or later. Fly ash has been utilized in many earlystrength projects because of many beneficial features other than economy.

Later age strength gain after 28 days can prove to be valuable. It may be used to obtainrequired strengths at lower cost. It may be relied upon in deciding structuralacceptability where compressive strength tests indicate lower than specified strengths.It also plays a key role in producing high strength concrete.

High compressive strengths from 6,000 psi to 14,000 psi are often required instructural concrete. High quality fly ash complying with ASTM C-618 is most advan-tageous in achieving these strength levels. The strength gain derived from 10 to 25%

fly ash (by weight of cementitious materials) cannot be equaled by adding cement. 1 Ithas also been found to produce the same high strength levels in concrete as silica-fume without the high cost.

Lubrication. Fly ash spheres impart a ball bearing lubrication to plastic concreteenhancing workability at the same slump as ordinary concrete while reducing waterconvenience. Enhanced workability contributes increased quality to structuralconcrete in several ways:

1. Concrete pumping is made easier. Flow rate may be increased without increasing line pressure, and line blockages are reduced. Record pumping time isachieved as a result of the use of fly ash. The technique of injecting concreteinto the bottom of the form from the pump hose is made possible by the

workability of the fly ash mix.

2. Form filling becomes easier. Fly ash concrete is more responsive to vibrationenabling forms to be fully filled more quickly and with less effort.

3. Segregation, voids, rock pockets and other defects are reduced because o

increased cohesiveness and workability. (Cost savings from reduced correctiveaction required on defects alone can be significant.)

Increased Durability. The pozzolanic activity which contributes cementitious valueto concrete also yields increased density and reduced permeability. As a resultpenetration of aggressive media is slowed or eliminated, thereby increasing concretedurability.

Fly ash is especially effective in the effort to restrict chloride ion penetration and theaccompanying disintegration it causes. Concrete for parking structures, highwaystructures or any other structures likely to be subject to chlorides should require fly ash.

Pozzolanic activity also chemically binds with cement alkalis, keeping them fromcombining with reactive aggregates, and also acts to reduce internal expansion.

Reduced cement content in fly ash concrete lowers the heat of hydration, which isespecially beneficial in mass concrete applications. Reduced temperature gain results

in reduced thermal shrinkage and less possibility of thermal cracking.

Concrete structures subject to high wind loading are often designed forstiffness. Concrete for use in these structures contains fly ash to help develop the highmodulus of elasticity required. Evaluations performed on concretes of normalstrength levels shows that fly ash concrete has a higher modulus of elasticity than plainconcrete at the same strength level.

Internal pressures generated during freeze/thaw cycles can rapidly destroy structuraconcrete. Fly ash concrete mixes exhibit lower permeability, greater density, andhigher strength, enabling them to better resist freeze/thaw cycles. Concrete mixescontaining fly ash perform as well as or better than ordinary mixes provided thatcomparable strength and air-entrainment factors are maintained in both mixes.2

Mix Selection. As with plant concrete mixes, sound laboratory methods or goodfield history of performance should be used to select fly ash concrete with the properproportions for the needs of the project.

It is recommended that optimum fly ash curves be developed through testing localmaterials if the maximum benefits of fly ash in structural concrete are to be achieved

Fly Ash for Structural ConcreteNUMBER

10BULLETIN

1. Buck, Ronald L., Petersen, C. F. and Winter, M. E., Proportioning and Controlling High Strength Concrete, Proportioning Concrete Mixes, SP-46, American Concrete Institute, Detroit, pp142, 145, (1964).

2. Meilenz, Richard C., Specifications and Methods of Using Fly Ash in Portland Cement Concrete, Ash Utilization, United States Department of the Interior, IC 8640pp. 63-64, (1973).

A major use for fly ash in the construction industry is in the production of high quality structural concrete. Fly ash

contributes beneficial properties to the concrete while helping to maintain economy. These properties include compressive

strength, lubrication and increased durability.

6000

4000

2000

1 3 7 28 90

FLY ASH CONCRTETE

Typical age-strength relationships (mixes designed for equal 28 day strengths)

ORDINARY PORTLANDCEMENT CONCRETE

AGE IN DAYS

STRENGTHPS1

For assistance in conducting these tests or for more information or answers to specific questions

about the use of fly ash in structural concrete, contact your nearest Headwaters Resources

technical representative, call 1-888-236-6236, or visit us online at www.flyash.com.

Rev. 3/05


11/31

Mix Homogeneity. The designer must be aware of the need toimprove gradation and maintain uniformity of the

various materials used in the pumped mix in order to achievegreater homogeneity of the total mix.1 Three mix proportioning methodsfrequently used to produce pumpable concrete are:

Maximum Density of Combined MaterialsMaximum Density Least VoidsMinimum Voids Minimum Area

Mixes must be designed with several factors in mind:

1. Pumped concrete must be more fluid, with enough fine material and

water to fill internal voids.2. Since the surface area and void content of fine material below 300

microns control the liquid under pressure, there must be more ofthese sizes than in a normal mix. Generally speaking, the finer thematerial, the greater the control.

3. The coarse aggregate grading should be continuous and often the sandcontent must be increased by up to five percent at the expense of thecoarser aggregate so as to balance the 500 micron - 5mm fractionagainst the finer solids.

Fly Ash Effective. Unfortunately, adding extra water and fine aggregateleads to a weaker concrete. The usual remedies for this are either to increasethe cement content, which is costly, or to use chemical admixtures, whichalso can be costly and may lead to segregation in marginal mixes. There isanother and far more effective alternative: fly ash.

There are many advantages to including fly ash in concrete mixes to bepumped. Among them are:

1. Particle Size. Fly ash meeting ASTM Specification 618 must have 66percent passing the 325 (45-micron) sieve, and these fineparticles are ideal for void filling. Just a small deficiency in the mixfines can often prevent successful pumping.

2. Particle Shape. Microscopic examination shows most fly ash particlesare spherical and act like miniature ball bearings, aiding the movementof the concrete by reducing frictional losses in the pump and piping.

Studies have shown that fly ash can be twice as effective as cement inimproving workability and, therefore, pumpability.2

Pozzolanic Activity. This chemical reaction combines the fly ashparticles with the calcium hydroxide liberated through the hydration ofcement to form additional cementitious compounds, which increaseconcrete strength.

Water Requirement. Excess water in pumped mixes resulting in over sixinch slumps will often cause material segregation and result in line blockage

As in conventionally placed mixes, pumped concrete mixes with excessivewater also contribute to lower strength, increased bleeding and shrinkageThe use of fly ash in pumped or conventionally placed mixes can reduce the

water requirement by 2% to 10% for any given slump.3

Sand/Coarse Aggregate Ratio. In pumped mixes, the inclusion of liberalquantities of coarse aggregate can be very beneficial because it reduces thetotal aggregate surface area, thereby increasing the effectiveness of theavailable cementitious paste. This approach is in keeping with theminimum voids, minimum area proportioning method. As aggregate sizeincreases, so does the optimum quantity of coarse aggregate. Unfortunatelythis process frequently is reversed in pump mixes, and sand will besubstituted for coarse aggregate to make pumping easier. When thathappens, there is a need to increase costly cementitious material tocompensate for strength loss. However, if fly ash is utilized, its unique

workability and pumpability properties permit a better balance of sand tocoarse aggregate, resulting in a more economical, pumpable concrete.

Fly Ash for Pumped ConcreteNUMBER

11BULLETIN

1. Proportioning Concrete Mixes - ACI Publications SP-46, p. 27.2. Missner, H.S., Effect of Inert Mineral Additives on Workability, Significance of Tests and Properties of Concrete and3. Concrete Making Materials, STP 169-A American Society for Testing and Materials, Philadelphia, 1966, pp. 404-414.

Pumped concrete must be designed so that it can be easily conveyed by pressure through a rigid pipe or flexible

hose for discharge directly into the desired area. Fly ash use can greatly improve pumpability while enhancing the

quality of the concrete and controlling costs.


for pumped concrete, contact your nearest Headwaters Resources technical representative,


Rev. 3/05


12/31

CDF, also known as flowable fill, is an engineered, controlled, fillmaterial which is self placing, self leveling, self compacting and non-settling. It is easily proportioned to suit almost any application while

using conventional materials found in almost every concrete productionfacility.

REASONS TO USE CDF

The first reason to use CDF was likely the need to be able to do a difficultjob well. Since that time, the list of reasons for its use has grown greatly andcontinues to grow. A few of those reasons to use CDF are:

1. CDF perfectly encapsulates whatever has been installed in the trenchand protects it against damage.

2. There is no damage to installed utilities as no mechanical force isneeded to place or compact CDF.

3. CDF does not settle after consolidation so there is complete long-term protection for encapsulated utilities.

4. The job can be done once and forgotten because CDF eliminatescostly repairs due to settlement.

5. CDF consolidates rapidly to allow placement of a permanentpavementpatch. Usually allowed to harden overnight, the filled trench can beplated until the following day and then paved.

6. Placing of CDF fills can be accomplished with reduced personnel andexpensive equipment.

7. Future access to the fill is assured by designing in excavatability of theCDF.

8. CDF protects utilities in fills against loss of support during adjacentexcavation operations. Loose pea gravel fill can flow out if exposed byexcavation, causing a loss of support. Should this occur, however,refilling is made easy with CDF.

9. Traffic accidents (and accompanying litigation) resulting from settledfills are eliminated. The public safety is maintained with non-settlingCDF.

10. CDF improves worker safety as no one need enter the excavation forplacing or consolidation.

11. Field inspection is eliminated as CDF can be depended upon toperform, whereas conventional fill materials must be tested for densityin each lift.

12. Excavation costs are reduced because excavations can be madenarrower, reducing the volume of spoils and fills needed.

13. CDF can be placed in any weather at any time. It will even displacestanding water, which reduces dewatering costs.

14. The speed of construction with CDF minimizes pavement downtimeand helps keep traffic moving.

15. CDF requires no storage or dumping area as it is delivered fresh fromthe ready-mix concrete truck directly into the void.

16. CDF is the perfect fill material for remote locations where access isdifficult. Simply pump CDF in place with a concrete pumpProportioning for pumpability is simple.

17. CDF is the most versatile of materials. It can be easily adjusted to meetrequirements for greater flowability, lower unit weight and higherstrength.

MATERIALS FOR CDF PRODUCTION

The materials used in the production of CDF are the very same utilized inthe production of portland cement concrete. These materials include:

Portland Cement used to provide a light degree of cementing action to themixture. Control of the degree of cementing action is necessary to provideexcavatability for future work. Cement contents typically range for 30#/cyfor normal excavatable fill up to 200#/cy where structural, non-excavatablefill is required. Cement type is not important.

Fly Ash used as a workability agent to provide mixes that can flow greatdistances without segregation. It also provides a slight cementing action. Flyash contents typically range from 200#/cy where limited flowability isnecessary, up to 1,000#/cy where long-range flow-ability/pumpability isnecessary.

Aggregate the same as is currently used in concrete or others not ofconcrete quality. Almost any aggregate can be used, provided it is free ofplastic fines.

Admixtures usually restricted to air-entraining agents but can include theuse of water-reducers.

Physical Properties A typical CDF mixture will have the followingapproximate characteristics:

1 day strength: 10-20 psi28 day strength: 50-100+ psi

Angle of internal friction: 30-55 degreesPermeability: 10-5 to 10-7 cm/sec

Fly Ash for Controlled Density FillNUMBER

12BULLETIN

The materials and methodology used for void filling have remained virtually unchanged for centuries. The filling

process has involved compacting granular materials into voids to provide stabilized fill. Modern technology has only

provided for mechanized compaction versus the use of manual labor. Now available is an engineered product designed

to eliminate failures inherent in the traditional method. This product is called Controlled Density Fill (CDF).

For more information or answers to specific questions about the use of fly ash in

controlled density fill, contact your nearest Headwaters Resources technical representative,


Rev. 3/05


13/31

The Romans used naturally occurring volcanic ash fromMount Vesuvius to cement the paving stones in theirroadways. Many miles of this ancient roadway although

rough by our standards still exist as useable highway.

Today in Europe, paving stones have been replaced by modern daypavement but a product almost identical to volcanic ash is stillused. In fact, most European highways have been constructed withfly ash in all levels, including the wearing course.

On this side of the Atlantic, it has been only in relatively recent yearsthat we have begun to recognize the value of fly ash in concretepavements.

Many States Use Ash. Roadways and interstate highways inAlabama, California, Georgia, Florida, Nebraska, Utah and approx-imately 20 other states and Canadian provinces have beensuccessfully constructed with fly ash, many dating back to the early50s and 60s. These roads are found in every type of climate fromvirtually subtropical to sub-zero.

In January of 1974, the Federal Highway Administration encouragedthe use of fly ash in concrete pavement with its Notice N 5080.4,which urged states to allow partial substitution of fly ash for cementwhenever feasible. The FHWA indicated that the replacement ofcement with fly ash of the order of 10% to 25% can be made givingequal or better concrete strength and durability.1 In addition, inJanuary 1983, the Environmental Protection Agency publishedfederal procurement guidelines for cement and concrete containingfly ash which encourage the utilization of fly ash and establishcompliance deadlines.

Compressive Strengths. Highway departments frequently specifya minimum 14-day flexural strength. These requirements can readilybe met through the utilization of proper mix designs incorporatingspecification fly ash. Equal compressive strengths at all ages can bereadily attained provided specification fly ash, properlyproportioned, is substituted for up to 25% of the cementitousmaterial.

Some of the reasons that fly ash is used in concrete paving have moreto do with the physical characteristics of fly ash than the chemicaland strength gain characteristics. With modern constructiontechniques such as paving trains using slipform equipment thefly ash facilitates placement of the concrete at lower slumps whilemaintaining excellent workability. This means less hand work for thepaving contractor and better surface texture and edge characteristicsfor the design engineers.

Denser Concrete. Using fly ash also results in a denser concrete one that will have much greater ultimate strength and durability.

Paving contractors are increasingly asking that fly ash be used in their

concrete because they are able to place the pavement or curb withless tearing; thus, a smaller finishing crew is required.

These are other advantages to using fly ash that result in a strongerand more durable pavement:

Fly ash concrete pavement will improve the resistance of theconcrete to sulfate attack.

The concrete will be more resistant to road salts andfreeze/thaw action as well as reduced alkali/silica reaction.

In many areas of the country, fly ash also can help keep theinitial cost of concrete pavement competitive with asphaltpavements.

Fly Ash for Pavement ConcreteNUMBER

13BULLETIN

Fly ash has been used in road paving for more than 2,000 years.

1. Use of Fly Ash in Portland Cement Concrete and Stabilized Base Construction, Federal Highway Administration (FHWA), Notice N 5080.4, p. 6, January 17, 1974.


concrete pavement, contact your nearest Headwaters Resources technical representative,


Rev. 3/05


14/31

Concrete pipe is made by essentially two different processes, oneusing extremely dry concrete mixtures and the other using plasticconcrete mixtures.

Dry cast concrete pipe is produced utilizing mechanical and/orvibratory compaction to consolidate dry concrete into a form. The form isremoved from the pipe as soon as the casting is finished. With removal ofthe form, the green pipe is carefully transported to its place of curing.

Atmospheric pressure curing at elevated temperature is typically used toobtain early age performance.

Wet cast pipe uses plastic concrete placed and compacted in a form, whichremains around the pipe until certain levels of performance are achieved.

Although declining in popularity, wet cast pipe may be manufactured by thespinning process (centrifugal) to remove excess water and air to producegreat density and low permeability.

Fly ash has found widespread use as a cementitious material and as anaggregate mineral filler to enhance quality and economy in themanufacturing of concrete pipe.

The major reasons for the use of fly ash in concrete pipe are:

Hostile Conditions. Pipe is inevitably subject to hostile conditions. It ismost often used to convey sewage to and through sewage treatment plants

where hydrogen sulfide gas attack may reduce portland cement concrete torubble. Sulfate attack from soluble sulfates is also of concern. Fly ash makesconcrete less permeable, and pipe containing it may be more resistant to

weak acids and sulfates (Davis 1954; K. Mather 1982). Factors pertaining to

the life of concrete pipe exposed to sulfate attack include the type ofcement, chemistry of fly ash, quality of concrete, bedding and backfill used,groundwater, sulfate concentration and severity of exposure.

Reduced Cement. Dry cast concrete pipe mixes without fly ashtypically use more cement than necessary for strength to obtain the required

workability. In a packerhead pipe casting operation, concrete with a verydry consistency is compacted into a vertical pipe form using a revolvingcompaction tool. Vibratory pipe casting uses mechanical vibration tocompact dry mix concrete into a form. Fly ash allows the producer toremove excess cement from the concrete without sacrificing strength, whileat the same time reducing the amount of water in the mix. Fly ash is usedas cementitious material and aggregate mineral filler to provide strength andadded workability and plasticity.

Workability. Pipe manufacturers throughout the world recognize that thespherical shape of fly ash makes dry harsh mixes, as used in packerhead and

vibratory machines, extremely workable. This added workability reducescycle time, wear on moving parts and forms, and makes a denser, lesspermeable and more airtight pipe. Increased workability translates intomore complete form filling in less time, with less effort and at lower cost.Equipment used in pipe production may last longer due to the lubricatingeffect of the fly ash. Fly ash increases the cohesiveness of the no-slump,freshly placed concrete, facilitating early form stripping and movement ofthe product for curing.

Fewer Rejects. Dry cast concrete pipe benefits from fly ash byobtaining more complete form filling with fewer voids and reduced collapse

Wet cast and centrifugal pipe also benefit from the workability anddensification that fly ash contributes to each mix. Most manufacturers usingfly ash in their mix have less pipe rejected because of voids and crazing.

Other benefits attributed to the use of fly ash include a reduction in the heatof hydration of concrete mixtures containing fly ash, which can reduce thenumber of hairline cracks on the inside surface of stored pipe sections (Cain1979). Concrete mixtures containing fly ash also tend to bleed less, whichis particularly beneficial in wet cast pipe.

The combined benefits: fewer rejects, lower cement requirements, reducedwear on machiner y and lowered cycle times, add up to reducedmanufacturing costs.

ASTM Specifications. Current ASTM specifications for the production of

concrete pipe address the use of fly ash meeting the conditions of ASTMC618 Class F or C in concrete pipe. These specifications allow for the useof portland-pozzolan cement per ASTM C595 containing a maximum of25% fly ash by weight. Where fly ash is used separately, it is limited tobetween 5% and 25% of total cementitious material. The cementitiousmaterials content for concrete for pipe production shall not be less than 470pounds per cubic yard. The concrete mixture shall also have a maximum

water/cementitious materials ratio of 0.53.

Fly Ash for Pipe ManufacturingNUMBER

14BULLETIN

Suggested additional reading:

How Fly Ash Improves Concrete Block, Ready-Mixed Concrete, Concrete Pipe, Concrete Industries Year Book 1976-1977, pp. 1-6.Cain, Craig J., Fly Ash in Concrete Pipe, Concrete Pipe News, Vol. 31, No. 6, Dec., pp.116-119.Davis, Raymond E. Pozzolanic Materials - With Special Reference to Their Use in Concrete Pipe, Technical Memorandum, American Concrete Pipe Association, Vienna, pp. 14-15, 1954.Mather, Katherine, 1982 Current Research in Sulfate Resistance at the Waterways Experiment Station, George Verbeck Symposium on Sulfate Resistance of Concrete, SP-77,

ACI, Detroit, pp. 63-74.

Class F fly ash has been used successfully in the manufacturing of concrete pipe for more than 30 years. It has become an

almost indispensable ingredient to the dry, harsh mixes typically used in modern pipe manufacturing.


for pipe manufacturing, contact your nearest Headwaters Resources technical


Rev. 3/05


15/31

Precast concrete products can be produced with or withoutreinforcement, but units typically consist of narrow, deepsections which are heavily reinforced, making concrete

placement very difficult. Reinforcement typically includes the use of fibers,conventional reinforcing steel, and prestressing steel tendons, eitherpretensioned or post-tensioned or combinations thereof. Mixtures musthave enough workability to flow well under vibration and totally fill the form

without segregation. Hand finishing is often required, necessitating amixture workable enough to allow for this kind of manipulation.

By definition, precast concrete products are cast and cured in other thantheir final position.1 This enables the use of reusable forms which, due toeconomic concerns, are cycled as rapidly as possible. For this reason, theseconcrete products generally achieve their competitive position in themarketplace by using a limited number of forms with a short productioncycle. Normal production schedules allow for one usage of forms per day;

however, 10 to 12 hour schedules are common. Accelerated curing, typicallyemployed to enhance early age concrete strength for handling, shipping, andproduct utilization, accelerates the pozzolanic reaction of fly ash to helpdevelop the necessary early strengths.

Concrete mixtures for these products are proportioned for high levels ofperformance at early ages. Compressive strengths of 3,500 to 5,000 psi (24to 28 MPa) are typically required at the time of form removal or stripping.These early concrete strengths are generally achieved with cementitiousmaterial contents of 600 to 750 lb/cy (355 to 445 kg/cm). Conventional andhigh-range water reducing agents are often employed to attain workabilityat very low water content. Non-chloride accelerating admixtures are alsoused when necessar y. While the early strength gain characteristics of fly ashhave generally been considered too slow for use in these mixtures,perceptions are changing toward the use of fly ash in these applications. Asis true of all mixtures used in precast concrete work, mixture proportioningand curing procedures used must produce adequate early strength, or theturnaround time on forms or molds will be increased.2

While early age strength levels are required for stripping andhandling, higher strength levels are required for the ultimate use of theproducts. The use of quality fly ash meeting ASTM C618specifications is a must in the production of high strength concrete of 6,000psi and higher.3 The strength gain achieved from the use of 10% to 15% flyash cannot be readily attained through the addition of a proportionateamount of cement.

Pretensioned hollow-core structural slabs are produced with no-slumpconcrete. It is consolidated and shaped as it passes through an

extrusion machine. The particle shape of the coarse aggregate and theamount of fine aggregate are very important to workability. Fly ash is widelyconsidered to be a beneficial ingredient to increase the workability of thesedry, harsh mixes.4 Early strength performance of thesemixtures using ClassF fly ash closely parallels mixtures without fly ash in terms of earlycompressive strength. No early strength reduction is apparent.

Although most concern is directed at obtaining desired early compressivestrengths, these concrete products must possess durability to resist

destructive attack from numerous environmental factors.5 Fly ash is seen asa major ingredient utilized in the production of durable concrete and assuch should be included in any concrete subject to severe environments.

Responding to a questionnaire presented in August 1986, 77 members ofthe Precast/Prestressed Concrete Institute (PCI) answered questions aboutheir use of fly ash in prestressed concrete products.6 Of the totarespondents, 32 percent indicated that they were currently using fly ash intheir products, 9 percent had used fly ash but had stopped, and 58 percenthad never used fly ash. Of those that were using fly ash, the average cementreplacement was 19%, with the lowest being 12% and the highest being30%.

Of the respondents using fly ash, 42 percent stated cost savings and 40percent stated increased workability of the mix as major reasons they usedfly ash. Other reasons for use of fly ash were: 1) increased 28 day strength

2) achieved 3,500 psi overnight, 3) better filling of voids, 4) reduction inpermeability, and 5) minimization of shrinkage.

Concerns as to the performance of Class F fly ash in prestressed concretewere addressed in a study by Dhir, Munday, and Ho in 1988.7 Concretespecimens were investigated at ages from 18 hours to 1 year into the areasof strength development (compressive and tensile) and deformationbehavior (elastic, creep and shrinkage). With various replacement ratesevaluated, it was concluded that concretes containing fly ash perform as wellas, or better than, concretes containing only rapid hardening cement. Thesmall amount of alkalis, sulfates, unburned carbon and chlorides present infly ash do not result in problems with regard to corrosion of thereinforcement.8

Fly ash may also be valuable as a mineral admixture to enhance

product quality. Fly ash used in precast concrete products improvesworkability, resulting in products with sharp, distinctive corners and edgesFly ash can also provide improved flowability, resulting in products withbetter surface appearance. Better flowability and workability propertiesachieved by using fly ash are particularly desirable for products with intri-cate shapes and surface patterns and for those that are heavily reinforcedReduced costs associated with repair of surface defects can be attributed tothe use of fly ash.

Fly Ash for Precast/Prestressed Concrete ProductsNUMBER

15BULLETIN

Production of precast concrete products involves intricate, difficult patterns. Fly ash concrete mixes can help precasters

solve challenges in many areas of production.

1. Cement and Concrete Terminology, American Concrete Institute Committee 116R-90, p. 46.

2. Ravina, Dan, Efficient Utilization of Coarse and Fine Fly Ash in Precast Concrete by Incorporating Therma

Curing, American Concrete Institute Journal, Proceedings V.78 No. 3, May-June 1981 pp. 194-200.

3. Blick, Ronald L., Peterson, C.F., Winter, M. E., Proportioning and Controlling High Strength Concrete

Proportioning Concrete Mixes, American Concrete Institute, SP-46, pp. 142, 145, 1974.

4. Juvas, Klaus, The Workability of No-Slump Concrete for Use in Hollow Core Slabs, Nordic Concret

Research, Publication No. 6, pp. 121-130, 1987.

5. Gerwick, Ben C., Jr., Practical Methods of Ensuring Durability of Prestressed Concrete Ocean Structures

Durability of Concrete, American Concrete Institute, SP-47, p. 318, 1975.

6. Shaikh, A.F., and Feely, J.P. 1986, Summary of Responses to a Questionnaire and the Use of Fly Ash in The

Precast and Prestressed Concrete Industry, PCI Journal, pp. 126-128, 1986.

7. Dhir, R.K., Munday, J.G. L., and Ho, N. Y., PFA in Structural Precast Concrete: Engineering Properties

Cement and Concrete Research, Vol. 18, pp. 852-862, 1988.

8. Visvesvaraya, H.C., Incidence of Corrosion of Steel Reinforcement in Fly Ash Concrete, Cement Research

Institute of India, Report RB-3-74, P. 2, 1974.


precast and prestressed concrete, contact your nearest Headwaters Resources technical


Rev. 3/05


16/31

Fly ash improves block manufacturing in two basic ways. It givesproducers the strength required and, at the same time, the addedplasticity that fly ash contributes (reported by Belot, 1976) to the

relatively harsh block mixes assures improved finish and texture; bettermold life, and better, sharper corners. Additional benefits of fly ash in blockinclude reduced permeability and shrinkage, increased durability and virtualelimination of efflorescence.

Fly Ash Chemical Activity. Fly ash is produced by burning powdered coalto generate electricity. Fly ash is a chemically active, finely divided mineralproduct high in silica, alumina and iron. Fly ash that has been burned in theprocess of manufacturing (in the same sense that portland cement clinker isburned) seeks lime. One hundred pounds of portland cement usuallyliberates from 12 to 20 pounds or more of free lime (calcium hydroxide)during hydration. Fly ash then chemically reacts with this free lime to formadditional stable cementitious compounds. The formation of insolublecementing compounds is accelerated and can be secured in a matter ofhours in the steam curing cycle of the concrete products plant (autoclave oratmospheric).

Steam Curing.Autoclave curing, though not as common as in the past, isstill used to manufacture high quality masonry units. Concrete masonryunits cured in high-pressure autoclaves show early strength equivalent tothat of 28-day moist-cured strength and reduction in volume change indrying (Hope 1981). The process uses temperatures of 275 to 375F(135 to 275C) and pressures of 75 to 170 psi (0.52 to 1.17MPa). These

conditions allow for the use of fly ash as a cement replacement up to 35percent for Class C and 30 percent for Class F fly ashes. Particular careshould be taken to insure that the fly ash meets the soundness requirementof ASTM C618, indicated in Note C, Table 2 especially where the fly ash

will constitute more than 20 percent of the total cementitious material.

Low-pressure steam curing is usually performed in insulated kilns atelevated temperatures, the exact temperature used being a function of thematerials and operation of the specific plant. This process allows for the useof fly ash as a cement replacement up to 35 percent for Class C and 25percent for Class F fly ash. Tests with 25 percent Class F fly ash weresuccessful with a curing temperature above 160F (71C) and indicate thatdrying shrinkage of low pressure steam-cured concrete units can be reducedby the addition of fly ash.

Accelerated curing techniques allow for a period of preset before theconcrete products are subjected to elevated temperatures. The preset periodmay lengthen slightly where cement is replaced with fly ash and if so, it mustbe allowed for.

Tests for resistance to freezing and thawing of concrete masonry unitscontaining fly ash indicate that such units, in general, could beexpected to perform well in vertical wall construction. For the more severecondition of horizontal exposure, a minimum compressive strength of3,000 psi (21MPa) based upon the net area of the unit is recommended

when normal weight aggregates are used. This is true whether fly ash is usedor not.

Air-entrainment is not practical at the extremely low or zero slumps usedfor concrete block. It could be applicable to slump block orquarry tile. To provide adequate freezing and thawing durability for unitsmade with slump concrete, air-entrainment is needed (Redmond 1969).

Acceptance by the engineering profession and most code bodies to useconcrete masonry units for high-strength, high-rise, load-bearingconstruction is increasing. To meet this demand, block producers find itnecessary to produce both light and normal weight units testing 3,500 psnet area (1,860 gross area assuming 53 percent solid units) and 5,000 psinet area (2,650 gross area), respectively. The 1,860 psi gross area strengthunits are known as high strength block and those of 2,650 psi gross areastrength are known as extra high strength block.

Trial Mixes. Proportioning mixtures for the manufacture of concretemasonry units is not an exact science. Conditions may vary widely fromplant to plant. When proportioning mixtures, concrete producers shouldcheck the grading and types of aggregates, cements, equipment, and kiln

temperatures, and then adjust trial batches with various amounts of fly ashto achieve specific technical or economic objectives (Valore 1970). Forassistance in this regard, the reader is referred to Siliceous Fines in theCementing Medium of Steam Cured Concrete Masonry Units, a 1967publication by the National Concrete Masonry Association.

Fly Ash for Block ManufacturingNUMBER

16BULLETIN

Suggested Reading:

Concrete Block, Ready-Mix Concrete and Concrete Pipe, Concrete Industries Yearbook, 1974-75.

How Fly Ash Improves Concrete Block, Ready-Mix Concrete, Concrete Pipe, Concrete Industries Yearbook 1976-77

Grant, William, Manufacture of Concrete Masonry Units, Concrete Publishing Corporation, Chicago, 1959.

American Concrete Institute Committee 517, Low Pressure Steam Curing of Concrete, Journal of the American

Concrete Institute, Aug. 1969.

Recommended Practice for Atmospheric Pressure Steam Curing of Concrete, Journal of the American Concrete

Institute, Aug. 1965.

American Concrete Institute Committee 516, High Pressure Steam Curing: Modern Practice and Properties o

Autoclaved Products, Journal of the American Concrete Institute, Aug. 1965.

Belot, J.R., Jr., Fly Ash in Concrete and Concrete Block Manufacturing, Proceedings, 1st Fly Ash Utilization Symposium

(Pittsburgh, Mar.) Information Circular No. 8348, Bureau of Mines, Washington D.C., 1967.

Hope, Brian B., Autoclaved Concrete Containing Fly Ash, Cement and Concrete Research, Vol. 11, No. 2, pp. 227

233, Mar. 1981.

Redmond, T. B., Jr., Freezing and Thawing Tests of Concrete Masonry Units with Cement and Cement-Fly Ash a

Cementitious Materials, National Concrete Masonry Association, Herndon, Oct. 1969.

Valore, R. C., Jr., Laboratory Evaluation of Fly Ash and Other Pozzolans for Use in Concrete Products, Proceedings

2nd Ash Utilization Symposium (Pittsburgh, Mar.), Information Circular No. 8488, U.S. Bureau of Mines,

Washington, D.C., 1970.

The manufacturing of concrete masonry units uses a dry, harsh concrete mixture compacted into molds with great

mechanical energy. When demolded, these units maintain their shape during handling and transportation into a

curing environment. Curing methods consist of the high pressure, high temperature autoclave, or the atmospheric

pressure, high temperature kiln. The use of high quality fly ash has become accepted practice in the industry.

For more information or answers to specific questions about the use of fly ash for concrete

block manufacturing contact your nearest Headwaters Resources technical representative,


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17/31

Modern fly ash production and use is an integral part ofconcrete construction. Architects and structural engineersroutinely design concrete mixes with fly ash for a wide range of

structures, roadways, marine and high strength applications. Provenimprovements in durability, permeability, shrinkage and long term strengthgain yield better quality concrete.

Traditional concrete for integrally colored, color hardened, stained ortextured architectural applications often suffers from the following flaws:

Poor Aesthetics: Straight portland cement mixtures produce

significant amounts of calcium hydroxide in the paste. This leaches outof hardened concrete in the form of free lime (efflorescence) and canovershadow integral color pigment, causing a bleached, streaking effect.It may take several years before efflorescence diminishes.

Lack Surface Integrity: The crystalline structure of calciumhydroxide is expansive. Decorative surface treatments like stains,penetrating colored sealers and acidic stains can be ruined by theleaching effect of efflorescence. In the case of stains, the acidic reactionthat produces color variation actually softens the matrix of the surfacepaste, allowing for greater moisture penetration, yielding moreefflorescence.

Shrinkage and Permeability: Integral color pigments increase pastevolume and require additional water. This increases shrinkage andsurface cracking potential. Higher water demand mixes are more

permeable, allowing for greater moisture absorption, which thenincreases the production of efflorescence.

Major sources of color variations in architectural concrete:

Change in cement, fly ash or aggregates source. Change in mix design proportions. No slump control. Water added to temper loads at the wash rack or on

the job. Change in placement or finishing techniques. Insufficient or improper curing schedule.

Benefits of fly ash in colored architectural concrete:

1. Fly ash chemically and physically combines with calcium hydroxide(efflorescence) to form additional binder glue (calcium silicatehydrate). This additional glue yields greater paste strength with fewer

voids. Efflorescence is greatly reduced.2. The water demand of fly ash mixes is lower, creating a dense, highly

impermeable matrix. This increases durability and reduces the effectsof carbonation. The potential for plastic shrinkage cracking is alsoreduced.

3. Architectural form finishes and textures are improved with fly ash. Thesmall, spherical fly ash particles aid in concrete mobility and pattern

transfer.4. Surface treatments easily adhere to fly ash concrete mixes and lastlonger because of the reduction of efflorescence blooms.

Suggested mix design criteria:

1. Choose the compressive strength criteria and design mixes based onwater / cement + fly ash (W/Cp) ratio. Do not factor colorpigment loading as part of this ratio.

2. Fly ash should be factored at 15-20% replacement of cement. Staywithin the limits of state or local codes.

3. Avoid fly ash sources with excessive L.O.I. (loss on ignition)specifications.

4. Use a Type A water reducer or midrange water reducer to aid inplacement slumps. Place concrete at moderate slumps (3-6) and

avoid temper water on the jobsite.5. Do not use calcium chloride or chloride based products withcolored concrete.

6. Specify a single source for cement, fly ash and aggregates for theduration of the job.

With proper controls , placement and finishing of colored fly ashconcrete is no different than straight cement concrete.

Fly Ash for Architectural ConcreteNUMBER

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Decorative and architectural concrete dates back centuries. Clay moldings from prehistoric caves illustrate mans desire to

enhance the beauty of his surroundings with art, color and architecture. Early Greek and Roman artists used volcanic ash

mixed with sand and lime to create statues and decorative moldings. Many believe that the longevity of early structures, some

still standing today, can be attributed to the pozzolanic activity of volcanic fly ash.

Utilizing fly ash can reduce

or eliminate efflorescence which

detracts from the beauty of

concrete finishes.


architectural concrete, contact your nearest Headwaters Resources technical representative,


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18/31

Stone matrix asphalt (SMA) is a durable, stable, rut-resistant hot mixasphalt (HMA) consisting of two parts: a coarse aggregate skeleton andan asphalt rich binder mortar.

The coarse aggregate provides stone-on-stone contact for bearing and rutresistance. The asphalt rich binder provides sufficient mortar of the desiredconsistency for durability, requiring a large amount of mineral filler such asfly ash to convert the fluid asphalt into asphalt mastic.

SMA has been used in Europe for 20 years and was originally designed toresist the abrasive nature of studded tires. The added benefit of resistanceto general rutting was also observed, leading to the installation of SMA ingeneral use highways. Because of the European success, five states

constructed SMA demonstration projects in 1991. Since that time, the useof SMA within the United States has increased significantly.

In 1997, the National Center for Asphalt Technology (NCAT)completed a performance evaluation of SMA pavements that was sponsoredby the Federal Highway Administration. For this evaluation, more than 100SMA mixtures from 140 SMA projects in more than 19 states wereevaluated. The report concluded, Over 90% of the SMA projects had

rutting measurements less than 4mm. Approximately 25% of the projectshad no measurable rutting. The resistance to rutting appears to be excellentconsidering the high traffic volume on most of the SMA mixtures.1

The crushed aggregate gradations for SMA are more gap-graded than HMAor Superpave dense-graded mixtures, with approximately 75% of theaggregates retained on a No. 4 sieve for SMA versus 50% for Superpave. Thegap-graduation of SMA will require a higher asphalt binder content in therange of 6.0%, versus a Superpave asphalt binder content of 4.5%. Minerafiller such as fly ash is required to stiffen the asphalt. A stabilizing additive isused to create mastic consistency, and to prevent draindown where theasphalt binder drains from the coarse aggregate during transportation andlaydown. In all cases the stabilizer has taken the form of either a fiber

(cellulose or mineral) or a polymer.

The mineral filler content [portion of the aggregate passing the0.075 mm (No. 200) sieve] in SMA can range up to 10% of the totalaggregate. This filler content is greater than that found in conventional HMAand is twice that of most Superpave mixes. The NCAT report concludedthat of the 140 SMA projects SMA mixtures were produced approximately80 percent of the time with 7-11 percent of the material passing the0.075 mm sieve. The high percentage of material passing the 200-meshsieve is typically not available as a residue from aggregate crushing and mustbe added in some other form to the SMA mix at the batch plant. Theuniform, well-graded nature of fly ash provides the high quality mineralfiller required for SMA.

Fly Ash for Stone Matrix AsphaltNUMBER

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Best known for its use as an ingredient in concrete mixes, fly ash also has physical properties that make it a valuable

component in the production of stone matrix asphalt.

1 Performance of Stone Matrix Asphalt (SMA) Mixtures in the United States, NCAT Report No. 97-1, National Center for Asphalt Technology, Auburn University, AL, 36849-5354, Januar y 1997.

100

90

80

70

60

50

40

30

20

10

0#200 #50 #30 #16 #8 #4 3/8" 1/2" 3/4"

Sieve

PercentPassing

SMA and Superpave Gradations

SMA

Superpave

For more information or specific questions about the use of

fly ash for stone matrix asphalt, contact your nearest Headwaters Resources technical

representative,call 1-888-236-6236, or visit us online at www.flyash.com.

Rev. 3/05


19/31

High Reactivity Metakaolin is an engineered, high strength,pozzolanic material. It is an economical alternative to silica fumeand can be utilized in high performance concrete.

Permeability is defined as the coefficient representing the rate at whichwater is transmitted through a saturated specimen of concrete under anexternally maintained hydraulic gradient.1 Permeability is inversely linkedto durability in that the lower the permeability, the higher the durability ofconcrete and, the permeability of concrete to water and chloride is themajor factor affecting the process of corrosion of embedded metals.2

Permeability is most frequently described by the chloride-ion permeabilitytest that measures the passage of electrical current through a concretespecimen exposed to a solution of sodium chloride. Limits of acceptabilityare as shown in the table below.3

Recent testing has shown that properly proportioned concretes using HRMas a direct replacement for silica-fume, along with a combination of high-range water reducing and air-entraining admixtures have the ability toproduce the same low levels of permeability as latex modified and silica-fume concrete.

Using HRM in the concrete mix greatly aids permeability and durability inthe following ways:

1 Through pozzolanic activity, HRM chemically combines with water andcalcium hydroxide, forming additional cementitious compounds thatresult in denser, higher strength concrete. The calcium hydroxidechemically combined with HRM is not subject to leaching, therebyhelping to maintain high density.

2 The conversion of soluble calcium hydroxide to cementitiouscompounds decreases bleed channels and void spaces and therebyreduces permeability.

3 At the same time, the above chemical reaction reduces the amount ocalcium hydroxide susceptible to attack by weak acids and salts.

4 Concrete density is also increased by the small, finely dividedparticles of HRM that act like micro-aggregates to help fill in the tiniest

voids in the concrete.

5 Alkali-silica reactivity (ASR) in concrete can induce expansion andcracking, increasing the concrete permeability. The expansion causedby ASR can be mitigated if a portion of the portland cement is replacedby a suitable metakaolin.5

Permeability of High Reactivity Metakaolin ConcreteNUMBER

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Permeability of concrete and the resulting level of durability are matters of great concern to designers of concrete

structures. High Reactivity Metakaolin (HRM) can be a superior tool in reducing permeability.

1 Admixtures for Concrete, American Concrete Institute, Journal of ACI Proceedings, Vol. 60, No. 11, November 1963, p. 1512.2 Guide to Durable Concrete, ACI 201.2R-92, American Concrete Institute, Section 4.4.2, April 1992.3 Suprenant, Bruce A., Testing for Chloride Permeability of Concrete, Concrete Construction, July 1991.4 M.A. Caldarone, K.A. Gruber, and R.G. Burg, High Reactivity Metakaolin: A New Generation Mineral Admixture, American Concrete Institute, Concrete International

November 1994.5 G.V. Walters

Documents

Fly Ash Types and Benefits