Fly Ash, Slag, Silica Fume, and Natural Pozzolans · Fly Ash, Slag, Silica Fume, and Natural...

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Fly Ash, Slag, Silica Fume, and Natural Pozzolans

Fly Ash, Slag, Silica Fume,and Natural Pozzolans

Also known as —Supplementary Cementing Materials (SCMs)

— a material that, when used in conjunction with portland cement, contributes to the properties of the hardened concrete through hydraulic or pozzolanic activity, or both.

Supplementary CementitiousMaterials (SCMs)

From left to right:■ Fly ash (Class C)■ Metakaolin (calcined clay)■ Silica fume ■ Fly ash (Class F) ■ Slag ■ Calcined shale

Supplementary Cementing Materials — Pozzolans

■ Pozzolan — a siliceous or alumino-siliceous material that, in a finely divided form and in the presence of moisture, chemically reacts with calcium hydroxide released by the hydration of portland cement to form compounds possessing cementing properties.

■ Natural Pozzolans — a natural material which may also be calcined and/or processed ( eg. metakaolin, rice husk, volcanic ash, calcined shale)

Specification and Class of Natural Pozzolans

ASTM C 618 (AASHTO M 295)ASTM C 618 (AASHTO M 295)

Class N—Raw or calcinednatural pozzolans including:

◆ Diatomaceous earths◆ Opaline cherts and shales◆ Tuffs and volcanic ashes or

pumicites◆ Calcined clays, including

metakaolin, and shales

Metakaolin

SEM Micrograph of Calcined Clay Particles

SEM Micrograph of Calcined Shale Particles

Specifications and Classes of Fly Ash

■ Class F—Fly ash with pozzolanic properties

■ Class C—Fly ash with pozzolanic and cementitiousproperties

Fly Ash

SEM Micrograph of Fly Ash Particles

Specifications and Grade of Ground Granulated Iron Blast-Furnace Slags

■ Grade 80Slags with a low activity index

■ Grade 100Slags with a moderate activity index

■ Grade 120Slags with a high activity index

SEM Micrograph of Slag Particles

Applications for Fly ash, Slag, Calcined Clay or Calcined Shale

Specification for Silica FumeASTM C 1240ASTM C 1240

Silica Fume—finely divided residue resulting from the production of silicon, ferro-silicon, or other silicon-containing alloys that is carried from the burning surface area of an electric-arc furnace by exhaust gases.

SEM Micrograph of Silica Fume Particles

Applications for Silica Fume and Metakaolin

Chemical Analysis of Typical Fly Ash, Slag, Silica Fume, Calcined Clay, Calcined Shale, and Metakaolin

0.3—1.51.90.66.32.2Total Na

eq. alk, %

0.4—22.20.40.72.0K2O, %

0.05—0.20.50.35.81.0Na2O, %

0.10.40.50.494.10.8SO3, %

0.1811.640215CaO, %

0.5840.41611Fe2O3, %

4320290.4121823Al2O3, %

53505890353552SiO2, %

Meta-kaolin

Calcinedshale

Calcinedclay

Silica fume

Groundslag

Class C fly ash

Class F fly ash

Selected Properties of Typical Fly Ash, Slag, Silica Fume, Calcined Clay, Calcined Shale, and Metakaolin

2.502.632.502.402.942.652.38Relative density

19,00073099020,000400420420Blaine fineness, m2/kg

0.73.01.53.01.00.52.8Loss on ignition, %

Meta-kaolin

Calcinedshale

Calcinedclay

Silica fume

Groundslag

Class C fly ash

Class F fly ash

Typical Amounts of SCM in Concrete by Mass of Cementing Materials

■ Fly ash◆ Class C 15% to 40%◆ Class F 15% to 20%

■ Slag 30% to 45%■ Silica fume 5% to 10%■ Calcined clay 15% to 35%

◆ Metakaolin 10%■ Calcined shale 15% to 35%

Effect of Fly Ash on Mixing Water Requirements

-1050F

-1550C

Class of fly ash

Change in mixing water requirement compared

to control, %

Fly ash content, % by mass of cementing

material

Effect of Fly Ash on Bleeding of Concrete

0.0591.75Control mixture

0.0441.31

0.0110.34Average of: Class C

Class F

mL/cm2Percent

BleedingFly ash mixtures

Effect of Fly Ash on Air-Entraining Admixture Dosage and Air Retention

5.35.66.06.6100Control mixture

4.54.75.36.3299F

5.85.86.06.5152C

9060300

Minutes after initial mixing

Air content, %

Fly ash mixtures

Percent of air-entraining admixture

relative to control

Effect of Slag on Heat of Hydration

Effect of Fly Ash on Setting Time of Concrete

Class F

Class C

——5:304:15Control mixture

1:150:356:454:50

0:450:306:154:40Average of:

FinalInitialFinalInitial

Retardation relative to

control, hr:minSetting time,

hr:minFly ash test mixtures

Varies

No/Little Effect

Increased

Reduced

Effects of Supplementary Cementing Materials on Freshly Mixed Concrete

Plastic Shrinkage Cracking

Pumpability

Finishability

Setting Time

Heat of Hydration

Air Content

Bleeding and Segregation

Workability

Water Requirements

Nat. Pozzolans

Silica fume

SlagFly ash

Compressive Strength Development

Long Term Strength Development

Cold Weather Strength Development

Abrasion Resistance Vs. Compressive Strength

Fly ash Calcined shale Slag Portland cement

Frost Resistance of Fly Ash Concrete

Class F

1012.50.002Control mixture

1021.80.004

1011.60.006Average of: Class C

Durability factorMass loss, %Expansion, %

Fly ash mixturesFrost resistance in water,

ASTM C 666 Method A (AASHTO T 161)

Results at 300 cycles

Deicer-Scaling Resistance of Fly Ash Concrete

Results at 300 cycles

Control mixture

Average of: Class C

Class F

Water cureCuring

compound

Deicer scaling resistance,

ASTM C 672

Scaling Resistance Vs. W/C-Ratio

Deicer-Scaling of Fly Ash Concrete (25% Replacement)

Deicer-Scaling of Fly Ash Concrete (50% Replacement)

Effect of Fly Ash and Slag on Alkali-Silica Reactivity

Reduction of ASR by CalcinedClay and Calcined Shale

Varies

No/Little Effect

Increased

Reduced

Effects of Supplementary Cementing Materials on Hardened Concrete

Carbonation

Concrete Color

Chemical Resistance

Alkali-Silica Reactivity

Permeability

Drying Shrinkage and Creep

Freeze-Thaw and Deicer-Scaling Resistance

Abrasion Resistance

Strength Gain

Nat. Pozzolans

Silica fume

SlagFly ash

Fly Ash, Slag, Silica Fume, and Natural Pozzolans · Fly Ash, Slag, Silica Fume, and Natural...

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