3 fly ash, slag, silica fume, and natural pozzolans

Fly Ash, Slag, Silica Fume, and Natural Pozzolans

ByProf. Adel El Kordi

&Dr. Meheddene Machaka

Structural EngineeringDepartment

Faculty of EngineeringBeirut Arab University

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CVLE 321

Fly Ash, Slag, Silica Fume, and Natural Pozzolans

Also known as —SupplementaryCementing Materials (SCMs)— a material that, when used in conjunctionwith Portland cement, contributes to theproperties of the hardened concrete throughhydraulic or pozzolanic activity, or both.

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Supplementary Cementitious Materials (SCMs)

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

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Supplementary Cementing Materials - Pozzolans

Pozzolan — a siliceous or alumino-siliceousmaterial that, in a finely divided form and inthe presence of moisture, chemically reactswith calcium hydroxide released by thehydration of portland cement to formcompounds possessing cementingproperties.

Natural Pozzolans — a natural materialwhich may also be calcined and/orprocessed ( eg. metakaolin, rice husk,volcanic ash, calcined shale)

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Specification and Class of Natural Pozzolans

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

ASTM C 618 (AASHTO M 295)

Metakaolin

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SEM Micrograph of Calcined Clay Particles

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SEM Micrograph of Calcined Shale Particles

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Specifications and Classes of Fly Ash

Class F—Fly ash withpozzolanic properties

Class C—Fly ash withpozzolanic and cementitiousproperties


Fly Ash

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SEM Micrograph of Fly Ash Particles

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Specifications and Grade of Ground Granulated Iron Blast-Furnace Slags

Grade 80Slags with a low activityindex

Grade 100Slags with a moderateactivity index

Grade 120Slags with a high activityindex


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SEM Micrograph of Slag Particles

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Applications forFly ash, Slag,Calcined Clay orCalcined Shale

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Specification for Silica Fume

ASTM C 1240Silica Fume—finely dividedresidue resulting from theproduction of silicon, ferro-silicon,or other silicon-containing alloysthat is carried from the burningsurface area of an electric-arcfurnace by exhaust gases.

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SEM Micrograph of Silica Fume Particles

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Applications for Silica Fume and Metakaolin

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

Class Ffly ash

Class Cfly ash

Ground slag

Silicafume

Calcinedclay

Calcinedshale

Meta-kaolin

SiO2, % 52 35 35 90 58 50 53

Al2O3, % 23 18 12 0.4 29 20 43

Fe2O3, % 11 6 1 0.4 4 8 0.5

CaO, % 5 21 40 1.6 1 8 0.1

SO3, % 0.8 4.1 9 0.4 0.5 0.4 0.1

Na2O, % 1.0 5.8 0.3 0.5 0.2 — 0.05

K2O, % 2.0 0.7 0.4 2.2 2 — 0.4

Total Naeq. alk, % 2.2 6.3 0.6 1.9 1.5 — 0.316

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

Class Ffly ash

Class Cfly ash

Groundslag

Silicafume

Calcinedclay

Calcinedshale

Meta-kaolin

Loss on ignition,% 2.8 0.5 1.0 3.0 1.5 3.0 0.7

Blaine fineness,m2/kg 420 420 400 20,000 990 730 19,000

Relativedensity 2.38 2.65 2.94 2.40 2.50 2.63 2.50

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Typical Amounts of SCM in Concreteby 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%

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Effect of Fly Ash on Mixing Water Requirements

Class offly ash

Fly ash content, % bymass of cementing

material

Change in mixing waterrequirement compared

to control, %C 25 -7F 25 -5C 50 -15F 50 -10

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Effect of Fly Ash on Bleeding of Concrete

Fly ash mixturesBleeding

Percent mL/cm2

Average of: Class CClass F

0.34 0.0111.31 0.044

Control mixture 1.75 0.059

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Effect of Fly Ash on Air-Entraining AdmixtureDosage and Air Retention

Fly ashmixtures

Percent of air-entraining admixture

relative to control

Air content, %Minutes after initial

mixing0 30 60 90

C 152 6.5 6.0 5.8 5.8F 299 6.3 5.3 4.7 4.5

Control mixture 100 6.6 6.0 5.6 5.3

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Effect of Slag on Heat of Hydration

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Effect of Fly Ash on Setting Time of Concrete

Fly ash test mixturesSetting time,

hr:min

Retardationrelative to

control, hr:minInitial Final Initial Final

Average of: Class C 4:40 6:15 0:30 0:45Class F 4:50 6:45 0:35 1:15

Control mixture 4:15 5:30 — —

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Effects of Supplementary Cementing Materialson Freshly Mixed Concrete

Reduced No/Little EffectFly ash Slag Silica

fumeNat.

PozzolansIncreased Varies

Water RequirementsWorkabilityBleeding and SegregationAir ContentHeat of HydrationSetting TimeFinishabilityPumpabilityPlastic Shrinkage Cracking 24

Compressive Strength Development

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Long Term Strength Development

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Cold Weather Strength Development

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Abrasion Resistance Vs. Compressive Strength

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Fly ash Calcined shale Slag Portland cement

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Frost Resistance of Fly Ash Concrete

Fly ash mixtures

Results at 300 cyclesFrost resistance in water,

ASTM C 666 Method A (AASHTO T 161)Expansion, % Mass loss, % Durability factor

Average of: Class C 0.006 1.6 101Class F 0.004 1.8 102

Control mixture 0.002 2.5 101

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Deicer-Scaling Resistance of Fly AshConcrete

Results at 300 cycles

Deicer scaling resistance,ASTM C 672

Water cure Curingcompound

Average of: Class CClass F

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Control mixture 2 2 31

Scaling Resistance Vs. W/C-Ratio

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

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

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Effect of Fly Ash and Slag on Alkali-Silica Reactivity

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Reduction of ASR by Calcined Clay and CalcinedShale

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Effects of Supplementary Cementing Materials on Hardened Concrete

Reduced No/Little EffectFly ash Slag Silica

fumeNat.

PozzolansIncreased Varies

Strength GainAbrasion ResistanceFreeze-Thaw and Deicer-Scaling ResistanceDrying Shrinkage and CreepPermeabilityAlkali-Silica ReactivityChemical ResistanceCarbonationConcrete Color 37