Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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.
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Supplementary CementitiousMaterials (SCMs)
From left to right:■ Fly ash (Class C)■ Metakaolin (calcined clay)■ Silica fume ■ Fly ash (Class F) ■ Slag ■ Calcined shale
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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)
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
SEM Micrograph of Calcined Clay Particles
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
SEM Micrograph of Calcined Shale Particles
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Specifications and Classes of Fly Ash
ASTM C 618 (AASHTO M 295)ASTM C 618 (AASHTO M 295)
■ Class F—Fly ash with pozzolanic properties
■ Class C—Fly ash with pozzolanic and cementitiousproperties
Fly Ash
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
SEM Micrograph of Fly Ash Particles
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Specifications and Grade of Ground Granulated Iron Blast-Furnace Slags
ASTM C 989 (AASHTO M 302)ASTM C 989 (AASHTO M 302)
■ Grade 80Slags with a low activity index
■ Grade 100Slags with a moderate activity index
■ Grade 120Slags with a high activity index
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
SEM Micrograph of Slag Particles
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Applications for Fly ash, Slag, Calcined Clay or Calcined Shale
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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.
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
SEM Micrograph of Silica Fume Particles
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Applications for Silica Fume and Metakaolin
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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%
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Effect of Fly Ash on Mixing Water Requirements
-1050F
-1550C
-525F
-725C
Class of fly ash
Change in mixing water requirement compared
to control, %
Fly ash content, % by mass of cementing
material
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Effect of Slag on Heat of Hydration
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Compressive Strength Development
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Long Term Strength Development
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Cold Weather Strength Development
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Abrasion Resistance Vs. Compressive Strength
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Fly ash Calcined shale Slag Portland cement
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Deicer-Scaling Resistance of Fly Ash Concrete
2
2
2
Results at 300 cycles
Control mixture
Average of: Class C
Class F
2
3
3
Water cureCuring
compound
Deicer scaling resistance,
ASTM C 672
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Scaling Resistance Vs. W/C-Ratio
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Deicer-Scaling of Fly Ash Concrete (25% Replacement)
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Deicer-Scaling of Fly Ash Concrete (50% Replacement)
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Effect of Fly Ash and Slag on Alkali-Silica Reactivity
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
Reduction of ASR by CalcinedClay and Calcined Shale
Fly Ash, Slag, Silica Fume, and Natural Pozzolans
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