POZZOLANSPOZZOLANS(Supplementary Cementitious (Supplementary Cementitious Materials)Materials)

PozzolanPozzolan

The name Pozzolan comes from the town The name Pozzolan comes from the town Pozzuoli, Italy. Pozzuoli, Italy.

Ancient Romans (Ancient Romans (~~100 B.C.) 100 B.C.) produced a produced a hydraulic binder by mixing hydrated lime hydraulic binder by mixing hydrated lime with soil (predominantly volcanic ash)with soil (predominantly volcanic ash)

Horasan mortar, mixing lime with finely Horasan mortar, mixing lime with finely divided burned clay, is extensively used by divided burned clay, is extensively used by OttomansOttomans

Nowadays, the word pozzolan covers a broad Nowadays, the word pozzolan covers a broad range of natural and artificial materials.range of natural and artificial materials.

PozzolanPozzolan

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.– Natural (Volcanic ash, volcanic tuff, Natural (Volcanic ash, volcanic tuff,

pumicite)pumicite)– Artificial (fly ash, silica-fume, granulated Artificial (fly ash, silica-fume, granulated

blast furnace slag)blast furnace slag)

PozzolanPozzolan

Siliceous or aluminous material, Siliceous or aluminous material, which in itself possesses little or no which in itself possesses little or no cementitiouscementitious value but will, value but will, in finely in finely divided formdivided form and in and in the presence of the presence of moisturemoisture, chemically react with , chemically react with calcium hydroxide Ca(OH)calcium hydroxide Ca(OH)2 2 to form to form compounds possessing hydraulic compounds possessing hydraulic cementitious properties.cementitious properties.

POZZOLANIC REACTIONSPOZZOLANIC REACTIONSCalcium Hydroxide+Silica+Water Calcium Hydroxide+Silica+Water → “Calcium-Silicate-Hydrate”→ “Calcium-Silicate-Hydrate”

(C-S-H)(C-S-H)C-S-H provides the hydraulic binding property of the material.C-S-H provides the hydraulic binding property of the material.

Pozzolanic Activity:Pozzolanic Activity: Capacity of pozzolan to form alumino-silicates Capacity of pozzolan to form alumino-silicates with lime to form cementitious products. (How good how effective with lime to form cementitious products. (How good how effective the pozzolan is!)the pozzolan is!)

POZZOLANS

Silica&Alumina(higher amounts)

Iron oxide, calcium oxide,magnesium oxide,

alkalies(lesser amounts)

FACTORS THAT AFFECT FACTORS THAT AFFECT THE ACTIVITY OF THE ACTIVITY OF POZZOLANSPOZZOLANS1) SiO1) SiO22 + Al + Al22OO33 + Fe + Fe22OO33 content content

2) The degree of amourpheness of 2) The degree of amourpheness of its structureits structure

3) Fineness of its particles3) Fineness of its particles

1) SiO1) SiO22 + Al + Al22OO33 + Fe + Fe22OO33 The greater amount of these, the greater its The greater amount of these, the greater its

activity.activity. ASTM C 618 & TS 25 ASTM C 618 & TS 25 → min “SiO→ min “SiO22+Al+Al22OO33+Fe+Fe22OO33” for ” for

natural pozzolans natural pozzolans >> 70% 70% Fly Ash - ASTMFly Ash - ASTM Class C→ from lignitide or subbituminous coals Class C→ from lignitide or subbituminous coals

(SiO(SiO22+Al+Al22OO33+Fe+Fe22OO33>>50%)50%) Class F→ from bituminous coals and Class F→ from bituminous coals and

SiOSiO22+Al+Al22OO33+Fe+Fe22OO33>>70%70% Silica fume → SiOSilica fume → SiO22 ≈ 85-98% ≈ 85-98% Blast Furnace Slag→ SiOBlast Furnace Slag→ SiO22 ~~ 30-40% 30-40%

AlAl22OO33 ~~ 7-19% 7-19%

CaO CaO ~~ 30-50% 30-50%

2) Amorphousness2) Amorphousness

For chemical reaction For chemical reaction → pozzolans must → pozzolans must be amorphousbe amorphous

Volcanic ash, volcanic tuff, fly ash, silica fume Volcanic ash, volcanic tuff, fly ash, silica fume are all amorphous by nature.are all amorphous by nature.

Clays → contain high amounts of silica & Clays → contain high amounts of silica & alumina but have a crystallic structure! alumina but have a crystallic structure! (Do not possess pozzolanic activity)(Do not possess pozzolanic activity)– However, by heat treatment, such as calcining However, by heat treatment, such as calcining

~~700-900700-900°°C crystallic structure is destroyed & a C crystallic structure is destroyed & a quasi-amorphous structure is obtained.quasi-amorphous structure is obtained.

Clay Clay → does not possess pozzolanic property→ does not possess pozzolanic propertyBurned clay Burned clay → possess pozzolanic property→ possess pozzolanic property

Blast furnace slag → contain high Blast furnace slag → contain high amounts of silica, alumina & lime.amounts of silica, alumina & lime.However, if molten slag is allowed to cool in However, if molten slag is allowed to cool in

air, it gains a crystal structure. * do not air, it gains a crystal structure. * do not possess pozzolanic property.possess pozzolanic property.

However, if it is cooled very rapidly by pouring However, if it is cooled very rapidly by pouring it into water, it becomes a granular material & it into water, it becomes a granular material & gains amorpousness. * possess pozzolanic gains amorpousness. * possess pozzolanic property.property.

2) Amorphousness2) Amorphousness

3) Fineness3) Fineness Pozzolanic activity increases as Pozzolanic activity increases as

fineness increases.fineness increases.

Volcanic ash, rice husk ash, fly ash, Volcanic ash, rice husk ash, fly ash, condensed silica fume are obtained condensed silica fume are obtained in finely divided form.in finely divided form.

Volcanic tuff, granulated blast Volcanic tuff, granulated blast furnace slag & burned clay must be furnace slag & burned clay must be ground.ground.

DETERMINATION OF DETERMINATION OF POZZOLANIC ACTIVITYPOZZOLANIC ACTIVITY

Pozzolanic activity is determined by Pozzolanic activity is determined by “strength activity indexes”“strength activity indexes”

Six mortar cubes are prepared (ASTM)Six mortar cubes are prepared (ASTM)

→→””Control Mixture” 500 g portland Control Mixture” 500 g portland cement+1375 g sand+242 ml watercement+1375 g sand+242 ml water

→”→”Test Mixture” 400g of portland Test Mixture” 400g of portland cement+100g of pozzolan+1375g of cement+100g of pozzolan+1375g of sand+some water for the same consistencysand+some water for the same consistency

Compressive testing at 7 or 28 daysCompressive testing at 7 or 28 days

Strength Activity Index (SAI) Strength Activity Index (SAI) ==A/B*100A/B*100

A=f’A=f’cc of test mixture of test mixture

B=f’B=f’cc of control mixture of control mixture

ASTM C 618 ASTM C 618 → SAI ≥ 75%→ SAI ≥ 75%

CHEMICAL COMPOSITION CHEMICAL COMPOSITION OF POZZOLANSOF POZZOLANS

Silica Fume is mostly SiOSilica Fume is mostly SiO22

G. G. Blast Furnace SlagG. G. Blast Furnace Slag→ high amounts → high amounts

of CaO (self-cementitious)of CaO (self-cementitious)

Class C Fly Ash has CaO (self-cementitious)Class C Fly Ash has CaO (self-cementitious)

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

Class F Class F fly ashfly ash

Class C Class C fly ashfly ash GroundslagGroundslag

Silica Silica fumefume

Calcined Calcined clayclay

Calcined Calcined shaleshale

Meta-Meta-kaolinkaolin

SiOSiO22, %, % 5252 3535 3535 9090 5858 5050 5353

AlAl22OO33, %, % 2323 1818 1212 0.40.4 2929 2020 4343

FeFe22OO33, %, % 1111 66 11 0.40.4 44 88 0.50.5

CaO, %CaO, % 55 2121 4040 1.61.6 11 88 0.10.1

SOSO33, %, % 0.80.8 4.14.1 99 0.40.4 0.50.5 0.40.4 0.10.1

NaNa22O, %O, % 1.01.0 5.85.8 0.30.3 0.50.5 0.20.2 —— 0.050.05

KK22O, %O, % 2.02.0 0.70.7 0.40.4 2.22.2 22 —— 0.40.4

Total Na Total Na

eq. alk, %eq. alk, %2.22.2 6.36.3 0.60.6 1.91.9 1.51.5 —— 0.30.3

Natural Pozzolans

Artificial Pozzolans

SILICA FUME FLY ASH

GRANULATED BLAST FURNACE SLAG

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

Class F Class F fly ashfly ash

Class C Class C fly ashfly ash

GrounGroundslagdslag

Silica Silica fumefume

Calcined Calcined clayclay

Calcined Calcined shaleshale

Meta-Meta-kaolinkaolin

Loss on ignition, Loss on ignition, %%

2.82.8 0.50.5 1.01.0 3.03.0 1.51.5 3.03.0 0.70.7

Blaine fineness, Blaine fineness, mm22/kg/kg

420420 420420 400400 20,00020,000 990990 730730 19,00019,000

Relative densityRelative density 2.382.38 2.652.65 2.942.94 2.402.40 2.502.50 2.632.63 2.502.50

Typical Amounts of Typical Amounts of PozzolansPozzolans in Concrete by in Concrete by Mass of Cementing Mass of Cementing MaterialsMaterials Fly ashFly ash

– Class CClass C 15% to 40%15% to 40%– Class FClass F 15% to 20%15% to 20%

SlagSlag 30% to 45%30% to 45% Silica fumeSilica fume 5% to 10% 5% to 10% Calcined clayCalcined clay 15% to 35%15% to 35%

– MetakaolinMetakaolin 10%10% Calcined shaleCalcined shale 15% to 35%15% to 35%

REQUIREMENTS FOR AN REQUIREMENTS FOR AN ACCEPTABLE QUALITY OF ACCEPTABLE QUALITY OF POZZOLANPOZZOLAN

TS 25 TS 25 → Natural Pozzolans→ Natural Pozzolans TS 639 → Fly AshTS 639 → Fly Ash ASTM C 618 → For Natural Pozzolan & Fly AshASTM C 618 → For Natural Pozzolan & Fly Ash

  Natural Class F Class C

Fineness (max. % retained when wet sieved on 45 m sieve) 34% 34% 34%

Strength Activity Index 75 75 75

min "SiO2+Al2O3+Fe2O3" 70 70 50

USES OF POZZOLANSUSES OF POZZOLANS

1) Direct use of Pozzolan by Mixing it with 1) Direct use of Pozzolan by Mixing it with Calcium Hydroxide Calcium Hydroxide

Extensively used in ancient times but not Extensively used in ancient times but not very common now.very common now.

2) Use of Pozzolan in Producing Blended 2) Use of Pozzolan in Producing Blended CementsCements

Grinding “Clinker+Pozzolan+Gypsum”Grinding “Clinker+Pozzolan+Gypsum”→ → Portland Pozzolan Cements Extensively usedPortland Pozzolan Cements Extensively used

3) Use of Pozzolan as an Admixture3) Use of Pozzolan as an Admixture

““Cement+Pozzolan+Aggregate+Water”→ Cement+Pozzolan+Aggregate+Water”→ ConcreteConcrete